diff --git a/.eslintrc.json b/.eslintrc.json
index b5328f41bb..3791be8e1d 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -2,15 +2,22 @@
     "root": true,
     "extends": [
         "eslint:recommended",
-        "plugin:jsonc/recommended-with-json"
+        "plugin:jsonc/recommended-with-json",
+        "plugin:@typescript-eslint/recommended"
     ],
+    "parser": "@typescript-eslint/parser",
     "parserOptions": {
         "ecmaVersion": 9,
         "sourceType": "script",
         "ecmaFeatures": {
             "globalReturn": false,
             "impliedStrict": true
-        }
+        },
+        "project": [
+            "./jsconfig.json",
+            "./dev/jsconfig.json",
+            "./test/jsconfig.json"
+        ]
     },
     "env": {
         "browser": true,
@@ -21,7 +28,10 @@
         "no-unsanitized",
         "header",
         "jsdoc",
-        "jsonc"
+        "jsonc",
+        "unused-imports",
+        "@typescript-eslint",
+        "@stylistic/ts"
     ],
     "ignorePatterns": [
         "/ext/lib/"
@@ -54,7 +64,7 @@
         "no-param-reassign": "off",
         "no-prototype-builtins": "error",
         "no-shadow": [
-            "error",
+            "off",
             {
                 "builtinGlobals": false
             }
@@ -233,7 +243,7 @@
         "no-unsanitized/property": "error",
         "jsdoc/check-access": "error",
         "jsdoc/check-alignment": "error",
-        "jsdoc/check-line-alignment": "error",
+        "jsdoc/check-line-alignment": ["error", "never", {"wrapIndent": "  "}],
         "jsdoc/check-param-names": "error",
         "jsdoc/check-property-names": "error",
         "jsdoc/check-tag-names": "error",
@@ -242,10 +252,6 @@
         "jsdoc/empty-tags": "error",
         "jsdoc/implements-on-classes": "error",
         "jsdoc/multiline-blocks": "error",
-        "jsdoc/newline-after-description": [
-            "error",
-            "never"
-        ],
         "jsdoc/no-bad-blocks": "error",
         "jsdoc/no-multi-asterisks": "error",
         "jsdoc/require-asterisk-prefix": "error",
@@ -253,23 +259,41 @@
             "error",
             "never"
         ],
-        "jsdoc/require-jsdoc": "off",
+        "jsdoc/require-jsdoc": [
+            "error",
+            {
+                "require": {
+                    "ClassDeclaration": false,
+                    "FunctionDeclaration": true,
+                    "MethodDefinition": false
+                },
+                "contexts": [
+                    "MethodDefinition[kind=constructor]>FunctionExpression>BlockStatement>ExpressionStatement>AssignmentExpression[left.object.type=ThisExpression]",
+                    "ClassDeclaration>Classbody>PropertyDefinition",
+                    "MethodDefinition[kind!=constructor][kind!=set]",
+                    "MethodDefinition[kind=constructor][value.params.length>0]"
+                ],
+                "checkGetters": "no-setter",
+                "checkSetters": "no-getter"
+            }
+        ],
+        "jsdoc/require-description": "off",
         "jsdoc/require-param": "error",
-        "jsdoc/require-param-description": "error",
+        "jsdoc/require-param-description": "off",
         "jsdoc/require-param-name": "error",
         "jsdoc/require-param-type": "error",
         "jsdoc/require-property": "error",
-        "jsdoc/require-property-description": "error",
+        "jsdoc/require-property-description": "off",
         "jsdoc/require-property-name": "error",
         "jsdoc/require-property-type": "error",
         "jsdoc/require-returns": "error",
         "jsdoc/require-returns-check": "error",
-        "jsdoc/require-returns-description": "error",
+        "jsdoc/require-returns-description": "off",
         "jsdoc/require-returns-type": "error",
         "jsdoc/require-throws": "error",
         "jsdoc/require-yields": "error",
         "jsdoc/require-yields-check": "error",
-        "jsdoc/tag-lines": "error",
+        "jsdoc/tag-lines": ["error", "never", {"startLines": 0}],
         "jsdoc/valid-types": "error",
         "jsonc/indent": [
             "error",
@@ -315,9 +339,162 @@
             {
                 "allowAllPropertiesOnSameLine": true
             }
-        ]
+        ],
+        "@typescript-eslint/ban-ts-comment": "off",
+        "@typescript-eslint/ban-types": [
+            "error",
+            {
+                "types": {
+                    "object": true
+                },
+                "extendDefaults": true
+            }
+        ],
+        "@typescript-eslint/consistent-type-exports": "off",
+        "@typescript-eslint/no-explicit-any": "error",
+        "@typescript-eslint/no-shadow": [
+            "error",
+            {
+                "builtinGlobals": false
+            }
+        ],
+        "@typescript-eslint/no-this-alias": "error",
+        "@typescript-eslint/no-unused-vars": "off",
+        "@typescript-eslint/no-var-requires": "off"
     },
     "overrides": [
+        {
+            "files": [
+                "*.ts"
+            ],
+            "rules": {
+                "no-undef": "off",
+                "unused-imports/no-unused-imports": "error",
+                "@typescript-eslint/no-unused-vars": [
+                    "error",
+                    {
+                        "vars": "local",
+                        "args": "after-used",
+                        "argsIgnorePattern": "^_",
+                        "caughtErrors": "none"
+                    }
+                ],
+                "comma-dangle": "off",
+                "@typescript-eslint/comma-dangle": [
+                    "error",
+                    {
+                        "arrays": "always-multiline",
+                        "objects": "always-multiline",
+                        "imports": "always-multiline",
+                        "exports": "always-multiline",
+                        "functions": "always-multiline",
+                        "enums": "always-multiline",
+                        "generics": "always-multiline",
+                        "tuples": "always-multiline"
+                    }
+                ],
+                "@stylistic/ts/block-spacing": "off",
+                "@stylistic/ts/brace-style": [
+                    "error",
+                    "1tbs",
+                    {
+                        "allowSingleLine": true
+                    }
+                ],
+                "@stylistic/ts/comma-dangle": [
+                    "error",
+                    {
+                        "arrays": "always-multiline",
+                        "objects": "always-multiline",
+                        "imports": "always-multiline",
+                        "exports": "always-multiline",
+                        "functions": "always-multiline",
+                        "enums": "always-multiline",
+                        "generics": "always-multiline",
+                        "tuples": "always-multiline"
+                    }
+                ],
+                "@stylistic/ts/comma-spacing": [
+                    "error",
+                    {
+                        "before": false,
+                        "after": true
+                    }
+                ],
+                "@stylistic/ts/function-call-spacing": [
+                    "error",
+                    "never"
+                ],
+                "@stylistic/ts/indent": [
+                    "error",
+                    4
+                ],
+                "@stylistic/ts/key-spacing": [
+                    "error",
+                    {
+                        "beforeColon": false,
+                        "afterColon": true,
+                        "mode": "strict"
+                    }
+                ],
+                "@stylistic/ts/keyword-spacing": [
+                    "error",
+                    {
+                        "before": true,
+                        "after": true
+                    }
+                ],
+                "@stylistic/ts/lines-around-comment": "off",
+                "@stylistic/ts/lines-between-class-members": [
+                    "error",
+                    "always"
+                ],
+                "@stylistic/ts/member-delimiter-style": [
+                    "error",
+                    {
+                        "multiline": {
+                            "delimiter": "semi",
+                            "requireLast": true
+                        },
+                        "singleline": {
+                            "delimiter": "comma",
+                            "requireLast": false
+                        },
+                        "multilineDetection": "brackets"
+                    }
+                ],
+                "@stylistic/ts/no-extra-parens": [
+                    "error",
+                    "all"
+                ],
+                "@stylistic/ts/no-extra-semi": "error",
+                "@stylistic/ts/object-curly-spacing": [
+                    "error",
+                    "never"
+                ],
+                "@stylistic/ts/padding-line-between-statements": "off",
+                "@stylistic/ts/quotes": [
+                    "error",
+                    "single",
+                    "avoid-escape"
+                ],
+                "@stylistic/ts/semi": "error",
+                "@stylistic/ts/space-before-blocks": [
+                    "error",
+                    "always"
+                ],
+                "@stylistic/ts/space-before-function-paren": [
+                    "error",
+                    {
+                        "anonymous": "never",
+                        "named": "never",
+                        "asyncArrow": "always"
+                    }
+                ],
+                "@stylistic/ts/space-infix-ops": "error",
+                "@stylistic/ts/type-annotation-spacing": "error"
+            }
+        },
         {
             "files": [
                 "*.json"
@@ -367,24 +544,35 @@
         {
             "files": [
                 "ext/js/core.js",
+                "ext/js/core/extension-error.js",
                 "ext/js/**/sandbox/**/*.js"
             ],
             "env": {
                 "webextensions": false
             }
         },
+        {
+            "files": [
+                "ext/**/*.js"
+            ],
+            "excludedFiles": [
+                "ext/js/core/extension-error.js"
+            ],
+            "globals": {
+                "ExtensionError": "readonly"
+            }
+        },
         {
             "files": [
                 "ext/**/*.js"
             ],
             "excludedFiles": [
                 "ext/js/core.js",
+                "ext/js/core/extension-error.js",
                 "ext/js/accessibility/google-docs.js",
                 "ext/js/**/sandbox/**/*.js"
             ],
             "globals": {
-                "serializeError": "readonly",
-                "deserializeError": "readonly",
                 "isObject": "readonly",
                 "stringReverse": "readonly",
                 "promiseTimeout": "readonly",
@@ -408,6 +596,7 @@
             ],
             "excludedFiles": [
                 "ext/js/core.js",
+                "ext/js/core/extension-error.js",
                 "ext/js/accessibility/google-docs.js",
                 "ext/js/yomichan.js",
                 "ext/js/**/sandbox/**/*.js"
@@ -475,6 +664,7 @@
         {
             "files": [
                 "ext/js/core.js",
+                "ext/js/core/extension-error.js",
                 "ext/js/yomichan.js",
                 "ext/js/accessibility/accessibility-controller.js",
                 "ext/js/background/backend.js",
@@ -522,6 +712,7 @@
         {
             "files": [
                 "ext/js/core.js",
+                "ext/js/core/extension-error.js",
                 "ext/js/data/database.js",
                 "ext/js/data/json-schema.js",
                 "ext/js/general/cache-map.js",
diff --git a/.vscode/extensions.json b/.vscode/extensions.json
new file mode 100644
index 0000000000..a5e243212b
--- /dev/null
+++ b/.vscode/extensions.json
@@ -0,0 +1,7 @@
+{
+    "recommendations": [
+        "dbaeumer.vscode-eslint",
+        "html-validate.vscode-html-validate",
+        "stylelint.vscode-stylelint"
+    ]
+}
\ No newline at end of file
diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000000..9bd9e1c0ab
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,9 @@
+{
+    "editor.tabSize": 4,
+    "editor.insertSpaces": true,
+    "eslint.validate": [
+        "javascript",
+        "typescript"
+    ],
+    "files.eol": "\n"
+}
\ No newline at end of file
diff --git a/dev/build-libs.js b/dev/build-libs.js
index 36c07edd0c..ec09c62678 100644
--- a/dev/build-libs.js
+++ b/dev/build-libs.js
@@ -20,6 +20,9 @@ const fs = require('fs');
 const path = require('path');
 const browserify = require('browserify');
 
+/**
+ * @returns {Promise<Buffer>}
+ */
 async function buildParse5() {
     const parse5Path = require.resolve('parse5');
     const cwd = process.cwd();
@@ -45,6 +48,9 @@ async function buildParse5() {
     }
 }
 
+/**
+ * @returns {{path: string, build: () => Promise<Buffer|string>}[]}
+ */
 function getBuildTargets() {
     const extLibPath = path.join(__dirname, '..', 'ext', 'lib');
     return [
@@ -52,6 +58,7 @@ function getBuildTargets() {
     ];
 }
 
+/** */
 async function main() {
     for (const {path: path2, build} of getBuildTargets()) {
         const content = await build();
diff --git a/dev/build.js b/dev/build.js
index 5222c4c899..cfc3fed4ae 100644
--- a/dev/build.js
+++ b/dev/build.js
@@ -26,6 +26,14 @@ const {getAllFiles, getArgs, testMain} = util;
 const {ManifestUtil} = require('./manifest-util');
 
 
+/**
+ * @param {string} directory
+ * @param {string[]} excludeFiles
+ * @param {string} outputFileName
+ * @param {string[]} sevenZipExes
+ * @param {?import('jszip').OnUpdateCallback} onUpdate
+ * @param {boolean} dryRun
+ */
 async function createZip(directory, excludeFiles, outputFileName, sevenZipExes, onUpdate, dryRun) {
     try {
         fs.unlinkSync(outputFileName);
@@ -55,9 +63,16 @@ async function createZip(directory, excludeFiles, outputFileName, sevenZipExes,
             }
         }
     }
-    return await createJSZip(directory, excludeFiles, outputFileName, onUpdate, dryRun);
+    await createJSZip(directory, excludeFiles, outputFileName, onUpdate, dryRun);
 }
 
+/**
+ * @param {string} directory
+ * @param {string[]} excludeFiles
+ * @param {string} outputFileName
+ * @param {?import('jszip').OnUpdateCallback} onUpdate
+ * @param {boolean} dryRun
+ */
 async function createJSZip(directory, excludeFiles, outputFileName, onUpdate, dryRun) {
     const JSZip = util.JSZip;
     const files = getAllFiles(directory);
@@ -87,6 +102,10 @@ async function createJSZip(directory, excludeFiles, outputFileName, onUpdate, dr
     }
 }
 
+/**
+ * @param {string[]} array
+ * @param {string[]} removeItems
+ */
 function removeItemsFromArray(array, removeItems) {
     for (const item of removeItems) {
         const index = getIndexOfFilePath(array, item);
@@ -96,6 +115,11 @@ function removeItemsFromArray(array, removeItems) {
     }
 }
 
+/**
+ * @param {string[]} array
+ * @param {string} item
+ * @returns {number}
+ */
 function getIndexOfFilePath(array, item) {
     const pattern = /\\/g;
     const separator = '/';
@@ -108,6 +132,15 @@ function getIndexOfFilePath(array, item) {
     return -1;
 }
 
+/**
+ * @param {string} buildDir
+ * @param {string} extDir
+ * @param {ManifestUtil} manifestUtil
+ * @param {string[]} variantNames
+ * @param {string} manifestPath
+ * @param {boolean} dryRun
+ * @param {boolean} dryRunBuildZip
+ */
 async function build(buildDir, extDir, manifestUtil, variantNames, manifestPath, dryRun, dryRunBuildZip) {
     const sevenZipExes = ['7za', '7z'];
 
@@ -117,6 +150,7 @@ async function build(buildDir, extDir, manifestUtil, variantNames, manifestPath,
     }
 
     const dontLogOnUpdate = !process.stdout.isTTY;
+    /** @type {import('jszip').OnUpdateCallback} */
     const onUpdate = (metadata) => {
         if (dontLogOnUpdate) { return; }
 
@@ -125,7 +159,7 @@ async function build(buildDir, extDir, manifestUtil, variantNames, manifestPath,
             message += ` (${metadata.currentFile})`;
         }
 
-        readline.clearLine(process.stdout);
+        readline.clearLine(process.stdout, 0);
         readline.cursorTo(process.stdout, 0);
         process.stdout.write(message);
     };
@@ -169,6 +203,10 @@ async function build(buildDir, extDir, manifestUtil, variantNames, manifestPath,
     }
 }
 
+/**
+ * @param {string} directory
+ * @param {string[]} files
+ */
 function ensureFilesExist(directory, files) {
     for (const file of files) {
         assert.ok(fs.existsSync(path.join(directory, file)));
@@ -176,18 +214,21 @@ function ensureFilesExist(directory, files) {
 }
 
 
+/**
+ * @param {string[]} argv
+ */
 async function main(argv) {
-    const args = getArgs(argv, new Map([
+    const args = getArgs(argv, new Map(/** @type {[key: string, value: (boolean|null|number|string|string[])][]} */ ([
         ['all', false],
         ['default', false],
         ['manifest', null],
         ['dry-run', false],
         ['dry-run-build-zip', false],
         [null, []]
-    ]));
+    ])));
 
-    const dryRun = args.get('dry-run');
-    const dryRunBuildZip = args.get('dry-run-build-zip');
+    const dryRun = /** @type {boolean} */ (args.get('dry-run'));
+    const dryRunBuildZip = /** @type {boolean} */ (args.get('dry-run-build-zip'));
 
     const manifestUtil = new ManifestUtil();
 
@@ -197,15 +238,15 @@ async function main(argv) {
     const manifestPath = path.join(extDir, 'manifest.json');
 
     try {
-        const variantNames = (
+        const variantNames = /** @type {string[]} */ ((
             argv.length === 0 || args.get('all') ?
             manifestUtil.getVariants().filter(({buildable}) => buildable !== false).map(({name}) => name) :
             args.get(null)
-        );
+        ));
         await build(buildDir, extDir, manifestUtil, variantNames, manifestPath, dryRun, dryRunBuildZip);
     } finally {
         // Restore manifest
-        const manifestName = (!args.get('default') && args.get('manifest') !== null) ? args.get('manifest') : null;
+        const manifestName = /** @type {?string} */ ((!args.get('default') && args.get('manifest') !== null) ? args.get('manifest') : null);
         const restoreManifest = manifestUtil.getManifest(manifestName);
         process.stdout.write('Restoring manifest...\n');
         if (!dryRun) {
diff --git a/dev/css-to-json-util.js b/dev/css-to-json-util.js
index 79aae3c9e1..8fb2f08502 100644
--- a/dev/css-to-json-util.js
+++ b/dev/css-to-json-util.js
@@ -19,6 +19,11 @@
 const fs = require('fs');
 const css = require('css');
 
+/**
+ * @param {import('css-style-applier').RawStyleData} rules
+ * @param {string[]} selectors
+ * @returns {number}
+ */
 function indexOfRule(rules, selectors) {
     const jj = selectors.length;
     for (let i = 0, ii = rules.length; i < ii; ++i) {
@@ -36,6 +41,12 @@ function indexOfRule(rules, selectors) {
     return -1;
 }
 
+/**
+ * @param {import('css-style-applier').RawStyleDataStyleArray} styles
+ * @param {string} property
+ * @param {Map<string, number>} removedProperties
+ * @returns {number}
+ */
 function removeProperty(styles, property, removedProperties) {
     let removeCount = removedProperties.get(property);
     if (typeof removeCount !== 'undefined') { return removeCount; }
@@ -52,6 +63,10 @@ function removeProperty(styles, property, removedProperties) {
     return removeCount;
 }
 
+/**
+ * @param {import('css-style-applier').RawStyleData} rules
+ * @returns {string}
+ */
 function formatRulesJson(rules) {
     // Manually format JSON, for improved compactness
     // return JSON.stringify(rules, null, 4);
@@ -85,27 +100,39 @@ function formatRulesJson(rules) {
     return result;
 }
 
+/**
+ * @param {string} cssFile
+ * @param {string} overridesCssFile
+ * @returns {import('css-style-applier').RawStyleData}
+ * @throws {Error}
+ */
 function generateRules(cssFile, overridesCssFile) {
     const content1 = fs.readFileSync(cssFile, {encoding: 'utf8'});
     const content2 = fs.readFileSync(overridesCssFile, {encoding: 'utf8'});
-    const stylesheet1 = css.parse(content1, {}).stylesheet;
-    const stylesheet2 = css.parse(content2, {}).stylesheet;
+    const stylesheet1 = /** @type {css.StyleRules} */ (css.parse(content1, {}).stylesheet);
+    const stylesheet2 = /** @type {css.StyleRules} */ (css.parse(content2, {}).stylesheet);
 
     const removePropertyPattern = /^remove-property\s+([\w\W]+)$/;
     const removeRulePattern = /^remove-rule$/;
     const propertySeparator = /\s+/;
 
+    /** @type {import('css-style-applier').RawStyleData} */
     const rules = [];
 
     // Default stylesheet
     for (const rule of stylesheet1.rules) {
         if (rule.type !== 'rule') { continue; }
-        const {selectors, declarations} = rule;
+        const {selectors, declarations} = /** @type {css.Rule} */ (rule);
+        if (typeof selectors === 'undefined') { continue; }
+        /** @type {import('css-style-applier').RawStyleDataStyleArray} */
         const styles = [];
-        for (const declaration of declarations) {
-            if (declaration.type !== 'declaration') { console.log(declaration); continue; }
-            const {property, value} = declaration;
-            styles.push([property, value]);
+        if (typeof declarations !== 'undefined') {
+            for (const declaration of declarations) {
+                if (declaration.type !== 'declaration') { console.log(declaration); continue; }
+                const {property, value} = /** @type {css.Declaration} */ (declaration);
+                if (typeof property !== 'string' || typeof value !== 'string') { continue; }
+                styles.push([property, value]);
+            }
         }
         if (styles.length > 0) {
             rules.push({selectors, styles});
@@ -115,7 +142,9 @@ function generateRules(cssFile, overridesCssFile) {
     // Overrides
     for (const rule of stylesheet2.rules) {
         if (rule.type !== 'rule') { continue; }
-        const {selectors, declarations} = rule;
+        const {selectors, declarations} = /** @type {css.Rule} */ (rule);
+        if (typeof selectors === 'undefined' || typeof declarations === 'undefined') { continue; }
+        /** @type {Map<string, number>} */
         const removedProperties = new Map();
         for (const declaration of declarations) {
             switch (declaration.type) {
@@ -129,16 +158,18 @@ function generateRules(cssFile, overridesCssFile) {
                             entry = {selectors, styles: []};
                             rules.push(entry);
                         }
-                        const {property, value} = declaration;
-                        removeProperty(entry.styles, property, removedProperties);
-                        entry.styles.push([property, value]);
+                        const {property, value} = /** @type {css.Declaration} */ (declaration);
+                        if (typeof property === 'string' && typeof value === 'string') {
+                            removeProperty(entry.styles, property, removedProperties);
+                            entry.styles.push([property, value]);
+                        }
                     }
                     break;
                 case 'comment':
                     {
                         const index = indexOfRule(rules, selectors);
                         if (index < 0) { throw new Error('Could not find rule with matching selectors'); }
-                        const comment = declaration.comment.trim();
+                        const comment = (/** @type {css.Comment} */ (declaration).comment || '').trim();
                         let m;
                         if ((m = removePropertyPattern.exec(comment)) !== null) {
                             for (const property of m[1].split(propertySeparator)) {
diff --git a/dev/data-error.js b/dev/data-error.js
new file mode 100644
index 0000000000..5034e3fd96
--- /dev/null
+++ b/dev/data-error.js
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+class DataError extends Error {
+    /**
+     * @param {string} message
+     */
+    constructor(message) {
+        super(message);
+        /** @type {unknown} */
+        this._data = void 0;
+    }
+
+    /** @type {unknown} */
+    get data() { return this._data; }
+    set data(value) { this._data = value; }
+}
+
+module.exports = {
+    DataError
+};
diff --git a/dev/data/manifest-variants.json b/dev/data/manifest-variants.json
index 3179734f0a..b6ed847d94 100644
--- a/dev/data/manifest-variants.json
+++ b/dev/data/manifest-variants.json
@@ -42,6 +42,7 @@
                 "all_frames": true,
                 "js": [
                     "js/core.js",
+                    "js/core/extension-error.js",
                     "js/yomichan.js",
                     "js/app/frontend.js",
                     "js/app/popup.js",
diff --git a/dev/database-vm.js b/dev/database-vm.js
index d557069114..2d424a0bcc 100644
--- a/dev/database-vm.js
+++ b/dev/database-vm.js
@@ -17,12 +17,13 @@
  */
 
 const fs = require('fs');
-const url = require('url');
+const url = require('node:url');
 const path = require('path');
 const {JSZip} = require('./util');
 const {VM} = require('./vm');
 require('fake-indexeddb/auto');
 
+/** @type {import('dev/vm').PseudoChrome} */
 const chrome = {
     runtime: {
         getURL: (path2) => {
@@ -31,6 +32,10 @@ const chrome = {
     }
 };
 
+/**
+ * @param {string} url2
+ * @returns {Promise<import('dev/vm').PseudoFetchResponse>}
+ */
 async function fetch(url2) {
     const extDir = path.join(__dirname, '..', 'ext');
     let filePath;
@@ -50,11 +55,18 @@ async function fetch(url2) {
     };
 }
 
+/**
+ * @param {string} data
+ * @returns {string}
+ */
 function atob(data) {
     return Buffer.from(data, 'base64').toString('ascii');
 }
 
 class DatabaseVM extends VM {
+    /**
+     * @param {import('core').UnknownObject} [globals]
+     */
     constructor(globals={}) {
         super(Object.assign({
             chrome,
@@ -65,11 +77,13 @@ class DatabaseVM extends VM {
             atob
         }, globals));
         this.context.window = this.context;
+        /** @type {IDBFactory} */
         this.indexedDB = global.indexedDB;
     }
 }
 
 class DatabaseVMDictionaryImporterMediaLoader {
+    /** @type {import('dictionary-importer-media-loader').GetImageDetailsFunction} */
     async getImageDetails(content) {
         // Placeholder values
         return {content, width: 100, height: 100};
diff --git a/dev/dictionary-validate.js b/dev/dictionary-validate.js
index 0c926acc93..5ec6fa1d2f 100644
--- a/dev/dictionary-validate.js
+++ b/dev/dictionary-validate.js
@@ -23,6 +23,10 @@ const {JSZip} = require('./util');
 const {createJsonSchema} = require('./schema-validate');
 
 
+/**
+ * @param {string} relativeFileName
+ * @returns {import('dev/dictionary-validate').Schema}
+ */
 function readSchema(relativeFileName) {
     const fileName = path.join(__dirname, relativeFileName);
     const source = fs.readFileSync(fileName, {encoding: 'utf8'});
@@ -30,17 +34,24 @@ function readSchema(relativeFileName) {
 }
 
 
+/**
+ * @param {import('dev/schema-validate').ValidateMode} mode
+ * @param {import('jszip')} zip
+ * @param {string} fileNameFormat
+ * @param {import('dev/dictionary-validate').Schema} schema
+ */
 async function validateDictionaryBanks(mode, zip, fileNameFormat, schema) {
     let jsonSchema;
     try {
         jsonSchema = createJsonSchema(mode, schema);
     } catch (e) {
-        e.message += `\n(in file ${fileNameFormat})}`;
-        throw e;
+        const e2 = e instanceof Error ? e : new Error(`${e}`);
+        e2.message += `\n(in file ${fileNameFormat})}`;
+        throw e2;
     }
     let index = 1;
     while (true) {
-        const fileName = fileNameFormat.replace(/\?/, index);
+        const fileName = fileNameFormat.replace(/\?/, `${index}`);
 
         const file = zip.files[fileName];
         if (!file) { break; }
@@ -49,14 +60,20 @@ async function validateDictionaryBanks(mode, zip, fileNameFormat, schema) {
         try {
             jsonSchema.validate(data);
         } catch (e) {
-            e.message += `\n(in file ${fileName})}`;
-            throw e;
+            const e2 = e instanceof Error ? e : new Error(`${e}`);
+            e2.message += `\n(in file ${fileName})}`;
+            throw e2;
         }
 
         ++index;
     }
 }
 
+/**
+ * @param {import('dev/schema-validate').ValidateMode} mode
+ * @param {import('jszip')} archive
+ * @param {import('dev/dictionary-validate').Schemas} schemas
+ */
 async function validateDictionary(mode, archive, schemas) {
     const fileName = 'index.json';
     const indexFile = archive.files[fileName];
@@ -71,8 +88,9 @@ async function validateDictionary(mode, archive, schemas) {
         const jsonSchema = createJsonSchema(mode, schemas.index);
         jsonSchema.validate(index);
     } catch (e) {
-        e.message += `\n(in file ${fileName})}`;
-        throw e;
+        const e2 = e instanceof Error ? e : new Error(`${e}`);
+        e2.message += `\n(in file ${fileName})}`;
+        throw e2;
     }
 
     await validateDictionaryBanks(mode, archive, 'term_bank_?.json', version === 1 ? schemas.termBankV1 : schemas.termBankV3);
@@ -82,6 +100,9 @@ async function validateDictionary(mode, archive, schemas) {
     await validateDictionaryBanks(mode, archive, 'tag_bank_?.json', schemas.tagBankV3);
 }
 
+/**
+ * @returns {import('dev/dictionary-validate').Schemas}
+ */
 function getSchemas() {
     return {
         index: readSchema('../ext/data/schemas/dictionary-index-schema.json'),
@@ -96,6 +117,10 @@ function getSchemas() {
 }
 
 
+/**
+ * @param {import('dev/schema-validate').ValidateMode} mode
+ * @param {string[]} dictionaryFileNames
+ */
 async function testDictionaryFiles(mode, dictionaryFileNames) {
     const schemas = getSchemas();
 
@@ -117,6 +142,7 @@ async function testDictionaryFiles(mode, dictionaryFileNames) {
 }
 
 
+/** */
 async function main() {
     const dictionaryFileNames = process.argv.slice(2);
     if (dictionaryFileNames.length === 0) {
@@ -127,6 +153,7 @@ async function main() {
         return;
     }
 
+    /** @type {import('dev/schema-validate').ValidateMode} */
     let mode = null;
     if (dictionaryFileNames[0] === '--ajv') {
         mode = 'ajv';
diff --git a/dev/generate-css-json.js b/dev/generate-css-json.js
index 787173abba..c14c0462f3 100644
--- a/dev/generate-css-json.js
+++ b/dev/generate-css-json.js
@@ -21,6 +21,9 @@ const path = require('path');
 const {testMain} = require('./util');
 const {formatRulesJson, generateRules} = require('./css-to-json-util');
 
+/**
+ * @returns {{cssFile: string, overridesCssFile: string, outputPath: string}[]}
+ */
 function getTargets() {
     return [
         {
@@ -36,6 +39,7 @@ function getTargets() {
     ];
 }
 
+/** */
 function main() {
     for (const {cssFile, overridesCssFile, outputPath} of getTargets()) {
         const json = formatRulesJson(generateRules(cssFile, overridesCssFile));
diff --git a/dev/jsconfig.json b/dev/jsconfig.json
new file mode 100644
index 0000000000..58eba952ce
--- /dev/null
+++ b/dev/jsconfig.json
@@ -0,0 +1,77 @@
+{
+    "compilerOptions": {
+        "module": "ES2015",
+        "target": "ES2022",
+        "checkJs": true,
+        "moduleResolution": "node",
+        "strict": true,
+        "strictNullChecks": true,
+        "noImplicitAny": true,
+        "strictPropertyInitialization": true,
+        "suppressImplicitAnyIndexErrors": false,
+        "skipLibCheck": false,
+        "baseUrl": ".",
+        "paths": {
+            "anki-templates": ["../types/ext/anki-templates"],
+            "anki-templates-internal": ["../types/ext/anki-templates-internal"],
+            "cache-map": ["../types/ext/cache-map"],
+            "core": ["../types/ext/core"],
+            "css-style-applier": ["../types/ext/css-style-applier"],
+            "database": ["../types/ext/database"],
+            "deinflector": ["../types/ext/deinflector"],
+            "dictionary": ["../types/ext/dictionary"],
+            "dictionary-data": ["../types/ext/dictionary-data"],
+            "dictionary-data-util": ["../types/ext/dictionary-data-util"],
+            "dictionary-database": ["../types/ext/dictionary-database"],
+            "dictionary-importer": ["../types/ext/dictionary-importer"],
+            "dictionary-importer-media-loader": ["../types/ext/dictionary-importer-media-loader"],
+            "dynamic-property": ["../types/ext/dynamic-property"],
+            "error": ["../types/ext/error"],
+            "event-listener-collection": ["../types/ext/event-listener-collection"],
+            "japanese-util": ["../types/ext/japanese-util"],
+            "json-schema": ["../types/ext/json-schema"],
+            "log": ["../types/ext/log"],
+            "settings": ["../types/ext/settings"],
+            "structured-content": ["../types/ext/structured-content"],
+            "translator": ["../types/ext/translator"],
+            "translation": ["../types/ext/translation"],
+            "translation-internal": ["../types/ext/translation-internal"],
+            "dev/*": ["../types/dev/*"]
+        },
+        "types": [
+            "node",
+            "events",
+            "browserify",
+            "jsdom",
+            "assert",
+            "css",
+            "chrome",
+            "ajv"
+        ]
+    },
+    "include": [
+        "**/*.js",
+        "../playwright.config.js",
+        "../ext/js/core.js",
+        "../ext/js/core/extension-error.js",
+        "../ext/js/data/database.js",
+        "../ext/js/data/json-schema.js",
+        "../ext/js/general/cache-map.js",
+        "../ext/js/data/sandbox/anki-note-data-creator.js",
+        "../ext/js/general/cache-map.js",
+        "../ext/js/general/regex-util.js",
+        "../ext/js/general/text-source-map.js",
+        "../ext/js/language/deinflector.js",
+        "../ext/js/language/dictionary-importer.js",
+        "../ext/js/language/dictionary-database.js",
+        "../ext/js/language/sandbox/dictionary-data-util.js",
+        "../ext/js/language/sandbox/japanese-util.js",
+        "../ext/js/language/translator.js",
+        "../ext/js/media/media-util.js",
+        "../types/dev/**/*.ts",
+        "../types/other/web-set-timeout.d.ts"
+    ],
+    "exclude": [
+        "../node_modules"
+    ]
+}
\ No newline at end of file
diff --git a/dev/lint/global-declarations.js b/dev/lint/global-declarations.js
index 7f90d227ca..648ad3681e 100644
--- a/dev/lint/global-declarations.js
+++ b/dev/lint/global-declarations.js
@@ -22,14 +22,27 @@ const assert = require('assert');
 const {getAllFiles} = require('../util');
 
 
+/**
+ * @param {string} string
+ * @returns {string}
+ */
 function escapeRegExp(string) {
     return string.replace(/[.*+\-?^${}()|[\]\\]/g, '\\$&');
 }
 
+/**
+ * @param {string} string
+ * @param {RegExp} pattern
+ * @returns {number}
+ */
 function countOccurences(string, pattern) {
     return (string.match(pattern) || []).length;
 }
 
+/**
+ * @param {string} string
+ * @returns {'\r'|'\n'|'\r\n'}
+ */
 function getNewline(string) {
     const count1 = countOccurences(string, /(?:^|[^\r])\n/g);
     const count2 = countOccurences(string, /\r\n/g);
@@ -41,6 +54,11 @@ function getNewline(string) {
     }
 }
 
+/**
+ * @param {string} string
+ * @param {string} substring
+ * @returns {number}
+ */
 function getSubstringCount(string, substring) {
     let count = 0;
     const pattern = new RegExp(`\\b${escapeRegExp(substring)}\\b`, 'g');
@@ -53,6 +71,11 @@ function getSubstringCount(string, substring) {
 }
 
 
+/**
+ * @param {string} fileName
+ * @param {boolean} fix
+ * @returns {boolean}
+ */
 function validateGlobals(fileName, fix) {
     const pattern = /\/\*\s*global\s+([\w\W]*?)\*\//g;
     const trimPattern = /^[\s,*]+|[\s,*]+$/g;
@@ -81,7 +104,7 @@ function validateGlobals(fileName, fix) {
             assert.strictEqual(actual, expected);
         } catch (e) {
             console.error(`Global declaration error encountered in ${fileName}:`);
-            console.error(e.message);
+            console.error(e instanceof Error ? e.message : `${e}`);
             if (!fix) {
                 return false;
             }
@@ -114,6 +137,7 @@ function validateGlobals(fileName, fix) {
 }
 
 
+/** */
 function main() {
     const fix = (process.argv.length >= 2 && process.argv[2] === '--fix');
     const directory = path.resolve(__dirname, '..', '..', 'ext');
diff --git a/dev/lint/html-scripts.js b/dev/lint/html-scripts.js
index db6e6ca490..da8c2c712d 100644
--- a/dev/lint/html-scripts.js
+++ b/dev/lint/html-scripts.js
@@ -23,6 +23,10 @@ const {JSDOM} = require('jsdom');
 const {getAllFiles} = require('../util');
 
 
+/**
+ * @param {string} fileName
+ * @returns {?fs.Stats}
+ */
 function lstatSyncSafe(fileName) {
     try {
         return fs.lstatSync(fileName);
@@ -31,6 +35,11 @@ function lstatSyncSafe(fileName) {
     }
 }
 
+/**
+ * @param {string} src
+ * @param {string} fileName
+ * @param {string} extDir
+ */
 function validatePath(src, fileName, extDir) {
     assert.ok(typeof src === 'string', `<script> missing src attribute in ${fileName}`);
     assert.ok(src.startsWith('/'), `<script> src attribute is not absolute in ${fileName} (src=${JSON.stringify(src)})`);
@@ -42,6 +51,11 @@ function validatePath(src, fileName, extDir) {
     assert.ok(stats.isFile(), `<script> src file invalid in ${fileName} (src=${JSON.stringify(src)})`);
 }
 
+/**
+ * @param {string} string
+ * @param {RegExp} pattern
+ * @returns {number}
+ */
 function getSubstringCount(string, pattern) {
     let count = 0;
     while (true) {
@@ -52,10 +66,14 @@ function getSubstringCount(string, pattern) {
     return count;
 }
 
+/**
+ * @param {string[]} scriptPaths
+ * @returns {string[]}
+ */
 function getSortedScriptPaths(scriptPaths) {
     // Sort file names without the extension
     const extensionPattern = /\.[^.]*$/;
-    scriptPaths = scriptPaths.map((value) => {
+    const scriptPaths2 = scriptPaths.map((value) => {
         const match = extensionPattern.exec(value);
         let ext = '';
         if (match !== null) {
@@ -66,12 +84,16 @@ function getSortedScriptPaths(scriptPaths) {
     });
 
     const stringComparer = new Intl.Collator('en-US'); // Invariant locale
-    scriptPaths.sort((a, b) => stringComparer.compare(a.value, b.value));
+    scriptPaths2.sort((a, b) => stringComparer.compare(a.value, b.value));
 
-    scriptPaths = scriptPaths.map(({value, ext}) => `${value}${ext}`);
-    return scriptPaths;
+    return scriptPaths2.map(({value, ext}) => `${value}${ext}`);
 }
 
+/**
+ * @param {string} fileName
+ * @param {import('jsdom').DOMWindow} window
+ * @throws {Error}
+ */
 function validateScriptOrder(fileName, window) {
     const {document, Node: {ELEMENT_NODE, TEXT_NODE}, NodeFilter} = window;
 
@@ -79,7 +101,7 @@ function validateScriptOrder(fileName, window) {
     if (scriptElements.length === 0) { return; }
 
     // Assert all scripts are siblings
-    const scriptContainerElement = scriptElements[0].parentNode;
+    const scriptContainerElement = /** @type {Node} */ (scriptElements[0].parentNode);
     for (const element of scriptElements) {
         if (element.parentNode !== scriptContainerElement) {
             assert.fail('All script nodes are not contained within the same element');
@@ -87,15 +109,17 @@ function validateScriptOrder(fileName, window) {
     }
 
     // Get script groupings and order
+    /** @type {string[][]} */
     const scriptGroups = [];
     const newlinePattern = /\n/g;
     let separatingText = '';
     const walker = document.createTreeWalker(scriptContainerElement, NodeFilter.SHOW_ELEMENT | NodeFilter.SHOW_TEXT);
     walker.firstChild();
-    for (let node = walker.currentNode; node !== null; node = walker.nextSibling()) {
+    for (let node = /** @type {?Node} */ (walker.currentNode); node !== null; node = walker.nextSibling()) {
         switch (node.nodeType) {
             case ELEMENT_NODE:
-                if (node.tagName.toLowerCase() === 'script') {
+                if (/** @type {Element} */ (node).tagName.toLowerCase() === 'script') {
+                    /** @type {string[]} */
                     let scriptGroup;
                     if (scriptGroups.length === 0 || getSubstringCount(separatingText, newlinePattern) >= 2) {
                         scriptGroup = [];
@@ -103,7 +127,7 @@ function validateScriptOrder(fileName, window) {
                     } else {
                         scriptGroup = scriptGroups[scriptGroups.length - 1];
                     }
-                    scriptGroup.push(node.src);
+                    scriptGroup.push(/** @type {HTMLScriptElement} */ (node).src);
                     separatingText = '';
                 }
                 break;
@@ -132,6 +156,10 @@ function validateScriptOrder(fileName, window) {
     }
 }
 
+/**
+ * @param {string} fileName
+ * @param {string} extDir
+ */
 function validateHtmlScripts(fileName, extDir) {
     const fullFileName = path.join(extDir, fileName);
     const domSource = fs.readFileSync(fullFileName, {encoding: 'utf8'});
@@ -152,6 +180,7 @@ function validateHtmlScripts(fileName, extDir) {
 }
 
 
+/** */
 function main() {
     try {
         const extDir = path.resolve(__dirname, '..', '..', 'ext');
diff --git a/dev/manifest-util.js b/dev/manifest-util.js
index 082cf57cf7..57cefc7bf7 100644
--- a/dev/manifest-util.js
+++ b/dev/manifest-util.js
@@ -21,6 +21,11 @@ const path = require('path');
 const childProcess = require('child_process');
 
 
+/**
+ * @template T
+ * @param {T} value
+ * @returns {T}
+ */
 function clone(value) {
     return JSON.parse(JSON.stringify(value));
 }
@@ -29,16 +34,24 @@ function clone(value) {
 class ManifestUtil {
     constructor() {
         const fileName = path.join(__dirname, 'data', 'manifest-variants.json');
-        const {manifest, variants, defaultVariant} = JSON.parse(fs.readFileSync(fileName));
+        const {manifest, variants, defaultVariant} = /** @type {import('dev/manifest').Manifest} */ (JSON.parse(fs.readFileSync(fileName, {encoding: 'utf8'})));
+        /** @type {chrome.runtime.Manifest} */
         this._manifest = manifest;
+        /** @type {import('dev/manifest').ManifestVariant[]} */
         this._variants = variants;
+        /** @type {string} */
         this._defaultVariant = defaultVariant;
+        /** @type {Map<string, import('dev/manifest').ManifestVariant>} */
         this._variantMap = new Map();
         for (const variant of variants) {
             this._variantMap.set(variant.name, variant);
         }
     }
 
+    /**
+     * @param {?string} [variantName]
+     * @returns {chrome.runtime.Manifest}
+     */
     getManifest(variantName) {
         if (typeof variantName === 'string') {
             const variant = this._variantMap.get(variantName);
@@ -57,20 +70,36 @@ class ManifestUtil {
         return clone(this._manifest);
     }
 
+    /**
+     * @returns {import('dev/manifest').ManifestVariant[]}
+     */
     getVariants() {
         return [...this._variants];
     }
 
+    /**
+     * @param {string} name
+     * @returns {import('dev/manifest').ManifestVariant|undefined}
+     */
     getVariant(name) {
         return this._variantMap.get(name);
     }
 
+    /**
+     * @param {chrome.runtime.Manifest} manifest
+     * @returns {string}
+     */
     static createManifestString(manifest) {
         return JSON.stringify(manifest, null, 4) + '\n';
     }
 
     // Private
 
+    /**
+     * @param {import('dev/manifest').Command} data
+     * @returns {string}
+     * @throws {Error}
+     */
     _evaluateModificationCommand(data) {
         const {command, args, trim} = data;
         const {stdout, stderr, status} = childProcess.spawnSync(command, args, {
@@ -87,6 +116,11 @@ class ManifestUtil {
         return result;
     }
 
+    /**
+     * @param {chrome.runtime.Manifest} manifest
+     * @param {import('dev/manifest').Modification[]} modifications
+     * @returns {chrome.runtime.Manifest}
+     */
     _applyModifications(manifest, modifications) {
         if (Array.isArray(modifications)) {
             for (const modification of modifications) {
@@ -95,6 +129,7 @@ class ManifestUtil {
                     case 'set':
                         {
                             let {value, before, after, command} = modification;
+                            /** @type {import('core').UnknownObject} */
                             const object = this._getObjectProperties(manifest, path2, path2.length - 1);
                             const key = path2[path2.length - 1];
 
@@ -119,6 +154,7 @@ class ManifestUtil {
                     case 'replace':
                         {
                             const {pattern, patternFlags, replacement} = modification;
+                            /** @type {import('core').UnknownObject} */
                             const value = this._getObjectProperties(manifest, path2, path2.length - 1);
                             const regex = new RegExp(pattern, patternFlags);
                             const last = path2[path2.length - 1];
@@ -129,6 +165,7 @@ class ManifestUtil {
                         break;
                     case 'delete':
                         {
+                            /** @type {import('core').UnknownObject} */
                             const value = this._getObjectProperties(manifest, path2, path2.length - 1);
                             const last = path2[path2.length - 1];
                             delete value[last];
@@ -137,6 +174,7 @@ class ManifestUtil {
                     case 'remove':
                         {
                             const {item} = modification;
+                            /** @type {unknown[]} */
                             const value = this._getObjectProperties(manifest, path2, path2.length);
                             const index = value.indexOf(item);
                             if (index >= 0) { value.splice(index, 1); }
@@ -145,6 +183,7 @@ class ManifestUtil {
                     case 'splice':
                         {
                             const {start, deleteCount, items} = modification;
+                            /** @type {unknown[]} */
                             const value = this._getObjectProperties(manifest, path2, path2.length);
                             const itemsNew = items.map((v) => clone(v));
                             value.splice(start, deleteCount, ...itemsNew);
@@ -156,7 +195,9 @@ class ManifestUtil {
                             const {newPath, before, after} = modification;
                             const oldKey = path2[path2.length - 1];
                             const newKey = newPath[newPath.length - 1];
+                            /** @type {import('core').UnknownObject} */
                             const oldObject = this._getObjectProperties(manifest, path2, path2.length - 1);
+                            /** @type {import('core').UnknownObject} */
                             const newObject = this._getObjectProperties(manifest, newPath, newPath.length - 1);
                             const oldObjectIsNewObject = this._arraysAreSame(path2, newPath, -1);
                             const value = oldObject[oldKey];
@@ -182,6 +223,7 @@ class ManifestUtil {
                     case 'add':
                         {
                             const {items} = modification;
+                            /** @type {unknown[]} */
                             const value = this._getObjectProperties(manifest, path2, path2.length);
                             const itemsNew = items.map((v) => clone(v));
                             value.push(...itemsNew);
@@ -194,6 +236,13 @@ class ManifestUtil {
         return manifest;
     }
 
+    /**
+     * @template T
+     * @param {T[]} array1
+     * @param {T[]} array2
+     * @param {number} lengthOffset
+     * @returns {boolean}
+     */
     _arraysAreSame(array1, array2, lengthOffset) {
         let ii = array1.length;
         if (ii !== array2.length) { return false; }
@@ -204,10 +253,21 @@ class ManifestUtil {
         return true;
     }
 
+    /**
+     * @param {import('core').UnknownObject} object
+     * @param {string|number} key
+     * @returns {number}
+     */
     _getObjectKeyIndex(object, key) {
-        return Object.keys(object).indexOf(key);
+        return Object.keys(object).indexOf(typeof key === 'string' ? key : `${key}`);
     }
 
+    /**
+     * @param {import('core').UnknownObject} object
+     * @param {string|number} key
+     * @param {unknown} value
+     * @param {number} index
+     */
     _setObjectKeyAtIndex(object, key, value, index) {
         if (index < 0 || typeof key === 'number' || Object.prototype.hasOwnProperty.call(object, key)) {
             object[key] = value;
@@ -227,13 +287,24 @@ class ManifestUtil {
         }
     }
 
+    /**
+     * @template [TReturn=unknown]
+     * @param {unknown} object
+     * @param {import('dev/manifest').PropertyPath} path2
+     * @param {number} count
+     * @returns {TReturn}
+     */
     _getObjectProperties(object, path2, count) {
         for (let i = 0; i < count; ++i) {
-            object = object[path2[i]];
+            object = /** @type {import('core').UnknownObject} */ (object)[path2[i]];
         }
-        return object;
+        return /** @type {TReturn} */ (object);
     }
 
+    /**
+     * @param {import('dev/manifest').ManifestVariant} variant
+     * @returns {import('dev/manifest').ManifestVariant[]}
+     */
     _getInheritanceChain(variant) {
         const visited = new Set();
         const inheritance = [];
@@ -254,6 +325,11 @@ class ManifestUtil {
         return inheritance;
     }
 
+    /**
+     * @param {chrome.runtime.Manifest} manifest
+     * @param {import('dev/manifest').ManifestVariant} variant
+     * @returns {chrome.runtime.Manifest}
+     */
     _createVariantManifest(manifest, variant) {
         let modifiedManifest = clone(manifest);
         for (const {modifications} of this._getInheritanceChain(variant)) {
diff --git a/dev/patch-dependencies.js b/dev/patch-dependencies.js
index 81572c5ca2..80b9d52ffa 100644
--- a/dev/patch-dependencies.js
+++ b/dev/patch-dependencies.js
@@ -40,6 +40,7 @@ function patchNwsapi() {
     testJSDOM();
 }
 
+/** */
 function main() {
     patchNwsapi();
 }
diff --git a/dev/schema-validate.js b/dev/schema-validate.js
index 1d7607b70c..de8bd499b3 100644
--- a/dev/schema-validate.js
+++ b/dev/schema-validate.js
@@ -19,43 +19,62 @@
 const fs = require('fs');
 const {performance} = require('perf_hooks');
 const {VM} = require('./vm');
+const {DataError} = require('./data-error');
 
 const vm = new VM();
 vm.execute([
     'js/core.js',
+    'js/core/extension-error.js',
     'js/general/cache-map.js',
     'js/data/json-schema.js'
 ]);
-const JsonSchema = vm.get('JsonSchema');
+/** @type {typeof JsonSchema} */
+const JsonSchema2 = vm.getSingle('JsonSchema');
 
 class JsonSchemaAjv {
+    /**
+     * @param {import('dev/schema-validate').Schema} schema
+     */
     constructor(schema) {
-        const Ajv = require('ajv');
+        const Ajv = /** @type {import('dev/schema-validate').Ajv} */ (/** @type {unknown} */ (require('ajv')));
         const ajv = new Ajv({
             meta: false,
             strictTuples: false,
             allowUnionTypes: true
         });
-        ajv.addMetaSchema(require('ajv/dist/refs/json-schema-draft-07.json'));
-        this._validate = ajv.compile(schema);
+        const metaSchemaPath = require.resolve('ajv/dist/refs/json-schema-draft-07.json');
+        const metaSchema = JSON.parse(fs.readFileSync(metaSchemaPath, {encoding: 'utf8'}));
+        ajv.addMetaSchema(metaSchema);
+        /** @type {import('ajv').ValidateFunction} */
+        this._validate = ajv.compile(/** @type {import('ajv').Schema} */ (schema));
     }
 
+    /**
+     * @param {unknown} data
+     * @throws {Error}
+     */
     validate(data) {
         if (this._validate(data)) { return; }
         const {errors} = this._validate;
-        const error = new Error('Schema validation failed');
+        const error = new DataError('Schema validation failed');
         error.data = JSON.parse(JSON.stringify(errors));
         throw error;
     }
 }
 
+/**
+ * @param {import('dev/schema-validate').ValidateMode} mode
+ * @param {import('dev/schema-validate').Schema} schema
+ * @returns {JsonSchema|JsonSchemaAjv}
+ */
 function createJsonSchema(mode, schema) {
     switch (mode) {
         case 'ajv': return new JsonSchemaAjv(schema);
-        default: return new JsonSchema(schema);
+        default: return new JsonSchema2(/** @type {import('json-schema').Schema} */ (schema));
     }
 }
 
+/** */
 function main() {
     const args = process.argv.slice(2);
     if (args.length < 2) {
@@ -66,6 +85,7 @@ function main() {
         return;
     }
 
+    /** @type {import('dev/schema-validate').ValidateMode} */
     let mode = null;
     if (args[0] === '--ajv') {
         mode = 'ajv';
diff --git a/dev/translator-vm.js b/dev/translator-vm.js
index e3b700ff07..a6ef118707 100644
--- a/dev/translator-vm.js
+++ b/dev/translator-vm.js
@@ -22,26 +22,45 @@ const assert = require('assert');
 const {DatabaseVM, DatabaseVMDictionaryImporterMediaLoader} = require('./database-vm');
 const {createDictionaryArchive} = require('./util');
 
+/**
+ * @template T
+ * @param {T} value
+ * @returns {T}
+ */
 function clone(value) {
     return JSON.parse(JSON.stringify(value));
 }
 
 class TranslatorVM extends DatabaseVM {
+    /**
+     * @param {import('core').UnknownObject} [globals]
+     */
     constructor(globals) {
         super(globals);
+        /** @type {?JapaneseUtil} */
         this._japaneseUtil = null;
+        /** @type {?Translator} */
         this._translator = null;
+        /** @type {?AnkiNoteDataCreator} */
         this._ankiNoteDataCreator = null;
+        /** @type {?string} */
         this._dictionaryName = null;
     }
 
+    /** @type {Translator} */
     get translator() {
+        if (this._translator === null) { throw new Error('Not prepared'); }
         return this._translator;
     }
 
+    /**
+     * @param {string} dictionaryDirectory
+     * @param {string} dictionaryName
+     */
     async prepare(dictionaryDirectory, dictionaryName) {
         this.execute([
             'js/core.js',
+            'js/core/extension-error.js',
             'js/data/sandbox/anki-note-data-creator.js',
             'js/data/database.js',
             'js/data/json-schema.js',
@@ -56,19 +75,18 @@ class TranslatorVM extends DatabaseVM {
             'js/language/translator.js',
             'js/media/media-util.js'
         ]);
-        const [
-            DictionaryImporter,
-            DictionaryDatabase,
-            JapaneseUtil,
-            Translator,
-            AnkiNoteDataCreator
-        ] = this.get([
+        const values = this.get([
             'DictionaryImporter',
             'DictionaryDatabase',
             'JapaneseUtil',
             'Translator',
             'AnkiNoteDataCreator'
         ]);
+        const DictionaryImporter2 = /** @type {typeof DictionaryImporter} */ (values[0]);
+        const DictionaryDatabase2 = /** @type {typeof DictionaryDatabase} */ (values[1]);
+        const JapaneseUtil2 = /** @type {typeof JapaneseUtil} */ (values[2]);
+        const Translator2 = /** @type {typeof Translator} */ (values[3]);
+        const AnkiNoteDataCreator2 = /** @type {typeof AnkiNoteDataCreator} */ (values[4]);
 
         // Dictionary
         this._dictionaryName = dictionaryName;
@@ -77,8 +95,8 @@ class TranslatorVM extends DatabaseVM {
 
         // Setup database
         const dictionaryImporterMediaLoader = new DatabaseVMDictionaryImporterMediaLoader();
-        const dictionaryImporter = new DictionaryImporter(dictionaryImporterMediaLoader, null);
-        const dictionaryDatabase = new DictionaryDatabase();
+        const dictionaryImporter = new DictionaryImporter2(dictionaryImporterMediaLoader);
+        const dictionaryDatabase = new DictionaryDatabase2();
         await dictionaryDatabase.prepare();
 
         const {errors} = await dictionaryImporter.importDictionary(
@@ -90,24 +108,34 @@ class TranslatorVM extends DatabaseVM {
         assert.deepStrictEqual(errors.length, 0);
 
         // Setup translator
-        this._japaneseUtil = new JapaneseUtil(null);
-        this._translator = new Translator({
+        this._japaneseUtil = new JapaneseUtil2(null);
+        this._translator = new Translator2({
             japaneseUtil: this._japaneseUtil,
             database: dictionaryDatabase
         });
-        const deinflectionReasions = JSON.parse(fs.readFileSync(path.join(__dirname, '..', 'ext', 'data/deinflect.json')));
+        const deinflectionReasions = JSON.parse(fs.readFileSync(path.join(__dirname, '..', 'ext', 'data/deinflect.json'), {encoding: 'utf8'}));
         this._translator.prepare(deinflectionReasions);
 
         // Assign properties
-        this._ankiNoteDataCreator = new AnkiNoteDataCreator(this._japaneseUtil);
+        this._ankiNoteDataCreator = new AnkiNoteDataCreator2(this._japaneseUtil);
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @param {import('settings').ResultOutputMode} mode
+     * @returns {import('anki-templates').NoteData}
+     * @throws {Error}
+     */
     createTestAnkiNoteData(dictionaryEntry, mode) {
+        if (this._ankiNoteDataCreator === null) {
+            throw new Error('Not prepared');
+        }
         const marker = '{marker}';
+        /** @type {import('anki-templates-internal').CreateDetails} */
         const data = {
             dictionaryEntry,
             resultOutputMode: mode,
-            mode: 'mode',
+            mode: 'test',
             glossaryLayoutMode: 'default',
             compactTags: false,
             context: {
@@ -122,8 +150,16 @@ class TranslatorVM extends DatabaseVM {
         return this._ankiNoteDataCreator.create(marker, data);
     }
 
+    /**
+     * @template {import('translation').FindTermsOptions|import('translation').FindKanjiOptions} T
+     * @param {import('dev/vm').OptionsPresetObject} optionsPresets
+     * @param {string|import('dev/vm').OptionsPresetObject|(string|import('dev/vm').OptionsPresetObject)[]} optionsArray
+     * @returns {T}
+     * @throws {Error}
+     */
     buildOptions(optionsPresets, optionsArray) {
         const dictionaryName = this._dictionaryName;
+        /** @type {import('core').UnknownObject} */
         const options = {};
         if (!Array.isArray(optionsArray)) { optionsArray = [optionsArray]; }
         for (const entry of optionsArray) {
@@ -174,7 +210,7 @@ class TranslatorVM extends DatabaseVM {
             null
         );
 
-        return options;
+        return /** @type {T} */ (options);
     }
 }
 
diff --git a/dev/util.js b/dev/util.js
index 65b1d98205..e6c1b49fdf 100644
--- a/dev/util.js
+++ b/dev/util.js
@@ -20,19 +20,30 @@ const fs = require('fs');
 const path = require('path');
 
 
+/** @type {?import('jszip')} */
 let JSZip = null;
 
 
+/**
+ * @returns {import('jszip')}
+ */
 function getJSZip() {
     if (JSZip === null) {
+        // @ts-ignore - Legacy support
         process.noDeprecation = true; // Suppress a warning about JSZip
         JSZip = require(path.join(__dirname, '../ext/lib/jszip.min.js'));
+        // @ts-ignore - Legacy support
         process.noDeprecation = false;
     }
-    return JSZip;
+    return /** @type {import('jszip')} */ (JSZip);
 }
 
 
+/**
+ * @param {string[]} args
+ * @param {Map<?string, (boolean|null|number|string|string[])>} argMap
+ * @returns {Map<?string, (boolean|null|number|string|string[])>}
+ */
 function getArgs(args, argMap) {
     let key = null;
     let canKey = true;
@@ -77,11 +88,16 @@ function getArgs(args, argMap) {
     return argMap;
 }
 
+/**
+ * @param {string} baseDirectory
+ * @param {?(fileName: string) => boolean} predicate
+ * @returns {string[]}
+ */
 function getAllFiles(baseDirectory, predicate=null) {
     const results = [];
     const directories = [baseDirectory];
     while (directories.length > 0) {
-        const directory = directories.shift();
+        const directory = /** @type {string} */ (directories.shift());
         const fileNames = fs.readdirSync(directory);
         for (const fileName of fileNames) {
             const fullFileName = path.join(directory, fileName);
@@ -99,6 +115,11 @@ function getAllFiles(baseDirectory, predicate=null) {
     return results;
 }
 
+/**
+ * @param {string} dictionaryDirectory
+ * @param {string} [dictionaryName]
+ * @returns {import('jszip')}
+ */
 function createDictionaryArchive(dictionaryDirectory, dictionaryName) {
     const fileNames = fs.readdirSync(dictionaryDirectory);
 
@@ -123,6 +144,10 @@ function createDictionaryArchive(dictionaryDirectory, dictionaryName) {
 }
 
 
+/**
+ * @param {(...args: import('core').SafeAny[]) => (unknown|Promise<unknown>)} func
+ * @param {...import('core').SafeAny} args
+ */
 async function testMain(func, ...args) {
     try {
         await func(...args);
@@ -134,6 +159,7 @@ async function testMain(func, ...args) {
 
 
 module.exports = {
+    /** @type {import('jszip')} */
     get JSZip() { return getJSZip(); },
     getArgs,
     getAllFiles,
diff --git a/dev/vm.js b/dev/vm.js
index c3266443cd..c22dba3213 100644
--- a/dev/vm.js
+++ b/dev/vm.js
@@ -23,6 +23,11 @@ const assert = require('assert');
 const crypto = require('crypto');
 
 
+/**
+ * @param {vm.Context} context
+ * @param {string[]} names
+ * @returns {unknown[]}
+ */
 function getContextEnvironmentRecords(context, names) {
     // Enables export of values from the declarative environment record
     if (!Array.isArray(names) || names.length === 0) {
@@ -52,6 +57,11 @@ function getContextEnvironmentRecords(context, names) {
     return Array.from(results);
 }
 
+/**
+ * @param {unknown} val1
+ * @param {unknown} val2
+ * @returns {boolean}
+ */
 function isDeepStrictEqual(val1, val2) {
     if (val1 === val2) { return true; }
 
@@ -61,13 +71,21 @@ function isDeepStrictEqual(val1, val2) {
         }
     } else if (typeof val1 === 'object' && val1 !== null) {
         if (typeof val2 === 'object' && val2 !== null) {
-            return isObjectDeepStrictEqual(val1, val2);
+            return isObjectDeepStrictEqual(
+                /** @type {import('core').UnknownObject} */ (val1),
+                /** @type {import('core').UnknownObject} */ (val2)
+            );
         }
     }
 
     return false;
 }
 
+/**
+ * @param {unknown[]} val1
+ * @param {unknown[]} val2
+ * @returns {boolean}
+ */
 function isArrayDeepStrictEqual(val1, val2) {
     const ii = val1.length;
     if (ii !== val2.length) { return false; }
@@ -81,6 +99,11 @@ function isArrayDeepStrictEqual(val1, val2) {
     return true;
 }
 
+/**
+ * @param {import('core').UnknownObject} val1
+ * @param {import('core').UnknownObject} val2
+ * @returns {boolean}
+ */
 function isObjectDeepStrictEqual(val1, val2) {
     const keys1 = Object.keys(val1);
     const keys2 = Object.keys(val2);
@@ -105,6 +128,7 @@ function isObjectDeepStrictEqual(val1, val2) {
     return true;
 }
 
+/** @type {import('dev/vm').VMAssert['deepStrictEqual']} */
 function deepStrictEqual(actual, expected) {
     try {
         // This will fail on prototype === comparison on cross context objects
@@ -117,9 +141,12 @@ function deepStrictEqual(actual, expected) {
 }
 
 
+/**
+ * @returns {(this: import('dev/vm').PseudoURL, url: string) => import('dev/vm').PseudoURL}
+ */
 function createURLClass() {
     const BaseURL = URL;
-    const result = function URL(url) {
+    return function URL(url) {
         const u = new BaseURL(url);
         this.hash = u.hash;
         this.host = u.host;
@@ -133,45 +160,76 @@ function createURLClass() {
         this.search = u.search;
         this.searchParams = u.searchParams;
         this.username = u.username;
+        this.toJSON = () => '<not implemented>';
+        this.toString = () => '<not implemented>';
+        return this;
     };
-    return result;
 }
 
 
 class VM {
+    /**
+     * @param {import('core').UnknownObject} [context]
+     */
     constructor(context={}) {
         context.URL = createURLClass();
         context.crypto = {
+            /**
+             * @param {Uint8Array} array
+             * @returns {Uint8Array}
+             */
             getRandomValues: (array) => {
                 const buffer = crypto.randomBytes(array.byteLength);
                 buffer.copy(array);
                 return array;
             }
         };
+        /** @type {vm.Context} */
         this._context = vm.createContext(context);
+        /** @type {import('dev/vm').VMAssert} */
         this._assert = {
             deepStrictEqual
         };
     }
 
+    /** @type {vm.Context} */
     get context() {
         return this._context;
     }
 
+    /** @type {import('dev/vm').VMAssert} */
     get assert() {
         return this._assert;
     }
 
+    /**
+     * @template [T=unknown[]]
+     * @param {string[]} names
+     * @returns {T}
+     * @throws {Error}
+     */
     get(names) {
-        if (typeof names === 'string') {
-            return getContextEnvironmentRecords(this._context, [names])[0];
-        } else if (Array.isArray(names)) {
-            return getContextEnvironmentRecords(this._context, names);
+        if (Array.isArray(names)) {
+            return /** @type {T} */ (getContextEnvironmentRecords(this._context, names));
         } else {
             throw new Error('Invalid argument');
         }
     }
 
+    /**
+     * @template [TResult=unknown]
+     * @param {string} name
+     * @returns {TResult}
+     * @throws {Error}
+     */
+    getSingle(name) {
+        return /** @type {TResult} */ (getContextEnvironmentRecords(this._context, [name])[0]);
+    }
+
+    /**
+     * @param {import('core').UnknownObject} values
+     * @throws {Error}
+     */
     set(values) {
         if (typeof values === 'object' && values !== null) {
             Object.assign(this._context, values);
@@ -180,14 +238,15 @@ class VM {
         }
     }
 
+    /**
+     * @param {string|string[]} fileNames
+     * @returns {unknown|unknown[]}
+     */
     execute(fileNames) {
         const single = !Array.isArray(fileNames);
-        if (single) {
-            fileNames = [fileNames];
-        }
-
+        const allFileNames = single ? [fileNames] : fileNames;
         const results = [];
-        for (const fileName of fileNames) {
+        for (const fileName of allFileNames) {
             const absoluteFileName = path.resolve(__dirname, '..', 'ext', fileName);
             const source = fs.readFileSync(absoluteFileName, {encoding: 'utf8'});
             const script = new vm.Script(source, {filename: absoluteFileName});
diff --git a/docs/interfaces/dictionary-entry.ts b/docs/interfaces/dictionary-entry.ts
deleted file mode 100644
index 2ad8f70f3d..0000000000
--- a/docs/interfaces/dictionary-entry.ts
+++ /dev/null
@@ -1,479 +0,0 @@
-/*
- * Copyright (C) 2023  Yomitan Authors
- * Copyright (C) 2021-2022  Yomichan Authors
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <https://www.gnu.org/licenses/>.
- */
-
-namespace Translation {
-    // Common
-
-    /**
-     * Enum representing the type of a `DictionaryEntry`.
-     * `'kanji'` corresponds to a KanjiDictionaryEntry.
-     * `'term'` corresponds to a TermDictionaryEntry.
-     */
-    export enum DictionaryEntryType {
-        Kanji = 'kanji',
-        Term = 'term',
-    }
-
-    /**
-     * A generic dictionary entry which is used as the base interface.
-     */
-    export interface DictionaryEntry {
-        /**
-         * The type of the entry.
-         */
-        type: DictionaryEntryType;
-    }
-
-    /**
-     * A tag represents some brief information about part of a dictionary entry.
-     */
-    export interface Tag {
-        /**
-         * The name of the tag.
-         */
-        name: string;
-        /**
-         * The category of the tag.
-         */
-        category: string;
-        /**
-         * A number indicating the sorting order of the tag.
-         */
-        order: number;
-        /**
-         * A score value for the tag.
-         */
-        score: number;
-        /**
-         * An array of descriptions for the tag. * If there are multiple entries,
-         * the values will typically have originated from different dictionaries.
-         * However, there is no correlation between the length of this array and
-         * the length of the `dictionaries` field, as duplicates are removed.
-         */
-        content: string[];
-        /**
-         * An array of dictionary names that contained a tag with this name and category.
-         */
-        dictionaries: string[];
-        /**
-         * Whether or not this tag is redundant with previous tags.
-         */
-        redundant: boolean;
-    }
-
-    // Kanji
-
-    /**
-     * A dictionary entry for a kanji character.
-     * `DictionaryEntry.type` is always `DictionaryEntryType.Kanji`.
-     */
-    export interface KanjiDictionaryEntry extends DictionaryEntry {
-        /**
-         * The kanji character that was looked up.
-         */
-        character: string;
-        /**
-         * The name of the dictionary that the information originated from.
-         */
-        dictionary: string;
-        /**
-         * Onyomi readings for the kanji character.
-         */
-        onyomi: string[];
-        /**
-         * Kunyomi readings for the kanji character.
-         */
-        kunyomi: string[];
-        /**
-         * Tags for the kanji character.
-         */
-        tags: Tag[];
-        /**
-         * An object containing stats about the kanji character.
-         */
-        stats: KanjiStatGroups;
-        /**
-         * Definitions for the kanji character.
-         */
-        definitions: string[];
-        /**
-         * Frequency information for the kanji character.
-         */
-        frequencies: KanjiFrequency[];
-    }
-
-    /**
-     * An object with groups of stats about a kanji character.
-     */
-    export interface KanjiStatGroups {
-        /**
-         * A group of stats.
-         * @param propName The name of the group.
-         */
-        [propName: string]: KanjiStat[];
-    }
-
-    /**
-     * A stat represents a generic piece of information about a kanji character.
-     */
-    export interface KanjiStat {
-        /**
-         * The name of the stat.
-         */
-        name: string;
-        /**
-         * The category of the stat.
-         */
-        category: string;
-        /**
-         * A description of the stat.
-         */
-        content: string;
-        /**
-         * A number indicating the sorting order of the stat.
-         */
-        order: number;
-        /**
-         * A score value for the stat.
-         */
-        score: number;
-        /**
-         * The name of the dictionary that the stat originated from.
-         */
-        dictionary: string;
-        /**
-         * A value for the stat.
-         */
-        value: number | string;
-    }
-
-    /**
-     * Frequency information corresponds to how frequently a character appears in a corpus,
-     * which can be a number of occurrences or an overall rank.
-     */
-    export interface KanjiFrequency {
-        /**
-         * The original order of the frequency, which is usually used for sorting.
-         */
-        index: number;
-        /**
-         * The name of the dictionary that the frequency information originated from.
-         */
-        dictionary: string;
-        /**
-         * The index of the dictionary in the original list of dictionaries used for the lookup.
-         */
-        dictionaryIndex: number;
-        /**
-         * The priority of the dictionary.
-         */
-        dictionaryPriority: number;
-        /**
-         * The kanji character for the frequency.
-         */
-        character: string;
-        /**
-         * The frequency for the character, as a number of occurrences or an overall rank.
-         */
-        frequency: number;
-        /**
-         * A display value to show to the user.
-         */
-        displayValue: string | null;
-        /**
-         * Whether or not the displayValue string was parsed to determine the frequency value.
-         */
-        displayValueParsed: boolean;
-    }
-
-    // Terms
-
-    /**
-     * A dictionary entry for a term or group of terms.
-     * `DictionaryEntry.type` is always `DictionaryEntryType.Term`.
-     */
-    export interface TermDictionaryEntry extends DictionaryEntry {
-        /**
-         * Whether or not any of the sources is a primary source. Primary sources are derived from the
-         * original search text, while non-primary sources originate from related terms.
-         */
-        isPrimary: boolean;
-        /**
-         * A list of inflections that was applied to get the term.
-         */
-        inflections: string[];
-        /**
-         * A score for the dictionary entry.
-         */
-        score: number;
-        /**
-         * The index of the dictionary in the original list of dictionaries used for the lookup.
-         */
-        dictionaryIndex: number;
-        /**
-         * The priority of the dictionary.
-         */
-        dictionaryPriority: number;
-        /**
-         * The number of primary sources that had an exact text match for the term.
-         */
-        sourceTermExactMatchCount: number;
-        /**
-         * The maximum length of the transformed text for all primary sources.
-         */
-        maxTransformedTextLength: number;
-        /**
-         * Headwords for the entry.
-         */
-        headwords: TermHeadword[];
-        /**
-         * Definitions for the entry.
-         */
-        definitions: TermDefinition[];
-        /**
-         * Pronunciations for the entry.
-         */
-        pronunciations: TermPronunciation[];
-        /**
-         * Frequencies for the entry.
-         */
-        frequencies: TermFrequency[];
-    }
-
-    /**
-     * A term headword is a combination of a term, reading, and auxiliary information.
-     */
-    export interface TermHeadword {
-        /**
-         * The original order of the headword, which is usually used for sorting.
-         */
-        index: number;
-        /**
-         * The text for the term.
-         */
-        term: string;
-        /**
-         * The reading of the term.
-         */
-        reading: string;
-        /**
-         * The sources of the term.
-         */
-        sources: TermSource[];
-        /**
-         * Tags for the headword.
-         */
-        tags: Tag[];
-        /**
-         * List of word classes (part of speech) for the headword.
-         */
-        wordClasses: string[];
-    }
-
-    /**
-     * A definition contains a list of entries and information about what what terms it corresponds to.
-     */
-    export interface TermDefinition {
-        /**
-         * The original order of the definition, which is usually used for sorting.
-         */
-        index: number;
-        /**
-         * A list of headwords that this definition corresponds to.
-         */
-        headwordIndices: number[];
-        /**
-         * The name of the dictionary that the definition information originated from.
-         */
-        dictionary: string;
-        /**
-         * The index of the dictionary in the original list of dictionaries used for the lookup.
-         */
-        dictionaryIndex: number;
-        /**
-         * The priority of the dictionary.
-         */
-        dictionaryPriority: number;
-        /**
-         * Database ID for the definition.
-         */
-        id: number[];
-        /**
-         * A score for the definition.
-         */
-        score: number;
-        /**
-         * A list of database sequence numbers for the term. A value of `-1` corresponds to no sequence.
-         * The list can have multiple values if multiple definitions with different sequences have been merged.
-         * The list should always have at least one item.
-         */
-        sequences: number;
-        /**
-         * Tags for the definition.
-         */
-        tags: Tag[];
-        /**
-         * The definition entries.
-         */
-        entries: string[];
-    }
-
-    /**
-     * A term pronunciation represents different ways to pronounce one of the headwords.
-     */
-    export interface TermPronunciation {
-        /**
-         * The original order of the pronunciation, which is usually used for sorting.
-         */
-        index: number;
-        /**
-         * Which headword this pronunciation corresponds to.
-         */
-        headwordIndex: number;
-        /**
-         * The name of the dictionary that the proununciation information originated from.
-         */
-        dictionary: string;
-        /**
-         * The index of the dictionary in the original list of dictionaries used for the lookup.
-         */
-        dictionaryIndex: number;
-        /**
-         * The priority of the dictionary.
-         */
-        dictionaryPriority: number;
-        /**
-         * The pitch accent representations for the term.
-         */
-        pitches: TermPitch[];
-    }
-
-    /**
-     * Pitch accent information for a term, represented as the position of the downstep.
-     */
-    export interface TermPitch {
-        /**
-         * Position of the downstep, as a number of mora.
-         */
-        position: number;
-        /**
-         * Positions of morae with a nasal sound.
-         */
-        nasalPositions: number[];
-        /**
-         * Positions of morae with a devoiced sound.
-         */
-        devoicePositions: [];
-        /**
-         * Tags for the pitch accent.
-         */
-        tags: Tag[];
-    }
-
-    /**
-     * Frequency information corresponds to how frequently a term appears in a corpus,
-     * which can be a number of occurrences or an overall rank.
-     */
-    export interface TermFrequency {
-        /**
-         * The original order of the frequency, which is usually used for sorting.
-         */
-        index: number;
-        /**
-         * Which headword this frequency corresponds to.
-         */
-        headwordIndex: number;
-        /**
-         * The name of the dictionary that the frequency information originated from.
-         */
-        dictionary: string;
-        /**
-         * The index of the dictionary in the original list of dictionaries used for the lookup.
-         */
-        dictionaryIndex: number;
-        /**
-         * The priority of the dictionary.
-         */
-        dictionaryPriority: number;
-        /**
-         * Whether or not the frequency had an explicit reading specified.
-         */
-        hasReading: boolean;
-        /**
-         * The frequency for the term, as a number of occurrences or an overall rank.
-         */
-        frequency: number;
-        /**
-         * A display value to show to the user.
-         */
-        displayValue: string | null;
-        /**
-         * Whether or not the displayValue string was parsed to determine the frequency value.
-         */
-        displayValueParsed: boolean;
-    }
-
-    /**
-     * Enum representing how the search term relates to the final term.
-     */
-     export enum TermSourceMatchType {
-        Exact = 'exact',
-        Prefix = 'prefix',
-        Suffix = 'suffix',
-    }
-
-    /**
-     * Enum representing what database field was used to match the source term.
-     */
-    export enum TermSourceMatchSource {
-        Term = 'term',
-        Reading = 'reading',
-        Sequence = 'sequence',
-    }
-
-    /**
-     * Source information represents how the original text was transformed to get to the final term.
-     */
-    export interface TermSource {
-        /**
-         * The original text that was searched.
-         */
-        originalText: string;
-        /**
-         * The original text after being transformed, but before applying deinflections.
-         */
-        transformedText: string;
-        /**
-         * The final text after applying deinflections.
-         */
-        deinflectedText: string;
-        /**
-         * How the deinflected text matches the value from the database.
-         */
-        matchType: TermSourceMatchType;
-        /**
-         * Which field was used to match the database entry.
-         */
-        matchSource: TermSourceMatchSource;
-        /**
-         * Whether or not this source is a primary source. Primary sources are derived from the
-         * original search text, while non-primary sources originate from related terms.
-         */
-        isPrimary: boolean;
-    }
-}
diff --git a/docs/interfaces/translator-types.ts b/docs/interfaces/translator-types.ts
deleted file mode 100644
index 305f5ef228..0000000000
--- a/docs/interfaces/translator-types.ts
+++ /dev/null
@@ -1,178 +0,0 @@
-/*
- * Copyright (C) 2023  Yomitan Authors
- * Copyright (C) 2022  Yomichan Authors
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <https://www.gnu.org/licenses/>.
- */
-
-namespace Translation {
-    // Kanji
-
-    /**
-     * An options object for use with `Translator.findKanji`.
-     */
-    export interface FindKanjiOptions {
-        /**
-         * The mapping of dictionaries to search for kanji in.
-         * The key is the dictionary name.
-         */
-        enabledDictionaryMap: Map<string, FindKanjiDictionary>;
-    }
-
-    /**
-     * Details about a dictionary.
-     */
-    export interface FindKanjiDictionary {
-        /**
-         * The index of the dictionary
-         */
-        index: number;
-        /**
-         * The priority of the dictionary
-         */
-        priority: number;
-    }
-
-    // Terms
-
-    /**
-     * An options object for use with `Translator.findTerms`.
-     */
-    export interface FindTermsOptions {
-        /**
-         * The matching type for looking up terms.
-         */
-        matchType: FindTermsMatchType;
-        /**
-         * The name of the primary dictionary to search.
-         */
-        mainDictionary: string;
-        /**
-         * The name of the frequency dictionary used for sorting
-         */
-        sortFrequencyDictionary: string | null;
-        /**
-         * The order used when using a sorting dictionary.
-         */
-        sortFrequencyDictionaryOrder: FindTermsSortOrder;
-        /**
-         * Whether or not non-Japanese characters should be searched.
-         */
-        removeNonJapaneseCharacters: boolean;
-        /**
-         * Whether or not half-width characters should be converted to full-width characters.
-         */
-        convertHalfWidthCharacters: FindTermsVariantMode;
-        /**
-         * Whether or not ASCII numeric characters should be converted to full-width numeric characters.
-         */
-        convertNumericCharacters: FindTermsVariantMode;
-        /**
-         * Whether or not alphabetic characters should be converted to kana.
-         */
-        convertAlphabeticCharacters: FindTermsVariantMode;
-        /**
-         * Whether or not hiragana characters should be converted to katakana.
-         */
-        convertHiraganaToKatakana: FindTermsVariantMode;
-        /**
-         * Whether or not katakana characters should be converted to hiragana.
-         */
-        convertKatakanaToHiragana: FindTermsVariantMode;
-        /**
-         * How emphatic character sequences should be collapsed.
-         */
-        collapseEmphaticSequences: FindTermsEmphaticSequencesMode;
-        /**
-         * An iterable sequence of text replacements to be applied during the term lookup process.
-         */
-        textReplacements: Iterable<(FindTermsTextReplacement | null)> | null;
-        /**
-         * The mapping of dictionaries to search for terms in.
-         * The key is the dictionary name.
-         */
-        enabledDictionaryMap: Map<string, FindTermDictionary>;
-        /**
-         * A set of dictionary names which should have definitions removed.
-         */
-        excludeDictionaryDefinitions: Set<string> | null;
-    }
-
-    /**
-     * The matching type for looking up terms.
-     */
-    export enum FindTermsMatchType {
-        Exact = 'exact',
-        Prefix = 'prefix',
-        Suffix = 'suffix',
-    }
-
-    /**
-     * A sorting order to use when finding terms.
-     */
-     export enum FindTermsSortOrder {
-        Ascending = 'ascending',
-        Descending = 'descending',
-    }
-
-    /**
-     * Mode describing how to handle variations.
-     */
-     export enum FindTermsVariantMode {
-        False = 'false',
-        True = 'true',
-        Variant = 'variant',
-    }
-
-    /**
-     * Mode describing how to handle emphatic sequence variations.
-     */
-     export enum FindTermsEmphaticSequencesMode {
-        False = 'false',
-        True = 'true',
-        Full = 'full',
-    }
-
-    /**
-     * Information about how text should be replaced when looking up terms.
-     */
-    export interface FindTermsTextReplacement {
-        /**
-         * The pattern to replace.
-         */
-        pattern: RegExp;
-        /**
-         * The replacement string. This can contain special sequences, such as `$&`.
-         */
-        replacement: string;
-    }
-
-    /**
-     * Details about a dictionary.
-     */
-    export interface FindTermDictionary {
-        /**
-         * The index of the dictionary
-         */
-        index: number;
-        /**
-         * The priority of the dictionary
-         */
-        priority: number;
-        /**
-         * Whether or not secondary term searches are allowed for this dictionary.
-         */
-        allowSecondarySearches: boolean;
-    }
-}
diff --git a/ext/action-popup.html b/ext/action-popup.html
index d153f6eb29..4d31abe8e1 100644
--- a/ext/action-popup.html
+++ b/ext/action-popup.html
@@ -83,6 +83,7 @@ <h3 id="extension-info">Yomitan</h3>
 
 <!-- Scripts -->
 <script src="/js/core.js"></script>
+<script src="/js/core/extension-error.js"></script>
 
 <script src="/js/yomichan.js"></script>
 
diff --git a/ext/background.html b/ext/background.html
index 71990295c8..8628591f77 100644
--- a/ext/background.html
+++ b/ext/background.html
@@ -21,6 +21,7 @@
 <script src="/lib/wanakana.min.js"></script>
 
 <script src="/js/core.js"></script>
+<script src="/js/core/extension-error.js"></script>
 
 <script src="/js/yomichan.js"></script>
 
diff --git a/ext/data/schemas/dictionary-term-bank-v3-schema.json b/ext/data/schemas/dictionary-term-bank-v3-schema.json
index 335144c7b4..68ec8c84d8 100644
--- a/ext/data/schemas/dictionary-term-bank-v3-schema.json
+++ b/ext/data/schemas/dictionary-term-bank-v3-schema.json
@@ -154,6 +154,10 @@
                                     "type": "string",
                                     "description": "Hover text for the image."
                                 },
+                                "description": {
+                                    "type": "string",
+                                    "description": "Description of the image."
+                                },
                                 "pixelated": {
                                     "type": "boolean",
                                     "description": "Whether or not the image should appear pixelated at sizes larger than the image's native resolution.",
diff --git a/ext/data/schemas/options-schema.json b/ext/data/schemas/options-schema.json
index 601f5d06ec..2903c3cedc 100644
--- a/ext/data/schemas/options-schema.json
+++ b/ext/data/schemas/options-schema.json
@@ -540,9 +540,12 @@
                                                         "searchKanji",
                                                         "scanOnTouchMove",
                                                         "scanOnTouchPress",
+                                                        "scanOnTouchRelease",
                                                         "scanOnPenMove",
                                                         "scanOnPenHover",
                                                         "scanOnPenReleaseHover",
+                                                        "scanOnPenPress",
+                                                        "scanOnPenRelease",
                                                         "preventTouchScrolling",
                                                         "preventPenScrolling"
                                                     ],
diff --git a/ext/info.html b/ext/info.html
index 38097502f2..bd10d7ea6a 100644
--- a/ext/info.html
+++ b/ext/info.html
@@ -61,6 +61,7 @@ <h2 id="links">Links</h2>
 
 <!-- Scripts -->
 <script src="/js/core.js"></script>
+<script src="/js/core/extension-error.js"></script>
 
 <script src="/js/yomichan.js"></script>
 
diff --git a/ext/js/accessibility/accessibility-controller.js b/ext/js/accessibility/accessibility-controller.js
index aa27cbf478..890647f5f0 100644
--- a/ext/js/accessibility/accessibility-controller.js
+++ b/ext/js/accessibility/accessibility-controller.js
@@ -25,15 +25,19 @@ class AccessibilityController {
      * @param {ScriptManager} scriptManager An instance of the `ScriptManager` class.
      */
     constructor(scriptManager) {
+        /** @type {ScriptManager} */
         this._scriptManager = scriptManager;
+        /** @type {?import('core').TokenObject} */
         this._updateGoogleDocsAccessibilityToken = null;
+        /** @type {?Promise<void>} */
         this._updateGoogleDocsAccessibilityPromise = null;
+        /** @type {boolean} */
         this._forceGoogleDocsHtmlRenderingAny = false;
     }
 
     /**
      * Updates the accessibility handlers.
-     * @param {object} fullOptions The full options object from the `Backend` instance.
+     * @param {import('settings').Options} fullOptions The full options object from the `Backend` instance.
      *   The value is treated as read-only and is not modified.
      */
     async update(fullOptions) {
@@ -50,8 +54,12 @@ class AccessibilityController {
 
     // Private
 
+    /**
+     * @param {boolean} forceGoogleDocsHtmlRenderingAny
+     */
     async _updateGoogleDocsAccessibility(forceGoogleDocsHtmlRenderingAny) {
         // Reentrant token
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._updateGoogleDocsAccessibilityToken = token;
 
@@ -69,6 +77,9 @@ class AccessibilityController {
         this._updateGoogleDocsAccessibilityPromise = null;
     }
 
+    /**
+     * @param {boolean} forceGoogleDocsHtmlRenderingAny
+     */
     async _updateGoogleDocsAccessibilityInner(forceGoogleDocsHtmlRenderingAny) {
         if (this._forceGoogleDocsHtmlRenderingAny === forceGoogleDocsHtmlRenderingAny) { return; }
 
@@ -78,6 +89,7 @@ class AccessibilityController {
         try {
             if (forceGoogleDocsHtmlRenderingAny) {
                 if (await this._scriptManager.isContentScriptRegistered(id)) { return; }
+                /** @type {import('script-manager').RegistrationDetails} */
                 const details = {
                     allFrames: true,
                     matchAboutBlank: true,
diff --git a/ext/js/accessibility/google-docs-util.js b/ext/js/accessibility/google-docs-util.js
index 3d9818ef41..6997dcb35f 100644
--- a/ext/js/accessibility/google-docs-util.js
+++ b/ext/js/accessibility/google-docs-util.js
@@ -30,8 +30,8 @@ class GoogleDocsUtil {
      * Coordinates are provided in [client space](https://developer.mozilla.org/en-US/docs/Web/CSS/CSSOM_View/Coordinate_systems).
      * @param {number} x The x coordinate to search at.
      * @param {number} y The y coordinate to search at.
-     * @param {GetRangeFromPointOptions} options Options to configure how element detection is performed.
-     * @returns {?TextSourceRange|TextSourceElement} A range for the hovered text or element, or `null` if no applicable content was found.
+     * @param {import('document-util').GetRangeFromPointOptions} options Options to configure how element detection is performed.
+     * @returns {?TextSourceRange} A range for the hovered text or element, or `null` if no applicable content was found.
      */
     static getRangeFromPoint(x, y, {normalizeCssZoom}) {
         const styleNode = this._getStyleNode();
@@ -47,10 +47,13 @@ class GoogleDocsUtil {
         return null;
     }
 
+    /**
+     * @returns {HTMLStyleElement}
+     */
     static _getStyleNode() {
         // This <style> node is necessary to force the SVG <rect> elements to have a fill,
         // which allows them to be included in document.elementsFromPoint's return value.
-        if (this._styleNode === null) {
+        if (typeof this._styleNode === 'undefined') {
             const style = document.createElement('style');
             style.textContent = [
                 '.kix-canvas-tile-content{pointer-events:none!important;}',
@@ -65,21 +68,34 @@ class GoogleDocsUtil {
         return this._styleNode;
     }
 
+    /**
+     * @param {Element} element
+     * @param {string} text
+     * @param {number} x
+     * @param {number} y
+     * @param {boolean} normalizeCssZoom
+     * @returns {TextSourceRange}
+     */
     static _createRange(element, text, x, y, normalizeCssZoom) {
         // Create imposter
         const content = document.createTextNode(text);
         const svgText = document.createElementNS('http://www.w3.org/2000/svg', 'text');
         const transform = element.getAttribute('transform') || '';
         const font = element.getAttribute('data-font-css') || '';
-        svgText.setAttribute('x', element.getAttribute('x'));
-        svgText.setAttribute('y', element.getAttribute('y'));
+        const elementX = element.getAttribute('x');
+        const elementY = element.getAttribute('y');
+        if (typeof elementX === 'string') { svgText.setAttribute('x', elementX); }
+        if (typeof elementY === 'string') { svgText.setAttribute('y', elementY); }
         svgText.appendChild(content);
         const textStyle = svgText.style;
         this._setImportantStyle(textStyle, 'all', 'initial');
         this._setImportantStyle(textStyle, 'transform', transform);
         this._setImportantStyle(textStyle, 'font', font);
         this._setImportantStyle(textStyle, 'text-anchor', 'start');
-        element.parentNode.appendChild(svgText);
+        const {parentNode} = element;
+        if (parentNode !== null) {
+            parentNode.appendChild(svgText);
+        }
 
         // Adjust offset
         const elementRect = element.getBoundingClientRect();
@@ -94,6 +110,13 @@ class GoogleDocsUtil {
         return TextSourceRange.createFromImposter(range, svgText, element);
     }
 
+    /**
+     * @param {Text} textNode
+     * @param {number} x
+     * @param {number} y
+     * @param {boolean} normalizeCssZoom
+     * @returns {Range}
+     */
     static _getRangeWithPoint(textNode, x, y, normalizeCssZoom) {
         if (normalizeCssZoom) {
             const scale = DocumentUtil.computeZoomScale(textNode);
@@ -102,7 +125,7 @@ class GoogleDocsUtil {
         }
         const range = document.createRange();
         let start = 0;
-        let end = textNode.nodeValue.length;
+        let end = /** @type {string} */ (textNode.nodeValue).length;
         while (end - start > 1) {
             const mid = Math.floor((start + end) / 2);
             range.setStart(textNode, mid);
@@ -118,9 +141,16 @@ class GoogleDocsUtil {
         return range;
     }
 
+    /**
+     * @param {CSSStyleDeclaration} style
+     * @param {string} propertyName
+     * @param {string} value
+     */
     static _setImportantStyle(style, propertyName, value) {
         style.setProperty(propertyName, value, 'important');
     }
 }
+
+/** @type {HTMLStyleElement|undefined} */
 // eslint-disable-next-line no-underscore-dangle
-GoogleDocsUtil._styleNode = null;
+GoogleDocsUtil._styleNode = void 0;
diff --git a/ext/js/accessibility/google-docs.js b/ext/js/accessibility/google-docs.js
index f9290078af..da6ab994e4 100644
--- a/ext/js/accessibility/google-docs.js
+++ b/ext/js/accessibility/google-docs.js
@@ -18,9 +18,17 @@
 
 (async () => {
     // Reentrant check
+    // @ts-ignore : Checking a property to the global object
     if (self.googleDocsAccessibilitySetup) { return; }
+    // @ts-ignore : Adding a property to the global object
     self.googleDocsAccessibilitySetup = true;
 
+    /**
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     * @returns {Promise<TReturn>}
+     */
     const invokeApi = (action, params) => {
         return new Promise((resolve, reject) => {
             chrome.runtime.sendMessage({action, params}, (response) => {
@@ -37,6 +45,7 @@
     };
 
     const optionsContext = {depth: 0, url: location.href};
+    /** @type {import('api').OptionsGetResult} */
     let options;
     try {
         options = await invokeApi('optionsGet', {optionsContext});
@@ -48,9 +57,8 @@
 
     // The extension ID below is on an allow-list that is used on the Google Docs webpage.
     /* eslint-disable */
-    const inject = () => {
-        window._docs_annotate_canvas_by_ext = 'ogmnaimimemjmbakcfefmnahgdfhfami';
-    };
+    // @ts-ignore : Adding a property to the global object
+    const inject = () => { window._docs_annotate_canvas_by_ext = 'ogmnaimimemjmbakcfefmnahgdfhfami'; };
     /* eslint-enable */
 
     let parent = document.head;
diff --git a/ext/js/app/content-script-main.js b/ext/js/app/content-script-main.js
index 0006a2440c..b6e200636e 100644
--- a/ext/js/app/content-script-main.js
+++ b/ext/js/app/content-script-main.js
@@ -46,7 +46,9 @@
             parentFrameId: null,
             useProxyPopup: false,
             pageType: 'web',
+            canUseWindowPopup: true,
             allowRootFramePopupProxy: true,
+            childrenSupported: true,
             hotkeyHandler
         });
         await frontend.prepare();
diff --git a/ext/js/app/frontend.js b/ext/js/app/frontend.js
index dc16701d39..9db555173b 100644
--- a/ext/js/app/frontend.js
+++ b/ext/js/app/frontend.js
@@ -20,6 +20,7 @@
  * DocumentUtil
  * GoogleDocsUtil
  * TextScanner
+ * TextSourceElement
  * TextSourceRange
  */
 
@@ -29,19 +30,7 @@
 class Frontend {
     /**
      * Creates a new instance.
-     * @param {object} details Details about how to set up the instance.
-     * @param {string} details.pageType The type of page, one of 'web', 'popup', or 'search'.
-     * @param {PopupFactory} details.popupFactory A PopupFactory instance to use for generating popups.
-     * @param {number} details.depth The nesting depth value of the popup.
-     * @param {number} details.tabId The tab ID of the host tab.
-     * @param {number} details.frameId The frame ID of the host frame.
-     * @param {?string} details.parentPopupId The popup ID of the parent popup if one exists, otherwise null.
-     * @param {?number} details.parentFrameId The frame ID of the parent popup if one exists, otherwise null.
-     * @param {boolean} details.useProxyPopup Whether or not proxy popups should be used.
-     * @param {boolean} details.canUseWindowPopup Whether or not window popups can be used.
-     * @param {boolean} details.allowRootFramePopupProxy Whether or not popups can be hosted in the root frame.
-     * @param {boolean} details.childrenSupported Whether popups can create child popups or not.
-     * @param {HotkeyHandler} details.hotkeyHandler A HotkeyHandler instance.
+     * @param {import('frontend').ConstructorDetails} details Details about how to set up the instance.
      */
     constructor({
         pageType,
@@ -57,24 +46,43 @@ class Frontend {
         childrenSupported=true,
         hotkeyHandler
     }) {
+        /** @type {import('frontend').PageType} */
         this._pageType = pageType;
+        /** @type {PopupFactory} */
         this._popupFactory = popupFactory;
+        /** @type {number} */
         this._depth = depth;
+        /** @type {number|undefined} */
         this._tabId = tabId;
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {?string} */
         this._parentPopupId = parentPopupId;
+        /** @type {?number} */
         this._parentFrameId = parentFrameId;
+        /** @type {boolean} */
         this._useProxyPopup = useProxyPopup;
+        /** @type {boolean} */
         this._canUseWindowPopup = canUseWindowPopup;
+        /** @type {boolean} */
         this._allowRootFramePopupProxy = allowRootFramePopupProxy;
+        /** @type {boolean} */
         this._childrenSupported = childrenSupported;
+        /** @type {HotkeyHandler} */
         this._hotkeyHandler = hotkeyHandler;
+        /** @type {?import('popup').PopupAny} */
         this._popup = null;
+        /** @type {boolean} */
         this._disabledOverride = false;
+        /** @type {?import('settings').ProfileOptions} */
         this._options = null;
+        /** @type {number} */
         this._pageZoomFactor = 1.0;
+        /** @type {number} */
         this._contentScale = 1.0;
+        /** @type {Promise<void>} */
         this._lastShowPromise = Promise.resolve();
+        /** @type {TextScanner} */
         this._textScanner = new TextScanner({
             node: window,
             ignoreElements: this._ignoreElements.bind(this),
@@ -83,19 +91,27 @@ class Frontend {
             searchTerms: true,
             searchKanji: true
         });
+        /** @type {boolean} */
         this._textScannerHasBeenEnabled = false;
+        /** @type {Map<'default'|'window'|'iframe'|'proxy', Promise<?import('popup').PopupAny>>} */
         this._popupCache = new Map();
+        /** @type {EventListenerCollection} */
         this._popupEventListeners = new EventListenerCollection();
+        /** @type {?import('core').TokenObject} */
         this._updatePopupToken = null;
+        /** @type {?number} */
         this._clearSelectionTimer = null;
+        /** @type {boolean} */
         this._isPointerOverPopup = false;
+        /** @type {?import('settings').OptionsContext} */
         this._optionsContextOverride = null;
 
-        this._runtimeMessageHandlers = new Map([
+        /** @type {import('core').MessageHandlerMap} */
+        this._runtimeMessageHandlers = new Map(/** @type {import('core').MessageHandlerArray} */ ([
             ['Frontend.requestReadyBroadcast',   {async: false, handler: this._onMessageRequestFrontendReadyBroadcast.bind(this)}],
             ['Frontend.setAllVisibleOverride',   {async: true,  handler: this._onApiSetAllVisibleOverride.bind(this)}],
             ['Frontend.clearAllVisibleOverride', {async: true,  handler: this._onApiClearAllVisibleOverride.bind(this)}]
-        ]);
+        ]));
 
         this._hotkeyHandler.registerActions([
             ['scanSelectedText', this._onActionScanSelectedText.bind(this)],
@@ -121,7 +137,7 @@ class Frontend {
 
     /**
      * Gets the popup instance.
-     * @type {Popup}
+     * @type {?import('popup').PopupAny}
      */
     get popup() {
         return this._popup;
@@ -144,8 +160,8 @@ class Frontend {
         window.addEventListener('resize', this._onResize.bind(this), false);
         DocumentUtil.addFullscreenChangeEventListener(this._updatePopup.bind(this));
 
-        const visualViewport = window.visualViewport;
-        if (visualViewport !== null && typeof visualViewport === 'object') {
+        const {visualViewport} = window;
+        if (typeof visualViewport !== 'undefined' && visualViewport !== null) {
             visualViewport.addEventListener('scroll', this._onVisualViewportScroll.bind(this));
             visualViewport.addEventListener('resize', this._onVisualViewportResize.bind(this));
         }
@@ -168,7 +184,7 @@ class Frontend {
 
         this._prepareSiteSpecific();
         this._updateContentScale();
-        this._signalFrontendReady();
+        this._signalFrontendReady(null);
     }
 
     /**
@@ -182,7 +198,7 @@ class Frontend {
 
     /**
      * Set or clear an override options context object.
-     * @param {?object} optionsContext An options context object to use as the override, or `null` to clear the override.
+     * @param {?import('settings').OptionsContext} optionsContext An options context object to use as the override, or `null` to clear the override.
      */
     setOptionsContextOverride(optionsContext) {
         this._optionsContextOverride = optionsContext;
@@ -190,7 +206,7 @@ class Frontend {
 
     /**
      * Performs a new search on a specific source.
-     * @param {TextSourceRange|TextSourceElement} textSource The text source to search.
+     * @param {import('text-source').TextSource} textSource The text source to search.
      */
     async setTextSource(textSource) {
         this._textScanner.setCurrentTextSource(null);
@@ -212,7 +228,7 @@ class Frontend {
 
     /**
      * Waits for the previous `showContent` call to be completed.
-     * @returns {Promise} A promise which is resolved when the previous `showContent` call has completed.
+     * @returns {Promise<void>} A promise which is resolved when the previous `showContent` call has completed.
      */
     showContentCompleted() {
         return this._lastShowPromise;
@@ -220,45 +236,73 @@ class Frontend {
 
     // Message handlers
 
+    /**
+     * @param {import('frontend').FrontendRequestReadyBroadcastParams} params
+     */
     _onMessageRequestFrontendReadyBroadcast({frameId}) {
         this._signalFrontendReady(frameId);
     }
 
     // Action handlers
 
+    /**
+     * @returns {void}
+     */
     _onActionScanSelectedText() {
         this._scanSelectedText(false);
     }
 
+    /**
+     * @returns {void}
+     */
     _onActionScanTextAtCaret() {
         this._scanSelectedText(true);
     }
 
     // API message handlers
 
+    /**
+     * @returns {string}
+     */
     _onApiGetUrl() {
         return window.location.href;
     }
 
+    /**
+     * @returns {void}
+     */
     _onApiClosePopup() {
         this._clearSelection(false);
     }
 
+    /**
+     * @returns {void}
+     */
     _onApiCopySelection() {
         // This will not work on Firefox if a popup has focus, which is usually the case when this function is called.
         document.execCommand('copy');
     }
 
+    /**
+     * @returns {string}
+     */
     _onApiGetSelectionText() {
-        return document.getSelection().toString();
+        const selection = document.getSelection();
+        return selection !== null ? selection.toString() : '';
     }
 
+    /**
+     * @returns {import('frontend').GetPopupInfoResult}
+     */
     _onApiGetPopupInfo() {
         return {
             popupId: (this._popup !== null ? this._popup.id : null)
         };
     }
 
+    /**
+     * @returns {{url: string, documentTitle: string}}
+     */
     _onApiGetPageInfo() {
         return {
             url: window.location.href,
@@ -266,6 +310,10 @@ class Frontend {
         };
     }
 
+    /**
+     * @param {{value: boolean, priority: number, awaitFrame: boolean}} params
+     * @returns {Promise<import('core').TokenString>}
+     */
     async _onApiSetAllVisibleOverride({value, priority, awaitFrame}) {
         const result = await this._popupFactory.setAllVisibleOverride(value, priority);
         if (awaitFrame) {
@@ -274,45 +322,71 @@ class Frontend {
         return result;
     }
 
+    /**
+     * @param {{token: import('core').TokenString}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiClearAllVisibleOverride({token}) {
         return await this._popupFactory.clearAllVisibleOverride(token);
     }
 
     // Private
 
+    /**
+     * @returns {void}
+     */
     _onResize() {
         this._updatePopupPosition();
     }
 
+    /** @type {import('extension').ChromeRuntimeOnMessageCallback} */
     _onRuntimeMessage({action, params}, sender, callback) {
         const messageHandler = this._runtimeMessageHandlers.get(action);
         if (typeof messageHandler === 'undefined') { return false; }
         return invokeMessageHandler(messageHandler, params, callback, sender);
     }
 
+    /**
+     * @param {{newZoomFactor: number}} params
+     */
     _onZoomChanged({newZoomFactor}) {
         this._pageZoomFactor = newZoomFactor;
         this._updateContentScale();
     }
 
+    /**
+     * @returns {void}
+     */
     _onClosePopups() {
         this._clearSelection(true);
     }
 
+    /**
+     * @returns {void}
+     */
     _onVisualViewportScroll() {
         this._updatePopupPosition();
     }
 
+    /**
+     * @returns {void}
+     */
     _onVisualViewportResize() {
         this._updateContentScale();
     }
 
+    /**
+     * @returns {void}
+     */
     _onTextScannerClear() {
         this._clearSelection(false);
     }
 
-    _onSearched({type, dictionaryEntries, sentence, inputInfo: {eventType, passive, detail}, textSource, optionsContext, detail: {documentTitle}, error}) {
-        const scanningOptions = this._options.scanning;
+    /**
+     * @param {import('text-scanner').SearchedEventDetails} details
+     */
+    _onSearched({type, dictionaryEntries, sentence, inputInfo: {eventType, passive, detail: inputInfoDetail}, textSource, optionsContext, detail, error}) {
+        const scanningOptions = /** @type {import('settings').ProfileOptions} */ (this._options).scanning;
 
         if (error !== null) {
             if (yomichan.isExtensionUnloaded) {
@@ -322,34 +396,43 @@ class Frontend {
             } else {
                 log.error(error);
             }
-        } if (type !== null) {
+        } if (type !== null && optionsContext !== null) {
             this._stopClearSelectionDelayed();
             let focus = (eventType === 'mouseMove');
-            if (isObject(detail)) {
-                const focus2 = detail.focus;
+            if (typeof inputInfoDetail === 'object' && inputInfoDetail !== null) {
+                const focus2 = inputInfoDetail.focus;
                 if (typeof focus2 === 'boolean') { focus = focus2; }
             }
-            this._showContent(textSource, focus, dictionaryEntries, type, sentence, documentTitle, optionsContext);
+            this._showContent(textSource, focus, dictionaryEntries, type, sentence, detail !== null ? detail.documentTitle : null, optionsContext);
         } else {
             if (scanningOptions.autoHideResults) {
-                this._clearSelectionDelayed(scanningOptions.hideDelay, false);
+                this._clearSelectionDelayed(scanningOptions.hideDelay, false, false);
             }
         }
     }
 
+    /**
+     * @returns {void}
+     */
     _onPopupFramePointerOver() {
         this._isPointerOverPopup = true;
         this._stopClearSelectionDelayed();
     }
 
+    /**
+     * @returns {void}
+     */
     _onPopupFramePointerOut() {
         this._isPointerOverPopup = false;
-        const scanningOptions = this._options.scanning;
+        const scanningOptions = /** @type {import('settings').ProfileOptions} */ (this._options).scanning;
         if (scanningOptions.hidePopupOnCursorExit) {
-            this._clearSelectionDelayed(scanningOptions.hidePopupOnCursorExitDelay, false);
+            this._clearSelectionDelayed(scanningOptions.hidePopupOnCursorExitDelay, false, false);
         }
     }
 
+    /**
+     * @param {boolean} passive
+     */
     _clearSelection(passive) {
         this._stopClearSelectionDelayed();
         if (this._popup !== null) {
@@ -360,6 +443,11 @@ class Frontend {
         this._textScanner.clearSelection();
     }
 
+    /**
+     * @param {number} delay
+     * @param {boolean} restart
+     * @param {boolean} passive
+     */
     _clearSelectionDelayed(delay, restart, passive) {
         if (!this._textScanner.hasSelection()) { return; }
         if (delay > 0) {
@@ -375,6 +463,9 @@ class Frontend {
         }
     }
 
+    /**
+     * @returns {void}
+     */
     _stopClearSelectionDelayed() {
         if (this._clearSelectionTimer !== null) {
             clearTimeout(this._clearSelectionTimer);
@@ -382,6 +473,9 @@ class Frontend {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _updateOptionsInternal() {
         const optionsContext = await this._getOptionsContext();
         const options = await yomichan.api.optionsGet(optionsContext);
@@ -422,12 +516,16 @@ class Frontend {
         await this._textScanner.searchLast();
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _updatePopup() {
-        const {usePopupWindow, showIframePopupsInRootFrame} = this._options.general;
+        const {usePopupWindow, showIframePopupsInRootFrame} = /** @type {import('settings').ProfileOptions} */ (this._options).general;
         const isIframe = !this._useProxyPopup && (window !== window.parent);
 
         const currentPopup = this._popup;
 
+        /** @type {Promise<?import('popup').PopupAny>|undefined} */
         let popupPromise;
         if (usePopupWindow && this._canUseWindowPopup) {
             popupPromise = this._popupCache.get('window');
@@ -462,6 +560,7 @@ class Frontend {
 
         // The token below is used as a unique identifier to ensure that a new _updatePopup call
         // hasn't been started during the await.
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._updatePopupToken = token;
         const popup = await popupPromise;
@@ -485,6 +584,9 @@ class Frontend {
         this._isPointerOverPopup = false;
     }
 
+    /**
+     * @returns {Promise<?import('popup').PopupAny>}
+     */
     async _getDefaultPopup() {
         const isXmlDocument = (typeof XMLDocument !== 'undefined' && document instanceof XMLDocument);
         if (isXmlDocument) {
@@ -498,6 +600,9 @@ class Frontend {
         });
     }
 
+    /**
+     * @returns {Promise<import('popup').PopupAny>}
+     */
     async _getProxyPopup() {
         return await this._popupFactory.getOrCreatePopup({
             frameId: this._parentFrameId,
@@ -507,6 +612,9 @@ class Frontend {
         });
     }
 
+    /**
+     * @returns {Promise<?import('popup').PopupAny>}
+     */
     async _getIframeProxyPopup() {
         const targetFrameId = 0; // Root frameId
         try {
@@ -516,7 +624,8 @@ class Frontend {
             return await this._getDefaultPopup();
         }
 
-        const {popupId} = await yomichan.crossFrame.invoke(targetFrameId, 'Frontend.getPopupInfo');
+        /** @type {import('frontend').GetPopupInfoResult} */
+        const {popupId} = await yomichan.crossFrame.invoke(targetFrameId, 'Frontend.getPopupInfo', {});
         if (popupId === null) {
             return null;
         }
@@ -533,6 +642,9 @@ class Frontend {
         return popup;
     }
 
+    /**
+     * @returns {Promise<import('popup').PopupAny>}
+     */
     async _getPopupWindow() {
         return await this._popupFactory.getOrCreatePopup({
             depth: this._depth,
@@ -541,6 +653,9 @@ class Frontend {
         });
     }
 
+    /**
+     * @returns {Element[]}
+     */
     _ignoreElements() {
         if (this._popup !== null) {
             const container = this._popup.container;
@@ -551,6 +666,11 @@ class Frontend {
         return [];
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @returns {Promise<boolean>}
+     */
     async _ignorePoint(x, y) {
         try {
             return this._popup !== null && await this._popup.containsPoint(x, y);
@@ -562,17 +682,44 @@ class Frontend {
         }
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     */
     _showExtensionUnloaded(textSource) {
-        if (textSource === null) {
-            textSource = this._textScanner.getCurrentTextSource();
-            if (textSource === null) { return; }
-        }
         this._showPopupContent(textSource, null, null);
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {boolean} focus
+     * @param {?import('dictionary').DictionaryEntry[]} dictionaryEntries
+     * @param {import('display').PageType} type
+     * @param {?import('display').HistoryStateSentence} sentence
+     * @param {?string} documentTitle
+     * @param {import('settings').OptionsContext} optionsContext
+     */
     _showContent(textSource, focus, dictionaryEntries, type, sentence, documentTitle, optionsContext) {
         const query = textSource.text();
         const {url} = optionsContext;
+        /** @type {import('display').HistoryState} */
+        const detailsState = {
+            focusEntry: 0,
+            optionsContext,
+            url
+        };
+        if (sentence !== null) { detailsState.sentence = sentence; }
+        if (documentTitle !== null) { detailsState.documentTitle = documentTitle; }
+        /** @type {import('display').HistoryContent} */
+        const detailsContent = {
+            contentOrigin: {
+                tabId: this._tabId,
+                frameId: this._frameId
+            }
+        };
+        if (dictionaryEntries !== null) {
+            detailsContent.dictionaryEntries = dictionaryEntries;
+        }
+        /** @type {import('display').ContentDetails} */
         const details = {
             focus,
             historyMode: 'clear',
@@ -581,28 +728,22 @@ class Frontend {
                 query,
                 wildcards: 'off'
             },
-            state: {
-                focusEntry: 0,
-                optionsContext,
-                url,
-                sentence,
-                documentTitle
-            },
-            content: {
-                dictionaryEntries,
-                contentOrigin: {
-                    tabId: this._tabId,
-                    frameId: this._frameId
-                }
-            }
+            state: detailsState,
+            content: detailsContent
         };
-        if (textSource.type === 'element' && textSource.fullContent !== query) {
+        if (textSource instanceof TextSourceElement && textSource.fullContent !== query) {
             details.params.full = textSource.fullContent;
             details.params['full-visible'] = 'true';
         }
         this._showPopupContent(textSource, optionsContext, details);
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {?import('settings').OptionsContext} optionsContext
+     * @param {?import('display').ContentDetails} details
+     * @returns {Promise<void>}
+     */
     _showPopupContent(textSource, optionsContext, details) {
         const sourceRects = [];
         for (const {left, top, right, bottom} of textSource.getRects()) {
@@ -627,6 +768,9 @@ class Frontend {
         return this._lastShowPromise;
     }
 
+    /**
+     * @returns {void}
+     */
     _updateTextScannerEnabled() {
         const enabled = (this._options !== null && this._options.general.enable && !this._disabledOverride);
         if (enabled === this._textScanner.isEnabled()) { return; }
@@ -639,15 +783,18 @@ class Frontend {
         }
     }
 
+    /**
+     * @returns {void}
+     */
     _updateContentScale() {
-        const {popupScalingFactor, popupScaleRelativeToPageZoom, popupScaleRelativeToVisualViewport} = this._options.general;
+        const {popupScalingFactor, popupScaleRelativeToPageZoom, popupScaleRelativeToVisualViewport} = /** @type {import('settings').ProfileOptions} */ (this._options).general;
         let contentScale = popupScalingFactor;
         if (popupScaleRelativeToPageZoom) {
             contentScale /= this._pageZoomFactor;
         }
         if (popupScaleRelativeToVisualViewport) {
-            const visualViewport = window.visualViewport;
-            const visualViewportScale = (visualViewport !== null && typeof visualViewport === 'object' ? visualViewport.scale : 1.0);
+            const {visualViewport} = window;
+            const visualViewportScale = (typeof visualViewport !== 'undefined' && visualViewport !== null ? visualViewport.scale : 1.0);
             contentScale /= visualViewportScale;
         }
         if (contentScale === this._contentScale) { return; }
@@ -659,6 +806,9 @@ class Frontend {
         this._updatePopupPosition();
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _updatePopupPosition() {
         const textSource = this._textScanner.getCurrentTextSource();
         if (
@@ -670,7 +820,11 @@ class Frontend {
         }
     }
 
-    _signalFrontendReady(targetFrameId=null) {
+    /**
+     * @param {?number} targetFrameId
+     */
+    _signalFrontendReady(targetFrameId) {
+        /** @type {import('frontend').FrontendReadyDetails} */
         const params = {frameId: this._frameId};
         if (targetFrameId === null) {
             yomichan.api.broadcastTab('frontendReady', params);
@@ -679,8 +833,14 @@ class Frontend {
         }
     }
 
+    /**
+     * @param {number} frameId
+     * @param {?number} timeout
+     * @returns {Promise<void>}
+     */
     async _waitForFrontendReady(frameId, timeout) {
         return new Promise((resolve, reject) => {
+            /** @type {?number} */
             let timeoutId = null;
 
             const cleanup = () => {
@@ -690,10 +850,11 @@ class Frontend {
                 }
                 chrome.runtime.onMessage.removeListener(onMessage);
             };
-            const onMessage = (message, sender, sendResponse) => {
+            /** @type {import('extension').ChromeRuntimeOnMessageCallback} */
+            const onMessage = (message, _sender, sendResponse) => {
                 try {
                     const {action, params} = message;
-                    if (action === 'frontendReady' && params.frameId === frameId) {
+                    if (action === 'frontendReady' && /** @type {import('frontend').FrontendReadyDetails} */ (params).frameId === frameId) {
                         cleanup();
                         resolve();
                         sendResponse();
@@ -716,6 +877,10 @@ class Frontend {
         });
     }
 
+    /**
+     * @param {import('settings').PreventMiddleMouseOptions} preventMiddleMouseOptions
+     * @returns {boolean}
+     */
     _getPreventMiddleMouseValueForPageType(preventMiddleMouseOptions) {
         switch (this._pageType) {
             case 'web': return preventMiddleMouseOptions.onWebPages;
@@ -725,6 +890,9 @@ class Frontend {
         }
     }
 
+    /**
+     * @returns {Promise<import('settings').OptionsContext>}
+     */
     async _getOptionsContext() {
         let optionsContext = this._optionsContextOverride;
         if (optionsContext === null) {
@@ -733,10 +901,13 @@ class Frontend {
         return optionsContext;
     }
 
+    /**
+     * @returns {Promise<{optionsContext: import('settings').OptionsContext, detail?: import('text-scanner').SearchResultDetail}>}
+     */
     async _getSearchContext() {
         let url = window.location.href;
         let documentTitle = document.title;
-        if (this._useProxyPopup) {
+        if (this._useProxyPopup && this._parentFrameId !== null) {
             try {
                 ({url, documentTitle} = await yomichan.crossFrame.invoke(this._parentFrameId, 'Frontend.getPageInfo', {}));
             } catch (e) {
@@ -755,6 +926,10 @@ class Frontend {
         };
     }
 
+    /**
+     * @param {boolean} allowEmptyRange
+     * @returns {Promise<boolean>}
+     */
     async _scanSelectedText(allowEmptyRange) {
         const range = this._getFirstSelectionRange(allowEmptyRange);
         if (range === null) { return false; }
@@ -763,8 +938,13 @@ class Frontend {
         return true;
     }
 
+    /**
+     * @param {boolean} allowEmptyRange
+     * @returns {?Range}
+     */
     _getFirstSelectionRange(allowEmptyRange) {
         const selection = window.getSelection();
+        if (selection === null) { return null; }
         for (let i = 0, ii = selection.rangeCount; i < ii; ++i) {
             const range = selection.getRangeAt(i);
             if (range.toString().length > 0 || allowEmptyRange) {
@@ -774,6 +954,9 @@ class Frontend {
         return null;
     }
 
+    /**
+     * @returns {void}
+     */
     _prepareSiteSpecific() {
         switch (location.hostname.toLowerCase()) {
             case 'docs.google.com':
@@ -782,6 +965,9 @@ class Frontend {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _prepareGoogleDocs() {
         if (typeof GoogleDocsUtil !== 'undefined') { return; }
         await yomichan.api.loadExtensionScripts([
diff --git a/ext/js/app/popup-factory.js b/ext/js/app/popup-factory.js
index eeb31a1bf0..686326ef4a 100644
--- a/ext/js/app/popup-factory.js
+++ b/ext/js/app/popup-factory.js
@@ -32,9 +32,13 @@ class PopupFactory {
      * @param {number} frameId The frame ID of the host frame.
      */
     constructor(frameId) {
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {FrameOffsetForwarder} */
         this._frameOffsetForwarder = new FrameOffsetForwarder(frameId);
+        /** @type {Map<string, import('popup').PopupAny>} */
         this._popups = new Map();
+        /** @type {Map<string, {popup: import('popup').PopupAny, token: string}[]>} */
         this._allPopupVisibilityTokenMap = new Map();
     }
 
@@ -46,17 +50,17 @@ class PopupFactory {
         yomichan.crossFrame.registerHandlers([
             ['PopupFactory.getOrCreatePopup',     {async: true,  handler: this._onApiGetOrCreatePopup.bind(this)}],
             ['PopupFactory.setOptionsContext',    {async: true,  handler: this._onApiSetOptionsContext.bind(this)}],
-            ['PopupFactory.hide',                 {async: false, handler: this._onApiHide.bind(this)}],
+            ['PopupFactory.hide',                 {async: true,  handler: this._onApiHide.bind(this)}],
             ['PopupFactory.isVisible',            {async: true,  handler: this._onApiIsVisibleAsync.bind(this)}],
             ['PopupFactory.setVisibleOverride',   {async: true,  handler: this._onApiSetVisibleOverride.bind(this)}],
             ['PopupFactory.clearVisibleOverride', {async: true,  handler: this._onApiClearVisibleOverride.bind(this)}],
             ['PopupFactory.containsPoint',        {async: true,  handler: this._onApiContainsPoint.bind(this)}],
             ['PopupFactory.showContent',          {async: true,  handler: this._onApiShowContent.bind(this)}],
-            ['PopupFactory.setCustomCss',         {async: false, handler: this._onApiSetCustomCss.bind(this)}],
-            ['PopupFactory.clearAutoPlayTimer',   {async: false, handler: this._onApiClearAutoPlayTimer.bind(this)}],
-            ['PopupFactory.setContentScale',      {async: false, handler: this._onApiSetContentScale.bind(this)}],
-            ['PopupFactory.updateTheme',          {async: false, handler: this._onApiUpdateTheme.bind(this)}],
-            ['PopupFactory.setCustomOuterCss',    {async: false, handler: this._onApiSetCustomOuterCss.bind(this)}],
+            ['PopupFactory.setCustomCss',         {async: true,  handler: this._onApiSetCustomCss.bind(this)}],
+            ['PopupFactory.clearAutoPlayTimer',   {async: true,  handler: this._onApiClearAutoPlayTimer.bind(this)}],
+            ['PopupFactory.setContentScale',      {async: true,  handler: this._onApiSetContentScale.bind(this)}],
+            ['PopupFactory.updateTheme',          {async: true,  handler: this._onApiUpdateTheme.bind(this)}],
+            ['PopupFactory.setCustomOuterCss',    {async: true,  handler: this._onApiSetCustomOuterCss.bind(this)}],
             ['PopupFactory.getFrameSize',         {async: true,  handler: this._onApiGetFrameSize.bind(this)}],
             ['PopupFactory.setFrameSize',         {async: true,  handler: this._onApiSetFrameSize.bind(this)}]
         ]);
@@ -64,13 +68,8 @@ class PopupFactory {
 
     /**
      * Gets or creates a popup based on a set of parameters
-     * @param {object} details Details about how to acquire the popup.
-     * @param {?number} [details.frameId] The ID of the frame that should host the popup.
-     * @param {?string} [details.id] A specific ID used to find an existing popup, or to assign to the new popup.
-     * @param {?string} [details.parentPopupId] The ID of the parent popup.
-     * @param {?number} [details.depth] A specific depth value to assign to the popup.
-     * @param {boolean} [details.popupWindow] Whether or not a separate popup window should be used, rather than an iframe.
-     * @param {boolean} [details.childrenSupported] Whether or not the popup is able to show child popups.
+     * @param {import('popup-factory').GetOrCreatePopupDetails} details Details about how to acquire the popup.
+     * @returns {Promise<import('popup').PopupAny>}
      */
     async getOrCreatePopup({
         frameId=null,
@@ -139,7 +138,7 @@ class PopupFactory {
                 if (parent.child !== null) {
                     throw new Error('Parent popup already has a child');
                 }
-                popup.parent = parent;
+                popup.parent = /** @type {Popup} */ (parent);
                 parent.child = popup;
             }
             this._popups.set(id, popup);
@@ -150,16 +149,18 @@ class PopupFactory {
                 throw new Error('Invalid frameId');
             }
             const useFrameOffsetForwarder = (parentPopupId === null);
-            ({id, depth, frameId} = await yomichan.crossFrame.invoke(frameId, 'PopupFactory.getOrCreatePopup', {
+            /** @type {{id: string, depth: number, frameId: number}} */
+            const info = await yomichan.crossFrame.invoke(frameId, 'PopupFactory.getOrCreatePopup', /** @type {import('popup-factory').GetOrCreatePopupDetails} */ ({
                 id,
                 parentPopupId,
                 frameId,
                 childrenSupported
             }));
+            id = info.id;
             const popup = new PopupProxy({
                 id,
-                depth,
-                frameId,
+                depth: info.depth,
+                frameId: info.frameId,
                 frameOffsetForwarder: useFrameOffsetForwarder ? this._frameOffsetForwarder : null
             });
             this._popups.set(id, popup);
@@ -171,24 +172,34 @@ class PopupFactory {
      * Force all popups to have a specific visibility value.
      * @param {boolean} value Whether or not the popups should be visible.
      * @param {number} priority The priority of the override.
-     * @returns {string} A token which can be passed to clearAllVisibleOverride.
+     * @returns {Promise<import('core').TokenString>} A token which can be passed to clearAllVisibleOverride.
      * @throws An exception is thrown if any popup fails to have its visibiltiy overridden.
      */
     async setAllVisibleOverride(value, priority) {
         const promises = [];
-        const errors = [];
         for (const popup of this._popups.values()) {
-            const promise = popup.setVisibleOverride(value, priority)
-                .then(
-                    (token) => ({popup, token}),
-                    (error) => { errors.push(error); return null; }
-                );
+            const promise = this._setPopupVisibleOverrideReturnTuple(popup, value, priority);
             promises.push(promise);
         }
 
-        const results = (await Promise.all(promises)).filter(({token}) => token !== null);
+        /** @type {undefined|unknown} */
+        let error = void 0;
+        /** @type {{popup: import('popup').PopupAny, token: string}[]} */
+        const results = [];
+        for (const promise of promises) {
+            try {
+                const {popup, token} = await promise;
+                if (token !== null) {
+                    results.push({popup, token});
+                }
+            } catch (e) {
+                if (typeof error === 'undefined') {
+                    error = new Error(`Failed to set popup visibility override: ${e}`);
+                }
+            }
+        }
 
-        if (errors.length === 0) {
+        if (typeof error === 'undefined') {
             const token = generateId(16);
             this._allPopupVisibilityTokenMap.set(token, results);
             return token;
@@ -196,13 +207,24 @@ class PopupFactory {
 
         // Revert on error
         await this._revertPopupVisibilityOverrides(results);
-        throw errors[0];
+        throw error;
+    }
+
+    /**
+     * @param {import('popup').PopupAny} popup
+     * @param {boolean} value
+     * @param {number} priority
+     * @returns {Promise<{popup: import('popup').PopupAny, token: ?string}>}
+     */
+    async _setPopupVisibleOverrideReturnTuple(popup, value, priority) {
+        const token = await popup.setVisibleOverride(value, priority);
+        return {popup, token};
     }
 
     /**
      * Clears a visibility override that was generated by `setAllVisibleOverride`.
-     * @param {string} token The token returned from `setAllVisibleOverride`.
-     * @returns {boolean} `true` if the override existed and was removed, `false` otherwise.
+     * @param {import('core').TokenString} token The token returned from `setAllVisibleOverride`.
+     * @returns {Promise<boolean>} `true` if the override existed and was removed, `false` otherwise.
      */
     async clearAllVisibleOverride(token) {
         const results = this._allPopupVisibilityTokenMap.get(token);
@@ -215,6 +237,10 @@ class PopupFactory {
 
     // API message handlers
 
+    /**
+     * @param {import('popup-factory').GetOrCreatePopupDetails} details
+     * @returns {Promise<{id: string, depth: number, frameId: number}>}
+     */
     async _onApiGetOrCreatePopup(details) {
         const popup = await this.getOrCreatePopup(details);
         return {
@@ -224,31 +250,53 @@ class PopupFactory {
         };
     }
 
+    /**
+     * @param {{id: string, optionsContext: import('settings').OptionsContext}} params
+     */
     async _onApiSetOptionsContext({id, optionsContext}) {
         const popup = this._getPopup(id);
-        return await popup.setOptionsContext(optionsContext);
+        await popup.setOptionsContext(optionsContext);
     }
 
-    _onApiHide({id, changeFocus}) {
+    /**
+     * @param {{id: string, changeFocus: boolean}} params
+     */
+    async _onApiHide({id, changeFocus}) {
         const popup = this._getPopup(id);
-        return popup.hide(changeFocus);
+        await popup.hide(changeFocus);
     }
 
+    /**
+     * @param {{id: string}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiIsVisibleAsync({id}) {
         const popup = this._getPopup(id);
         return await popup.isVisible();
     }
 
+    /**
+     * @param {{id: string, value: boolean, priority: number}} params
+     * @returns {Promise<?import('core').TokenString>}
+     */
     async _onApiSetVisibleOverride({id, value, priority}) {
         const popup = this._getPopup(id);
         return await popup.setVisibleOverride(value, priority);
     }
 
+    /**
+     * @param {{id: string, token: import('core').TokenString}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiClearVisibleOverride({id, token}) {
         const popup = this._getPopup(id);
         return await popup.clearVisibleOverride(token);
     }
 
+    /**
+     * @param {{id: string, x: number, y: number}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiContainsPoint({id, x, y}) {
         const popup = this._getPopup(id);
         const offset = this._getPopupOffset(popup);
@@ -257,6 +305,10 @@ class PopupFactory {
         return await popup.containsPoint(x, y);
     }
 
+    /**
+     * @param {{id: string, details: import('popup').ContentDetails, displayDetails: ?import('display').ContentDetails}} params
+     * @returns {Promise<void>}
+     */
     async _onApiShowContent({id, details, displayDetails}) {
         const popup = this._getPopup(id);
         if (!this._popupCanShow(popup)) { return; }
@@ -273,36 +325,64 @@ class PopupFactory {
         return await popup.showContent(details, displayDetails);
     }
 
-    _onApiSetCustomCss({id, css}) {
+    /**
+     * @param {{id: string, css: string}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiSetCustomCss({id, css}) {
         const popup = this._getPopup(id);
-        return popup.setCustomCss(css);
+        await popup.setCustomCss(css);
     }
 
-    _onApiClearAutoPlayTimer({id}) {
+    /**
+     * @param {{id: string}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiClearAutoPlayTimer({id}) {
         const popup = this._getPopup(id);
-        return popup.clearAutoPlayTimer();
+        await popup.clearAutoPlayTimer();
     }
 
-    _onApiSetContentScale({id, scale}) {
+    /**
+     * @param {{id: string, scale: number}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiSetContentScale({id, scale}) {
         const popup = this._getPopup(id);
-        return popup.setContentScale(scale);
+        await popup.setContentScale(scale);
     }
 
-    _onApiUpdateTheme({id}) {
+    /**
+     * @param {{id: string}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiUpdateTheme({id}) {
         const popup = this._getPopup(id);
-        return popup.updateTheme();
+        await popup.updateTheme();
     }
 
-    _onApiSetCustomOuterCss({id, css, useWebExtensionApi}) {
+    /**
+     * @param {{id: string, css: string, useWebExtensionApi: boolean}} params
+     * @returns {Promise<void>}
+     */
+    async _onApiSetCustomOuterCss({id, css, useWebExtensionApi}) {
         const popup = this._getPopup(id);
-        return popup.setCustomOuterCss(css, useWebExtensionApi);
+        await popup.setCustomOuterCss(css, useWebExtensionApi);
     }
 
+    /**
+     * @param {{id: string}} params
+     * @returns {Promise<import('popup').ValidSize>}
+     */
     async _onApiGetFrameSize({id}) {
         const popup = this._getPopup(id);
         return await popup.getFrameSize();
     }
 
+    /**
+     * @param {{id: string, width: number, height: number}} params
+     * @returns {Promise<boolean>}
+     */
     async _onApiSetFrameSize({id, width, height}) {
         const popup = this._getPopup(id);
         return await popup.setFrameSize(width, height);
@@ -310,6 +390,11 @@ class PopupFactory {
 
     // Private functions
 
+    /**
+     * @param {string} id
+     * @returns {import('popup').PopupAny}
+     * @throws {Error}
+     */
     _getPopup(id) {
         const popup = this._popups.get(id);
         if (typeof popup === 'undefined') {
@@ -318,6 +403,10 @@ class PopupFactory {
         return popup;
     }
 
+    /**
+     * @param {import('popup').PopupAny} popup
+     * @returns {{x: number, y: number}}
+     */
     _getPopupOffset(popup) {
         const {parent} = popup;
         if (parent !== null) {
@@ -329,11 +418,19 @@ class PopupFactory {
         return {x: 0, y: 0};
     }
 
+    /**
+     * @param {import('popup').PopupAny} popup
+     * @returns {boolean}
+     */
     _popupCanShow(popup) {
         const parent = popup.parent;
         return parent === null || parent.isVisibleSync();
     }
 
+    /**
+     * @param {{popup: import('popup').PopupAny, token: string}[]} overrides
+     * @returns {Promise<boolean[]>}
+     */
     async _revertPopupVisibilityOverrides(overrides) {
         const promises = [];
         for (const value of overrides) {
diff --git a/ext/js/app/popup-proxy.js b/ext/js/app/popup-proxy.js
index e7e51ddfa9..fa330970de 100644
--- a/ext/js/app/popup-proxy.js
+++ b/ext/js/app/popup-proxy.js
@@ -19,15 +19,12 @@
 /**
  * This class is a proxy for a Popup that is hosted in a different frame.
  * It effectively forwards all API calls to the underlying Popup.
+ * @augments EventDispatcher<import('popup').PopupAnyEventType>
  */
 class PopupProxy extends EventDispatcher {
     /**
      * Creates a new instance.
-     * @param {object} details Details about how to set up the instance.
-     * @param {string} details.id The ID of the popup.
-     * @param {number} details.depth The depth of the popup.
-     * @param {number} details.frameId The ID of the host frame.
-     * @param {FrameOffsetForwarder} details.frameOffsetForwarder A `FrameOffsetForwarder` instance which is used to determine frame positioning.
+     * @param {import('popup').PopupProxyConstructorDetails} details Details about how to set up the instance.
      */
     constructor({
         id,
@@ -36,15 +33,24 @@ class PopupProxy extends EventDispatcher {
         frameOffsetForwarder
     }) {
         super();
+        /** @type {string} */
         this._id = id;
+        /** @type {number} */
         this._depth = depth;
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {?FrameOffsetForwarder} */
         this._frameOffsetForwarder = frameOffsetForwarder;
 
+        /** @type {number} */
         this._frameOffsetX = 0;
+        /** @type {number} */
         this._frameOffsetY = 0;
+        /** @type {?Promise<?[x: number, y: number]>} */
         this._frameOffsetPromise = null;
+        /** @type {?number} */
         this._frameOffsetUpdatedAt = null;
+        /** @type {number} */
         this._frameOffsetExpireTimeout = 1000;
     }
 
@@ -59,7 +65,7 @@ class PopupProxy extends EventDispatcher {
     /**
      * The parent of the popup, which is always `null` for `PopupProxy` instances,
      * since any potential parent popups are in a different frame.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get parent() {
         return null;
@@ -77,7 +83,7 @@ class PopupProxy extends EventDispatcher {
     /**
      * The popup child popup, which is always null for `PopupProxy` instances,
      * since any potential child popups are in a different frame.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get child() {
         return null;
@@ -94,7 +100,7 @@ class PopupProxy extends EventDispatcher {
 
     /**
      * The depth of the popup.
-     * @type {numer}
+     * @type {number}
      */
     get depth() {
         return this._depth;
@@ -103,7 +109,7 @@ class PopupProxy extends EventDispatcher {
     /**
      * Gets the content window of the frame. This value is null,
      * since the window is hosted in a different frame.
-     * @type {Window}
+     * @type {?Window}
      */
     get frameContentWindow() {
         return null;
@@ -111,7 +117,7 @@ class PopupProxy extends EventDispatcher {
 
     /**
      * Gets the DOM node that contains the frame.
-     * @type {Element}
+     * @type {?Element}
      */
     get container() {
         return null;
@@ -127,11 +133,11 @@ class PopupProxy extends EventDispatcher {
 
     /**
      * Sets the options context for the popup.
-     * @param {object} optionsContext The options context object.
+     * @param {import('settings').OptionsContext} optionsContext The options context object.
      * @returns {Promise<void>}
      */
-    setOptionsContext(optionsContext) {
-        return this._invokeSafe('PopupFactory.setOptionsContext', {id: this._id, optionsContext});
+    async setOptionsContext(optionsContext) {
+        await this._invokeSafe('PopupFactory.setOptionsContext', {id: this._id, optionsContext}, void 0);
     }
 
     /**
@@ -139,8 +145,8 @@ class PopupProxy extends EventDispatcher {
      * @param {boolean} changeFocus Whether or not the parent popup or host frame should be focused.
      * @returns {Promise<void>}
      */
-    hide(changeFocus) {
-        return this._invokeSafe('PopupFactory.hide', {id: this._id, changeFocus});
+    async hide(changeFocus) {
+        await this._invokeSafe('PopupFactory.hide', {id: this._id, changeFocus}, void 0);
     }
 
     /**
@@ -155,7 +161,7 @@ class PopupProxy extends EventDispatcher {
      * Force assigns the visibility of the popup.
      * @param {boolean} value Whether or not the popup should be visible.
      * @param {number} priority The priority of the override.
-     * @returns {Promise<string?>} A token used which can be passed to `clearVisibleOverride`,
+     * @returns {Promise<?import('core').TokenString>} A token used which can be passed to `clearVisibleOverride`,
      *   or null if the override wasn't assigned.
      */
     setVisibleOverride(value, priority) {
@@ -164,7 +170,7 @@ class PopupProxy extends EventDispatcher {
 
     /**
      * Clears a visibility override that was generated by `setVisibleOverride`.
-     * @param {string} token The token returned from `setVisibleOverride`.
+     * @param {import('core').TokenString} token The token returned from `setVisibleOverride`.
      * @returns {Promise<boolean>} `true` if the override existed and was removed, `false` otherwise.
      */
     clearVisibleOverride(token) {
@@ -188,8 +194,8 @@ class PopupProxy extends EventDispatcher {
 
     /**
      * Shows and updates the positioning and content of the popup.
-     * @param {Popup.ContentDetails} details Settings for the outer popup.
-     * @param {Display.ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
+     * @param {import('popup').ContentDetails} details Settings for the outer popup.
+     * @param {?import('display').ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
      * @returns {Promise<void>}
      */
     async showContent(details, displayDetails) {
@@ -203,7 +209,7 @@ class PopupProxy extends EventDispatcher {
                 sourceRect.bottom += this._frameOffsetY;
             }
         }
-        return await this._invokeSafe('PopupFactory.showContent', {id: this._id, details, displayDetails});
+        await this._invokeSafe('PopupFactory.showContent', {id: this._id, details, displayDetails}, void 0);
     }
 
     /**
@@ -211,16 +217,16 @@ class PopupProxy extends EventDispatcher {
      * @param {string} css The CSS rules.
      * @returns {Promise<void>}
      */
-    setCustomCss(css) {
-        return this._invokeSafe('PopupFactory.setCustomCss', {id: this._id, css});
+    async setCustomCss(css) {
+        await this._invokeSafe('PopupFactory.setCustomCss', {id: this._id, css}, void 0);
     }
 
     /**
      * Stops the audio auto-play timer, if one has started.
      * @returns {Promise<void>}
      */
-    clearAutoPlayTimer() {
-        return this._invokeSafe('PopupFactory.clearAutoPlayTimer', {id: this._id});
+    async clearAutoPlayTimer() {
+        await this._invokeSafe('PopupFactory.clearAutoPlayTimer', {id: this._id}, void 0);
     }
 
     /**
@@ -228,8 +234,8 @@ class PopupProxy extends EventDispatcher {
      * @param {number} scale The scaling factor.
      * @returns {Promise<void>}
      */
-    setContentScale(scale) {
-        return this._invokeSafe('PopupFactory.setContentScale', {id: this._id, scale});
+    async setContentScale(scale) {
+        await this._invokeSafe('PopupFactory.setContentScale', {id: this._id, scale}, void 0);
     }
 
     /**
@@ -244,8 +250,8 @@ class PopupProxy extends EventDispatcher {
      * Updates the outer theme of the popup.
      * @returns {Promise<void>}
      */
-    updateTheme() {
-        return this._invokeSafe('PopupFactory.updateTheme', {id: this._id});
+    async updateTheme() {
+        await this._invokeSafe('PopupFactory.updateTheme', {id: this._id}, void 0);
     }
 
     /**
@@ -255,13 +261,13 @@ class PopupProxy extends EventDispatcher {
      *   When web extension APIs are used, a DOM node is not generated, making it harder to detect the changes.
      * @returns {Promise<void>}
      */
-    setCustomOuterCss(css, useWebExtensionApi) {
-        return this._invokeSafe('PopupFactory.setCustomOuterCss', {id: this._id, css, useWebExtensionApi});
+    async setCustomOuterCss(css, useWebExtensionApi) {
+        await this._invokeSafe('PopupFactory.setCustomOuterCss', {id: this._id, css, useWebExtensionApi}, void 0);
     }
 
     /**
      * Gets the rectangle of the DOM frame, synchronously.
-     * @returns {Popup.ValidRect} The rect.
+     * @returns {import('popup').ValidRect} The rect.
      *   `valid` is `false` for `PopupProxy`, since the DOM node is hosted in a different frame.
      */
     getFrameRect() {
@@ -270,7 +276,7 @@ class PopupProxy extends EventDispatcher {
 
     /**
      * Gets the size of the DOM frame.
-     * @returns {Promise<{width: number, height: number, valid: boolean}>} The size and whether or not it is valid.
+     * @returns {Promise<import('popup').ValidSize>} The size and whether or not it is valid.
      */
     getFrameSize() {
         return this._invokeSafe('PopupFactory.getFrameSize', {id: this._id}, {width: 0, height: 0, valid: false});
@@ -283,16 +289,32 @@ class PopupProxy extends EventDispatcher {
      * @returns {Promise<boolean>} `true` if the size assignment was successful, `false` otherwise.
      */
     setFrameSize(width, height) {
-        return this._invokeSafe('PopupFactory.setFrameSize', {id: this._id, width, height});
+        return this._invokeSafe('PopupFactory.setFrameSize', {id: this._id, width, height}, false);
     }
 
     // Private
 
-    _invoke(action, params={}) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn>}
+     */
+    _invoke(action, params) {
         return yomichan.crossFrame.invoke(this._frameId, action, params);
     }
 
-    async _invokeSafe(action, params={}, defaultReturnValue) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @template [TReturnDefault=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @param {TReturnDefault} defaultReturnValue
+     * @returns {Promise<TReturn|TReturnDefault>}
+     */
+    async _invokeSafe(action, params, defaultReturnValue) {
         try {
             return await this._invoke(action, params);
         } catch (e) {
@@ -301,10 +323,13 @@ class PopupProxy extends EventDispatcher {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _updateFrameOffset() {
         const now = Date.now();
         const firstRun = this._frameOffsetUpdatedAt === null;
-        const expired = firstRun || this._frameOffsetUpdatedAt < now - this._frameOffsetExpireTimeout;
+        const expired = firstRun || /** @type {number} */ (this._frameOffsetUpdatedAt) < now - this._frameOffsetExpireTimeout;
         if (this._frameOffsetPromise === null && !expired) { return; }
 
         if (this._frameOffsetPromise !== null) {
@@ -320,8 +345,11 @@ class PopupProxy extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} now
+     */
     async _updateFrameOffsetInner(now) {
-        this._frameOffsetPromise = this._frameOffsetForwarder.getOffset();
+        this._frameOffsetPromise = /** @type {FrameOffsetForwarder} */ (this._frameOffsetForwarder).getOffset();
         try {
             const offset = await this._frameOffsetPromise;
             if (offset !== null) {
diff --git a/ext/js/app/popup-window.js b/ext/js/app/popup-window.js
index 32e8b25099..af53461c34 100644
--- a/ext/js/app/popup-window.js
+++ b/ext/js/app/popup-window.js
@@ -18,14 +18,12 @@
 
 /**
  * This class represents a popup that is hosted in a new native window.
+ * @augments EventDispatcher<import('popup').PopupAnyEventType>
  */
 class PopupWindow extends EventDispatcher {
     /**
      * Creates a new instance.
-     * @param {object} details Details about how to set up the instance.
-     * @param {string} details.id The ID of the popup.
-     * @param {number} details.depth The depth of the popup.
-     * @param {number} details.frameId The ID of the host frame.
+     * @param {import('popup').PopupWindowConstructorDetails} details Details about how to set up the instance.
      */
     constructor({
         id,
@@ -33,9 +31,13 @@ class PopupWindow extends EventDispatcher {
         frameId
     }) {
         super();
+        /** @type {string} */
         this._id = id;
+        /** @type {number} */
         this._depth = depth;
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {?number} */
         this._popupTabId = null;
     }
 
@@ -47,6 +49,9 @@ class PopupWindow extends EventDispatcher {
         return this._id;
     }
 
+    /**
+     * @type {?Popup}
+     */
     get parent() {
         return null;
     }
@@ -64,7 +69,7 @@ class PopupWindow extends EventDispatcher {
     /**
      * The popup child popup, which is always null for `PopupWindow` instances,
      * since any potential child popups are in a different frame.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get child() {
         return null;
@@ -81,7 +86,7 @@ class PopupWindow extends EventDispatcher {
 
     /**
      * The depth of the popup.
-     * @type {numer}
+     * @type {number}
      */
     get depth() {
         return this._depth;
@@ -90,7 +95,7 @@ class PopupWindow extends EventDispatcher {
     /**
      * Gets the content window of the frame. This value is null,
      * since the window is hosted in a different frame.
-     * @type {Window}
+     * @type {?Window}
      */
     get frameContentWindow() {
         return null;
@@ -98,7 +103,7 @@ class PopupWindow extends EventDispatcher {
 
     /**
      * Gets the DOM node that contains the frame.
-     * @type {Element}
+     * @type {?Element}
      */
     get container() {
         return null;
@@ -114,11 +119,11 @@ class PopupWindow extends EventDispatcher {
 
     /**
      * Sets the options context for the popup.
-     * @param {object} optionsContext The options context object.
+     * @param {import('settings').OptionsContext} optionsContext The options context object.
      * @returns {Promise<void>}
      */
-    setOptionsContext(optionsContext) {
-        return this._invoke(false, 'Display.setOptionsContext', {id: this._id, optionsContext});
+    async setOptionsContext(optionsContext) {
+        await this._invoke(false, 'Display.setOptionsContext', {id: this._id, optionsContext});
     }
 
     /**
@@ -141,7 +146,7 @@ class PopupWindow extends EventDispatcher {
      * Force assigns the visibility of the popup.
      * @param {boolean} _value Whether or not the popup should be visible.
      * @param {number} _priority The priority of the override.
-     * @returns {Promise<string?>} A token used which can be passed to `clearVisibleOverride`,
+     * @returns {Promise<?import('core').TokenString>} A token used which can be passed to `clearVisibleOverride`,
      *   or null if the override wasn't assigned.
      */
     async setVisibleOverride(_value, _priority) {
@@ -150,10 +155,10 @@ class PopupWindow extends EventDispatcher {
 
     /**
      * Clears a visibility override that was generated by `setVisibleOverride`.
-     * @param {string} _token The token returned from `setVisibleOverride`.
-     * @returns {boolean} `true` if the override existed and was removed, `false` otherwise.
+     * @param {import('core').TokenString} _token The token returned from `setVisibleOverride`.
+     * @returns {Promise<boolean>} `true` if the override existed and was removed, `false` otherwise.
      */
-    clearVisibleOverride(_token) {
+    async clearVisibleOverride(_token) {
         return false;
     }
 
@@ -169,8 +174,8 @@ class PopupWindow extends EventDispatcher {
 
     /**
      * Shows and updates the positioning and content of the popup.
-     * @param {Popup.ContentDetails} _details Settings for the outer popup.
-     * @param {Display.ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
+     * @param {import('popup').ContentDetails} _details Settings for the outer popup.
+     * @param {?import('display').ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
      * @returns {Promise<void>}
      */
     async showContent(_details, displayDetails) {
@@ -183,23 +188,23 @@ class PopupWindow extends EventDispatcher {
      * @param {string} css The CSS rules.
      * @returns {Promise<void>}
      */
-    setCustomCss(css) {
-        return this._invoke(false, 'Display.setCustomCss', {id: this._id, css});
+    async setCustomCss(css) {
+        await this._invoke(false, 'Display.setCustomCss', {id: this._id, css});
     }
 
     /**
      * Stops the audio auto-play timer, if one has started.
      * @returns {Promise<void>}
      */
-    clearAutoPlayTimer() {
-        return this._invoke(false, 'Display.clearAutoPlayTimer', {id: this._id});
+    async clearAutoPlayTimer() {
+        await this._invoke(false, 'Display.clearAutoPlayTimer', {id: this._id});
     }
 
     /**
      * Sets the scaling factor of the popup content.
      * @param {number} _scale The scaling factor.
      */
-    setContentScale(_scale) {
+    async setContentScale(_scale) {
         // NOP
     }
 
@@ -231,7 +236,7 @@ class PopupWindow extends EventDispatcher {
 
     /**
      * Gets the rectangle of the DOM frame, synchronously.
-     * @returns {Popup.ValidRect} The rect.
+     * @returns {import('popup').ValidRect} The rect.
      *   `valid` is `false` for `PopupProxy`, since the DOM node is hosted in a different frame.
      */
     getFrameRect() {
@@ -240,7 +245,7 @@ class PopupWindow extends EventDispatcher {
 
     /**
      * Gets the size of the DOM frame.
-     * @returns {Promise<{width: number, height: number, valid: boolean}>} The size and whether or not it is valid.
+     * @returns {Promise<import('popup').ValidSize>} The size and whether or not it is valid.
      */
     async getFrameSize() {
         return {width: 0, height: 0, valid: false};
@@ -258,9 +263,17 @@ class PopupWindow extends EventDispatcher {
 
     // Private
 
-    async _invoke(open, action, params={}, defaultReturnValue) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @param {boolean} open
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn|undefined>}
+     */
+    async _invoke(open, action, params) {
         if (yomichan.isExtensionUnloaded) {
-            return defaultReturnValue;
+            return void 0;
         }
 
         const frameId = 0;
@@ -276,7 +289,7 @@ class PopupWindow extends EventDispatcher {
         }
 
         if (!open) {
-            return defaultReturnValue;
+            return void 0;
         }
 
         const {tabId} = await yomichan.api.getOrCreateSearchPopup({focus: 'ifCreated'});
diff --git a/ext/js/app/popup.js b/ext/js/app/popup.js
index 8d140064ea..0d4bad5cb1 100644
--- a/ext/js/app/popup.js
+++ b/ext/js/app/popup.js
@@ -25,53 +25,12 @@
 
 /**
  * This class is the container which hosts the display of search results.
+ * @augments EventDispatcher<import('popup').PopupAnyEventType>
  */
 class Popup extends EventDispatcher {
-    /**
-     * Information about how popup content should be shown, specifically related to the outer popup frame.
-     * @typedef {object} ContentDetails
-     * @property {?object} optionsContext The options context for the content to show.
-     * @property {Rect[]} sourceRects The rectangles of the source content.
-     * @property {'horizontal-tb' | 'vertical-rl' | 'vertical-lr' | 'sideways-rl' | 'sideways-lr'} writingMode The normalized CSS writing-mode value of the source content.
-     */
-
-    /**
-     * A rectangle representing a DOM region, similar to DOMRect.
-     * @typedef {object} Rect
-     * @property {number} left The left position of the rectangle.
-     * @property {number} top The top position of the rectangle.
-     * @property {number} right The right position of the rectangle.
-     * @property {number} bottom The bottom position of the rectangle.
-     */
-
-    /**
-     * A rectangle representing a DOM region, similar to DOMRect but with a `valid` property.
-     * @typedef {object} ValidRect
-     * @property {number} left The left position of the rectangle.
-     * @property {number} top The top position of the rectangle.
-     * @property {number} right The right position of the rectangle.
-     * @property {number} bottom The bottom position of the rectangle.
-     * @property {boolean} valid Whether or not the rectangle is valid.
-     */
-
-    /**
-     * A rectangle representing a DOM region for placing the popup frame.
-     * @typedef {object} SizeRect
-     * @property {number} left The left position of the rectangle.
-     * @property {number} top The top position of the rectangle.
-     * @property {number} width The width of the rectangle.
-     * @property {number} height The height of the rectangle.
-     * @property {boolean} after Whether or not the rectangle is positioned to the right of the source rectangle.
-     * @property {boolean} below Whether or not the rectangle is positioned below the source rectangle.
-     */
-
     /**
      * Creates a new instance.
-     * @param {object} details The details used to construct the new instance.
-     * @param {string} details.id The ID of the popup.
-     * @param {number} details.depth The depth of the popup.
-     * @param {number} details.frameId The ID of the host frame.
-     * @param {boolean} details.childrenSupported Whether or not the popup is able to show child popups.
+     * @param {import('popup').PopupConstructorDetails} details The details used to construct the new instance.
      */
     constructor({
         id,
@@ -80,48 +39,83 @@ class Popup extends EventDispatcher {
         childrenSupported
     }) {
         super();
+        /** @type {string} */
         this._id = id;
+        /** @type {number} */
         this._depth = depth;
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {boolean} */
         this._childrenSupported = childrenSupported;
+        /** @type {?Popup} */
         this._parent = null;
+        /** @type {?Popup} */
         this._child = null;
+        /** @type {?Promise<boolean>} */
         this._injectPromise = null;
+        /** @type {boolean} */
         this._injectPromiseComplete = false;
+        /** @type {DynamicProperty<boolean>} */
         this._visible = new DynamicProperty(false);
+        /** @type {boolean} */
         this._visibleValue = false;
+        /** @type {?import('settings').OptionsContext} */
         this._optionsContext = null;
+        /** @type {number} */
         this._contentScale = 1.0;
+        /** @type {string} */
         this._targetOrigin = chrome.runtime.getURL('/').replace(/\/$/, '');
 
-        this._optionsAssigned = false;
+        /** @type {number} */
         this._initialWidth = 400;
+        /** @type {number} */
         this._initialHeight = 250;
+        /** @type {number} */
         this._horizontalOffset = 0;
+        /** @type {number} */
         this._verticalOffset = 10;
+        /** @type {number} */
         this._horizontalOffset2 = 10;
+        /** @type {number} */
         this._verticalOffset2 = 0;
+        /** @type {import('settings').PopupVerticalTextPosition} */
         this._verticalTextPosition = 'before';
+        /** @type {boolean} */
         this._horizontalTextPositionBelow = true;
+        /** @type {import('settings').PopupDisplayMode} */
         this._displayMode = 'default';
+        /** @type {boolean} */
         this._displayModeIsFullWidth = false;
+        /** @type {boolean} */
         this._scaleRelativeToVisualViewport = true;
+        /** @type {boolean} */
         this._useSecureFrameUrl = true;
+        /** @type {boolean} */
         this._useShadowDom = true;
+        /** @type {string} */
         this._customOuterCss = '';
 
+        /** @type {?number} */
         this._frameSizeContentScale = null;
+        /** @type {?FrameClient} */
         this._frameClient = null;
+        /** @type {HTMLIFrameElement} */
         this._frame = document.createElement('iframe');
         this._frame.className = 'yomichan-popup';
         this._frame.style.width = '0';
         this._frame.style.height = '0';
+        /** @type {boolean} */
+        this._frameConnected = false;
 
+        /** @type {HTMLElement} */
         this._container = this._frame;
+        /** @type {?ShadowRoot} */
         this._shadow = null;
 
+        /** @type {ThemeController} */
         this._themeController = new ThemeController(this._frame);
 
+        /** @type {EventListenerCollection} */
         this._fullscreenEventListeners = new EventListenerCollection();
     }
 
@@ -135,7 +129,7 @@ class Popup extends EventDispatcher {
 
     /**
      * The parent of the popup.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get parent() {
         return this._parent;
@@ -151,7 +145,7 @@ class Popup extends EventDispatcher {
 
     /**
      * The child of the popup.
-     * @type {Popup}
+     * @type {?Popup}
      */
     get child() {
         return this._child;
@@ -167,7 +161,7 @@ class Popup extends EventDispatcher {
 
     /**
      * The depth of the popup.
-     * @type {numer}
+     * @type {number}
      */
     get depth() {
         return this._depth;
@@ -215,11 +209,13 @@ class Popup extends EventDispatcher {
 
     /**
      * Sets the options context for the popup.
-     * @param {object} optionsContext The options context object.
+     * @param {import('settings').OptionsContext} optionsContext The options context object.
      */
     async setOptionsContext(optionsContext) {
         await this._setOptionsContext(optionsContext);
-        await this._invokeSafe('Display.setOptionsContext', {optionsContext});
+        if (this._frameConnected) {
+            await this._invokeSafe('Display.setOptionsContext', {optionsContext});
+        }
     }
 
     /**
@@ -252,7 +248,7 @@ class Popup extends EventDispatcher {
      * Force assigns the visibility of the popup.
      * @param {boolean} value Whether or not the popup should be visible.
      * @param {number} priority The priority of the override.
-     * @returns {Promise<string?>} A token used which can be passed to `clearVisibleOverride`,
+     * @returns {Promise<?import('core').TokenString>} A token used which can be passed to `clearVisibleOverride`,
      *   or null if the override wasn't assigned.
      */
     async setVisibleOverride(value, priority) {
@@ -261,7 +257,7 @@ class Popup extends EventDispatcher {
 
     /**
      * Clears a visibility override that was generated by `setVisibleOverride`.
-     * @param {string} token The token returned from `setVisibleOverride`.
+     * @param {import('core').TokenString} token The token returned from `setVisibleOverride`.
      * @returns {Promise<boolean>} `true` if the override existed and was removed, `false` otherwise.
      */
     async clearVisibleOverride(token) {
@@ -275,7 +271,8 @@ class Popup extends EventDispatcher {
      * @returns {Promise<boolean>} `true` if the point is contained within the popup's rect, `false` otherwise.
      */
     async containsPoint(x, y) {
-        for (let popup = this; popup !== null && popup.isVisibleSync(); popup = popup.child) {
+        // eslint-disable-next-line @typescript-eslint/no-this-alias
+        for (let popup = /** @type {?Popup} */ (this); popup !== null && popup.isVisibleSync(); popup = popup.child) {
             const rect = popup.getFrameRect();
             if (rect.valid && x >= rect.left && y >= rect.top && x < rect.right && y < rect.bottom) {
                 return true;
@@ -286,12 +283,12 @@ class Popup extends EventDispatcher {
 
     /**
      * Shows and updates the positioning and content of the popup.
-     * @param {ContentDetails} details Settings for the outer popup.
-     * @param {Display.ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
+     * @param {import('popup').ContentDetails} details Settings for the outer popup.
+     * @param {?import('display').ContentDetails} displayDetails The details parameter passed to `Display.setContent`.
      * @returns {Promise<void>}
      */
     async showContent(details, displayDetails) {
-        if (!this._optionsAssigned) { throw new Error('Options not assigned'); }
+        if (this._optionsContext === null) { throw new Error('Options not assigned'); }
 
         const {optionsContext, sourceRects, writingMode} = details;
         if (optionsContext !== null) {
@@ -309,25 +306,27 @@ class Popup extends EventDispatcher {
      * Sets the custom styles for the popup content.
      * @param {string} css The CSS rules.
      */
-    setCustomCss(css) {
-        this._invokeSafe('Display.setCustomCss', {css});
+    async setCustomCss(css) {
+        await this._invokeSafe('Display.setCustomCss', {css});
     }
 
     /**
      * Stops the audio auto-play timer, if one has started.
      */
-    clearAutoPlayTimer() {
-        this._invokeSafe('Display.clearAutoPlayTimer');
+    async clearAutoPlayTimer() {
+        if (this._frameConnected) {
+            await this._invokeSafe('Display.clearAutoPlayTimer', {});
+        }
     }
 
     /**
      * Sets the scaling factor of the popup content.
      * @param {number} scale The scaling factor.
      */
-    setContentScale(scale) {
+    async setContentScale(scale) {
         this._contentScale = scale;
         this._frame.style.fontSize = `${scale}px`;
-        this._invokeSafe('Display.setContentScale', {scale});
+        await this._invokeSafe('Display.setContentScale', {scale});
     }
 
     /**
@@ -360,12 +359,14 @@ class Popup extends EventDispatcher {
             parentNode = this._shadow;
         }
         const node = await dynamicLoader.loadStyle('yomichan-popup-outer-user-stylesheet', 'code', css, useWebExtensionApi, parentNode);
-        this.trigger('customOuterCssChanged', {node, useWebExtensionApi, inShadow});
+        /** @type {import('popup').CustomOuterCssChangedEvent} */
+        const event = {node, useWebExtensionApi, inShadow};
+        this.trigger('customOuterCssChanged', event);
     }
 
     /**
      * Gets the rectangle of the DOM frame, synchronously.
-     * @returns {ValidRect} The rect.
+     * @returns {import('popup').ValidRect} The rect.
      *   `valid` is `false` for `PopupProxy`, since the DOM node is hosted in a different frame.
      */
     getFrameRect() {
@@ -375,7 +376,7 @@ class Popup extends EventDispatcher {
 
     /**
      * Gets the size of the DOM frame.
-     * @returns {Promise<{width: number, height: number, valid: boolean}>} The size and whether or not it is valid.
+     * @returns {Promise<import('popup').ValidSize>} The size and whether or not it is valid.
      */
     async getFrameSize() {
         const {width, height} = this._getFrameBoundingClientRect();
@@ -395,14 +396,23 @@ class Popup extends EventDispatcher {
 
     // Private functions
 
+    /**
+     * @returns {void}
+     */
     _onFrameMouseOver() {
         this.trigger('framePointerOver', {});
     }
 
+    /**
+     * @returns {void}
+     */
     _onFrameMouseOut() {
         this.trigger('framePointerOut', {});
     }
 
+    /**
+     * @returns {Promise<boolean>}
+     */
     _inject() {
         let injectPromise = this._injectPromise;
         if (injectPromise === null) {
@@ -419,19 +429,25 @@ class Popup extends EventDispatcher {
         return injectPromise;
     }
 
+    /**
+     * @returns {Promise<boolean>}
+     */
     async _injectInner1() {
         try {
             await this._injectInner2();
             return true;
         } catch (e) {
             this._resetFrame();
-            if (e.source === this) { return false; } // Passive error
+            if (e instanceof PopupError && e.source === this) { return false; } // Passive error
             throw e;
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _injectInner2() {
-        if (!this._optionsAssigned) {
+        if (this._optionsContext === null) {
             throw new Error('Options not initialized');
         }
 
@@ -439,6 +455,7 @@ class Popup extends EventDispatcher {
 
         await this._setUpContainer(this._useShadowDom);
 
+        /** @type {import('frame-client').SetupFrameFunction} */
         const setupFrame = (frame) => {
             frame.removeAttribute('src');
             frame.removeAttribute('srcdoc');
@@ -447,9 +464,8 @@ class Popup extends EventDispatcher {
             const {contentDocument} = frame;
             if (contentDocument === null) {
                 // This can occur when running inside a sandboxed frame without "allow-same-origin"
-                const error = new Error('Popup not supoprted in this context');
-                error.source = this; // Used to detect a passive error which should be ignored
-                throw error;
+                // Custom error is used to detect a passive error which should be ignored
+                throw new PopupError('Popup not supported in this context', this);
             }
             const url = chrome.runtime.getURL('/popup.html');
             if (useSecurePopupFrameUrl) {
@@ -462,23 +478,32 @@ class Popup extends EventDispatcher {
         const frameClient = new FrameClient();
         this._frameClient = frameClient;
         await frameClient.connect(this._frame, this._targetOrigin, this._frameId, setupFrame);
+        this._frameConnected = true;
 
         // Configure
-        await this._invokeSafe('Display.configure', {
+        /** @type {import('display').ConfigureMessageDetails} */
+        const configureParams = {
             depth: this._depth,
             parentPopupId: this._id,
             parentFrameId: this._frameId,
             childrenSupported: this._childrenSupported,
             scale: this._contentScale,
             optionsContext: this._optionsContext
-        });
+        };
+        await this._invokeSafe('Display.configure', configureParams);
     }
 
+    /**
+     * @returns {void}
+     */
     _onFrameLoad() {
         if (!this._injectPromiseComplete) { return; }
         this._resetFrame();
     }
 
+    /**
+     * @returns {void}
+     */
     _resetFrame() {
         const parent = this._container.parentNode;
         if (parent !== null) {
@@ -488,10 +513,14 @@ class Popup extends EventDispatcher {
         this._frame.removeAttribute('srcdoc');
 
         this._frameClient = null;
+        this._frameConnected = false;
         this._injectPromise = null;
         this._injectPromiseComplete = false;
     }
 
+    /**
+     * @param {boolean} usePopupShadowDom
+     */
     async _setUpContainer(usePopupShadowDom) {
         if (usePopupShadowDom && typeof this._frame.attachShadow === 'function') {
             const container = document.createElement('div');
@@ -514,6 +543,9 @@ class Popup extends EventDispatcher {
         await this._injectStyles();
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _injectStyles() {
         try {
             await this._injectPopupOuterStylesheet();
@@ -528,7 +560,11 @@ class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _injectPopupOuterStylesheet() {
+        /** @type {'code'|'file'|'file-content'} */
         let fileType = 'file';
         let useWebExtensionApi = true;
         let parentNode = null;
@@ -540,6 +576,9 @@ class Popup extends EventDispatcher {
         await dynamicLoader.loadStyle('yomichan-popup-outer-stylesheet', fileType, '/css/popup-outer.css', useWebExtensionApi, parentNode);
     }
 
+    /**
+     * @param {boolean} observe
+     */
     _observeFullscreen(observe) {
         if (!observe) {
             this._fullscreenEventListeners.removeAllEventListeners();
@@ -554,6 +593,9 @@ class Popup extends EventDispatcher {
         DocumentUtil.addFullscreenChangeEventListener(this._onFullscreenChanged.bind(this), this._fullscreenEventListeners);
     }
 
+    /**
+     * @returns {void}
+     */
     _onFullscreenChanged() {
         const parent = this._getFrameParentElement();
         if (parent !== null && this._container.parentNode !== parent) {
@@ -561,6 +603,10 @@ class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('popup').Rect[]} sourceRects
+     * @param {import('document-util').NormalizedWritingMode} writingMode
+     */
     async _show(sourceRects, writingMode) {
         const injected = await this._inject();
         if (!injected) { return; }
@@ -588,16 +634,26 @@ class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} width
+     * @param {number} height
+     */
     _setFrameSize(width, height) {
         const {style} = this._frame;
         style.width = `${width}px`;
         style.height = `${height}px`;
     }
 
+    /**
+     * @param {boolean} visible
+     */
     _setVisible(visible) {
         this._visible.defaultValue = visible;
     }
 
+    /**
+     * @param {import('dynamic-property').ChangeEventDetails<boolean>} event
+     */
     _onVisibleChange({value}) {
         if (this._visibleValue === value) { return; }
         this._visibleValue = value;
@@ -605,6 +661,9 @@ class Popup extends EventDispatcher {
         this._invokeSafe('Display.visibilityChanged', {value});
     }
 
+    /**
+     * @returns {void}
+     */
     _focusParent() {
         if (this._parent !== null) {
             // Chrome doesn't like focusing iframe without contentWindow.
@@ -621,23 +680,43 @@ class Popup extends EventDispatcher {
         }
     }
 
-    async _invoke(action, params={}) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn>}
+     */
+    async _invoke(action, params) {
         const contentWindow = this._frame.contentWindow;
-        if (this._frameClient === null || !this._frameClient.isConnected() || contentWindow === null) { return; }
+        if (this._frameClient === null || !this._frameClient.isConnected() || contentWindow === null) {
+            throw new Error(`Failed to invoke action ${action}: frame state invalid`);
+        }
 
         const message = this._frameClient.createMessage({action, params});
         return await yomichan.crossFrame.invoke(this._frameClient.frameId, 'popupMessage', message);
     }
 
-    async _invokeSafe(action, params={}, defaultReturnValue) {
+    /**
+     * @template {import('core').SerializableObject} TParams
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn|undefined>}
+     */
+    async _invokeSafe(action, params) {
         try {
             return await this._invoke(action, params);
         } catch (e) {
             if (!yomichan.isExtensionUnloaded) { throw e; }
-            return defaultReturnValue;
+            return void 0;
         }
     }
 
+    /**
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     */
     _invokeWindow(action, params={}) {
         const contentWindow = this._frame.contentWindow;
         if (this._frameClient === null || !this._frameClient.isConnected() || contentWindow === null) { return; }
@@ -646,10 +725,16 @@ class Popup extends EventDispatcher {
         contentWindow.postMessage(message, this._targetOrigin);
     }
 
+    /**
+     * @returns {void}
+     */
     _onExtensionUnloaded() {
         this._invokeWindow('Display.extensionUnloaded');
     }
 
+    /**
+     * @returns {Element}
+     */
     _getFrameParentElement() {
         let defaultParent = document.body;
         if (defaultParent !== null && defaultParent.tagName.toLowerCase() === 'frameset') {
@@ -659,7 +744,8 @@ class Popup extends EventDispatcher {
         if (
             fullscreenElement === null ||
             fullscreenElement.shadowRoot ||
-            fullscreenElement.openOrClosedShadowRoot // Available to Firefox 63+ for WebExtensions
+            // @ts-ignore - openOrClosedShadowRoot is available to Firefox 63+ for WebExtensions
+            fullscreenElement.openOrClosedShadowRoot
         ) {
             return defaultParent;
         }
@@ -675,10 +761,10 @@ class Popup extends EventDispatcher {
 
     /**
      * Computes the position where the popup should be placed relative to the source content.
-     * @param {Rect[]} sourceRects The rectangles of the source content.
-     * @param {string} writingMode The CSS writing mode of the source text.
-     * @param {Rect} viewport The viewport that the popup can be placed within.
-     * @returns {SizeRect} The calculated rectangle for where to position the popup.
+     * @param {import('popup').Rect[]} sourceRects The rectangles of the source content.
+     * @param {import('document-util').NormalizedWritingMode} writingMode The CSS writing mode of the source text.
+     * @param {import('popup').Rect} viewport The viewport that the popup can be placed within.
+     * @returns {import('popup').SizeRect} The calculated rectangle for where to position the popup.
      */
     _getPosition(sourceRects, writingMode, viewport) {
         sourceRects = this._convertSourceRectsCoordinateSpace(sourceRects);
@@ -705,6 +791,7 @@ class Popup extends EventDispatcher {
         horizontalOffset *= contentScale;
         verticalOffset *= contentScale;
 
+        /** @type {?import('popup').SizeRect} */
         let best = null;
         const sourceRectsLength = sourceRects.length;
         for (let i = 0, ii = (sourceRectsLength > 1 ? sourceRectsLength : 0); i <= ii; ++i) {
@@ -720,19 +807,20 @@ class Popup extends EventDispatcher {
                 if (result.height >= frameHeight) { break; }
             }
         }
-        return best;
+        // Given the loop conditions, this is guaranteed to be non-null
+        return /** @type {import('popup').SizeRect} */ (best);
     }
 
     /**
      * Computes the position where the popup should be placed for horizontal text.
-     * @param {Rect} sourceRect The rectangle of the source content.
+     * @param {import('popup').Rect} sourceRect The rectangle of the source content.
      * @param {number} frameWidth The preferred width of the frame.
      * @param {number} frameHeight The preferred height of the frame.
-     * @param {Rect} viewport The viewport that the frame can be placed within.
+     * @param {import('popup').Rect} viewport The viewport that the frame can be placed within.
      * @param {number} horizontalOffset The horizontal offset from the source rect that the popup will be placed.
      * @param {number} verticalOffset The vertical offset from the source rect that the popup will be placed.
      * @param {boolean} preferBelow Whether or not the popup is preferred to be placed below the source content.
-     * @returns {SizeRect} The calculated rectangle for where to position the popup.
+     * @returns {import('popup').SizeRect} The calculated rectangle for where to position the popup.
      */
     _getPositionForHorizontalText(sourceRect, frameWidth, frameHeight, viewport, horizontalOffset, verticalOffset, preferBelow) {
         const [left, width, after] = this._getConstrainedPosition(
@@ -756,14 +844,14 @@ class Popup extends EventDispatcher {
 
     /**
      * Computes the position where the popup should be placed for vertical text.
-     * @param {Rect} sourceRect The rectangle of the source content.
+     * @param {import('popup').Rect} sourceRect The rectangle of the source content.
      * @param {number} frameWidth The preferred width of the frame.
      * @param {number} frameHeight The preferred height of the frame.
-     * @param {Rect} viewport The viewport that the frame can be placed within.
+     * @param {import('popup').Rect} viewport The viewport that the frame can be placed within.
      * @param {number} horizontalOffset The horizontal offset from the source rect that the popup will be placed.
      * @param {number} verticalOffset The vertical offset from the source rect that the popup will be placed.
      * @param {boolean} preferRight Whether or not the popup is preferred to be placed to the right of the source content.
-     * @returns {SizeRect} The calculated rectangle for where to position the popup.
+     * @returns {import('popup').SizeRect} The calculated rectangle for where to position the popup.
      */
     _getPositionForVerticalText(sourceRect, frameWidth, frameHeight, viewport, horizontalOffset, verticalOffset, preferRight) {
         const [left, width, after] = this._getConstrainedPositionBinary(
@@ -785,6 +873,11 @@ class Popup extends EventDispatcher {
         return {left, top, width, height, after, below};
     }
 
+    /**
+     * @param {import('settings').PopupVerticalTextPosition} positionPreference
+     * @param {import('document-util').NormalizedWritingMode} writingMode
+     * @returns {boolean}
+     */
     _isVerticalTextPopupOnRight(positionPreference, writingMode) {
         switch (positionPreference) {
             case 'before':
@@ -799,6 +892,10 @@ class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('document-util').NormalizedWritingMode} writingMode
+     * @returns {boolean}
+     */
     _isWritingModeLeftToRight(writingMode) {
         switch (writingMode) {
             case 'vertical-lr':
@@ -809,6 +906,15 @@ class Popup extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} positionBefore
+     * @param {number} positionAfter
+     * @param {number} size
+     * @param {number} minLimit
+     * @param {number} maxLimit
+     * @param {boolean} after
+     * @returns {[position: number, size: number, after: boolean]}
+     */
     _getConstrainedPosition(positionBefore, positionAfter, size, minLimit, maxLimit, after) {
         size = Math.min(size, maxLimit - minLimit);
 
@@ -824,6 +930,15 @@ class Popup extends EventDispatcher {
         return [position, size, after];
     }
 
+    /**
+     * @param {number} positionBefore
+     * @param {number} positionAfter
+     * @param {number} size
+     * @param {number} minLimit
+     * @param {number} maxLimit
+     * @param {boolean} after
+     * @returns {[position: number, size: number, after: boolean]}
+     */
     _getConstrainedPositionBinary(positionBefore, positionAfter, size, minLimit, maxLimit, after) {
         const overflowBefore = minLimit - (positionBefore - size);
         const overflowAfter = (positionAfter + size) - maxLimit;
@@ -847,11 +962,11 @@ class Popup extends EventDispatcher {
     /**
      * Gets the visual viewport.
      * @param {boolean} useVisualViewport Whether or not the `window.visualViewport` should be used.
-     * @returns {Rect} The rectangle of the visual viewport.
+     * @returns {import('popup').Rect} The rectangle of the visual viewport.
      */
     _getViewport(useVisualViewport) {
-        const visualViewport = window.visualViewport;
-        if (visualViewport !== null && typeof visualViewport === 'object') {
+        const {visualViewport} = window;
+        if (typeof visualViewport !== 'undefined' && visualViewport !== null) {
             const left = visualViewport.offsetLeft;
             const top = visualViewport.offsetTop;
             const width = visualViewport.width;
@@ -882,6 +997,9 @@ class Popup extends EventDispatcher {
         };
     }
 
+    /**
+     * @param {import('settings').OptionsContext} optionsContext
+     */
     async _setOptionsContext(optionsContext) {
         this._optionsContext = optionsContext;
         const options = await yomichan.api.optionsGet(optionsContext);
@@ -902,10 +1020,12 @@ class Popup extends EventDispatcher {
         this._useSecureFrameUrl = general.useSecurePopupFrameUrl;
         this._useShadowDom = general.usePopupShadowDom;
         this._customOuterCss = general.customPopupOuterCss;
-        this._optionsAssigned = true;
         this.updateTheme();
     }
 
+    /**
+     * @param {import('settings').OptionsContext} optionsContext
+     */
     async _setOptionsContextIfDifferent(optionsContext) {
         if (deepEqual(this._optionsContext, optionsContext)) { return; }
         await this._setOptionsContext(optionsContext);
@@ -913,8 +1033,8 @@ class Popup extends EventDispatcher {
 
     /**
      * Computes the bounding rectangle for a set of rectangles.
-     * @param {Rect[]} sourceRects An array of rectangles.
-     * @returns {Rect} The bounding rectangle for all of the source rectangles.
+     * @param {import('popup').Rect[]} sourceRects An array of rectangles.
+     * @returns {import('popup').Rect} The bounding rectangle for all of the source rectangles.
      */
     _getBoundingSourceRect(sourceRects) {
         switch (sourceRects.length) {
@@ -934,8 +1054,8 @@ class Popup extends EventDispatcher {
 
     /**
      * Checks whether or not a rectangle is overlapping any other rectangles.
-     * @param {SizeRect} sizeRect The rectangles to check for overlaps.
-     * @param {Rect[]} sourceRects The list of rectangles to compare against.
+     * @param {import('popup').SizeRect} sizeRect The rectangles to check for overlaps.
+     * @param {import('popup').Rect[]} sourceRects The list of rectangles to compare against.
      * @param {number} ignoreIndex The index of an item in `sourceRects` to ignore.
      * @returns {boolean} `true` if `sizeRect` overlaps any one of `sourceRects`, excluding `sourceRects[ignoreIndex]`; `false` otherwise.
      */
@@ -968,8 +1088,8 @@ class Popup extends EventDispatcher {
 
     /**
      * Converts the coordinate space of source rectangles.
-     * @param {Rect[]} sourceRects The list of rectangles to convert.
-     * @returns {Rect[]} Either an updated list of rectangles, or `sourceRects` if no change is required.
+     * @param {import('popup').Rect[]} sourceRects The list of rectangles to convert.
+     * @returns {import('popup').Rect[]} Either an updated list of rectangles, or `sourceRects` if no change is required.
      */
     _convertSourceRectsCoordinateSpace(sourceRects) {
         let scale = DocumentUtil.computeZoomScale(this._container);
@@ -984,9 +1104,9 @@ class Popup extends EventDispatcher {
 
     /**
      * Creates a scaled rectangle.
-     * @param {Rect} rect The rectangle to scale.
+     * @param {import('popup').Rect} rect The rectangle to scale.
      * @param {number} scale The scale factor.
-     * @returns {Rect} A new rectangle which has been scaled.
+     * @returns {import('popup').Rect} A new rectangle which has been scaled.
      */
     _createScaledRect(rect, scale) {
         return {
@@ -997,3 +1117,18 @@ class Popup extends EventDispatcher {
         };
     }
 }
+
+class PopupError extends ExtensionError {
+    /**
+     * @param {string} message
+     * @param {Popup} source
+     */
+    constructor(message, source) {
+        super(message);
+        /** @type {Popup} */
+        this._source = source;
+    }
+
+    /** @type {Popup} */
+    get source() { return this._source; }
+}
diff --git a/ext/js/app/theme-controller.js b/ext/js/app/theme-controller.js
index f8d5410b94..2ff83129c3 100644
--- a/ext/js/app/theme-controller.js
+++ b/ext/js/app/theme-controller.js
@@ -22,13 +22,18 @@
 class ThemeController {
     /**
      * Creates a new instance of the class.
-     * @param {?Element} element A DOM element which theme properties are applied to.
+     * @param {?HTMLElement} element A DOM element which theme properties are applied to.
      */
     constructor(element) {
+        /** @type {?HTMLElement} */
         this._element = element;
-        this._theme = 'default';
-        this._outerTheme = 'default';
+        /** @type {'light'|'dark'|'browser'} */
+        this._theme = 'light';
+        /** @type {'light'|'dark'|'browser'|'site'} */
+        this._outerTheme = 'light';
+        /** @type {?('dark'|'light')} */
         this._siteTheme = null;
+        /** @type {'dark'|'light'} */
         this._browserTheme = 'light';
     }
 
@@ -42,7 +47,7 @@ class ThemeController {
 
     /**
      * Sets the DOM element which theme properties are applied to.
-     * @param {?Element} value The DOM element to assign.
+     * @param {?HTMLElement} value The DOM element to assign.
      */
     set element(value) {
         this._element = value;
@@ -50,7 +55,7 @@ class ThemeController {
 
     /**
      * Gets the main theme for the content.
-     * @type {string}
+     * @type {'light'|'dark'|'browser'}
      */
     get theme() {
         return this._theme;
@@ -58,7 +63,7 @@ class ThemeController {
 
     /**
      * Sets the main theme for the content.
-     * @param {string} value The theme value to assign.
+     * @param {'light'|'dark'|'browser'} value The theme value to assign.
      */
     set theme(value) {
         this._theme = value;
@@ -66,7 +71,7 @@ class ThemeController {
 
     /**
      * Gets the outer theme for the content.
-     * @type {string}
+     * @type {'light'|'dark'|'browser'|'site'}
      */
     get outerTheme() {
         return this._outerTheme;
@@ -74,7 +79,7 @@ class ThemeController {
 
     /**
      * Sets the outer theme for the content.
-     * @param {string} value The outer theme value to assign.
+     * @param {'light'|'dark'|'browser'|'site'} value The outer theme value to assign.
      */
     set outerTheme(value) {
         this._outerTheme = value;
@@ -83,7 +88,7 @@ class ThemeController {
     /**
      * Gets the override value for the site theme.
      * If this value is `null`, the computed value will be used.
-     * @type {?string}
+     * @type {?('dark'|'light')}
      */
     get siteTheme() {
         return this._siteTheme;
@@ -92,7 +97,7 @@ class ThemeController {
     /**
      * Sets the override value for the site theme.
      * If this value is `null`, the computed value will be used.
-     * @param {?string} value The site theme value to assign.
+     * @param {?('dark'|'light')} value The site theme value to assign.
      */
     set siteTheme(value) {
         this._siteTheme = value;
@@ -101,7 +106,7 @@ class ThemeController {
     /**
      * Gets the browser's preferred color theme.
      * The value can be either 'light' or 'dark'.
-     * @type {?string}
+     * @type {'dark'|'light'}
      */
     get browserTheme() {
         return this._browserTheme;
@@ -152,7 +157,6 @@ class ThemeController {
     /**
      * Event handler for when the preferred browser theme changes.
      * @param {MediaQueryList|MediaQueryListEvent} detail The object containing event details.
-     * @param {boolean} detail.matches The object containing event details.
      */
     _onPrefersColorSchemeDarkChange({matches}) {
         this._browserTheme = (matches ? 'dark' : 'light');
diff --git a/ext/js/background/backend.js b/ext/js/background/backend.js
index db6cfadab7..9fa82cd416 100644
--- a/ext/js/background/backend.js
+++ b/ext/js/background/backend.js
@@ -48,63 +48,95 @@ class Backend {
      * Creates a new instance.
      */
     constructor() {
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = new JapaneseUtil(wanakana);
+        /** @type {Environment} */
         this._environment = new Environment();
+        /** @type {DictionaryDatabase} */
         this._dictionaryDatabase = new DictionaryDatabase();
+        /** @type {Translator} */
         this._translator = new Translator({
             japaneseUtil: this._japaneseUtil,
             database: this._dictionaryDatabase
         });
+        /** @type {AnkiConnect} */
         this._anki = new AnkiConnect();
+        /** @type {Mecab} */
         this._mecab = new Mecab();
+        /** @type {ClipboardReader} */
         this._clipboardReader = new ClipboardReader({
             // eslint-disable-next-line no-undef
             document: (typeof document === 'object' && document !== null ? document : null),
             pasteTargetSelector: '#clipboard-paste-target',
             richContentPasteTargetSelector: '#clipboard-rich-content-paste-target'
         });
+        /** @type {ClipboardMonitor} */
         this._clipboardMonitor = new ClipboardMonitor({
             japaneseUtil: this._japaneseUtil,
             clipboardReader: this._clipboardReader
         });
+        /** @type {?import('settings').Options} */
         this._options = null;
+        /** @type {JsonSchema[]} */
         this._profileConditionsSchemaCache = [];
+        /** @type {ProfileConditionsUtil} */
         this._profileConditionsUtil = new ProfileConditionsUtil();
+        /** @type {?string} */
         this._defaultAnkiFieldTemplates = null;
+        /** @type {RequestBuilder} */
         this._requestBuilder = new RequestBuilder();
+        /** @type {AudioDownloader} */
         this._audioDownloader = new AudioDownloader({
             japaneseUtil: this._japaneseUtil,
             requestBuilder: this._requestBuilder
         });
+        /** @type {OptionsUtil} */
         this._optionsUtil = new OptionsUtil();
+        /** @type {ScriptManager} */
         this._scriptManager = new ScriptManager();
+        /** @type {AccessibilityController} */
         this._accessibilityController = new AccessibilityController(this._scriptManager);
 
+        /** @type {?number} */
         this._searchPopupTabId = null;
+        /** @type {?Promise<{tab: chrome.tabs.Tab, created: boolean}>} */
         this._searchPopupTabCreatePromise = null;
 
+        /** @type {boolean} */
         this._isPrepared = false;
+        /** @type {boolean} */
         this._prepareError = false;
+        /** @type {?Promise<void>} */
         this._preparePromise = null;
+        /** @type {import('core').DeferredPromiseDetails<void>} */
         const {promise, resolve, reject} = deferPromise();
+        /** @type {Promise<void>} */
         this._prepareCompletePromise = promise;
+        /** @type {() => void} */
         this._prepareCompleteResolve = resolve;
+        /** @type {(reason?: unknown) => void} */
         this._prepareCompleteReject = reject;
 
+        /** @type {?string} */
         this._defaultBrowserActionTitle = null;
+        /** @type {?number} */
         this._badgePrepareDelayTimer = null;
+        /** @type {?import('log').LogLevel} */
         this._logErrorLevel = null;
+        /** @type {?chrome.permissions.Permissions} */
         this._permissions = null;
+        /** @type {PermissionsUtil} */
         this._permissionsUtil = new PermissionsUtil();
 
-        this._messageHandlers = new Map([
+        /** @type {import('backend').MessageHandlerMap} */
+        this._messageHandlers = new Map(/** @type {import('backend').MessageHandlerMapInit} */ ([
             ['requestBackendReadySignal',    {async: false, contentScript: true,  handler: this._onApiRequestBackendReadySignal.bind(this)}],
             ['optionsGet',                   {async: false, contentScript: true,  handler: this._onApiOptionsGet.bind(this)}],
             ['optionsGetFull',               {async: false, contentScript: true,  handler: this._onApiOptionsGetFull.bind(this)}],
             ['kanjiFind',                    {async: true,  contentScript: true,  handler: this._onApiKanjiFind.bind(this)}],
             ['termsFind',                    {async: true,  contentScript: true,  handler: this._onApiTermsFind.bind(this)}],
             ['parseText',                    {async: true,  contentScript: true,  handler: this._onApiParseText.bind(this)}],
-            ['getAnkiConnectVersion',        {async: true,  contentScript: true,  handler: this._onApGetAnkiConnectVersion.bind(this)}],
+            ['getAnkiConnectVersion',        {async: true,  contentScript: true,  handler: this._onApiGetAnkiConnectVersion.bind(this)}],
             ['isAnkiConnected',              {async: true,  contentScript: true,  handler: this._onApiIsAnkiConnected.bind(this)}],
             ['addAnkiNote',                  {async: true,  contentScript: true,  handler: this._onApiAddAnkiNote.bind(this)}],
             ['getAnkiNoteInfo',              {async: true,  contentScript: true,  handler: this._onApiGetAnkiNoteInfo.bind(this)}],
@@ -140,17 +172,20 @@ class Backend {
             ['getTermFrequencies',           {async: true,  contentScript: true,  handler: this._onApiGetTermFrequencies.bind(this)}],
             ['findAnkiNotes',                {async: true,  contentScript: true,  handler: this._onApiFindAnkiNotes.bind(this)}],
             ['loadExtensionScripts',         {async: true,  contentScript: true,  handler: this._onApiLoadExtensionScripts.bind(this)}]
-        ]);
-        this._messageHandlersWithProgress = new Map([
-        ]);
-
-        this._commandHandlers = new Map([
+        ]));
+        /** @type {import('backend').MessageHandlerWithProgressMap} */
+        this._messageHandlersWithProgress = new Map(/** @type {import('backend').MessageHandlerWithProgressMapInit} */ ([
+            // Empty
+        ]));
+
+        /** @type {Map<string, (params?: import('core').SerializableObject) => void>} */
+        this._commandHandlers = new Map(/** @type {[name: string, handler: (params?: import('core').SerializableObject) => void][]} */ ([
             ['toggleTextScanning', this._onCommandToggleTextScanning.bind(this)],
             ['openInfoPage',       this._onCommandOpenInfoPage.bind(this)],
             ['openSettingsPage',   this._onCommandOpenSettingsPage.bind(this)],
             ['openSearchPage',     this._onCommandOpenSearchPage.bind(this)],
             ['openPopupWindow',    this._onCommandOpenPopupWindow.bind(this)]
-        ]);
+        ]));
     }
 
     /**
@@ -161,9 +196,9 @@ class Backend {
         if (this._preparePromise === null) {
             const promise = this._prepareInternal();
             promise.then(
-                (value) => {
+                () => {
                     this._isPrepared = true;
-                    this._prepareCompleteResolve(value);
+                    this._prepareCompleteResolve();
                 },
                 (error) => {
                     this._prepareError = true;
@@ -178,6 +213,9 @@ class Backend {
 
     // Private
 
+    /**
+     * @returns {void}
+     */
     _prepareInternalSync() {
         if (isObject(chrome.commands) && isObject(chrome.commands.onCommand)) {
             const onCommand = this._onWebExtensionEventWrapper(this._onCommand.bind(this));
@@ -204,6 +242,9 @@ class Backend {
         chrome.runtime.onInstalled.addListener(this._onInstalled.bind(this));
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _prepareInternal() {
         try {
             this._prepareInternalSync();
@@ -216,7 +257,7 @@ class Backend {
             }, 1000);
             this._updateBadge();
 
-            yomichan.on('log', this._onLog.bind(this));
+            log.on('log', this._onLog.bind(this));
 
             await this._requestBuilder.prepare();
             await this._environment.prepare();
@@ -228,16 +269,16 @@ class Backend {
                 log.error(e);
             }
 
-            const deinflectionReasions = await this._fetchAsset('/data/deinflect.json', true);
+            const deinflectionReasions = /** @type {import('deinflector').ReasonsRaw} */ (await this._fetchJson('/data/deinflect.json'));
             this._translator.prepare(deinflectionReasions);
 
             await this._optionsUtil.prepare();
-            this._defaultAnkiFieldTemplates = (await this._fetchAsset('/data/templates/default-anki-field-templates.handlebars')).trim();
+            this._defaultAnkiFieldTemplates = (await this._fetchText('/data/templates/default-anki-field-templates.handlebars')).trim();
             this._options = await this._optionsUtil.load();
 
             this._applyOptions('background');
 
-            const options = this._getProfileOptions({current: true});
+            const options = this._getProfileOptions({current: true}, false);
             if (options.general.showGuide) {
                 this._openWelcomeGuidePageOnce();
             }
@@ -259,20 +300,30 @@ class Backend {
 
     // Event handlers
 
+    /**
+     * @param {{text: string}} params
+     */
     async _onClipboardTextChange({text}) {
-        const {clipboard: {maximumSearchLength}} = this._getProfileOptions({current: true});
+        const {clipboard: {maximumSearchLength}} = this._getProfileOptions({current: true}, false);
         if (text.length > maximumSearchLength) {
             text = text.substring(0, maximumSearchLength);
         }
         try {
             const {tab, created} = await this._getOrCreateSearchPopup();
+            const {id} = tab;
+            if (typeof id !== 'number') {
+                throw new Error('Tab does not have an id');
+            }
             await this._focusTab(tab);
-            await this._updateSearchQuery(tab.id, text, !created);
+            await this._updateSearchQuery(id, text, !created);
         } catch (e) {
             // NOP
         }
     }
 
+    /**
+     * @param {{level: import('log').LogLevel}} params
+     */
     _onLog({level}) {
         const levelValue = this._getErrorLevelValue(level);
         if (levelValue <= this._getErrorLevelValue(this._logErrorLevel)) { return; }
@@ -283,8 +334,13 @@ class Backend {
 
     // WebExtension event handlers (with prepared checks)
 
+    /**
+     * @template {(...args: import('core').SafeAny[]) => void} T
+     * @param {T} handler
+     * @returns {T}
+     */
     _onWebExtensionEventWrapper(handler) {
-        return (...args) => {
+        return /** @type {T} */ ((...args) => {
             if (this._isPrepared) {
                 handler(...args);
                 return;
@@ -294,9 +350,10 @@ class Backend {
                 () => { handler(...args); },
                 () => {} // NOP
             );
-        };
+        });
     }
 
+    /** @type {import('extension').ChromeRuntimeOnMessageCallback} */
     _onMessageWrapper(message, sender, sendResponse) {
         if (this._isPrepared) {
             return this._onMessage(message, sender, sendResponse);
@@ -311,10 +368,19 @@ class Backend {
 
     // WebExtension event handlers
 
+    /**
+     * @param {string} command
+     */
     _onCommand(command) {
-        this._runCommand(command);
+        this._runCommand(command, void 0);
     }
 
+    /**
+     * @param {{action: string, params?: import('core').SerializableObject}} message
+     * @param {chrome.runtime.MessageSender} sender
+     * @param {(response?: unknown) => void} callback
+     * @returns {boolean}
+     */
     _onMessage({action, params}, sender, callback) {
         const messageHandler = this._messageHandlers.get(action);
         if (typeof messageHandler === 'undefined') { return false; }
@@ -323,7 +389,7 @@ class Backend {
             try {
                 this._validatePrivilegedMessageSender(sender);
             } catch (error) {
-                callback({error: serializeError(error)});
+                callback({error: ExtensionError.serialize(error)});
                 return false;
             }
         }
@@ -331,6 +397,9 @@ class Backend {
         return invokeMessageHandler(messageHandler, params, callback, sender);
     }
 
+    /**
+     * @param {chrome.runtime.Port} port
+     */
     _onConnect(port) {
         try {
             let details;
@@ -341,11 +410,15 @@ class Backend {
             }
             if (details.name !== 'background-cross-frame-communication-port') { return; }
 
-            const senderTabId = (port.sender && port.sender.tab ? port.sender.tab.id : null);
+            const {sender} = port;
+            if (!sender || !sender.tab) {
+                throw new Error('Port does not have an associated tab');
+            }
+            const senderTabId = sender.tab.id;
             if (typeof senderTabId !== 'number') {
                 throw new Error('Port does not have an associated tab ID');
             }
-            const senderFrameId = port.sender.frameId;
+            const senderFrameId = sender.frameId;
             if (typeof senderFrameId !== 'number') {
                 throw new Error('Port does not have an associated frame ID');
             }
@@ -359,6 +432,7 @@ class Backend {
                 sourceTabId: senderTabId,
                 sourceFrameId: senderFrameId
             };
+            /** @type {?chrome.runtime.Port} */
             let forwardPort = chrome.tabs.connect(targetTabId, {frameId: targetFrameId, name: JSON.stringify(details2)});
 
             const cleanup = () => {
@@ -367,13 +441,10 @@ class Backend {
                     forwardPort.disconnect();
                     forwardPort = null;
                 }
-                if (port !== null) {
-                    port.disconnect();
-                    port = null;
-                }
+                port.disconnect();
             };
 
-            port.onMessage.addListener((message) => { forwardPort.postMessage(message); });
+            port.onMessage.addListener((message) => { if (forwardPort !== null) { forwardPort.postMessage(message); } });
             forwardPort.onMessage.addListener((message) => { port.postMessage(message); });
             port.onDisconnect.addListener(cleanup);
             forwardPort.onDisconnect.addListener(cleanup);
@@ -383,14 +454,23 @@ class Backend {
         }
     }
 
+    /**
+     * @param {chrome.tabs.ZoomChangeInfo} event
+     */
     _onZoomChange({tabId, oldZoomFactor, newZoomFactor}) {
-        this._sendMessageTabIgnoreResponse(tabId, {action: 'Yomichan.zoomChanged', params: {oldZoomFactor, newZoomFactor}});
+        this._sendMessageTabIgnoreResponse(tabId, {action: 'Yomichan.zoomChanged', params: {oldZoomFactor, newZoomFactor}}, {});
     }
 
+    /**
+     * @returns {void}
+     */
     _onPermissionsChanged() {
         this._checkPermissions();
     }
 
+    /**
+     * @param {chrome.runtime.InstalledDetails} event
+     */
     _onInstalled({reason}) {
         if (reason !== 'install') { return; }
         this._requestPersistentStorage();
@@ -398,6 +478,7 @@ class Backend {
 
     // Message handlers
 
+    /** @type {import('api').Handler<import('api').RequestBackendReadySignalDetails, import('api').RequestBackendReadySignalResult, true>} */
     _onApiRequestBackendReadySignal(_params, sender) {
         // tab ID isn't set in background (e.g. browser_action)
         const data = {action: 'Yomichan.backendReady', params: {}};
@@ -405,21 +486,27 @@ class Backend {
             this._sendMessageIgnoreResponse(data);
             return false;
         } else {
-            this._sendMessageTabIgnoreResponse(sender.tab.id, data);
+            const {id} = sender.tab;
+            if (typeof id === 'number') {
+                this._sendMessageTabIgnoreResponse(id, data, {});
+            }
             return true;
         }
     }
 
+    /** @type {import('api').Handler<import('api').OptionsGetDetails, import('api').OptionsGetResult>} */
     _onApiOptionsGet({optionsContext}) {
-        return this._getProfileOptions(optionsContext);
+        return this._getProfileOptions(optionsContext, false);
     }
 
+    /** @type {import('api').Handler<import('api').OptionsGetFullDetails, import('api').OptionsGetFullResult>} */
     _onApiOptionsGetFull() {
-        return this._getOptionsFull();
+        return this._getOptionsFull(false);
     }
 
+    /** @type {import('api').Handler<import('api').KanjiFindDetails, import('api').KanjiFindResult>} */
     async _onApiKanjiFind({text, optionsContext}) {
-        const options = this._getProfileOptions(optionsContext);
+        const options = this._getProfileOptions(optionsContext, false);
         const {general: {maxResults}} = options;
         const findKanjiOptions = this._getTranslatorFindKanjiOptions(options);
         const dictionaryEntries = await this._translator.findKanji(text, findKanjiOptions);
@@ -427,8 +514,9 @@ class Backend {
         return dictionaryEntries;
     }
 
+    /** @type {import('api').Handler<import('api').TermsFindDetails, import('api').TermsFindResult>} */
     async _onApiTermsFind({text, details, optionsContext}) {
-        const options = this._getProfileOptions(optionsContext);
+        const options = this._getProfileOptions(optionsContext, false);
         const {general: {resultOutputMode: mode, maxResults}} = options;
         const findTermsOptions = this._getTranslatorFindTermsOptions(mode, details, options);
         const {dictionaryEntries, originalTextLength} = await this._translator.findTerms(mode, text, findTermsOptions);
@@ -436,12 +524,14 @@ class Backend {
         return {dictionaryEntries, originalTextLength};
     }
 
+    /** @type {import('api').Handler<import('api').ParseTextDetails, import('api').ParseTextResult>} */
     async _onApiParseText({text, optionsContext, scanLength, useInternalParser, useMecabParser}) {
         const [internalResults, mecabResults] = await Promise.all([
             (useInternalParser ? this._textParseScanning(text, scanLength, optionsContext) : null),
             (useMecabParser ? this._textParseMecab(text) : null)
         ]);
 
+        /** @type {import('api').ParseTextResultItem[]} */
         const results = [];
 
         if (internalResults !== null) {
@@ -467,20 +557,26 @@ class Backend {
         return results;
     }
 
-    async _onApGetAnkiConnectVersion() {
+    /** @type {import('api').Handler<import('api').GetAnkiConnectVersionDetails, import('api').GetAnkiConnectVersionResult>} */
+    async _onApiGetAnkiConnectVersion() {
         return await this._anki.getVersion();
     }
 
+    /** @type {import('api').Handler<import('api').IsAnkiConnectedDetails, import('api').IsAnkiConnectedResult>} */
     async _onApiIsAnkiConnected() {
         return await this._anki.isConnected();
     }
 
+    /** @type {import('api').Handler<import('api').AddAnkiNoteDetails, import('api').AddAnkiNoteResult>} */
     async _onApiAddAnkiNote({note}) {
         return await this._anki.addNote(note);
     }
 
+    /** @type {import('api').Handler<import('api').GetAnkiNoteInfoDetails, import('api').GetAnkiNoteInfoResult>} */
     async _onApiGetAnkiNoteInfo({notes, fetchAdditionalInfo}) {
+        /** @type {import('anki').NoteInfoWrapper[]} */
         const results = [];
+        /** @type {{note: import('anki').Note, info: import('anki').NoteInfoWrapper}[]} */
         const cannotAdd = [];
         const canAddArray = await this._anki.canAddNotes(notes);
 
@@ -513,6 +609,7 @@ class Backend {
         return results;
     }
 
+    /** @type {import('api').Handler<import('api').InjectAnkiNoteMediaDetails, import('api').InjectAnkiNoteMediaResult>} */
     async _onApiInjectAnkiNoteMedia({timestamp, definitionDetails, audioDetails, screenshotDetails, clipboardDetails, dictionaryMediaDetails}) {
         return await this._injectAnkNoteMedia(
             this._anki,
@@ -525,13 +622,14 @@ class Backend {
         );
     }
 
+    /** @type {import('api').Handler<import('api').NoteViewDetails, import('api').NoteViewResult>} */
     async _onApiNoteView({noteId, mode, allowFallback}) {
         if (mode === 'edit') {
             try {
                 await this._anki.guiEditNote(noteId);
                 return 'edit';
             } catch (e) {
-                if (!this._anki.isErrorUnsupportedAction(e)) {
+                if (!(e instanceof Error && this._anki.isErrorUnsupportedAction(e))) {
                     throw e;
                 } else if (!allowFallback) {
                     throw new Error('Mode not supported');
@@ -543,6 +641,7 @@ class Backend {
         return 'browse';
     }
 
+    /** @type {import('api').Handler<import('api').SuspendAnkiCardsForNoteDetails, import('api').SuspendAnkiCardsForNoteResult>} */
     async _onApiSuspendAnkiCardsForNote({noteId}) {
         const cardIds = await this._anki.findCardsForNote(noteId);
         const count = cardIds.length;
@@ -553,76 +652,93 @@ class Backend {
         return count;
     }
 
+    /** @type {import('api').Handler<import('api').CommandExecDetails, import('api').CommandExecResult>} */
     _onApiCommandExec({command, params}) {
         return this._runCommand(command, params);
     }
 
+    /** @type {import('api').Handler<import('api').GetTermAudioInfoListDetails, import('api').GetTermAudioInfoListResult>} */
     async _onApiGetTermAudioInfoList({source, term, reading}) {
         return await this._audioDownloader.getTermAudioInfoList(source, term, reading);
     }
 
+    /** @type {import('api').Handler<import('api').SendMessageToFrameDetails, import('api').SendMessageToFrameResult, true>} */
     _onApiSendMessageToFrame({frameId: targetFrameId, action, params}, sender) {
-        if (!(sender && sender.tab)) {
-            return false;
-        }
-
-        const tabId = sender.tab.id;
+        if (!sender) { return false; }
+        const {tab} = sender;
+        if (!tab) { return false; }
+        const {id} = tab;
+        if (typeof id !== 'number') { return false; }
         const frameId = sender.frameId;
-        this._sendMessageTabIgnoreResponse(tabId, {action, params, frameId}, {frameId: targetFrameId});
+        /** @type {import('extension').ChromeRuntimeMessageWithFrameId} */
+        const message = {action, params, frameId};
+        this._sendMessageTabIgnoreResponse(id, message, {frameId: targetFrameId});
         return true;
     }
 
+    /** @type {import('api').Handler<import('api').BroadcastTabDetails, import('api').BroadcastTabResult, true>} */
     _onApiBroadcastTab({action, params}, sender) {
-        if (!(sender && sender.tab)) {
-            return false;
-        }
-
-        const tabId = sender.tab.id;
+        if (!sender) { return false; }
+        const {tab} = sender;
+        if (!tab) { return false; }
+        const {id} = tab;
+        if (typeof id !== 'number') { return false; }
         const frameId = sender.frameId;
-        this._sendMessageTabIgnoreResponse(tabId, {action, params, frameId});
+        /** @type {import('extension').ChromeRuntimeMessageWithFrameId} */
+        const message = {action, params, frameId};
+        this._sendMessageTabIgnoreResponse(id, message, {});
         return true;
     }
 
-    _onApiFrameInformationGet(params, sender) {
+    /** @type {import('api').Handler<import('api').FrameInformationGetDetails, import('api').FrameInformationGetResult, true>} */
+    _onApiFrameInformationGet(_params, sender) {
         const tab = sender.tab;
         const tabId = tab ? tab.id : void 0;
         const frameId = sender.frameId;
         return Promise.resolve({tabId, frameId});
     }
 
+    /** @type {import('api').Handler<import('api').InjectStylesheetDetails, import('api').InjectStylesheetResult, true>} */
     async _onApiInjectStylesheet({type, value}, sender) {
         const {frameId, tab} = sender;
-        if (!isObject(tab)) { throw new Error('Invalid tab'); }
+        if (typeof tab !== 'object' || tab === null || typeof tab.id !== 'number') { throw new Error('Invalid tab'); }
         return await this._scriptManager.injectStylesheet(type, value, tab.id, frameId, false, true, 'document_start');
     }
 
+    /** @type {import('api').Handler<import('api').GetStylesheetContentDetails, import('api').GetStylesheetContentResult>} */
     async _onApiGetStylesheetContent({url}) {
         if (!url.startsWith('/') || url.startsWith('//') || !url.endsWith('.css')) {
             throw new Error('Invalid URL');
         }
-        return await this._fetchAsset(url);
+        return await this._fetchText(url);
     }
 
+    /** @type {import('api').Handler<import('api').GetEnvironmentInfoDetails, import('api').GetEnvironmentInfoResult>} */
     _onApiGetEnvironmentInfo() {
         return this._environment.getInfo();
     }
 
+    /** @type {import('api').Handler<import('api').ClipboardGetDetails, import('api').ClipboardGetResult>} */
     async _onApiClipboardGet() {
         return this._clipboardReader.getText(false);
     }
 
+    /** @type {import('api').Handler<import('api').GetDisplayTemplatesHtmlDetails, import('api').GetDisplayTemplatesHtmlResult>} */
     async _onApiGetDisplayTemplatesHtml() {
-        return await this._fetchAsset('/display-templates.html');
+        return await this._fetchText('/display-templates.html');
     }
 
-    _onApiGetZoom(params, sender) {
-        if (!sender || !sender.tab) {
-            return Promise.reject(new Error('Invalid tab'));
-        }
-
+    /** @type {import('api').Handler<import('api').GetZoomDetails, import('api').GetZoomResult, true>} */
+    _onApiGetZoom(_params, sender) {
         return new Promise((resolve, reject) => {
+            if (!sender || !sender.tab) {
+                reject(new Error('Invalid tab'));
+                return;
+            }
+
             const tabId = sender.tab.id;
             if (!(
+                typeof tabId === 'number' &&
                 chrome.tabs !== null &&
                 typeof chrome.tabs === 'object' &&
                 typeof chrome.tabs.getZoom === 'function'
@@ -642,34 +758,41 @@ class Backend {
         });
     }
 
+    /** @type {import('api').Handler<import('api').GetDefaultAnkiFieldTemplatesDetails, import('api').GetDefaultAnkiFieldTemplatesResult>} */
     _onApiGetDefaultAnkiFieldTemplates() {
-        return this._defaultAnkiFieldTemplates;
+        return /** @type {string} */ (this._defaultAnkiFieldTemplates);
     }
 
+    /** @type {import('api').Handler<import('api').GetDictionaryInfoDetails, import('api').GetDictionaryInfoResult>} */
     async _onApiGetDictionaryInfo() {
         return await this._dictionaryDatabase.getDictionaryInfo();
     }
 
+    /** @type {import('api').Handler<import('api').PurgeDatabaseDetails, import('api').PurgeDatabaseResult>} */
     async _onApiPurgeDatabase() {
         await this._dictionaryDatabase.purge();
         this._triggerDatabaseUpdated('dictionary', 'purge');
     }
 
+    /** @type {import('api').Handler<import('api').GetMediaDetails, import('api').GetMediaResult>} */
     async _onApiGetMedia({targets}) {
         return await this._getNormalizedDictionaryDatabaseMedia(targets);
     }
 
+    /** @type {import('api').Handler<import('api').LogDetails, import('api').LogResult>} */
     _onApiLog({error, level, context}) {
-        log.log(deserializeError(error), level, context);
+        log.log(ExtensionError.deserialize(error), level, context);
     }
 
+    /** @type {import('api').Handler<import('api').LogIndicatorClearDetails, import('api').LogIndicatorClearResult>} */
     _onApiLogIndicatorClear() {
         if (this._logErrorLevel === null) { return; }
         this._logErrorLevel = null;
         this._updateBadge();
     }
 
-    _onApiCreateActionPort(params, sender) {
+    /** @type {import('api').Handler<import('api').CreateActionPortDetails, import('api').CreateActionPortResult, true>} */
+    _onApiCreateActionPort(_params, sender) {
         if (!sender || !sender.tab) { throw new Error('Invalid sender'); }
         const tabId = sender.tab.id;
         if (typeof tabId !== 'number') { throw new Error('Sender has invalid tab ID'); }
@@ -692,10 +815,12 @@ class Backend {
         return details;
     }
 
+    /** @type {import('api').Handler<import('api').ModifySettingsDetails, import('api').ModifySettingsResult>} */
     _onApiModifySettings({targets, source}) {
         return this._modifySettings(targets, source);
     }
 
+    /** @type {import('api').Handler<import('api').GetSettingsDetails, import('api').GetSettingsResult>} */
     _onApiGetSettings({targets}) {
         const results = [];
         for (const target of targets) {
@@ -703,39 +828,48 @@ class Backend {
                 const result = this._getSetting(target);
                 results.push({result: clone(result)});
             } catch (e) {
-                results.push({error: serializeError(e)});
+                results.push({error: ExtensionError.serialize(e)});
             }
         }
         return results;
     }
 
+    /** @type {import('api').Handler<import('api').SetAllSettingsDetails, import('api').SetAllSettingsResult>} */
     async _onApiSetAllSettings({value, source}) {
         this._optionsUtil.validate(value);
         this._options = clone(value);
         await this._saveOptions(source);
     }
 
-    async _onApiGetOrCreateSearchPopup({focus=false, text=null}) {
+    /** @type {import('api').Handler<import('api').GetOrCreateSearchPopupDetails, import('api').GetOrCreateSearchPopupResult>} */
+    async _onApiGetOrCreateSearchPopup({focus=false, text}) {
         const {tab, created} = await this._getOrCreateSearchPopup();
         if (focus === true || (focus === 'ifCreated' && created)) {
             await this._focusTab(tab);
         }
         if (typeof text === 'string') {
-            await this._updateSearchQuery(tab.id, text, !created);
+            const {id} = tab;
+            if (typeof id === 'number') {
+                await this._updateSearchQuery(id, text, !created);
+            }
         }
-        return {tabId: tab.id, windowId: tab.windowId};
+        const {id} = tab;
+        return {tabId: typeof id === 'number' ? id : null, windowId: tab.windowId};
     }
 
+    /** @type {import('api').Handler<import('api').IsTabSearchPopupDetails, import('api').IsTabSearchPopupResult>} */
     async _onApiIsTabSearchPopup({tabId}) {
         const baseUrl = chrome.runtime.getURL('/search.html');
-        const tab = typeof tabId === 'number' ? await this._checkTabUrl(tabId, (url) => url.startsWith(baseUrl)) : null;
+        const tab = typeof tabId === 'number' ? await this._checkTabUrl(tabId, (url) => url !== null && url.startsWith(baseUrl)) : null;
         return (tab !== null);
     }
 
+    /** @type {import('api').Handler<import('api').TriggerDatabaseUpdatedDetails, import('api').TriggerDatabaseUpdatedResult>} */
     _onApiTriggerDatabaseUpdated({type, cause}) {
         this._triggerDatabaseUpdated(type, cause);
     }
 
+    /** @type {import('api').Handler<import('api').TestMecabDetails, import('api').TestMecabResult>} */
     async _onApiTestMecab() {
         if (!this._mecab.isEnabled()) {
             throw new Error('MeCab not enabled');
@@ -772,18 +906,22 @@ class Backend {
         return true;
     }
 
+    /** @type {import('api').Handler<import('api').TextHasJapaneseCharactersDetails, import('api').TextHasJapaneseCharactersResult>} */
     _onApiTextHasJapaneseCharacters({text}) {
         return this._japaneseUtil.isStringPartiallyJapanese(text);
     }
 
+    /** @type {import('api').Handler<import('api').GetTermFrequenciesDetails, import('api').GetTermFrequenciesResult>} */
     async _onApiGetTermFrequencies({termReadingList, dictionaries}) {
         return await this._translator.getTermFrequencies(termReadingList, dictionaries);
     }
 
+    /** @type {import('api').Handler<import('api').FindAnkiNotesDetails, import('api').FindAnkiNotesResult>} */
     async _onApiFindAnkiNotes({query}) {
         return await this._anki.findNotes(query);
     }
 
+    /** @type {import('api').Handler<import('api').LoadExtensionScriptsDetails, import('api').LoadExtensionScriptsResult, true>} */
     async _onApiLoadExtensionScripts({files}, sender) {
         if (!sender || !sender.tab) { throw new Error('Invalid sender'); }
         const tabId = sender.tab.id;
@@ -796,18 +934,30 @@ class Backend {
 
     // Command handlers
 
+    /**
+     * @param {undefined|{mode: 'existingOrNewTab'|'newTab', query?: string}} params
+     */
     async _onCommandOpenSearchPage(params) {
-        const {mode='existingOrNewTab', query} = params || {};
+        /** @type {'existingOrNewTab'|'newTab'} */
+        let mode = 'existingOrNewTab';
+        let query = '';
+        if (typeof params === 'object' && params !== null) {
+            mode = this._normalizeOpenSettingsPageMode(params.mode, mode);
+            const paramsQuery = params.query;
+            if (typeof paramsQuery === 'string') { query = paramsQuery; }
+        }
 
         const baseUrl = chrome.runtime.getURL('/search.html');
+        /** @type {{[key: string]: string}} */
         const queryParams = {};
-        if (query && query.length > 0) { queryParams.query = query; }
+        if (query.length > 0) { queryParams.query = query; }
         const queryString = new URLSearchParams(queryParams).toString();
         let url = baseUrl;
         if (queryString.length > 0) {
             url += `?${queryString}`;
         }
 
+        /** @type {import('backend').FindTabsPredicate} */
         const predicate = ({url: url2}) => {
             if (url2 === null || !url2.startsWith(baseUrl)) { return false; }
             const parsedUrl = new URL(url2);
@@ -817,15 +967,19 @@ class Backend {
         };
 
         const openInTab = async () => {
-            const tabInfo = await this._findTabs(1000, false, predicate, false);
+            const tabInfo = /** @type {?import('backend').TabInfo} */ (await this._findTabs(1000, false, predicate, false));
             if (tabInfo !== null) {
                 const {tab} = tabInfo;
-                await this._focusTab(tab);
-                if (queryParams.query) {
-                    await this._updateSearchQuery(tab.id, queryParams.query, true);
+                const {id} = tab;
+                if (typeof id === 'number') {
+                    await this._focusTab(tab);
+                    if (queryParams.query) {
+                        await this._updateSearchQuery(id, queryParams.query, true);
+                    }
+                    return true;
                 }
-                return true;
             }
+            return false;
         };
 
         switch (mode) {
@@ -843,46 +997,73 @@ class Backend {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _onCommandOpenInfoPage() {
         await this._openInfoPage();
     }
 
+    /**
+     * @param {undefined|{mode: 'existingOrNewTab'|'newTab'}} params
+     */
     async _onCommandOpenSettingsPage(params) {
-        const {mode='existingOrNewTab'} = params || {};
+        /** @type {'existingOrNewTab'|'newTab'} */
+        let mode = 'existingOrNewTab';
+        if (typeof params === 'object' && params !== null) {
+            mode = this._normalizeOpenSettingsPageMode(params.mode, mode);
+        }
         await this._openSettingsPage(mode);
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _onCommandToggleTextScanning() {
-        const options = this._getProfileOptions({current: true});
-        await this._modifySettings([{
+        const options = this._getProfileOptions({current: true}, false);
+        /** @type {import('settings-modifications').ScopedModificationSet} */
+        const modification = {
             action: 'set',
             path: 'general.enable',
             value: !options.general.enable,
             scope: 'profile',
             optionsContext: {current: true}
-        }], 'backend');
+        };
+        await this._modifySettings([modification], 'backend');
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _onCommandOpenPopupWindow() {
         await this._onApiGetOrCreateSearchPopup({focus: true});
     }
 
     // Utilities
 
+    /**
+     * @param {import('settings-modifications').ScopedModification[]} targets
+     * @param {string} source
+     * @returns {Promise<import('core').Response<import('settings-modifications').ModificationResult>[]>}
+     */
     async _modifySettings(targets, source) {
+        /** @type {import('core').Response<import('settings-modifications').ModificationResult>[]} */
         const results = [];
         for (const target of targets) {
             try {
                 const result = this._modifySetting(target);
                 results.push({result: clone(result)});
             } catch (e) {
-                results.push({error: serializeError(e)});
+                results.push({error: ExtensionError.serialize(e)});
             }
         }
         await this._saveOptions(source);
         return results;
     }
 
+    /**
+     * @returns {Promise<{tab: chrome.tabs.Tab, created: boolean}>}
+     */
     _getOrCreateSearchPopup() {
         if (this._searchPopupTabCreatePromise === null) {
             const promise = this._getOrCreateSearchPopup2();
@@ -892,9 +1073,16 @@ class Backend {
         return this._searchPopupTabCreatePromise;
     }
 
+    /**
+     * @returns {Promise<{tab: chrome.tabs.Tab, created: boolean}>}
+     */
     async _getOrCreateSearchPopup2() {
         // Use existing tab
         const baseUrl = chrome.runtime.getURL('/search.html');
+        /**
+         * @param {?string} url
+         * @returns {boolean}
+         */
         const urlPredicate = (url) => url !== null && url.startsWith(baseUrl);
         if (this._searchPopupTabId !== null) {
             const tab = await this._checkTabUrl(this._searchPopupTabId, urlPredicate);
@@ -908,8 +1096,11 @@ class Backend {
         const existingTabInfo = await this._findSearchPopupTab(urlPredicate);
         if (existingTabInfo !== null) {
             const existingTab = existingTabInfo.tab;
-            this._searchPopupTabId = existingTab.id;
-            return {tab: existingTab, created: false};
+            const {id} = existingTab;
+            if (typeof id === 'number') {
+                this._searchPopupTabId = id;
+                return {tab: existingTab, created: false};
+            }
         }
 
         // chrome.windows not supported (e.g. on Firefox mobile)
@@ -918,38 +1109,48 @@ class Backend {
         }
 
         // Create a new window
-        const options = this._getProfileOptions({current: true});
+        const options = this._getProfileOptions({current: true}, false);
         const createData = this._getSearchPopupWindowCreateData(baseUrl, options);
         const {popupWindow: {windowState}} = options;
         const popupWindow = await this._createWindow(createData);
-        if (windowState !== 'normal') {
+        if (windowState !== 'normal' && typeof popupWindow.id === 'number') {
             await this._updateWindow(popupWindow.id, {state: windowState});
         }
 
         const {tabs} = popupWindow;
-        if (tabs.length === 0) {
+        if (!Array.isArray(tabs) || tabs.length === 0) {
             throw new Error('Created window did not contain a tab');
         }
 
         const tab = tabs[0];
-        await this._waitUntilTabFrameIsReady(tab.id, 0, 2000);
+        const {id} = tab;
+        if (typeof id !== 'number') {
+            throw new Error('Tab does not have an id');
+        }
+        await this._waitUntilTabFrameIsReady(id, 0, 2000);
 
         await this._sendMessageTabPromise(
-            tab.id,
+            id,
             {action: 'SearchDisplayController.setMode', params: {mode: 'popup'}},
             {frameId: 0}
         );
 
-        this._searchPopupTabId = tab.id;
+        this._searchPopupTabId = id;
         return {tab, created: true};
     }
 
+    /**
+     * @param {(url: ?string) => boolean} urlPredicate
+     * @returns {Promise<?import('backend').TabInfo>}
+     */
     async _findSearchPopupTab(urlPredicate) {
+        /** @type {import('backend').FindTabsPredicate} */
         const predicate = async ({url, tab}) => {
-            if (!urlPredicate(url)) { return false; }
+            const {id} = tab;
+            if (typeof id === 'undefined' || !urlPredicate(url)) { return false; }
             try {
                 const mode = await this._sendMessageTabPromise(
-                    tab.id,
+                    id,
                     {action: 'SearchDisplayController.getMode', params: {}},
                     {frameId: 0}
                 );
@@ -958,9 +1159,14 @@ class Backend {
                 return false;
             }
         };
-        return await this._findTabs(1000, false, predicate, true);
+        return /** @type {?import('backend').TabInfo} */ (await this._findTabs(1000, false, predicate, true));
     }
 
+    /**
+     * @param {string} url
+     * @param {import('settings').ProfileOptions} options
+     * @returns {chrome.windows.CreateData}
+     */
     _getSearchPopupWindowCreateData(url, options) {
         const {popupWindow: {width, height, left, top, useLeft, useTop, windowType}} = options;
         return {
@@ -974,6 +1180,10 @@ class Backend {
         };
     }
 
+    /**
+     * @param {chrome.windows.CreateData} createData
+     * @returns {Promise<chrome.windows.Window>}
+     */
     _createWindow(createData) {
         return new Promise((resolve, reject) => {
             chrome.windows.create(
@@ -983,13 +1193,18 @@ class Backend {
                     if (error) {
                         reject(new Error(error.message));
                     } else {
-                        resolve(result);
+                        resolve(/** @type {chrome.windows.Window} */ (result));
                     }
                 }
             );
         });
     }
 
+    /**
+     * @param {number} windowId
+     * @param {chrome.windows.UpdateInfo} updateInfo
+     * @returns {Promise<chrome.windows.Window>}
+     */
     _updateWindow(windowId, updateInfo) {
         return new Promise((resolve, reject) => {
             chrome.windows.update(
@@ -1007,21 +1222,31 @@ class Backend {
         });
     }
 
-    _updateSearchQuery(tabId, text, animate) {
-        return this._sendMessageTabPromise(
+    /**
+     * @param {number} tabId
+     * @param {string} text
+     * @param {boolean} animate
+     * @returns {Promise<void>}
+     */
+    async _updateSearchQuery(tabId, text, animate) {
+        await this._sendMessageTabPromise(
             tabId,
             {action: 'SearchDisplayController.updateSearchQuery', params: {text, animate}},
             {frameId: 0}
         );
     }
 
+    /**
+     * @param {string} source
+     */
     _applyOptions(source) {
-        const options = this._getProfileOptions({current: true});
+        const options = this._getProfileOptions({current: true}, false);
         this._updateBadge();
 
         const enabled = options.general.enable;
 
-        let {apiKey} = options.anki;
+        /** @type {?string} */
+        let apiKey = options.anki.apiKey;
         if (apiKey === '') { apiKey = null; }
         this._anki.server = options.anki.server;
         this._anki.enabled = options.anki.enable && enabled;
@@ -1040,16 +1265,33 @@ class Backend {
         this._sendMessageAllTabsIgnoreResponse('Yomichan.optionsUpdated', {source});
     }
 
-    _getOptionsFull(useSchema=false) {
+    /**
+     * @param {boolean} useSchema
+     * @returns {import('settings').Options}
+     * @throws {Error}
+     */
+    _getOptionsFull(useSchema) {
         const options = this._options;
-        return useSchema ? this._optionsUtil.createValidatingProxy(options) : options;
+        if (options === null) { throw new Error('Options is null'); }
+        return useSchema ? /** @type {import('settings').Options} */ (this._optionsUtil.createValidatingProxy(options)) : options;
     }
 
-    _getProfileOptions(optionsContext, useSchema=false) {
+    /**
+     * @param {import('settings').OptionsContext} optionsContext
+     * @param {boolean} useSchema
+     * @returns {import('settings').ProfileOptions}
+     */
+    _getProfileOptions(optionsContext, useSchema) {
         return this._getProfile(optionsContext, useSchema).options;
     }
 
-    _getProfile(optionsContext, useSchema=false) {
+    /**
+     * @param {import('settings').OptionsContext} optionsContext
+     * @param {boolean} useSchema
+     * @returns {import('settings').Profile}
+     * @throws {Error}
+     */
+    _getProfile(optionsContext, useSchema) {
         const options = this._getOptionsFull(useSchema);
         const profiles = options.profiles;
         if (!optionsContext.current) {
@@ -1075,8 +1317,13 @@ class Backend {
         return profiles[profileCurrent];
     }
 
+    /**
+     * @param {import('settings').Options} options
+     * @param {import('settings').OptionsContext} optionsContext
+     * @returns {?import('settings').Profile}
+     */
     _getProfileFromContext(options, optionsContext) {
-        optionsContext = this._profileConditionsUtil.normalizeContext(optionsContext);
+        const normalizedOptionsContext = this._profileConditionsUtil.normalizeContext(optionsContext);
 
         let index = 0;
         for (const profile of options.profiles) {
@@ -1090,7 +1337,7 @@ class Backend {
                 this._profileConditionsSchemaCache.push(schema);
             }
 
-            if (conditionGroups.length > 0 && schema.isValid(optionsContext)) {
+            if (conditionGroups.length > 0 && schema.isValid(normalizedOptionsContext)) {
                 return profile;
             }
             ++index;
@@ -1099,20 +1346,36 @@ class Backend {
         return null;
     }
 
+    /**
+     * @param {string} message
+     * @param {unknown} data
+     * @returns {ExtensionError}
+     */
     _createDataError(message, data) {
-        const error = new Error(message);
+        const error = new ExtensionError(message);
         error.data = data;
         return error;
     }
 
+    /**
+     * @returns {void}
+     */
     _clearProfileConditionsSchemaCache() {
         this._profileConditionsSchemaCache = [];
     }
 
-    _checkLastError() {
+    /**
+     * @param {unknown} _ignore
+     */
+    _checkLastError(_ignore) {
         // NOP
     }
 
+    /**
+     * @param {string} command
+     * @param {import('core').SerializableObject|undefined} params
+     * @returns {boolean}
+     */
     _runCommand(command, params) {
         const handler = this._commandHandlers.get(command);
         if (typeof handler !== 'function') { return false; }
@@ -1121,12 +1384,20 @@ class Backend {
         return true;
     }
 
+    /**
+     * @param {string} text
+     * @param {number} scanLength
+     * @param {import('settings').OptionsContext} optionsContext
+     * @returns {Promise<import('api').ParseTextLine[]>}
+     */
     async _textParseScanning(text, scanLength, optionsContext) {
         const jp = this._japaneseUtil;
+        /** @type {import('translator').FindTermsMode} */
         const mode = 'simple';
-        const options = this._getProfileOptions(optionsContext);
-        const details = {matchType: 'exact', deinflect: true};
+        const options = this._getProfileOptions(optionsContext, false);
+        const details = {matchType: /** @type {import('translation').FindTermsMatchType} */ ('exact'), deinflect: true};
         const findTermsOptions = this._getTranslatorFindTermsOptions(mode, details, options);
+        /** @type {import('api').ParseTextLine[]} */
         const results = [];
         let previousUngroupedSegment = null;
         let i = 0;
@@ -1137,7 +1408,7 @@ class Backend {
                 text.substring(i, i + scanLength),
                 findTermsOptions
             );
-            const codePoint = text.codePointAt(i);
+            const codePoint = /** @type {number} */ (text.codePointAt(i));
             const character = String.fromCodePoint(codePoint);
             if (
                 dictionaryEntries.length > 0 &&
@@ -1166,6 +1437,10 @@ class Backend {
         return results;
     }
 
+    /**
+     * @param {string} text
+     * @returns {Promise<import('backend').MecabParseResults>}
+     */
     async _textParseMecab(text) {
         const jp = this._japaneseUtil;
 
@@ -1176,8 +1451,10 @@ class Backend {
             return [];
         }
 
+        /** @type {import('backend').MecabParseResults} */
         const results = [];
         for (const {name, lines} of parseTextResults) {
+            /** @type {import('api').ParseTextLine[]} */
             const result = [];
             for (const line of lines) {
                 for (const {term, reading, source} of line) {
@@ -1198,30 +1475,43 @@ class Backend {
         return results;
     }
 
+    /**
+     * @param {chrome.runtime.Port} port
+     * @param {chrome.runtime.MessageSender} sender
+     * @param {import('backend').MessageHandlerWithProgressMap} handlers
+     */
     _createActionListenerPort(port, sender, handlers) {
+        let done = false;
         let hasStarted = false;
+        /** @type {?string} */
         let messageString = '';
 
+        /**
+         * @param {...unknown} data
+         */
         const onProgress = (...data) => {
             try {
-                if (port === null) { return; }
-                port.postMessage({type: 'progress', data});
+                if (done) { return; }
+                port.postMessage(/** @type {import('backend').InvokeWithProgressResponseProgressMessage} */ ({type: 'progress', data}));
             } catch (e) {
                 // NOP
             }
         };
 
+        /**
+         * @param {import('backend').InvokeWithProgressRequestMessage} message
+         */
         const onMessage = (message) => {
             if (hasStarted) { return; }
 
             try {
-                const {action, data} = message;
+                const {action} = message;
                 switch (action) {
                     case 'fragment':
-                        messageString += data;
+                        messageString += message.data;
                         break;
                     case 'invoke':
-                        {
+                        if (messageString !== null) {
                             hasStarted = true;
                             port.onMessage.removeListener(onMessage);
 
@@ -1236,10 +1526,13 @@ class Backend {
             }
         };
 
+        /**
+         * @param {{action: string, params?: import('core').SerializableObject}} message
+         */
         const onMessageComplete = async (message) => {
             try {
                 const {action, params} = message;
-                port.postMessage({type: 'ack'});
+                port.postMessage(/** @type {import('backend').InvokeWithProgressResponseAcknowledgeMessage} */ ({type: 'ack'}));
 
                 const messageHandler = handlers.get(action);
                 if (typeof messageHandler === 'undefined') {
@@ -1253,7 +1546,7 @@ class Backend {
 
                 const promiseOrResult = handler(params, sender, onProgress);
                 const result = async ? await promiseOrResult : promiseOrResult;
-                port.postMessage({type: 'complete', data: result});
+                port.postMessage(/** @type {import('backend').InvokeWithProgressResponseCompleteMessage} */ ({type: 'complete', data: result}));
             } catch (e) {
                 cleanup(e);
             }
@@ -1263,23 +1556,29 @@ class Backend {
             cleanup(null);
         };
 
+        /**
+         * @param {unknown} error
+         */
         const cleanup = (error) => {
-            if (port === null) { return; }
+            if (done) { return; }
             if (error !== null) {
-                port.postMessage({type: 'error', data: serializeError(error)});
+                port.postMessage(/** @type {import('backend').InvokeWithProgressResponseErrorMessage} */ ({type: 'error', data: ExtensionError.serialize(error)}));
             }
             if (!hasStarted) {
                 port.onMessage.removeListener(onMessage);
             }
             port.onDisconnect.removeListener(onDisconnect);
-            port = null;
-            handlers = null;
+            done = true;
         };
 
         port.onMessage.addListener(onMessage);
         port.onDisconnect.addListener(onDisconnect);
     }
 
+    /**
+     * @param {?import('log').LogLevel} errorLevel
+     * @returns {number}
+     */
     _getErrorLevelValue(errorLevel) {
         switch (errorLevel) {
             case 'info': return 0;
@@ -1290,19 +1589,32 @@ class Backend {
         }
     }
 
+    /**
+     * @param {import('settings-modifications').OptionsScope} target
+     * @returns {import('settings').Options|import('settings').ProfileOptions}
+     * @throws {Error}
+     */
     _getModifySettingObject(target) {
         const scope = target.scope;
         switch (scope) {
             case 'profile':
-                if (!isObject(target.optionsContext)) { throw new Error('Invalid optionsContext'); }
-                return this._getProfileOptions(target.optionsContext, true);
+            {
+                const {optionsContext} = target;
+                if (typeof optionsContext !== 'object' || optionsContext === null) { throw new Error('Invalid optionsContext'); }
+                return /** @type {import('settings').ProfileOptions} */ (this._getProfileOptions(optionsContext, true));
+            }
             case 'global':
-                return this._getOptionsFull(true);
+                return /** @type {import('settings').Options} */ (this._getOptionsFull(true));
             default:
                 throw new Error(`Invalid scope: ${scope}`);
         }
     }
 
+    /**
+     * @param {import('settings-modifications').OptionsScope&import('settings-modifications').Read} target
+     * @returns {unknown}
+     * @throws {Error}
+     */
     _getSetting(target) {
         const options = this._getModifySettingObject(target);
         const accessor = new ObjectPropertyAccessor(options);
@@ -1311,6 +1623,11 @@ class Backend {
         return accessor.get(ObjectPropertyAccessor.getPathArray(path));
     }
 
+    /**
+     * @param {import('settings-modifications').ScopedModification} target
+     * @returns {import('settings-modifications').ModificationResult}
+     * @throws {Error}
+     */
     _modifySetting(target) {
         const options = this._getModifySettingObject(target);
         const accessor = new ObjectPropertyAccessor(options);
@@ -1366,10 +1683,14 @@ class Backend {
         }
     }
 
+    /**
+     * @param {chrome.runtime.MessageSender} sender
+     * @throws {Error}
+     */
     _validatePrivilegedMessageSender(sender) {
         let {url} = sender;
         if (typeof url === 'string' && yomichan.isExtensionUrl(url)) { return; }
-        const {tab} = url;
+        const {tab} = sender;
         if (typeof tab === 'object' && tab !== null) {
             ({url} = tab);
             if (typeof url === 'string' && yomichan.isExtensionUrl(url)) { return; }
@@ -1377,6 +1698,9 @@ class Backend {
         throw new Error('Invalid message sender');
     }
 
+    /**
+     * @returns {Promise<string>}
+     */
     _getBrowserIconTitle() {
         return (
             isObject(chrome.action) &&
@@ -1386,6 +1710,9 @@ class Backend {
         );
     }
 
+    /**
+     * @returns {void}
+     */
     _updateBadge() {
         let title = this._defaultBrowserActionTitle;
         if (title === null || !isObject(chrome.action)) {
@@ -1421,7 +1748,7 @@ class Backend {
                 status = 'Loading';
             }
         } else {
-            const options = this._getProfileOptions({current: true});
+            const options = this._getProfileOptions({current: true}, false);
             if (!options.general.enable) {
                 text = 'off';
                 color = '#555555';
@@ -1451,6 +1778,10 @@ class Backend {
         }
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     * @returns {boolean}
+     */
     _isAnyDictionaryEnabled(options) {
         for (const {enabled} of options.dictionaries) {
             if (enabled) {
@@ -1460,21 +1791,18 @@ class Backend {
         return false;
     }
 
-    _anyOptionsMatches(predicate) {
-        for (const {options} of this._options.profiles) {
-            const value = predicate(options);
-            if (value) { return value; }
-        }
-        return false;
-    }
-
+    /**
+     * @param {number} tabId
+     * @returns {Promise<?string>}
+     */
     async _getTabUrl(tabId) {
         try {
-            const {url} = await this._sendMessageTabPromise(
+            const response = await this._sendMessageTabPromise(
                 tabId,
                 {action: 'Yomichan.getUrl', params: {}},
                 {frameId: 0}
             );
+            const url = typeof response === 'object' && response !== null ? /** @type {import('core').SerializableObject} */ (response).url : void 0;
             if (typeof url === 'string') {
                 return url;
             }
@@ -1484,6 +1812,9 @@ class Backend {
         return null;
     }
 
+    /**
+     * @returns {Promise<chrome.tabs.Tab[]>}
+     */
     _getAllTabs() {
         return new Promise((resolve, reject) => {
             chrome.tabs.query({}, (tabs) => {
@@ -1497,21 +1828,33 @@ class Backend {
         });
     }
 
+    /**
+     * @param {number} timeout
+     * @param {boolean} multiple
+     * @param {import('backend').FindTabsPredicate} predicate
+     * @param {boolean} predicateIsAsync
+     * @returns {Promise<import('backend').TabInfo[]|(?import('backend').TabInfo)>}
+     */
     async _findTabs(timeout, multiple, predicate, predicateIsAsync) {
         // This function works around the need to have the "tabs" permission to access tab.url.
         const tabs = await this._getAllTabs();
 
         let done = false;
+        /**
+         * @param {chrome.tabs.Tab} tab
+         * @param {(tabInfo: import('backend').TabInfo) => boolean} add
+         */
         const checkTab = async (tab, add) => {
-            const url = await this._getTabUrl(tab.id);
+            const {id} = tab;
+            const url = typeof id === 'number' ? await this._getTabUrl(id) : null;
 
             if (done) { return; }
 
             let okay = false;
             const item = {tab, url};
             try {
-                okay = predicate(item);
-                if (predicateIsAsync) { okay = await okay; }
+                const okayOrPromise = predicate(item);
+                okay = predicateIsAsync ? await okayOrPromise : /** @type {boolean} */ (okayOrPromise);
             } catch (e) {
                 // NOP
             }
@@ -1524,7 +1867,12 @@ class Backend {
         };
 
         if (multiple) {
+            /** @type {import('backend').TabInfo[]} */
             const results = [];
+            /**
+             * @param {import('backend').TabInfo} value
+             * @returns {boolean}
+             */
             const add = (value) => {
                 results.push(value);
                 return false;
@@ -1536,8 +1884,13 @@ class Backend {
             ]);
             return results;
         } else {
-            const {promise, resolve} = deferPromise();
+            const {promise, resolve} = /** @type {import('core').DeferredPromiseDetails<void>} */ (deferPromise());
+            /** @type {?import('backend').TabInfo} */
             let result = null;
+            /**
+             * @param {import('backend').TabInfo} value
+             * @returns {boolean}
+             */
             const add = (value) => {
                 result = value;
                 resolve();
@@ -1554,9 +1907,17 @@ class Backend {
         }
     }
 
+    /**
+     * @param {chrome.tabs.Tab} tab
+     */
     async _focusTab(tab) {
-        await new Promise((resolve, reject) => {
-            chrome.tabs.update(tab.id, {active: true}, () => {
+        await /** @type {Promise<void>} */ (new Promise((resolve, reject) => {
+            const {id} = tab;
+            if (typeof id !== 'number') {
+                reject(new Error('Cannot focus a tab without an id'));
+                return;
+            }
+            chrome.tabs.update(id, {active: true}, () => {
                 const e = chrome.runtime.lastError;
                 if (e) {
                     reject(new Error(e.message));
@@ -1564,7 +1925,7 @@ class Backend {
                     resolve();
                 }
             });
-        });
+        }));
 
         if (!(typeof chrome.windows === 'object' && chrome.windows !== null)) {
             // Windows not supported (e.g. on Firefox mobile)
@@ -1583,7 +1944,7 @@ class Backend {
                 });
             });
             if (!tabWindow.focused) {
-                await new Promise((resolve, reject) => {
+                await /** @type {Promise<void>} */ (new Promise((resolve, reject) => {
                     chrome.windows.update(tab.windowId, {focused: true}, () => {
                         const e = chrome.runtime.lastError;
                         if (e) {
@@ -1592,23 +1953,31 @@ class Backend {
                             resolve();
                         }
                     });
-                });
+                }));
             }
         } catch (e) {
             // Edge throws exception for no reason here.
         }
     }
 
+    /**
+     * @param {number} tabId
+     * @param {number} frameId
+     * @param {?number} [timeout=null]
+     * @returns {Promise<void>}
+     */
     _waitUntilTabFrameIsReady(tabId, frameId, timeout=null) {
         return new Promise((resolve, reject) => {
+            /** @type {?number} */
             let timer = null;
+            /** @type {?import('extension').ChromeRuntimeOnMessageCallback} */
             let onMessage = (message, sender) => {
                 if (
                     !sender.tab ||
                     sender.tab.id !== tabId ||
                     sender.frameId !== frameId ||
-                    !isObject(message) ||
-                    message.action !== 'yomichanReady'
+                    !(typeof message === 'object' && message !== null) ||
+                    /** @type {import('core').SerializableObject} */ (message).action !== 'yomichanReady'
                 ) {
                     return;
                 }
@@ -1649,7 +2018,11 @@ class Backend {
         });
     }
 
-    async _fetchAsset(url, json=false) {
+    /**
+     * @param {string} url
+     * @returns {Promise<Response>}
+     */
+    async _fetchAsset(url) {
         const response = await fetch(chrome.runtime.getURL(url), {
             method: 'GET',
             mode: 'no-cors',
@@ -1661,30 +2034,71 @@ class Backend {
         if (!response.ok) {
             throw new Error(`Failed to fetch ${url}: ${response.status}`);
         }
-        return await (json ? response.json() : response.text());
+        return response;
     }
 
-    _sendMessageIgnoreResponse(...args) {
+    /**
+     * @param {string} url
+     * @returns {Promise<string>}
+     */
+    async _fetchText(url) {
+        const response = await this._fetchAsset(url);
+        return await response.text();
+    }
+
+    /**
+     * @param {string} url
+     * @returns {Promise<unknown>}
+     */
+    async _fetchJson(url) {
+        const response = await this._fetchAsset(url);
+        return await response.json();
+    }
+
+    /**
+     * @param {{action: string, params: import('core').SerializableObject}} message
+     */
+    _sendMessageIgnoreResponse(message) {
         const callback = () => this._checkLastError(chrome.runtime.lastError);
-        chrome.runtime.sendMessage(...args, callback);
+        chrome.runtime.sendMessage(message, callback);
     }
 
-    _sendMessageTabIgnoreResponse(...args) {
+    /**
+     * @param {number} tabId
+     * @param {{action: string, params?: import('core').SerializableObject, frameId?: number}} message
+     * @param {chrome.tabs.MessageSendOptions} options
+     */
+    _sendMessageTabIgnoreResponse(tabId, message, options) {
         const callback = () => this._checkLastError(chrome.runtime.lastError);
-        chrome.tabs.sendMessage(...args, callback);
+        chrome.tabs.sendMessage(tabId, message, options, callback);
     }
 
+    /**
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     */
     _sendMessageAllTabsIgnoreResponse(action, params) {
         const callback = () => this._checkLastError(chrome.runtime.lastError);
         chrome.tabs.query({}, (tabs) => {
             for (const tab of tabs) {
-                chrome.tabs.sendMessage(tab.id, {action, params}, callback);
+                const {id} = tab;
+                if (typeof id !== 'number') { continue; }
+                chrome.tabs.sendMessage(id, {action, params}, callback);
             }
         });
     }
 
-    _sendMessageTabPromise(...args) {
+    /**
+     * @param {number} tabId
+     * @param {{action: string, params?: import('core').SerializableObject}} message
+     * @param {chrome.tabs.MessageSendOptions} options
+     * @returns {Promise<unknown>}
+     */
+    _sendMessageTabPromise(tabId, message, options) {
         return new Promise((resolve, reject) => {
+            /**
+             * @param {unknown} response
+             */
             const callback = (response) => {
                 try {
                     resolve(this._getMessageResponseResult(response));
@@ -1693,25 +2107,35 @@ class Backend {
                 }
             };
 
-            chrome.tabs.sendMessage(...args, callback);
+            chrome.tabs.sendMessage(tabId, message, options, callback);
         });
     }
 
+    /**
+     * @param {unknown} response
+     * @returns {unknown}
+     * @throws {Error}
+     */
     _getMessageResponseResult(response) {
-        let error = chrome.runtime.lastError;
+        const error = chrome.runtime.lastError;
         if (error) {
             throw new Error(error.message);
         }
-        if (!isObject(response)) {
+        if (typeof response !== 'object' || response === null) {
             throw new Error('Tab did not respond');
         }
-        error = response.error;
-        if (error) {
-            throw deserializeError(error);
+        const responseError = /** @type {import('core').SerializedError|undefined} */ (/** @type {import('core').SerializableObject} */ (response).error);
+        if (typeof responseError === 'object' && responseError !== null) {
+            throw ExtensionError.deserialize(responseError);
         }
-        return response.result;
+        return /** @type {import('core').SerializableObject} */ (response).result;
     }
 
+    /**
+     * @param {number} tabId
+     * @param {(url: ?string) => boolean} urlPredicate
+     * @returns {Promise<?chrome.tabs.Tab>}
+     */
     async _checkTabUrl(tabId, urlPredicate) {
         let tab;
         try {
@@ -1725,6 +2149,13 @@ class Backend {
         return isValidTab ? tab : null;
     }
 
+    /**
+     * @param {number} tabId
+     * @param {number} frameId
+     * @param {'jpeg'|'png'} format
+     * @param {number} quality
+     * @returns {Promise<string>}
+     */
     async _getScreenshot(tabId, frameId, format, quality) {
         const tab = await this._getTabById(tabId);
         const {windowId} = tab;
@@ -1760,6 +2191,16 @@ class Backend {
         }
     }
 
+    /**
+     * @param {AnkiConnect} ankiConnect
+     * @param {number} timestamp
+     * @param {import('api').InjectAnkiNoteMediaDefinitionDetails} definitionDetails
+     * @param {?import('api').InjectAnkiNoteMediaAudioDetails} audioDetails
+     * @param {?import('api').InjectAnkiNoteMediaScreenshotDetails} screenshotDetails
+     * @param {?import('api').InjectAnkiNoteMediaClipboardDetails} clipboardDetails
+     * @param {import('api').InjectAnkiNoteMediaDictionaryMediaDetails[]} dictionaryMediaDetails
+     * @returns {Promise<import('api').InjectAnkiNoteMediaResult>}
+     */
     async _injectAnkNoteMedia(ankiConnect, timestamp, definitionDetails, audioDetails, screenshotDetails, clipboardDetails, dictionaryMediaDetails) {
         let screenshotFileName = null;
         let clipboardImageFileName = null;
@@ -1772,7 +2213,7 @@ class Backend {
                 screenshotFileName = await this._injectAnkiNoteScreenshot(ankiConnect, timestamp, definitionDetails, screenshotDetails);
             }
         } catch (e) {
-            errors.push(serializeError(e));
+            errors.push(ExtensionError.serialize(e));
         }
 
         try {
@@ -1780,7 +2221,7 @@ class Backend {
                 clipboardImageFileName = await this._injectAnkiNoteClipboardImage(ankiConnect, timestamp, definitionDetails);
             }
         } catch (e) {
-            errors.push(serializeError(e));
+            errors.push(ExtensionError.serialize(e));
         }
 
         try {
@@ -1788,7 +2229,7 @@ class Backend {
                 clipboardText = await this._clipboardReader.getText(false);
             }
         } catch (e) {
-            errors.push(serializeError(e));
+            errors.push(ExtensionError.serialize(e));
         }
 
         try {
@@ -1796,19 +2237,20 @@ class Backend {
                 audioFileName = await this._injectAnkiNoteAudio(ankiConnect, timestamp, definitionDetails, audioDetails);
             }
         } catch (e) {
-            errors.push(serializeError(e));
+            errors.push(ExtensionError.serialize(e));
         }
 
+        /** @type {import('api').InjectAnkiNoteDictionaryMediaResult[]} */
         let dictionaryMedia;
         try {
             let errors2;
             ({results: dictionaryMedia, errors: errors2} = await this._injectAnkiNoteDictionaryMedia(ankiConnect, timestamp, definitionDetails, dictionaryMediaDetails));
             for (const error of errors2) {
-                errors.push(serializeError(error));
+                errors.push(ExtensionError.serialize(error));
             }
         } catch (e) {
             dictionaryMedia = [];
-            errors.push(serializeError(e));
+            errors.push(ExtensionError.serialize(e));
         }
 
         return {
@@ -1821,16 +2263,17 @@ class Backend {
         };
     }
 
+    /**
+     * @param {AnkiConnect} ankiConnect
+     * @param {number} timestamp
+     * @param {import('api').InjectAnkiNoteMediaDefinitionDetails} definitionDetails
+     * @param {import('api').InjectAnkiNoteMediaAudioDetails} details
+     * @returns {Promise<?string>}
+     */
     async _injectAnkiNoteAudio(ankiConnect, timestamp, definitionDetails, details) {
-        const {type, term, reading} = definitionDetails;
-        if (
-            type === 'kanji' ||
-            typeof term !== 'string' ||
-            typeof reading !== 'string' ||
-            (term.length === 0 && reading.length === 0)
-        ) {
-            return null;
-        }
+        if (definitionDetails.type !== 'term') { return null; }
+        const {term, reading} = definitionDetails;
+        if (term.length === 0 && reading.length === 0) { return null; }
 
         const {sources, preferredAudioIndex, idleTimeout} = details;
         let data;
@@ -1850,15 +2293,20 @@ class Backend {
             return null;
         }
 
-        let extension = MediaUtil.getFileExtensionFromAudioMediaType(contentType);
+        let extension = contentType !== null ? MediaUtil.getFileExtensionFromAudioMediaType(contentType) : null;
         if (extension === null) { extension = '.mp3'; }
         let fileName = this._generateAnkiNoteMediaFileName('yomichan_audio', extension, timestamp, definitionDetails);
         fileName = fileName.replace(/\]/g, '');
-        fileName = await ankiConnect.storeMediaFile(fileName, data);
-
-        return fileName;
+        return await ankiConnect.storeMediaFile(fileName, data);
     }
 
+    /**
+     * @param {AnkiConnect} ankiConnect
+     * @param {number} timestamp
+     * @param {import('api').InjectAnkiNoteMediaDefinitionDetails} definitionDetails
+     * @param {import('api').InjectAnkiNoteMediaScreenshotDetails} details
+     * @returns {Promise<?string>}
+     */
     async _injectAnkiNoteScreenshot(ankiConnect, timestamp, definitionDetails, details) {
         const {tabId, frameId, format, quality} = details;
         const dataUrl = await this._getScreenshot(tabId, frameId, format, quality);
@@ -1869,12 +2317,16 @@ class Backend {
             throw new Error('Unknown media type for screenshot image');
         }
 
-        let fileName = this._generateAnkiNoteMediaFileName('yomichan_browser_screenshot', extension, timestamp, definitionDetails);
-        fileName = await ankiConnect.storeMediaFile(fileName, data);
-
-        return fileName;
+        const fileName = this._generateAnkiNoteMediaFileName('yomichan_browser_screenshot', extension, timestamp, definitionDetails);
+        return await ankiConnect.storeMediaFile(fileName, data);
     }
 
+    /**
+     * @param {AnkiConnect} ankiConnect
+     * @param {number} timestamp
+     * @param {import('api').InjectAnkiNoteMediaDefinitionDetails} definitionDetails
+     * @returns {Promise<?string>}
+     */
     async _injectAnkiNoteClipboardImage(ankiConnect, timestamp, definitionDetails) {
         const dataUrl = await this._clipboardReader.getImage();
         if (dataUrl === null) {
@@ -1887,12 +2339,17 @@ class Backend {
             throw new Error('Unknown media type for clipboard image');
         }
 
-        let fileName = this._generateAnkiNoteMediaFileName('yomichan_clipboard_image', extension, timestamp, definitionDetails);
-        fileName = await ankiConnect.storeMediaFile(fileName, data);
-
-        return fileName;
+        const fileName = this._generateAnkiNoteMediaFileName('yomichan_clipboard_image', extension, timestamp, definitionDetails);
+        return await ankiConnect.storeMediaFile(fileName, data);
     }
 
+    /**
+     * @param {AnkiConnect} ankiConnect
+     * @param {number} timestamp
+     * @param {import('api').InjectAnkiNoteMediaDefinitionDetails} definitionDetails
+     * @param {import('api').InjectAnkiNoteMediaDictionaryMediaDetails[]} dictionaryMediaDetails
+     * @returns {Promise<{results: import('api').InjectAnkiNoteDictionaryMediaResult[], errors: unknown[]}>}
+     */
     async _injectAnkiNoteDictionaryMedia(ankiConnect, timestamp, definitionDetails, dictionaryMediaDetails) {
         const targets = [];
         const detailsList = [];
@@ -1916,6 +2373,7 @@ class Backend {
         }
 
         const errors = [];
+        /** @type {import('api').InjectAnkiNoteDictionaryMediaResult[]} */
         const results = [];
         for (let i = 0, ii = detailsList.length; i < ii; ++i) {
             const {dictionary, path, media} = detailsList[i];
@@ -1923,7 +2381,12 @@ class Backend {
             if (media !== null) {
                 const {content, mediaType} = media;
                 const extension = MediaUtil.getFileExtensionFromImageMediaType(mediaType);
-                fileName = this._generateAnkiNoteMediaFileName(`yomichan_dictionary_media_${i + 1}`, extension, timestamp, definitionDetails);
+                fileName = this._generateAnkiNoteMediaFileName(
+                    `yomichan_dictionary_media_${i + 1}`,
+                    extension !== null ? extension : '',
+                    timestamp,
+                    definitionDetails
+                );
                 try {
                     fileName = await ankiConnect.storeMediaFile(fileName, content);
                 } catch (e) {
@@ -1937,18 +2400,27 @@ class Backend {
         return {results, errors};
     }
 
+    /**
+     * @param {unknown} error
+     * @returns {?ExtensionError}
+     */
     _getAudioDownloadError(error) {
-        if (isObject(error.data)) {
-            const {errors} = error.data;
+        if (error instanceof ExtensionError && typeof error.data === 'object' && error.data !== null) {
+            const {errors} = /** @type {import('core').SerializableObject} */ (error.data);
             if (Array.isArray(errors)) {
                 for (const error2 of errors) {
+                    if (!(error2 instanceof Error)) { continue; }
                     if (error2.name === 'AbortError') {
                         return this._createAudioDownloadError('Audio download was cancelled due to an idle timeout', 'audio-download-idle-timeout', errors);
                     }
-                    if (!isObject(error2.data)) { continue; }
-                    const {details} = error2.data;
-                    if (!isObject(details)) { continue; }
-                    switch (details.error) {
+                    if (!(error2 instanceof ExtensionError)) { continue; }
+                    const {data} = error2;
+                    if (!(typeof data === 'object' && data !== null)) { continue; }
+                    const {details} = /** @type {import('core').SerializableObject} */ (data);
+                    if (!(typeof details === 'object' && details !== null)) { continue; }
+                    const error3 = /** @type {import('core').SerializableObject} */ (details).error;
+                    if (typeof error3 !== 'string') { continue; }
+                    switch (error3) {
                         case 'net::ERR_FAILED':
                             // This is potentially an error due to the extension not having enough URL privileges.
                             // The message logged to the console looks like this:
@@ -1965,23 +2437,38 @@ class Backend {
         return null;
     }
 
+    /**
+     * @param {string} message
+     * @param {?string} issueId
+     * @param {?(Error[])} errors
+     * @returns {ExtensionError}
+     */
     _createAudioDownloadError(message, issueId, errors) {
-        const error = new Error(message);
+        const error = new ExtensionError(message);
         const hasErrors = Array.isArray(errors);
         const hasIssueId = (typeof issueId === 'string');
         if (hasErrors || hasIssueId) {
+            /** @type {{errors?: import('core').SerializedError[], referenceUrl?: string}} */
+            const data = {};
             error.data = {};
             if (hasErrors) {
                 // Errors need to be serialized since they are passed to other frames
-                error.data.errors = errors.map((e) => serializeError(e));
+                data.errors = errors.map((e) => ExtensionError.serialize(e));
             }
             if (hasIssueId) {
-                error.data.referenceUrl = `/issues.html#${issueId}`;
+                data.referenceUrl = `/issues.html#${issueId}`;
             }
         }
         return error;
     }
 
+    /**
+     * @param {string} prefix
+     * @param {string} extension
+     * @param {number} timestamp
+     * @param {import('api').InjectAnkiNoteMediaDefinitionDetails} definitionDetails
+     * @returns {string}
+     */
     _generateAnkiNoteMediaFileName(prefix, extension, timestamp, definitionDetails) {
         let fileName = prefix;
 
@@ -2009,11 +2496,19 @@ class Backend {
         return fileName;
     }
 
+    /**
+     * @param {string} fileName
+     * @returns {string}
+     */
     _replaceInvalidFileNameCharacters(fileName) {
         // eslint-disable-next-line no-control-regex
         return fileName.replace(/[<>:"/\\|?*\x00-\x1F]/g, '-');
     }
 
+    /**
+     * @param {Date} date
+     * @returns {string}
+     */
     _ankNoteDateToString(date) {
         const year = date.getUTCFullYear();
         const month = date.getUTCMonth().toString().padStart(2, '0');
@@ -2024,6 +2519,11 @@ class Backend {
         return `${year}-${month}-${day}-${hours}-${minutes}-${seconds}`;
     }
 
+    /**
+     * @param {string} dataUrl
+     * @returns {{mediaType: string, data: string}}
+     * @throws {Error}
+     */
     _getDataUrlInfo(dataUrl) {
         const match = /^data:([^,]*?)(;base64)?,/.exec(dataUrl);
         if (match === null) {
@@ -2039,28 +2539,35 @@ class Backend {
         return {mediaType, data};
     }
 
+    /**
+     * @param {import('backend').DatabaseUpdateType} type
+     * @param {import('backend').DatabaseUpdateCause} cause
+     */
     _triggerDatabaseUpdated(type, cause) {
         this._translator.clearDatabaseCaches();
         this._sendMessageAllTabsIgnoreResponse('Yomichan.databaseUpdated', {type, cause});
     }
 
+    /**
+     * @param {string} source
+     */
     async _saveOptions(source) {
         this._clearProfileConditionsSchemaCache();
-        const options = this._getOptionsFull();
+        const options = this._getOptionsFull(false);
         await this._optionsUtil.save(options);
         this._applyOptions(source);
     }
 
     /**
      * Creates an options object for use with `Translator.findTerms`.
-     * @param {string} mode The display mode for the dictionary entries.
-     * @param {{matchType: string, deinflect: boolean}} details Custom info for finding terms.
-     * @param {object} options The options.
-     * @returns {FindTermsOptions} An options object.
+     * @param {import('translator').FindTermsMode} mode The display mode for the dictionary entries.
+     * @param {import('api').FindTermsDetails} details Custom info for finding terms.
+     * @param {import('settings').ProfileOptions} options The options.
+     * @returns {import('translation').FindTermsOptions} An options object.
      */
     _getTranslatorFindTermsOptions(mode, details, options) {
         let {matchType, deinflect} = details;
-        if (typeof matchType !== 'string') { matchType = 'exact'; }
+        if (typeof matchType !== 'string') { matchType = /** @type {import('translation').FindTermsMatchType} */ ('exact'); }
         if (typeof deinflect !== 'boolean') { deinflect = true; }
         const enabledDictionaryMap = this._getTranslatorEnabledDictionaryMap(options);
         const {
@@ -2108,14 +2615,18 @@ class Backend {
 
     /**
      * Creates an options object for use with `Translator.findKanji`.
-     * @param {object} options The options.
-     * @returns {FindKanjiOptions} An options object.
+     * @param {import('settings').ProfileOptions} options The options.
+     * @returns {import('translation').FindKanjiOptions} An options object.
      */
     _getTranslatorFindKanjiOptions(options) {
         const enabledDictionaryMap = this._getTranslatorEnabledDictionaryMap(options);
         return {enabledDictionaryMap};
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     * @returns {Map<string, import('translation').FindTermDictionary>}
+     */
     _getTranslatorEnabledDictionaryMap(options) {
         const enabledDictionaryMap = new Map();
         for (const dictionary of options.dictionaries) {
@@ -2129,18 +2640,25 @@ class Backend {
         return enabledDictionaryMap;
     }
 
+    /**
+     * @param {import('settings').TranslationTextReplacementOptions} textReplacementsOptions
+     * @returns {(?(import('translation').FindTermsTextReplacement[]))[]}
+     */
     _getTranslatorTextReplacements(textReplacementsOptions) {
+        /** @type {(?(import('translation').FindTermsTextReplacement[]))[]} */
         const textReplacements = [];
         for (const group of textReplacementsOptions.groups) {
+            /** @type {import('translation').FindTermsTextReplacement[]} */
             const textReplacementsEntries = [];
-            for (let {pattern, ignoreCase, replacement} of group) {
+            for (const {pattern, ignoreCase, replacement} of group) {
+                let patternRegExp;
                 try {
-                    pattern = new RegExp(pattern, ignoreCase ? 'gi' : 'g');
+                    patternRegExp = new RegExp(pattern, ignoreCase ? 'gi' : 'g');
                 } catch (e) {
                     // Invalid pattern
                     continue;
                 }
-                textReplacementsEntries.push({pattern, replacement});
+                textReplacementsEntries.push({pattern: patternRegExp, replacement});
             }
             if (textReplacementsEntries.length > 0) {
                 textReplacements.push(textReplacementsEntries);
@@ -2152,6 +2670,9 @@ class Backend {
         return textReplacements;
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _openWelcomeGuidePageOnce() {
         if (isObject(chrome.storage) && isObject(chrome.storage.session)) {
             // Chrome
@@ -2169,20 +2690,33 @@ class Backend {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _openWelcomeGuidePage() {
         await this._createTab(chrome.runtime.getURL('/welcome.html'));
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _openInfoPage() {
         await this._createTab(chrome.runtime.getURL('/info.html'));
     }
 
+    /**
+     * @param {'existingOrNewTab'|'newTab'} mode
+     */
     async _openSettingsPage(mode) {
         const manifest = chrome.runtime.getManifest();
-        const url = chrome.runtime.getURL(manifest.options_ui.page);
+        const optionsUI = manifest.options_ui;
+        if (typeof optionsUI === 'undefined') { throw new Error('Failed to find options_ui'); }
+        const {page} = optionsUI;
+        if (typeof page === 'undefined') { throw new Error('Failed to find options_ui.page'); }
+        const url = chrome.runtime.getURL(page);
         switch (mode) {
             case 'existingOrNewTab':
-                await new Promise((resolve, reject) => {
+                await /** @type {Promise<void>} */ (new Promise((resolve, reject) => {
                     chrome.runtime.openOptionsPage(() => {
                         const e = chrome.runtime.lastError;
                         if (e) {
@@ -2191,7 +2725,7 @@ class Backend {
                             resolve();
                         }
                     });
-                });
+                }));
                 break;
             case 'newTab':
                 await this._createTab(url);
@@ -2199,6 +2733,10 @@ class Backend {
         }
     }
 
+    /**
+     * @param {string} url
+     * @returns {Promise<chrome.tabs.Tab>}
+     */
     _createTab(url) {
         return new Promise((resolve, reject) => {
             chrome.tabs.create({url}, (tab) => {
@@ -2212,6 +2750,10 @@ class Backend {
         });
     }
 
+    /**
+     * @param {number} tabId
+     * @returns {Promise<chrome.tabs.Tab>}
+     */
     _getTabById(tabId) {
         return new Promise((resolve, reject) => {
             chrome.tabs.get(
@@ -2228,20 +2770,33 @@ class Backend {
         });
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _checkPermissions() {
         this._permissions = await this._permissionsUtil.getAllPermissions();
         this._updateBadge();
     }
 
+    /**
+     * @returns {boolean}
+     */
     _canObservePermissionsChanges() {
         return isObject(chrome.permissions) && isObject(chrome.permissions.onAdded) && isObject(chrome.permissions.onRemoved);
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     * @returns {boolean}
+     */
     _hasRequiredPermissionsForSettings(options) {
         if (!this._canObservePermissionsChanges()) { return true; }
         return this._permissions === null || this._permissionsUtil.hasRequiredPermissionsForOptions(this._permissions, options);
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _requestPersistentStorage() {
         try {
             if (await navigator.storage.persisted()) { return; }
@@ -2263,14 +2818,32 @@ class Backend {
         }
     }
 
+    /**
+     * @param {{path: string, dictionary: string}[]} targets
+     * @returns {Promise<import('dictionary-database').MediaDataStringContent[]>}
+     */
     async _getNormalizedDictionaryDatabaseMedia(targets) {
-        const results = await this._dictionaryDatabase.getMedia(targets);
-        for (const item of results) {
-            const {content} = item;
-            if (content instanceof ArrayBuffer) {
-                item.content = ArrayBufferUtil.arrayBufferToBase64(content);
-            }
+        const results = [];
+        for (const item of await this._dictionaryDatabase.getMedia(targets)) {
+            const {content, dictionary, height, mediaType, path, width} = item;
+            const content2 = ArrayBufferUtil.arrayBufferToBase64(content);
+            results.push({content: content2, dictionary, height, mediaType, path, width});
         }
         return results;
     }
+
+    /**
+     * @param {unknown} mode
+     * @param {'existingOrNewTab'|'newTab'} defaultValue
+     * @returns {'existingOrNewTab'|'newTab'}
+     */
+    _normalizeOpenSettingsPageMode(mode, defaultValue) {
+        switch (mode) {
+            case 'existingOrNewTab':
+            case 'newTab':
+                return mode;
+            default:
+                return defaultValue;
+        }
+    }
 }
diff --git a/ext/js/background/profile-conditions-util.js b/ext/js/background/profile-conditions-util.js
index 1e2c01f8b3..7210ca98e7 100644
--- a/ext/js/background/profile-conditions-util.js
+++ b/ext/js/background/profile-conditions-util.js
@@ -24,68 +24,56 @@
  * Utility class to help processing profile conditions.
  */
 class ProfileConditionsUtil {
-    /**
-     * A group of conditions.
-     * @typedef {object} ProfileConditionGroup
-     * @property {ProfileCondition[]} conditions The list of conditions for this group.
-     */
-
-    /**
-     * A single condition.
-     * @typedef {object} ProfileCondition
-     * @property {string} type The type of the condition.
-     * @property {string} operator The condition operator.
-     * @property {string} value The value to compare against.
-     */
-
     /**
      * Creates a new instance.
      */
     constructor() {
+        /** @type {RegExp} */
         this._splitPattern = /[,;\s]+/;
+        /** @type {Map<string, {operators: Map<string, import('profile-conditions-util').CreateSchemaFunction>}>} */
         this._descriptors = new Map([
             [
                 'popupLevel',
                 {
-                    operators: new Map([
+                    operators: new Map(/** @type {import('profile-conditions-util').OperatorMapArray} */ ([
                         ['equal',              this._createSchemaPopupLevelEqual.bind(this)],
                         ['notEqual',           this._createSchemaPopupLevelNotEqual.bind(this)],
                         ['lessThan',           this._createSchemaPopupLevelLessThan.bind(this)],
                         ['greaterThan',        this._createSchemaPopupLevelGreaterThan.bind(this)],
                         ['lessThanOrEqual',    this._createSchemaPopupLevelLessThanOrEqual.bind(this)],
                         ['greaterThanOrEqual', this._createSchemaPopupLevelGreaterThanOrEqual.bind(this)]
-                    ])
+                    ]))
                 }
             ],
             [
                 'url',
                 {
-                    operators: new Map([
+                    operators: new Map(/** @type {import('profile-conditions-util').OperatorMapArray} */ ([
                         ['matchDomain', this._createSchemaUrlMatchDomain.bind(this)],
                         ['matchRegExp', this._createSchemaUrlMatchRegExp.bind(this)]
-                    ])
+                    ]))
                 }
             ],
             [
                 'modifierKeys',
                 {
-                    operators: new Map([
+                    operators: new Map(/** @type {import('profile-conditions-util').OperatorMapArray} */ ([
                         ['are', this._createSchemaModifierKeysAre.bind(this)],
                         ['areNot', this._createSchemaModifierKeysAreNot.bind(this)],
                         ['include', this._createSchemaModifierKeysInclude.bind(this)],
                         ['notInclude', this._createSchemaModifierKeysNotInclude.bind(this)]
-                    ])
+                    ]))
                 }
             ],
             [
                 'flags',
                 {
-                    operators: new Map([
+                    operators: new Map(/** @type {import('profile-conditions-util').OperatorMapArray} */ ([
                         ['are', this._createSchemaFlagsAre.bind(this)],
                         ['areNot', this._createSchemaFlagsAreNot.bind(this)],
                         ['include', this._createSchemaFlagsInclude.bind(this)],
                         ['notInclude', this._createSchemaFlagsNotInclude.bind(this)]
-                    ])
+                    ]))
                 }
             ]
         ]);
@@ -93,7 +81,7 @@ class ProfileConditionsUtil {
 
     /**
      * Creates a new JSON schema descriptor for the given set of condition groups.
-     * @param {ProfileConditionGroup[]} conditionGroups An array of condition groups.
+     * @param {import('settings').ProfileConditionGroup[]} conditionGroups An array of condition groups.
      *   For a profile match, all of the items must return successfully in at least one of the groups.
      * @returns {JsonSchema} A new `JsonSchema` object.
      */
@@ -129,11 +117,11 @@ class ProfileConditionsUtil {
     /**
      * Creates a normalized version of the context object to test,
      * assigning dependent fields as needed.
-     * @param {object} context A context object which is used during schema validation.
-     * @returns {object} A normalized context object.
+     * @param {import('settings').OptionsContext} context A context object which is used during schema validation.
+     * @returns {import('profile-conditions-util').NormalizedOptionsContext} A normalized context object.
      */
     normalizeContext(context) {
-        const normalizedContext = Object.assign({}, context);
+        const normalizedContext = /** @type {import('profile-conditions-util').NormalizedOptionsContext} */ (Object.assign({}, context));
         const {url} = normalizedContext;
         if (typeof url === 'string') {
             try {
@@ -151,10 +139,18 @@ class ProfileConditionsUtil {
 
     // Private
 
+    /**
+     * @param {string} value
+     * @returns {string[]}
+     */
     _split(value) {
         return value.split(this._splitPattern);
     }
 
+    /**
+     * @param {string} value
+     * @returns {number}
+     */
     _stringToNumber(value) {
         const number = Number.parseFloat(value);
         return Number.isFinite(number) ? number : 0;
@@ -162,64 +158,94 @@ class ProfileConditionsUtil {
 
     // popupLevel schema creation functions
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaPopupLevelEqual(value) {
-        value = this._stringToNumber(value);
+        const number = this._stringToNumber(value);
         return {
             required: ['depth'],
             properties: {
-                depth: {const: value}
+                depth: {const: number}
             }
         };
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaPopupLevelNotEqual(value) {
         return {
-            not: [this._createSchemaPopupLevelEqual(value)]
+            not: {
+                anyOf: [this._createSchemaPopupLevelEqual(value)]
+            }
         };
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaPopupLevelLessThan(value) {
-        value = this._stringToNumber(value);
+        const number = this._stringToNumber(value);
         return {
             required: ['depth'],
             properties: {
-                depth: {type: 'number', exclusiveMaximum: value}
+                depth: {type: 'number', exclusiveMaximum: number}
             }
         };
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaPopupLevelGreaterThan(value) {
-        value = this._stringToNumber(value);
+        const number = this._stringToNumber(value);
         return {
             required: ['depth'],
             properties: {
-                depth: {type: 'number', exclusiveMinimum: value}
+                depth: {type: 'number', exclusiveMinimum: number}
             }
         };
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaPopupLevelLessThanOrEqual(value) {
-        value = this._stringToNumber(value);
+        const number = this._stringToNumber(value);
         return {
             required: ['depth'],
             properties: {
-                depth: {type: 'number', maximum: value}
+                depth: {type: 'number', maximum: number}
             }
         };
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaPopupLevelGreaterThanOrEqual(value) {
-        value = this._stringToNumber(value);
+        const number = this._stringToNumber(value);
         return {
             required: ['depth'],
             properties: {
-                depth: {type: 'number', minimum: value}
+                depth: {type: 'number', minimum: number}
             }
         };
     }
 
     // url schema creation functions
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaUrlMatchDomain(value) {
         const oneOf = [];
         for (let domain of this._split(value)) {
@@ -235,6 +261,10 @@ class ProfileConditionsUtil {
         };
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaUrlMatchRegExp(value) {
         return {
             required: ['url'],
@@ -246,47 +276,91 @@ class ProfileConditionsUtil {
 
     // modifierKeys schema creation functions
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaModifierKeysAre(value) {
         return this._createSchemaArrayCheck('modifierKeys', value, true, false);
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaModifierKeysAreNot(value) {
         return {
-            not: [this._createSchemaArrayCheck('modifierKeys', value, true, false)]
+            not: {
+                anyOf: [this._createSchemaArrayCheck('modifierKeys', value, true, false)]
+            }
         };
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaModifierKeysInclude(value) {
         return this._createSchemaArrayCheck('modifierKeys', value, false, false);
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaModifierKeysNotInclude(value) {
         return this._createSchemaArrayCheck('modifierKeys', value, false, true);
     }
 
     // modifierKeys schema creation functions
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaFlagsAre(value) {
         return this._createSchemaArrayCheck('flags', value, true, false);
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaFlagsAreNot(value) {
         return {
-            not: [this._createSchemaArrayCheck('flags', value, true, false)]
+            not: {
+                anyOf: [this._createSchemaArrayCheck('flags', value, true, false)]
+            }
         };
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaFlagsInclude(value) {
         return this._createSchemaArrayCheck('flags', value, false, false);
     }
 
+    /**
+     * @param {string} value
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaFlagsNotInclude(value) {
         return this._createSchemaArrayCheck('flags', value, false, true);
     }
 
     // Generic
 
+    /**
+     * @param {string} key
+     * @param {string} value
+     * @param {boolean} exact
+     * @param {boolean} none
+     * @returns {import('json-schema').Schema}
+     */
     _createSchemaArrayCheck(key, value, exact, none) {
+        /** @type {import('json-schema').Schema[]} */
         const containsList = [];
         for (const item of this._split(value)) {
             if (item.length === 0) { continue; }
@@ -297,6 +371,7 @@ class ProfileConditionsUtil {
             });
         }
         const containsListCount = containsList.length;
+        /** @type {import('json-schema').Schema} */
         const schema = {
             type: 'array'
         };
@@ -305,7 +380,7 @@ class ProfileConditionsUtil {
         }
         if (none) {
             if (containsListCount > 0) {
-                schema.not = containsList;
+                schema.not = {anyOf: containsList};
             }
         } else {
             schema.minItems = containsListCount;
diff --git a/ext/js/background/request-builder.js b/ext/js/background/request-builder.js
index eca7d0d387..83a81145b5 100644
--- a/ext/js/background/request-builder.js
+++ b/ext/js/background/request-builder.js
@@ -21,18 +21,15 @@
  * with additional controls over anonymity and error handling.
  */
 class RequestBuilder {
-    /**
-     * A progress callback for a fetch read.
-     * @callback ProgressCallback
-     * @param {boolean} complete Whether or not the data has been completely read.
-     */
-
     /**
      * Creates a new instance.
      */
     constructor() {
+        /** @type {string[]} */
         this._onBeforeSendHeadersExtraInfoSpec = ['blocking', 'requestHeaders', 'extraHeaders'];
+        /** @type {TextEncoder} */
         this._textEncoder = new TextEncoder();
+        /** @type {Set<number>} */
         this._ruleIds = new Set();
     }
 
@@ -54,11 +51,11 @@ class RequestBuilder {
      * @returns {Promise<Response>} The response of the `fetch` call.
      */
     async fetchAnonymous(url, init) {
-        fetch(1, 2);
         if (isObject(chrome.declarativeNetRequest)) {
             return await this._fetchAnonymousDeclarative(url, init);
         }
         const originURL = this._getOriginURL(url);
+        /** @type {[key: string, value: ?chrome.webRequest.HttpHeader][]} */
         const headerModifications = [
             ['cookie', null],
             ['origin', {name: 'Origin', value: originURL}]
@@ -69,14 +66,18 @@ class RequestBuilder {
     /**
      * Reads the array buffer body of a fetch response, with an optional `onProgress` callback.
      * @param {Response} response The response of a `fetch` call.
-     * @param {ProgressCallback} onProgress The progress callback
+     * @param {?(done: boolean) => void} onProgress The progress callback.
      * @returns {Promise<Uint8Array>} The resulting binary data.
      */
     static async readFetchResponseArrayBuffer(response, onProgress) {
+        /** @type {ReadableStreamDefaultReader<Uint8Array>|undefined} */
         let reader;
         try {
-            if (typeof onProgress === 'function') {
-                reader = response.body.getReader();
+            if (onProgress !== null) {
+                const {body} = response;
+                if (body !== null) {
+                    reader = body.getReader();
+                }
             }
         } catch (e) {
             // Not supported
@@ -84,15 +85,15 @@ class RequestBuilder {
 
         if (typeof reader === 'undefined') {
             const result = await response.arrayBuffer();
-            if (typeof onProgress === 'function') {
+            if (onProgress !== null) {
                 onProgress(true);
             }
-            return result;
+            return new Uint8Array(result);
         }
 
         const contentLengthString = response.headers.get('Content-Length');
         const contentLength = contentLengthString !== null ? Number.parseInt(contentLengthString, 10) : null;
-        let target = Number.isFinite(contentLength) ? new Uint8Array(contentLength) : null;
+        let target = contentLength !== null && Number.isFinite(contentLength) ? new Uint8Array(contentLength) : null;
         let targetPosition = 0;
         let totalLength = 0;
         const targets = [];
@@ -100,7 +101,9 @@ class RequestBuilder {
         while (true) {
             const {done, value} = await reader.read();
             if (done) { break; }
-            onProgress(false);
+            if (onProgress !== null) {
+                onProgress(false);
+            }
             if (target === null) {
                 targets.push({array: value, length: value.length});
             } else if (targetPosition + value.length > target.length) {
@@ -119,33 +122,55 @@ class RequestBuilder {
             target = target.slice(0, totalLength);
         }
 
-        onProgress(true);
+        if (onProgress !== null) {
+            onProgress(true);
+        }
 
-        return target;
+        return /** @type {Uint8Array} */ (target);
     }
 
     // Private
 
+    /**
+     * @param {string} url
+     * @param {RequestInit} init
+     * @param {?([key: string, value: ?chrome.webRequest.HttpHeader][])} headerModifications
+     * @returns {Promise<Response>}
+     */
     async _fetchInternal(url, init, headerModifications) {
+        /** @type {chrome.webRequest.RequestFilter} */
         const filter = {
             urls: [this._getMatchURL(url)],
             types: ['xmlhttprequest']
         };
 
+        /** @type {?string} */
         let requestId = null;
+        /**
+         * @param {chrome.webRequest.WebRequestHeadersDetails} details
+         * @returns {chrome.webRequest.BlockingResponse}
+         */
         const onBeforeSendHeadersCallback = (details) => {
             if (requestId !== null || details.url !== url) { return {}; }
             ({requestId} = details);
 
             if (headerModifications === null) { return {}; }
 
-            const requestHeaders = details.requestHeaders;
+            let requestHeaders = details.requestHeaders;
+            if (typeof requestHeaders === 'undefined') { requestHeaders = []; }
             this._modifyHeaders(requestHeaders, headerModifications);
             return {requestHeaders};
         };
 
+        /** @type {?number} */
         let errorDetailsTimer = null;
-        let {promise: errorDetailsPromise, resolve: errorDetailsResolve} = deferPromise();
+        const promiseDetails = /** @type {import('core').DeferredPromiseDetails<?chrome.webRequest.WebResponseErrorDetails>} */ (deferPromise());
+        const errorDetailsPromise = promiseDetails.promise;
+        /** @type {?(value: ?chrome.webRequest.WebResponseErrorDetails) => void} */
+        let errorDetailsResolve = promiseDetails.resolve;
+        /**
+         * @param {chrome.webRequest.WebResponseErrorDetails} details
+         */
         const onErrorOccurredCallback = (details) => {
             if (errorDetailsResolve === null || details.requestId !== requestId) { return; }
             if (errorDetailsTimer !== null) {
@@ -156,10 +181,11 @@ class RequestBuilder {
             errorDetailsResolve = null;
         };
 
-        const eventListeners = [];
+        /** @type {import('request-builder').FetchEventListeners} */
+        const eventListeners = {onBeforeSendHeaders: null, onErrorOccurred: null};
         const onBeforeSendHeadersExtraInfoSpec = (headerModifications !== null ? this._onBeforeSendHeadersExtraInfoSpec : []);
-        this._addWebRequestEventListener(chrome.webRequest.onBeforeSendHeaders, onBeforeSendHeadersCallback, filter, onBeforeSendHeadersExtraInfoSpec, eventListeners);
-        this._addWebRequestEventListener(chrome.webRequest.onErrorOccurred, onErrorOccurredCallback, filter, void 0, eventListeners);
+        this._hookOnBeforeSendHeaders(eventListeners, onBeforeSendHeadersCallback, filter, onBeforeSendHeadersExtraInfoSpec);
+        this._hookOnErrorOccurred(eventListeners, onErrorOccurredCallback, filter);
 
         try {
             return await fetch(url, init);
@@ -176,7 +202,9 @@ class RequestBuilder {
             const details = await errorDetailsPromise;
             if (details !== null) {
                 const data = {details};
-                this._assignErrorData(e, data);
+                const error = new ExtensionError(e instanceof Error ? e.message : `${e}`);
+                error.data = data;
+                throw error;
             }
             throw e;
         } finally {
@@ -184,20 +212,22 @@ class RequestBuilder {
         }
     }
 
-    _addWebRequestEventListener(target, callback, filter, extraInfoSpec, eventListeners) {
+    /**
+     * @param {import('request-builder').FetchEventListeners} eventListeners
+     * @param {(details: chrome.webRequest.WebRequestHeadersDetails) => (chrome.webRequest.BlockingResponse|void)} callback
+     * @param {chrome.webRequest.RequestFilter} filter
+     * @param {string[]} extraInfoSpec
+     */
+    _hookOnBeforeSendHeaders(eventListeners, callback, filter, extraInfoSpec) {
         try {
             for (let i = 0; i < 2; ++i) {
                 try {
-                    if (typeof extraInfoSpec === 'undefined') {
-                        target.addListener(callback, filter);
-                    } else {
-                        target.addListener(callback, filter, extraInfoSpec);
-                    }
+                    chrome.webRequest.onBeforeSendHeaders.addListener(callback, filter, extraInfoSpec);
                     break;
                 } catch (e) {
                     // Firefox doesn't support the 'extraHeaders' option and will throw the following error:
                     // Type error for parameter extraInfoSpec (Error processing 2: Invalid enumeration value "extraHeaders") for [target].
-                    if (i === 0 && `${e.message}`.includes('extraHeaders') && Array.isArray(extraInfoSpec)) {
+                    if (i === 0 && e instanceof Error && `${e.message}`.includes('extraHeaders') && Array.isArray(extraInfoSpec)) {
                         const index = extraInfoSpec.indexOf('extraHeaders');
                         if (index >= 0) {
                             extraInfoSpec.splice(index, 1);
@@ -211,39 +241,69 @@ class RequestBuilder {
             console.log(e);
             return;
         }
-        eventListeners.push({target, callback});
+        eventListeners.onBeforeSendHeaders = callback;
     }
 
+    /**
+     * @param {import('request-builder').FetchEventListeners} eventListeners
+     * @param {(details: chrome.webRequest.WebResponseErrorDetails) => void} callback
+     * @param {chrome.webRequest.RequestFilter} filter
+     */
+    _hookOnErrorOccurred(eventListeners, callback, filter) {
+        try {
+            chrome.webRequest.onErrorOccurred.addListener(callback, filter);
+        } catch (e) {
+            console.log(e);
+            return;
+        }
+        eventListeners.onErrorOccurred = callback;
+    }
+
+    /**
+     * @param {import('request-builder').FetchEventListeners} eventListeners
+     */
     _removeWebRequestEventListeners(eventListeners) {
-        for (const {target, callback} of eventListeners) {
-            try {
-                target.removeListener(callback);
-            } catch (e) {
-                console.log(e);
-            }
+        const {onBeforeSendHeaders, onErrorOccurred} = eventListeners;
+        if (onBeforeSendHeaders !== null) {
+            chrome.webRequest.onBeforeSendHeaders.removeListener(onBeforeSendHeaders);
+        }
+        if (onErrorOccurred !== null) {
+            chrome.webRequest.onErrorOccurred.removeListener(onErrorOccurred);
         }
     }
 
+    /**
+     * @param {string} url
+     * @returns {string}
+     */
     _getMatchURL(url) {
         const url2 = new URL(url);
         return `${url2.protocol}//${url2.host}${url2.pathname}${url2.search}`.replace(/\*/g, '%2a');
     }
 
+    /**
+     * @param {string} url
+     * @returns {string}
+     */
     _getOriginURL(url) {
         const url2 = new URL(url);
         return `${url2.protocol}//${url2.host}`;
     }
 
+    /**
+     * @param {chrome.webRequest.HttpHeader[]} headers
+     * @param {[key: string, value: ?chrome.webRequest.HttpHeader][]} modifications
+     */
     _modifyHeaders(headers, modifications) {
-        modifications = new Map(modifications);
+        const modificationsMap = new Map(modifications);
 
         for (let i = 0, ii = headers.length; i < ii; ++i) {
             const header = headers[i];
             const name = header.name.toLowerCase();
-            const modification = modifications.get(name);
+            const modification = modificationsMap.get(name);
             if (typeof modification === 'undefined') { continue; }
 
-            modifications.delete(name);
+            modificationsMap.delete(name);
 
             if (modification === null) {
                 headers.splice(i, 1);
@@ -254,17 +314,21 @@ class RequestBuilder {
             }
         }
 
-        for (const header of modifications.values()) {
+        for (const header of modificationsMap.values()) {
             if (header !== null) {
                 headers.push(header);
             }
         }
     }
 
+
+    /**
+     * @returns {Promise<void>}
+     */
     async _clearDynamicRules() {
         if (!isObject(chrome.declarativeNetRequest)) { return; }
 
-        const rules = this._getDynamicRules();
+        const rules = await this._getDynamicRules();
 
         if (rules.length === 0) { return; }
 
@@ -276,6 +340,11 @@ class RequestBuilder {
         await this._updateDynamicRules({removeRuleIds});
     }
 
+    /**
+     * @param {string} url
+     * @param {RequestInit} init
+     * @returns {Promise<Response>}
+     */
     async _fetchAnonymousDeclarative(url, init) {
         const id = this._getNewRuleId();
         const originUrl = this._getOriginURL(url);
@@ -283,21 +352,26 @@ class RequestBuilder {
 
         this._ruleIds.add(id);
         try {
+            /** @type {chrome.declarativeNetRequest.Rule[]} */
             const addRules = [{
                 id,
                 priority: 1,
                 condition: {
                     urlFilter: `|${this._escapeDnrUrl(url)}|`,
+                    // @ts-ignore - TS throws an error about the enum value for some reason despite being valid
                     resourceTypes: ['xmlhttprequest']
                 },
                 action: {
+                    // @ts-ignore - TS throws an error about the enum value for some reason despite being valid
                     type: 'modifyHeaders',
                     requestHeaders: [
                         {
+                            // @ts-ignore - TS throws an error about the enum value for some reason despite being valid
                             operation: 'remove',
                             header: 'Cookie'
                         },
                         {
+                            // @ts-ignore - TS throws an error about the enum value for some reason despite being valid
                             operation: 'set',
                             header: 'Origin',
                             value: originUrl
@@ -305,6 +379,7 @@ class RequestBuilder {
                     ],
                     responseHeaders: [
                         {
+                            // @ts-ignore - TS throws an error about the enum value for some reason despite being valid
                             operation: 'remove',
                             header: 'Set-Cookie'
                         }
@@ -323,6 +398,9 @@ class RequestBuilder {
         }
     }
 
+    /**
+     * @returns {Promise<chrome.declarativeNetRequest.Rule[]>}
+     */
     _getDynamicRules() {
         return new Promise((resolve, reject) => {
             chrome.declarativeNetRequest.getDynamicRules((result) => {
@@ -336,6 +414,10 @@ class RequestBuilder {
         });
     }
 
+    /**
+     * @param {chrome.declarativeNetRequest.UpdateRuleOptions} options
+     * @returns {Promise<void>}
+     */
     _updateDynamicRules(options) {
         return new Promise((resolve, reject) => {
             chrome.declarativeNetRequest.updateDynamicRules(options, () => {
@@ -349,6 +431,10 @@ class RequestBuilder {
         });
     }
 
+    /**
+     * @param {chrome.declarativeNetRequest.UpdateRuleOptions} options
+     * @returns {Promise<boolean>}
+     */
     async _tryUpdateDynamicRules(options) {
         try {
             await this._updateDynamicRules(options);
@@ -358,6 +444,10 @@ class RequestBuilder {
         }
     }
 
+    /**
+     * @returns {number}
+     * @throws {Error}
+     */
     _getNewRuleId() {
         let id = 1;
         while (this._ruleIds.has(id)) {
@@ -368,10 +458,18 @@ class RequestBuilder {
         return id;
     }
 
+    /**
+     * @param {string} url
+     * @returns {string}
+     */
     _escapeDnrUrl(url) {
         return url.replace(/[|*^]/g, (char) => this._urlEncodeUtf8(char));
     }
 
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
     _urlEncodeUtf8(text) {
         const array = this._textEncoder.encode(text);
         let result = '';
@@ -381,25 +479,11 @@ class RequestBuilder {
         return result;
     }
 
-    _assignErrorData(error, data) {
-        try {
-            error.data = data;
-        } catch (e) {
-            // On Firefox, assigning DOMException.data can fail in certain contexts.
-            // https://bugzilla.mozilla.org/show_bug.cgi?id=1776555
-            try {
-                Object.defineProperty(error, 'data', {
-                    configurable: true,
-                    enumerable: true,
-                    writable: true,
-                    value: data
-                });
-            } catch (e2) {
-                // NOP
-            }
-        }
-    }
-
+    /**
+     * @param {{array: Uint8Array, length: number}[]} items
+     * @param {number} totalLength
+     * @returns {Uint8Array}
+     */
     static _joinUint8Arrays(items, totalLength) {
         if (items.length === 1) {
             const {array, length} = items[0];
diff --git a/ext/js/background/script-manager.js b/ext/js/background/script-manager.js
index 722a46f064..8a1ef413cf 100644
--- a/ext/js/background/script-manager.js
+++ b/ext/js/background/script-manager.js
@@ -24,20 +24,21 @@ class ScriptManager {
      * Creates a new instance of the class.
      */
     constructor() {
+        /** @type {Map<string, ?browser.contentScripts.RegisteredContentScript>} */
         this._contentScriptRegistrations = new Map();
     }
 
     /**
      * Injects a stylesheet into a tab.
-     * @param {string} type The type of content to inject; either 'file' or 'code'.
+     * @param {'file'|'code'} type The type of content to inject; either 'file' or 'code'.
      * @param {string} content The content to inject.
      *   If type is 'file', this argument should be a path to a file.
      *   If type is 'code', this argument should be the CSS content.
      * @param {number} tabId The id of the tab to inject into.
-     * @param {number} [frameId] The id of the frame to inject into.
-     * @param {boolean} [allFrames] Whether or not the stylesheet should be injected into all frames.
-     * @param {boolean} [matchAboutBlank] Whether or not the stylesheet should be injected into about:blank frames.
-     * @param {string} [runAt] The time to inject the stylesheet at.
+     * @param {number|undefined} frameId The id of the frame to inject into.
+     * @param {boolean} allFrames Whether or not the stylesheet should be injected into all frames.
+     * @param {boolean} matchAboutBlank Whether or not the stylesheet should be injected into about:blank frames.
+     * @param {import('script-manager').RunAt} runAt The time to inject the stylesheet at.
      * @returns {Promise<void>}
      */
     injectStylesheet(type, content, tabId, frameId, allFrames, matchAboutBlank, runAt) {
@@ -54,11 +55,11 @@ class ScriptManager {
      * Injects a script into a tab.
      * @param {string} file The path to a file to inject.
      * @param {number} tabId The id of the tab to inject into.
-     * @param {number} [frameId] The id of the frame to inject into.
-     * @param {boolean} [allFrames] Whether or not the script should be injected into all frames.
-     * @param {boolean} [matchAboutBlank] Whether or not the script should be injected into about:blank frames.
-     * @param {string} [runAt] The time to inject the script at.
-     * @returns {Promise<{frameId: number, result: object}>} The id of the frame and the result of the script injection.
+     * @param {number|undefined} frameId The id of the frame to inject into.
+     * @param {boolean} allFrames Whether or not the script should be injected into all frames.
+     * @param {boolean} matchAboutBlank Whether or not the script should be injected into about:blank frames.
+     * @param {import('script-manager').RunAt} runAt The time to inject the script at.
+     * @returns {Promise<{frameId: number|undefined, result: unknown}>} The id of the frame and the result of the script injection.
      */
     injectScript(file, tabId, frameId, allFrames, matchAboutBlank, runAt) {
         if (isObject(chrome.tabs) && typeof chrome.tabs.executeScript === 'function') {
@@ -105,16 +106,7 @@ class ScriptManager {
      * there is a possibility that the script can be injected more than once due to the events used.
      * Therefore, a reentrant check may need to be performed by the content script.
      * @param {string} id A unique identifier for the registration.
-     * @param {object} details The script registration details.
-     * @param {boolean} [details.allFrames] Same as `all_frames` in the `content_scripts` manifest key.
-     * @param {string[]} [details.css] List of CSS paths.
-     * @param {string[]} [details.excludeMatches] Same as `exclude_matches` in the `content_scripts` manifest key.
-     * @param {string[]} [details.js] List of script paths.
-     * @param {boolean} [details.matchAboutBlank] Same as `match_about_blank` in the `content_scripts` manifest key.
-     * @param {string[]} details.matches Same as `matches` in the `content_scripts` manifest key.
-     * @param {string} [details.urlMatches] Regex match pattern to use as a fallback
-     *   when native content script registration isn't supported. Should be equivalent to `matches`.
-     * @param {string} [details.runAt] Same as `run_at` in the `content_scripts` manifest key.
+     * @param {import('script-manager').RegistrationDetails} details The script registration details.
      * @throws An error is thrown if the id is already in use.
      */
     async registerContentScript(id, details) {
@@ -128,7 +120,7 @@ class ScriptManager {
             isObject(browser.contentScripts) &&
             typeof browser.contentScripts.register === 'function'
         ) {
-            const details2 = this._convertContentScriptRegistrationDetails(details, id, true);
+            const details2 = this._createContentScriptRegistrationOptionsFirefox(details);
             const registration = await browser.contentScripts.register(details2);
             this._contentScriptRegistrations.set(id, registration);
             return;
@@ -136,8 +128,8 @@ class ScriptManager {
 
         // Chrome
         if (isObject(chrome.scripting) && typeof chrome.scripting.registerContentScripts === 'function') {
-            const details2 = this._convertContentScriptRegistrationDetails(details, id, false);
-            await new Promise((resolve, reject) => {
+            const details2 = this._createContentScriptRegistrationOptionsChrome(details, id);
+            await /** @type {Promise<void>} */ (new Promise((resolve, reject) => {
                 chrome.scripting.registerContentScripts([details2], () => {
                     const e = chrome.runtime.lastError;
                     if (e) {
@@ -146,7 +138,7 @@ class ScriptManager {
                         resolve();
                     }
                 });
-            });
+            }));
             this._contentScriptRegistrations.set(id, null);
             return;
         }
@@ -176,7 +168,7 @@ class ScriptManager {
         const registration = this._contentScriptRegistrations.get(id);
         if (typeof registration === 'undefined') { return false; }
         this._contentScriptRegistrations.delete(id);
-        if (isObject(registration) && typeof registration.unregister === 'function') {
+        if (registration !== null && typeof registration.unregister === 'function') {
             await registration.unregister();
         }
         return true;
@@ -209,8 +201,19 @@ class ScriptManager {
 
     // Private
 
+    /**
+     * @param {'file'|'code'} type
+     * @param {string} content
+     * @param {number} tabId
+     * @param {number|undefined} frameId
+     * @param {boolean} allFrames
+     * @param {boolean} matchAboutBlank
+     * @param {import('script-manager').RunAt} runAt
+     * @returns {Promise<void>}
+     */
     _injectStylesheetMV2(type, content, tabId, frameId, allFrames, matchAboutBlank, runAt) {
         return new Promise((resolve, reject) => {
+            /** @type {chrome.tabs.InjectDetails} */
             const details = (
                 type === 'file' ?
                 {
@@ -242,17 +245,27 @@ class ScriptManager {
         });
     }
 
+    /**
+     * @param {'file'|'code'} type
+     * @param {string} content
+     * @param {number} tabId
+     * @param {number|undefined} frameId
+     * @param {boolean} allFrames
+     * @returns {Promise<void>}
+     */
     _injectStylesheetMV3(type, content, tabId, frameId, allFrames) {
         return new Promise((resolve, reject) => {
-            const details = (
-                type === 'file' ?
-                {origin: chrome.scripting.StyleOrigin.AUTHOR, files: [content]} :
-                {origin: chrome.scripting.StyleOrigin.USER,   css: content}
-            );
-            details.target = {
+            /** @type {chrome.scripting.InjectionTarget} */
+            const target = {
                 tabId,
                 allFrames
             };
+            /** @type {chrome.scripting.CSSInjection} */
+            const details = (
+                type === 'file' ?
+                {origin: 'AUTHOR', files: [content], target} :
+                {origin: 'USER', css: content, target}
+            );
             if (!allFrames && typeof frameId === 'number') {
                 details.target.frameIds = [frameId];
             }
@@ -267,8 +280,18 @@ class ScriptManager {
         });
     }
 
+    /**
+     * @param {string} file
+     * @param {number} tabId
+     * @param {number|undefined} frameId
+     * @param {boolean} allFrames
+     * @param {boolean} matchAboutBlank
+     * @param {import('script-manager').RunAt} runAt
+     * @returns {Promise<{frameId: number|undefined, result: unknown}>} The id of the frame and the result of the script injection.
+     */
     _injectScriptMV2(file, tabId, frameId, allFrames, matchAboutBlank, runAt) {
         return new Promise((resolve, reject) => {
+            /** @type {chrome.tabs.InjectDetails} */
             const details = {
                 allFrames,
                 frameId,
@@ -288,8 +311,16 @@ class ScriptManager {
         });
     }
 
+    /**
+     * @param {string} file
+     * @param {number} tabId
+     * @param {number|undefined} frameId
+     * @param {boolean} allFrames
+     * @returns {Promise<{frameId: number|undefined, result: unknown}>} The id of the frame and the result of the script injection.
+     */
     _injectScriptMV3(file, tabId, frameId, allFrames) {
         return new Promise((resolve, reject) => {
+            /** @type {chrome.scripting.ScriptInjection<unknown[], unknown>} */
             const details = {
                 injectImmediately: true,
                 files: [file],
@@ -310,6 +341,10 @@ class ScriptManager {
         });
     }
 
+    /**
+     * @param {string} id
+     * @returns {Promise<void>}
+     */
     _unregisterContentScriptChrome(id) {
         return new Promise((resolve, reject) => {
             chrome.scripting.unregisterContentScripts({ids: [id]}, () => {
@@ -323,73 +358,132 @@ class ScriptManager {
         });
     }
 
-    _convertContentScriptRegistrationDetails(details, id, firefoxConvention) {
-        const {allFrames, css, excludeMatches, js, matchAboutBlank, matches, runAt} = details;
-        const details2 = {};
-        if (!firefoxConvention) {
-            details2.id = id;
-            details2.persistAcrossSessions = true;
+    /**
+     * @param {import('script-manager').RegistrationDetails} details
+     * @returns {browser.contentScripts.RegisteredContentScriptOptions}
+     */
+    _createContentScriptRegistrationOptionsFirefox(details) {
+        const {css, js, matchAboutBlank} = details;
+        /** @type {browser.contentScripts.RegisteredContentScriptOptions} */
+        const options = {};
+        if (typeof matchAboutBlank !== 'undefined') {
+            options.matchAboutBlank = matchAboutBlank;
+        }
+        if (Array.isArray(css)) {
+            options.css = css.map((file) => ({file}));
+        }
+        if (Array.isArray(js)) {
+            options.js = js.map((file) => ({file}));
         }
+        this._initializeContentScriptRegistrationOptionsGeneric(details, options);
+        return options;
+    }
+
+    /**
+     * @param {import('script-manager').RegistrationDetails} details
+     * @param {string} id
+     * @returns {chrome.scripting.RegisteredContentScript}
+     */
+    _createContentScriptRegistrationOptionsChrome(details, id) {
+        const {css, js} = details;
+        /** @type {chrome.scripting.RegisteredContentScript} */
+        const options = {
+            id: id,
+            persistAcrossSessions: true
+        };
+        if (Array.isArray(css)) {
+            options.css = [...css];
+        }
+        if (Array.isArray(js)) {
+            options.js = [...js];
+        }
+        this._initializeContentScriptRegistrationOptionsGeneric(details, options);
+        return options;
+    }
+
+    /**
+     * @param {import('script-manager').RegistrationDetails} details
+     * @param {chrome.scripting.RegisteredContentScript|browser.contentScripts.RegisteredContentScriptOptions} options
+     */
+    _initializeContentScriptRegistrationOptionsGeneric(details, options) {
+        const {allFrames, excludeMatches, matches, runAt} = details;
         if (typeof allFrames !== 'undefined') {
-            details2.allFrames = allFrames;
+            options.allFrames = allFrames;
         }
         if (Array.isArray(excludeMatches)) {
-            details2.excludeMatches = [...excludeMatches];
+            options.excludeMatches = [...excludeMatches];
         }
         if (Array.isArray(matches)) {
-            details2.matches = [...matches];
+            options.matches = [...matches];
         }
         if (typeof runAt !== 'undefined') {
-            details2.runAt = runAt;
-        }
-        if (firefoxConvention && typeof matchAboutBlank !== 'undefined') {
-            details2.matchAboutBlank = matchAboutBlank;
+            options.runAt = runAt;
         }
-        if (Array.isArray(css)) {
-            details2.css = this._convertFileArray(css, firefoxConvention);
-        }
-        if (Array.isArray(js)) {
-            details2.js = this._convertFileArray(js, firefoxConvention);
-        }
-        return details2;
     }
 
+    /**
+     * @param {string[]} array
+     * @param {boolean} firefoxConvention
+     * @returns {string[]|browser.extensionTypes.ExtensionFileOrCode[]}
+     */
     _convertFileArray(array, firefoxConvention) {
         return firefoxConvention ? array.map((file) => ({file})) : [...array];
     }
 
+    /**
+     * @param {string} id
+     * @param {import('script-manager').RegistrationDetails} details
+     */
     _registerContentScriptFallback(id, details) {
         const {allFrames, css, js, matchAboutBlank, runAt, urlMatches} = details;
-        const details2 = {allFrames, css, js, matchAboutBlank, runAt, urlRegex: null};
+        /** @type {import('script-manager').ContentScriptInjectionDetails} */
+        const details2 = {allFrames, css, js, matchAboutBlank, runAt, urlRegex: /** @type {?RegExp} */ (null)};
+        /** @type {() => Promise<void>} */
         let unregister;
         const webNavigationEvent = this._getWebNavigationEvent(runAt);
-        if (isObject(webNavigationEvent)) {
+        if (typeof webNavigationEvent === 'object' && webNavigationEvent !== null) {
+            /**
+             * @param {chrome.webNavigation.WebNavigationFramedCallbackDetails} details
+             */
             const onTabCommitted = ({url, tabId, frameId}) => {
                 this._injectContentScript(true, details2, null, url, tabId, frameId);
             };
             const filter = {url: [{urlMatches}]};
             webNavigationEvent.addListener(onTabCommitted, filter);
-            unregister = () => webNavigationEvent.removeListener(onTabCommitted);
+            unregister = async () => webNavigationEvent.removeListener(onTabCommitted);
         } else {
+            /**
+             * @param {number} tabId
+             * @param {chrome.tabs.TabChangeInfo} changeInfo
+             * @param {chrome.tabs.Tab} tab
+             */
             const onTabUpdated = (tabId, {status}, {url}) => {
                 if (typeof status === 'string' && typeof url === 'string') {
                     this._injectContentScript(false, details2, status, url, tabId, void 0);
                 }
             };
-            const extraParameters = {url: [urlMatches], properties: ['status']};
             try {
                 // Firefox
-                chrome.tabs.onUpdated.addListener(onTabUpdated, extraParameters);
+                /** @type {browser.tabs.UpdateFilter} */
+                const extraParameters = {urls: [urlMatches], properties: ['status']};
+                browser.tabs.onUpdated.addListener(
+                    /** @type {(tabId: number, changeInfo: browser.tabs._OnUpdatedChangeInfo, tab: browser.tabs.Tab) => void} */ (onTabUpdated),
+                    extraParameters
+                );
             } catch (e) {
                 // Chrome
                 details2.urlRegex = new RegExp(urlMatches);
                 chrome.tabs.onUpdated.addListener(onTabUpdated);
             }
-            unregister = () => chrome.tabs.onUpdated.removeListener(onTabUpdated);
+            unregister = async () => chrome.tabs.onUpdated.removeListener(onTabUpdated);
         }
         this._contentScriptRegistrations.set(id, {unregister});
     }
 
+    /**
+     * @param {import('script-manager').RunAt} runAt
+     * @returns {?(chrome.webNavigation.WebNavigationFramedEvent|chrome.webNavigation.WebNavigationTransitionalEvent)}
+     */
     _getWebNavigationEvent(runAt) {
         const {webNavigation} = chrome;
         if (!isObject(webNavigation)) { return null; }
@@ -403,6 +497,14 @@ class ScriptManager {
         }
     }
 
+    /**
+     * @param {boolean} isWebNavigation
+     * @param {import('script-manager').ContentScriptInjectionDetails} details
+     * @param {?string} status
+     * @param {string} url
+     * @param {number} tabId
+     * @param {number|undefined} frameId
+     */
     async _injectContentScript(isWebNavigation, details, status, url, tabId, frameId) {
         const {urlRegex} = details;
         if (urlRegex !== null && !urlRegex.test(url)) { return; }
diff --git a/ext/js/comm/anki-connect.js b/ext/js/comm/anki-connect.js
index b5e4d16d3b..355f42c5f5 100644
--- a/ext/js/comm/anki-connect.js
+++ b/ext/js/comm/anki-connect.js
@@ -28,17 +28,23 @@ class AnkiConnect {
      * Creates a new instance.
      */
     constructor() {
+        /** @type {boolean} */
         this._enabled = false;
+        /** @type {?string} */
         this._server = null;
+        /** @type {number} */
         this._localVersion = 2;
+        /** @type {number} */
         this._remoteVersion = 0;
+        /** @type {?Promise<number>} */
         this._versionCheckPromise = null;
+        /** @type {?string} */
         this._apiKey = null;
     }
 
     /**
      * Gets the URL of the AnkiConnect server.
-     * @type {string}
+     * @type {?string}
      */
     get server() {
         return this._server;
@@ -91,7 +97,7 @@ class AnkiConnect {
      */
     async isConnected() {
         try {
-            await this._invoke('version');
+            await this._getVersion();
             return true;
         } catch (e) {
             return false;
@@ -100,74 +106,114 @@ class AnkiConnect {
 
     /**
      * Gets the AnkiConnect API version number.
-     * @returns {Promise<number>} The version number
+     * @returns {Promise<?number>} The version number
      */
     async getVersion() {
         if (!this._enabled) { return null; }
         await this._checkVersion();
-        return await this._invoke('version', {});
+        return await this._getVersion();
     }
 
+    /**
+     * @param {import('anki').Note} note
+     * @returns {Promise<?import('anki').NoteId>}
+     */
     async addNote(note) {
         if (!this._enabled) { return null; }
         await this._checkVersion();
-        return await this._invoke('addNote', {note});
+        const result = await this._invoke('addNote', {note});
+        if (result !== null && typeof result !== 'number') {
+            throw this._createUnexpectedResultError('number|null', result);
+        }
+        return result;
     }
 
+    /**
+     * @param {import('anki').Note[]} notes
+     * @returns {Promise<boolean[]>}
+     */
     async canAddNotes(notes) {
         if (!this._enabled) { return []; }
         await this._checkVersion();
-        return await this._invoke('canAddNotes', {notes});
+        const result = await this._invoke('canAddNotes', {notes});
+        return this._normalizeArray(result, notes.length, 'boolean');
     }
 
-    async notesInfo(notes) {
+    /**
+     * @param {import('anki').NoteId[]} noteIds
+     * @returns {Promise<(?import('anki').NoteInfo)[]>}
+     */
+    async notesInfo(noteIds) {
         if (!this._enabled) { return []; }
         await this._checkVersion();
-        return await this._invoke('notesInfo', {notes});
+        const result = await this._invoke('notesInfo', {notes: noteIds});
+        return this._normalizeNoteInfoArray(result);
     }
 
+    /**
+     * @returns {Promise<string[]>}
+     */
     async getDeckNames() {
         if (!this._enabled) { return []; }
         await this._checkVersion();
-        return await this._invoke('deckNames');
+        const result = await this._invoke('deckNames', {});
+        return this._normalizeArray(result, -1, 'string');
     }
 
+    /**
+     * @returns {Promise<string[]>}
+     */
     async getModelNames() {
         if (!this._enabled) { return []; }
         await this._checkVersion();
-        return await this._invoke('modelNames');
+        const result = await this._invoke('modelNames', {});
+        return this._normalizeArray(result, -1, 'string');
     }
 
+    /**
+     * @param {string} modelName
+     * @returns {Promise<string[]>}
+     */
     async getModelFieldNames(modelName) {
         if (!this._enabled) { return []; }
         await this._checkVersion();
-        return await this._invoke('modelFieldNames', {modelName});
+        const result = await this._invoke('modelFieldNames', {modelName});
+        return this._normalizeArray(result, -1, 'string');
     }
 
+    /**
+     * @param {string} query
+     * @returns {Promise<import('anki').CardId[]>}
+     */
     async guiBrowse(query) {
         if (!this._enabled) { return []; }
         await this._checkVersion();
-        return await this._invoke('guiBrowse', {query});
+        const result = await this._invoke('guiBrowse', {query});
+        return this._normalizeArray(result, -1, 'number');
     }
 
+    /**
+     * @param {import('anki').NoteId} noteId
+     * @returns {Promise<import('anki').CardId[]>}
+     */
     async guiBrowseNote(noteId) {
         return await this.guiBrowse(`nid:${noteId}`);
     }
 
     /**
      * Opens the note editor GUI.
-     * @param {number} noteId The ID of the note.
-     * @returns {Promise<null>} Nothing is returned.
+     * @param {import('anki').NoteId} noteId The ID of the note.
+     * @returns {Promise<void>} Nothing is returned.
      */
     async guiEditNote(noteId) {
-        return await this._invoke('guiEditNote', {note: noteId});
+        await this._invoke('guiEditNote', {note: noteId});
     }
 
     /**
      * Stores a file with the specified base64-encoded content inside Anki's media folder.
      * @param {string} fileName The name of the file.
      * @param {string} content The base64-encoded content of the file.
-     * @returns {?string} The actual file name used to store the file, which may be different; or `null` if the file was not stored.
+     * @returns {Promise<?string>} The actual file name used to store the file, which may be different; or `null` if the file was not stored.
      * @throws {Error} An error is thrown is this object is not enabled.
      */
     async storeMediaFile(fileName, content) {
@@ -175,28 +221,39 @@ class AnkiConnect {
             throw new Error('AnkiConnect not enabled');
         }
         await this._checkVersion();
-        return await this._invoke('storeMediaFile', {filename: fileName, data: content});
+        const result = await this._invoke('storeMediaFile', {filename: fileName, data: content});
+        if (result !== null && typeof result !== 'string') {
+            throw this._createUnexpectedResultError('string|null', result);
+        }
+        return result;
     }
 
     /**
      * Finds notes matching a query.
      * @param {string} query Searches for notes matching a query.
-     * @returns {number[]} An array of note IDs.
+     * @returns {Promise<import('anki').NoteId[]>} An array of note IDs.
      * @see https://docs.ankiweb.net/searching.html
      */
     async findNotes(query) {
         if (!this._enabled) { return []; }
         await this._checkVersion();
-        return await this._invoke('findNotes', {query});
+        const result = await this._invoke('findNotes', {query});
+        return this._normalizeArray(result, -1, 'number');
     }
 
+    /**
+     * @param {import('anki').Note[]} notes
+     * @returns {Promise<import('anki').NoteId[][]>}
+     */
     async findNoteIds(notes) {
         if (!this._enabled) { return []; }
         await this._checkVersion();
 
         const actions = [];
         const actionsTargetsList = [];
+        /** @type {Map<string, import('anki').NoteId[][]>} */
         const actionsTargetsMap = new Map();
+        /** @type {import('anki').NoteId[][]} */
         const allNoteIds = [];
 
         for (const note of notes) {
@@ -208,14 +265,15 @@ class AnkiConnect {
                 actionsTargetsMap.set(query, actionsTargets);
                 actions.push({action: 'findNotes', params: {query}});
             }
+            /** @type {import('anki').NoteId[]} */
             const noteIds = [];
             allNoteIds.push(noteIds);
             actionsTargets.push(noteIds);
         }
 
-        const result = await this._invoke('multi', {actions});
+        const result = await this._invokeMulti(actions);
         for (let i = 0, ii = Math.min(result.length, actionsTargetsList.length); i < ii; ++i) {
-            const noteIds = result[i];
+            const noteIds = /** @type {number[]} */ (this._normalizeArray(result[i], -1, 'number'));
             for (const actionsTargets of actionsTargetsList[i]) {
                 for (const noteId of noteIds) {
                     actionsTargets.push(noteId);
@@ -225,18 +283,32 @@ class AnkiConnect {
         return allNoteIds;
     }
 
+    /**
+     * @param {import('anki').CardId[]} cardIds
+     * @returns {Promise<boolean>}
+     */
     async suspendCards(cardIds) {
         if (!this._enabled) { return false; }
         await this._checkVersion();
-        return await this._invoke('suspend', {cards: cardIds});
+        const result = await this._invoke('suspend', {cards: cardIds});
+        return typeof result === 'boolean' && result;
     }
 
+    /**
+     * @param {string} query
+     * @returns {Promise<import('anki').CardId[]>}
+     */
     async findCards(query) {
         if (!this._enabled) { return []; }
         await this._checkVersion();
-        return await this._invoke('findCards', {query});
+        const result = await this._invoke('findCards', {query});
+        return this._normalizeArray(result, -1, 'number');
     }
 
+    /**
+     * @param {import('anki').NoteId} noteId
+     * @returns {Promise<import('anki').CardId[]>}
+     */
     async findCardsForNote(noteId) {
         return await this.findCards(`nid:${noteId}`);
     }
@@ -245,16 +317,26 @@ class AnkiConnect {
      * Gets information about the AnkiConnect APIs available.
      * @param {string[]} scopes A list of scopes to get information about.
      * @param {?string[]} actions A list of actions to check for
-     * @returns {object} Information about the APIs.
+     * @returns {Promise<import('anki').ApiReflectResult>} Information about the APIs.
      */
     async apiReflect(scopes, actions=null) {
-        return await this._invoke('apiReflect', {scopes, actions});
+        const result = await this._invoke('apiReflect', {scopes, actions});
+        if (!(typeof result === 'object' && result !== null)) {
+            throw this._createUnexpectedResultError('object', result);
+        }
+        const {scopes: resultScopes, actions: resultActions} = /** @type {import('core').SerializableObject} */ (result);
+        const resultScopes2 = /** @type {string[]} */ (this._normalizeArray(resultScopes, -1, 'string', ', field scopes'));
+        const resultActions2 = /** @type {string[]} */ (this._normalizeArray(resultActions, -1, 'string', ', field scopes'));
+        return {
+            scopes: resultScopes2,
+            actions: resultActions2
+        };
     }
 
     /**
      * Checks whether a specific API action exists.
      * @param {string} action The action to check for.
-     * @returns {boolean} Whether or not the action exists.
+     * @returns {Promise<boolean>} Whether or not the action exists.
      */
     async apiExists(action) {
         const {actions} = await this.apiReflect(['actions'], [action]);
@@ -267,9 +349,9 @@ class AnkiConnect {
      * @returns {boolean} Whether or not the error indicates the action is not supported.
      */
     isErrorUnsupportedAction(error) {
-        if (error instanceof Error) {
+        if (error instanceof ExtensionError) {
             const {data} = error;
-            if (isObject(data) && data.apiError === 'unsupported action') {
+            if (typeof data === 'object' && data !== null && /** @type {import('core').SerializableObject} */ (data).apiError === 'unsupported action') {
                 return true;
             }
         }
@@ -278,10 +360,13 @@ class AnkiConnect {
 
     // Private
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _checkVersion() {
         if (this._remoteVersion < this._localVersion) {
             if (this._versionCheckPromise === null) {
-                const promise = this._invoke('version');
+                const promise = this._getVersion();
                 promise
                     .catch(() => {})
                     .finally(() => { this._versionCheckPromise = null; });
@@ -294,11 +379,18 @@ class AnkiConnect {
         }
     }
 
+    /**
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     * @returns {Promise<unknown>}
+     */
     async _invoke(action, params) {
+        /** @type {import('anki').MessageBody} */
         const body = {action, params, version: this._localVersion};
         if (this._apiKey !== null) { body.key = this._apiKey; }
         let response;
         try {
+            if (this._server === null) { throw new Error('Server URL is null'); }
             response = await fetch(this._server, {
                 method: 'POST',
                 mode: 'cors',
@@ -312,33 +404,34 @@ class AnkiConnect {
                 body: JSON.stringify(body)
             });
         } catch (e) {
-            const error = new Error('Anki connection failure');
+            const error = new ExtensionError('Anki connection failure');
             error.data = {action, params, originalError: e};
             throw error;
         }
 
         if (!response.ok) {
-            const error = new Error(`Anki connection error: ${response.status}`);
+            const error = new ExtensionError(`Anki connection error: ${response.status}`);
             error.data = {action, params, status: response.status};
             throw error;
         }
 
         let responseText = null;
+        /** @type {unknown} */
         let result;
         try {
             responseText = await response.text();
             result = JSON.parse(responseText);
         } catch (e) {
-            const error = new Error('Invalid Anki response');
+            const error = new ExtensionError('Invalid Anki response');
             error.data = {action, params, status: response.status, responseText, originalError: e};
             throw error;
         }
 
-        if (isObject(result)) {
-            const apiError = result.error;
+        if (typeof result === 'object' && result !== null && !Array.isArray(result)) {
+            const apiError = /** @type {import('core').SerializableObject} */ (result).error;
             if (typeof apiError !== 'undefined') {
-                const error = new Error(`Anki error: ${apiError}`);
-                error.data = {action, params, status: response.status, apiError};
+                const error = new ExtensionError(`Anki error: ${apiError}`);
+                error.data = {action, params, status: response.status, apiError: typeof apiError === 'string' ? apiError : `${apiError}`};
                 throw error;
             }
         }
@@ -346,10 +439,30 @@ class AnkiConnect {
         return result;
     }
 
+    /**
+     * @param {{action: string, params: import('core').SerializableObject}[]} actions
+     * @returns {Promise<unknown[]>}
+     */
+    async _invokeMulti(actions) {
+        const result = await this._invoke('multi', {actions});
+        if (!Array.isArray(result)) {
+            throw this._createUnexpectedResultError('array', result);
+        }
+        return result;
+    }
+
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
     _escapeQuery(text) {
         return text.replace(/"/g, '');
     }
 
+    /**
+     * @param {import('anki').NoteFields} fields
+     * @returns {string}
+     */
     _fieldsToQuery(fields) {
         const fieldNames = Object.keys(fields);
         if (fieldNames.length === 0) {
@@ -360,6 +473,10 @@ class AnkiConnect {
         return `"${key.toLowerCase()}:${this._escapeQuery(fields[key])}"`;
     }
 
+    /**
+     * @param {import('anki').Note} note
+     * @returns {?('collection'|'deck'|'deck-root')}
+     */
     _getDuplicateScopeFromNote(note) {
         const {options} = note;
         if (typeof options === 'object' && options !== null) {
@@ -371,6 +488,10 @@ class AnkiConnect {
         return null;
     }
 
+    /**
+     * @param {import('anki').Note} note
+     * @returns {string}
+     */
     _getNoteQuery(note) {
         let query = '';
         switch (this._getDuplicateScopeFromNote(note)) {
@@ -384,4 +505,121 @@ class AnkiConnect {
         query += this._fieldsToQuery(note.fields);
         return query;
     }
+
+    /**
+     * @returns {Promise<number>}
+     */
+    async _getVersion() {
+        const version = await this._invoke('version', {});
+        return typeof version === 'number' ? version : 0;
+    }
+
+    /**
+     * @param {string} message
+     * @param {unknown} data
+     * @returns {ExtensionError}
+     */
+    _createError(message, data) {
+        const error = new ExtensionError(message);
+        error.data = data;
+        return error;
+    }
+
+    /**
+     * @param {string} expectedType
+     * @param {unknown} result
+     * @param {string} [context]
+     * @returns {ExtensionError}
+     */
+    _createUnexpectedResultError(expectedType, result, context) {
+        return this._createError(`Unexpected type${typeof context === 'string' ? context : ''}: expected ${expectedType}, received ${this._getTypeName(result)}`, result);
+    }
+
+    /**
+     * @param {unknown} value
+     * @returns {string}
+     */
+    _getTypeName(value) {
+        if (value === null) { return 'null'; }
+        return Array.isArray(value) ? 'array' : typeof value;
+    }
+
+    /**
+     * @template [T=unknown]
+     * @param {unknown} result
+     * @param {number} expectedCount
+     * @param {'boolean'|'string'|'number'} type
+     * @param {string} [context]
+     * @returns {T[]}
+     * @throws {Error}
+     */
+    _normalizeArray(result, expectedCount, type, context) {
+        if (!Array.isArray(result)) {
+            throw this._createUnexpectedResultError(`${type}[]`, result, context);
+        }
+        if (expectedCount < 0) {
+            expectedCount = result.length;
+        } else if (expectedCount !== result.length) {
+            throw this._createError(`Unexpected result array size${context}: expected ${expectedCount}, received ${result.length}`, result);
+        }
+        for (let i = 0; i < expectedCount; ++i) {
+            const item = /** @type {unknown} */ (result[i]);
+            if (typeof item !== type) {
+                throw this._createError(`Unexpected result type at index ${i}${context}: expected ${type}, received ${this._getTypeName(item)}`, result);
+            }
+        }
+        return /** @type {T[]} */ (result);
+    }
+
+    /**
+     * @param {unknown} result
+     * @returns {(?import('anki').NoteInfo)[]}
+     * @throws {Error}
+     */
+    _normalizeNoteInfoArray(result) {
+        if (!Array.isArray(result)) {
+            throw this._createUnexpectedResultError('array', result, '');
+        }
+        /** @type {(?import('anki').NoteInfo)[]} */
+        const result2 = [];
+        for (let i = 0, ii = result.length; i < ii; ++i) {
+            const item = /** @type {unknown} */ (result[i]);
+            if (item === null || typeof item !== 'object') {
+                throw this._createError(`Unexpected result type at index ${i}: expected Notes.NoteInfo, received ${this._getTypeName(item)}`, result);
+            }
+            const {noteId} = /** @type {{[key: string]: unknown}} */ (item);
+            if (typeof noteId !== 'number') {
+                result2.push(null);
+                continue;
+            }
+
+            const {tags, fields, modelName, cards} = /** @type {{[key: string]: unknown}} */ (item);
+            if (typeof modelName !== 'string') {
+                throw this._createError(`Unexpected result type at index ${i}, field modelName: expected string, received ${this._getTypeName(modelName)}`, result);
+            }
+            if (typeof fields !== 'object' || fields === null) {
+                throw this._createError(`Unexpected result type at index ${i}, field fields: expected string, received ${this._getTypeName(fields)}`, result);
+            }
+            const tags2 = /** @type {string[]} */ (this._normalizeArray(tags, -1, 'string', ', field tags'));
+            const cards2 = /** @type {number[]} */ (this._normalizeArray(cards, -1, 'number', ', field cards'));
+            /** @type {{[key: string]: import('anki').NoteFieldInfo}} */
+            const fields2 = {};
+            for (const [key, fieldInfo] of Object.entries(fields)) {
+                if (typeof fieldInfo !== 'object' || fieldInfo === null) { continue; }
+                const {value, order} = fieldInfo;
+                if (typeof value !== 'string' || typeof order !== 'number') { continue; }
+                fields2[key] = {value, order};
+            }
+            /** @type {import('anki').NoteInfo} */
+            const item2 = {
+                noteId,
+                tags: tags2,
+                fields: fields2,
+                modelName,
+                cards: cards2
+            };
+            result2.push(item2);
+        }
+        return result2;
+    }
 }
diff --git a/ext/js/comm/api.js b/ext/js/comm/api.js
index de12bb6cb2..b0a8df9907 100644
--- a/ext/js/comm/api.js
+++ b/ext/js/comm/api.js
@@ -17,177 +17,415 @@
  */
 
 class API {
+    /**
+     * @param {Yomichan} yomichan
+     */
     constructor(yomichan) {
+        /** @type {Yomichan} */
         this._yomichan = yomichan;
     }
 
+    /**
+     * @param {import('api').OptionsGetDetails['optionsContext']} optionsContext
+     * @returns {Promise<import('api').OptionsGetResult>}
+     */
     optionsGet(optionsContext) {
-        return this._invoke('optionsGet', {optionsContext});
+        /** @type {import('api').OptionsGetDetails} */
+        const details = {optionsContext};
+        return this._invoke('optionsGet', details);
     }
 
+    /**
+     * @returns {Promise<import('api').OptionsGetFullResult>}
+     */
     optionsGetFull() {
         return this._invoke('optionsGetFull');
     }
 
+    /**
+     * @param {import('api').TermsFindDetails['text']} text
+     * @param {import('api').TermsFindDetails['details']} details
+     * @param {import('api').TermsFindDetails['optionsContext']} optionsContext
+     * @returns {Promise<import('api').TermsFindResult>}
+     */
     termsFind(text, details, optionsContext) {
-        return this._invoke('termsFind', {text, details, optionsContext});
-    }
-
+        /** @type {import('api').TermsFindDetails} */
+        const details2 = {text, details, optionsContext};
+        return this._invoke('termsFind', details2);
+    }
+
+    /**
+     * @param {import('api').ParseTextDetails['text']} text
+     * @param {import('api').ParseTextDetails['optionsContext']} optionsContext
+     * @param {import('api').ParseTextDetails['scanLength']} scanLength
+     * @param {import('api').ParseTextDetails['useInternalParser']} useInternalParser
+     * @param {import('api').ParseTextDetails['useMecabParser']} useMecabParser
+     * @returns {Promise<import('api').ParseTextResult>}
+     */
     parseText(text, optionsContext, scanLength, useInternalParser, useMecabParser) {
-        return this._invoke('parseText', {text, optionsContext, scanLength, useInternalParser, useMecabParser});
+        /** @type {import('api').ParseTextDetails} */
+        const details = {text, optionsContext, scanLength, useInternalParser, useMecabParser};
+        return this._invoke('parseText', details);
     }
 
+    /**
+     * @param {import('api').KanjiFindDetails['text']} text
+     * @param {import('api').KanjiFindDetails['optionsContext']} optionsContext
+     * @returns {Promise<import('api').KanjiFindResult>}
+     */
     kanjiFind(text, optionsContext) {
-        return this._invoke('kanjiFind', {text, optionsContext});
+        /** @type {import('api').KanjiFindDetails} */
+        const details = {text, optionsContext};
+        return this._invoke('kanjiFind', details);
     }
 
+    /**
+     * @returns {Promise<import('api').IsAnkiConnectedResult>}
+     */
     isAnkiConnected() {
         return this._invoke('isAnkiConnected');
     }
 
+    /**
+     * @returns {Promise<import('api').GetAnkiConnectVersionResult>}
+     */
     getAnkiConnectVersion() {
         return this._invoke('getAnkiConnectVersion');
     }
 
+    /**
+     * @param {import('api').AddAnkiNoteDetails['note']} note
+     * @returns {Promise<import('api').AddAnkiNoteResult>}
+     */
     addAnkiNote(note) {
-        return this._invoke('addAnkiNote', {note});
+        /** @type {import('api').AddAnkiNoteDetails} */
+        const details = {note};
+        return this._invoke('addAnkiNote', details);
     }
 
+    /**
+     * @param {import('api').GetAnkiNoteInfoDetails['notes']} notes
+     * @param {import('api').GetAnkiNoteInfoDetails['fetchAdditionalInfo']} fetchAdditionalInfo
+     * @returns {Promise<import('api').GetAnkiNoteInfoResult>}
+     */
     getAnkiNoteInfo(notes, fetchAdditionalInfo) {
-        return this._invoke('getAnkiNoteInfo', {notes, fetchAdditionalInfo});
-    }
-
+        /** @type {import('api').GetAnkiNoteInfoDetails} */
+        const details = {notes, fetchAdditionalInfo};
+        return this._invoke('getAnkiNoteInfo', details);
+    }
+
+    /**
+     * @param {import('api').InjectAnkiNoteMediaDetails['timestamp']} timestamp
+     * @param {import('api').InjectAnkiNoteMediaDetails['definitionDetails']} definitionDetails
+     * @param {import('api').InjectAnkiNoteMediaDetails['audioDetails']} audioDetails
+     * @param {import('api').InjectAnkiNoteMediaDetails['screenshotDetails']} screenshotDetails
+     * @param {import('api').InjectAnkiNoteMediaDetails['clipboardDetails']} clipboardDetails
+     * @param {import('api').InjectAnkiNoteMediaDetails['dictionaryMediaDetails']} dictionaryMediaDetails
+     * @returns {Promise<import('api').InjectAnkiNoteMediaResult>}
+     */
     injectAnkiNoteMedia(timestamp, definitionDetails, audioDetails, screenshotDetails, clipboardDetails, dictionaryMediaDetails) {
-        return this._invoke('injectAnkiNoteMedia', {timestamp, definitionDetails, audioDetails, screenshotDetails, clipboardDetails, dictionaryMediaDetails});
+        /** @type {import('api').InjectAnkiNoteMediaDetails} */
+        const details = {timestamp, definitionDetails, audioDetails, screenshotDetails, clipboardDetails, dictionaryMediaDetails};
+        return this._invoke('injectAnkiNoteMedia', details);
     }
 
+    /**
+     * @param {import('api').NoteViewDetails['noteId']} noteId
+     * @param {import('api').NoteViewDetails['mode']} mode
+     * @param {import('api').NoteViewDetails['allowFallback']} allowFallback
+     * @returns {Promise<import('api').NoteViewResult>}
+     */
     noteView(noteId, mode, allowFallback) {
-        return this._invoke('noteView', {noteId, mode, allowFallback});
+        /** @type {import('api').NoteViewDetails} */
+        const details = {noteId, mode, allowFallback};
+        return this._invoke('noteView', details);
     }
 
+    /**
+     * @param {import('api').SuspendAnkiCardsForNoteDetails['noteId']} noteId
+     * @returns {Promise<import('api').SuspendAnkiCardsForNoteResult>}
+     */
     suspendAnkiCardsForNote(noteId) {
-        return this._invoke('suspendAnkiCardsForNote', {noteId});
+        /** @type {import('api').SuspendAnkiCardsForNoteDetails} */
+        const details = {noteId};
+        return this._invoke('suspendAnkiCardsForNote', details);
     }
 
+    /**
+     * @param {import('api').GetTermAudioInfoListDetails['source']} source
+     * @param {import('api').GetTermAudioInfoListDetails['term']} term
+     * @param {import('api').GetTermAudioInfoListDetails['reading']} reading
+     * @returns {Promise<import('api').GetTermAudioInfoListResult>}
+     */
     getTermAudioInfoList(source, term, reading) {
-        return this._invoke('getTermAudioInfoList', {source, term, reading});
+        /** @type {import('api').GetTermAudioInfoListDetails} */
+        const details = {source, term, reading};
+        return this._invoke('getTermAudioInfoList', details);
     }
 
+    /**
+     * @param {import('api').CommandExecDetails['command']} command
+     * @param {import('api').CommandExecDetails['params']} [params]
+     * @returns {Promise<import('api').CommandExecResult>}
+     */
     commandExec(command, params) {
-        return this._invoke('commandExec', {command, params});
+        /** @type {import('api').CommandExecDetails} */
+        const details = {command, params};
+        return this._invoke('commandExec', details);
     }
 
+    /**
+     * @param {import('api').SendMessageToFrameDetails['frameId']} frameId
+     * @param {import('api').SendMessageToFrameDetails['action']} action
+     * @param {import('api').SendMessageToFrameDetails['params']} [params]
+     * @returns {Promise<import('api').SendMessageToFrameResult>}
+     */
     sendMessageToFrame(frameId, action, params) {
-        return this._invoke('sendMessageToFrame', {frameId, action, params});
+        /** @type {import('api').SendMessageToFrameDetails} */
+        const details = {frameId, action, params};
+        return this._invoke('sendMessageToFrame', details);
     }
 
+    /**
+     * @param {import('api').BroadcastTabDetails['action']} action
+     * @param {import('api').BroadcastTabDetails['params']} params
+     * @returns {Promise<import('api').BroadcastTabResult>}
+     */
     broadcastTab(action, params) {
-        return this._invoke('broadcastTab', {action, params});
+        /** @type {import('api').BroadcastTabDetails} */
+        const details = {action, params};
+        return this._invoke('broadcastTab', details);
     }
 
+    /**
+     * @returns {Promise<import('api').FrameInformationGetResult>}
+     */
     frameInformationGet() {
         return this._invoke('frameInformationGet');
     }
 
+    /**
+     * @param {import('api').InjectStylesheetDetails['type']} type
+     * @param {import('api').InjectStylesheetDetails['value']} value
+     * @returns {Promise<import('api').InjectStylesheetResult>}
+     */
     injectStylesheet(type, value) {
-        return this._invoke('injectStylesheet', {type, value});
+        /** @type {import('api').InjectStylesheetDetails} */
+        const details = {type, value};
+        return this._invoke('injectStylesheet', details);
     }
 
+    /**
+     * @param {import('api').GetStylesheetContentDetails['url']} url
+     * @returns {Promise<import('api').GetStylesheetContentResult>}
+     */
     getStylesheetContent(url) {
-        return this._invoke('getStylesheetContent', {url});
+        /** @type {import('api').GetStylesheetContentDetails} */
+        const details = {url};
+        return this._invoke('getStylesheetContent', details);
     }
 
+    /**
+     * @returns {Promise<import('api').GetEnvironmentInfoResult>}
+     */
     getEnvironmentInfo() {
         return this._invoke('getEnvironmentInfo');
     }
 
+    /**
+     * @returns {Promise<import('api').ClipboardGetResult>}
+     */
     clipboardGet() {
         return this._invoke('clipboardGet');
     }
 
+    /**
+     * @returns {Promise<import('api').GetDisplayTemplatesHtmlResult>}
+     */
     getDisplayTemplatesHtml() {
         return this._invoke('getDisplayTemplatesHtml');
     }
 
+    /**
+     * @returns {Promise<import('api').GetZoomResult>}
+     */
     getZoom() {
         return this._invoke('getZoom');
     }
 
+    /**
+     * @returns {Promise<import('api').GetDefaultAnkiFieldTemplatesResult>}
+     */
     getDefaultAnkiFieldTemplates() {
         return this._invoke('getDefaultAnkiFieldTemplates');
     }
 
+    /**
+     * @returns {Promise<import('api').GetDictionaryInfoResult>}
+     */
     getDictionaryInfo() {
         return this._invoke('getDictionaryInfo');
     }
 
+    /**
+     * @returns {Promise<import('api').PurgeDatabaseResult>}
+     */
     purgeDatabase() {
         return this._invoke('purgeDatabase');
     }
 
+    /**
+     * @param {import('api').GetMediaDetails['targets']} targets
+     * @returns {Promise<import('api').GetMediaResult>}
+     */
     getMedia(targets) {
-        return this._invoke('getMedia', {targets});
+        /** @type {import('api').GetMediaDetails} */
+        const details = {targets};
+        return this._invoke('getMedia', details);
     }
 
+    /**
+     * @param {import('api').LogDetails['error']} error
+     * @param {import('api').LogDetails['level']} level
+     * @param {import('api').LogDetails['context']} context
+     * @returns {Promise<import('api').LogResult>}
+     */
     log(error, level, context) {
-        return this._invoke('log', {error, level, context});
+        /** @type {import('api').LogDetails} */
+        const details = {error, level, context};
+        return this._invoke('log', details);
     }
 
+    /**
+     * @returns {Promise<import('api').LogIndicatorClearResult>}
+     */
     logIndicatorClear() {
         return this._invoke('logIndicatorClear');
     }
 
+    /**
+     * @param {import('api').ModifySettingsDetails['targets']} targets
+     * @param {import('api').ModifySettingsDetails['source']} source
+     * @returns {Promise<import('api').ModifySettingsResult>}
+     */
     modifySettings(targets, source) {
-        return this._invoke('modifySettings', {targets, source});
+        const details = {targets, source};
+        return this._invoke('modifySettings', details);
     }
 
+    /**
+     * @param {import('api').GetSettingsDetails['targets']} targets
+     * @returns {Promise<import('api').GetSettingsResult>}
+     */
     getSettings(targets) {
-        return this._invoke('getSettings', {targets});
+        /** @type {import('api').GetSettingsDetails} */
+        const details = {targets};
+        return this._invoke('getSettings', details);
     }
 
+    /**
+     * @param {import('api').SetAllSettingsDetails['value']} value
+     * @param {import('api').SetAllSettingsDetails['source']} source
+     * @returns {Promise<import('api').SetAllSettingsResult>}
+     */
     setAllSettings(value, source) {
-        return this._invoke('setAllSettings', {value, source});
+        /** @type {import('api').SetAllSettingsDetails} */
+        const details = {value, source};
+        return this._invoke('setAllSettings', details);
     }
 
+    /**
+     * @param {import('api').GetOrCreateSearchPopupDetails} details
+     * @returns {Promise<import('api').GetOrCreateSearchPopupResult>}
+     */
     getOrCreateSearchPopup(details) {
-        return this._invoke('getOrCreateSearchPopup', isObject(details) ? details : {});
+        return this._invoke('getOrCreateSearchPopup', details);
     }
 
+    /**
+     * @param {import('api').IsTabSearchPopupDetails['tabId']} tabId
+     * @returns {Promise<import('api').IsTabSearchPopupResult>}
+     */
     isTabSearchPopup(tabId) {
-        return this._invoke('isTabSearchPopup', {tabId});
+        /** @type {import('api').IsTabSearchPopupDetails} */
+        const details = {tabId};
+        return this._invoke('isTabSearchPopup', details);
     }
 
+    /**
+     * @param {import('api').TriggerDatabaseUpdatedDetails['type']} type
+     * @param {import('api').TriggerDatabaseUpdatedDetails['cause']} cause
+     * @returns {Promise<import('api').TriggerDatabaseUpdatedResult>}
+     */
     triggerDatabaseUpdated(type, cause) {
-        return this._invoke('triggerDatabaseUpdated', {type, cause});
+        /** @type {import('api').TriggerDatabaseUpdatedDetails} */
+        const details = {type, cause};
+        return this._invoke('triggerDatabaseUpdated', details);
     }
 
+    /**
+     * @returns {Promise<import('api').TestMecabResult>}
+     */
     testMecab() {
-        return this._invoke('testMecab', {});
+        return this._invoke('testMecab');
     }
 
+    /**
+     * @param {import('api').TextHasJapaneseCharactersDetails['text']} text
+     * @returns {Promise<import('api').TextHasJapaneseCharactersResult>}
+     */
     textHasJapaneseCharacters(text) {
-        return this._invoke('textHasJapaneseCharacters', {text});
+        /** @type {import('api').TextHasJapaneseCharactersDetails} */
+        const details = {text};
+        return this._invoke('textHasJapaneseCharacters', details);
     }
 
+    /**
+     * @param {import('api').GetTermFrequenciesDetails['termReadingList']} termReadingList
+     * @param {import('api').GetTermFrequenciesDetails['dictionaries']} dictionaries
+     * @returns {Promise<import('api').GetTermFrequenciesResult>}
+     */
     getTermFrequencies(termReadingList, dictionaries) {
-        return this._invoke('getTermFrequencies', {termReadingList, dictionaries});
+        /** @type {import('api').GetTermFrequenciesDetails} */
+        const details = {termReadingList, dictionaries};
+        return this._invoke('getTermFrequencies', details);
     }
 
+    /**
+     * @param {import('api').FindAnkiNotesDetails['query']} query
+     * @returns {Promise<import('api').FindAnkiNotesResult>}
+     */
     findAnkiNotes(query) {
-        return this._invoke('findAnkiNotes', {query});
+        /** @type {import('api').FindAnkiNotesDetails} */
+        const details = {query};
+        return this._invoke('findAnkiNotes', details);
     }
 
+    /**
+     * @param {import('api').LoadExtensionScriptsDetails['files']} files
+     * @returns {Promise<import('api').LoadExtensionScriptsResult>}
+     */
     loadExtensionScripts(files) {
-        return this._invoke('loadExtensionScripts', {files});
+        /** @type {import('api').LoadExtensionScriptsDetails} */
+        const details = {files};
+        return this._invoke('loadExtensionScripts', details);
     }
 
     // Utilities
 
-    _createActionPort(timeout=5000) {
+    /**
+     * @param {number} timeout
+     * @returns {Promise<chrome.runtime.Port>}
+     */
+    _createActionPort(timeout) {
         return new Promise((resolve, reject) => {
+            /** @type {?number} */
             let timer = null;
             const portDetails = deferPromise();
 
+            /**
+             * @param {chrome.runtime.Port} port
+             */
             const onConnect = async (port) => {
                 try {
                     const {name: expectedName, id: expectedId} = await portDetails.promise;
@@ -204,6 +442,9 @@ class API {
                 resolve(port);
             };
 
+            /**
+             * @param {Error} e
+             */
             const onError = (e) => {
                 if (timer !== null) {
                     clearTimeout(timer);
@@ -221,14 +462,24 @@ class API {
         });
     }
 
-    _invokeWithProgress(action, params, onProgress, timeout=5000) {
+    /**
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     * @param {?(...args: unknown[]) => void} onProgress0
+     * @param {number} [timeout]
+     * @returns {Promise<TReturn>}
+     */
+    _invokeWithProgress(action, params, onProgress0, timeout=5000) {
         return new Promise((resolve, reject) => {
+            /** @type {?chrome.runtime.Port} */
             let port = null;
 
-            if (typeof onProgress !== 'function') {
-                onProgress = () => {};
-            }
+            const onProgress = typeof onProgress0 === 'function' ? onProgress0 : () => {};
 
+            /**
+             * @param {import('backend').InvokeWithProgressResponseMessage<TReturn>} message
+             */
             const onMessage = (message) => {
                 switch (message.type) {
                     case 'progress':
@@ -244,7 +495,7 @@ class API {
                         break;
                     case 'error':
                         cleanup();
-                        reject(deserializeError(message.data));
+                        reject(ExtensionError.deserialize(message.data));
                         break;
                 }
             };
@@ -261,7 +512,6 @@ class API {
                     port.disconnect();
                     port = null;
                 }
-                onProgress = null;
             };
 
             (async () => {
@@ -275,20 +525,23 @@ class API {
                     const fragmentSize = 1e7; // 10 MB
                     for (let i = 0, ii = messageString.length; i < ii; i += fragmentSize) {
                         const data = messageString.substring(i, i + fragmentSize);
-                        port.postMessage({action: 'fragment', data});
+                        port.postMessage(/** @type {import('backend').InvokeWithProgressRequestFragmentMessage} */ ({action: 'fragment', data}));
                     }
-                    port.postMessage({action: 'invoke'});
+                    port.postMessage(/** @type {import('backend').InvokeWithProgressRequestInvokeMessage} */ ({action: 'invoke'}));
                 } catch (e) {
                     cleanup();
                     reject(e);
-                } finally {
-                    action = null;
-                    params = null;
                 }
             })();
         });
     }
 
+    /**
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {import('core').SerializableObject} [params]
+     * @returns {Promise<TReturn>}
+     */
     _invoke(action, params={}) {
         const data = {action, params};
         return new Promise((resolve, reject) => {
@@ -297,7 +550,7 @@ class API {
                     this._checkLastError(chrome.runtime.lastError);
                     if (response !== null && typeof response === 'object') {
                         if (typeof response.error !== 'undefined') {
-                            reject(deserializeError(response.error));
+                            reject(ExtensionError.deserialize(response.error));
                         } else {
                             resolve(response.result);
                         }
@@ -312,7 +565,10 @@ class API {
         });
     }
 
-    _checkLastError() {
+    /**
+     * @param {chrome.runtime.LastError|undefined} _ignore
+     */
+    _checkLastError(_ignore) {
         // NOP
     }
 }
diff --git a/ext/js/comm/clipboard-monitor.js b/ext/js/comm/clipboard-monitor.js
index fbf56432a2..aa4ce908c2 100644
--- a/ext/js/comm/clipboard-monitor.js
+++ b/ext/js/comm/clipboard-monitor.js
@@ -16,17 +16,32 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/**
+ * @augments EventDispatcher<import('clipboard-monitor').EventType>
+ */
 class ClipboardMonitor extends EventDispatcher {
+    /**
+     * @param {{japaneseUtil: JapaneseUtil, clipboardReader: import('clipboard-monitor').ClipboardReaderLike}} details
+     */
     constructor({japaneseUtil, clipboardReader}) {
         super();
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
+        /** @type {import('clipboard-monitor').ClipboardReaderLike} */
         this._clipboardReader = clipboardReader;
+        /** @type {?number} */
         this._timerId = null;
+        /** @type {?import('core').TokenObject} */
         this._timerToken = null;
+        /** @type {number} */
         this._interval = 250;
+        /** @type {?string} */
         this._previousText = null;
     }
 
+    /**
+     * @returns {void}
+     */
     start() {
         this.stop();
 
@@ -34,6 +49,7 @@ class ClipboardMonitor extends EventDispatcher {
         // hasn't been started during the await call. The check below the await call
         // will exit early if the reference has changed.
         let canChange = false;
+        /** @type {?import('core').TokenObject} */
         const token = {};
         const intervalCallback = async () => {
             this._timerId = null;
@@ -53,7 +69,7 @@ class ClipboardMonitor extends EventDispatcher {
             ) {
                 this._previousText = text;
                 if (canChange && this._japaneseUtil.isStringPartiallyJapanese(text)) {
-                    this.trigger('change', {text});
+                    this.trigger('change', /** @type {import('clipboard-monitor').ChangeEvent} */ ({text}));
                 }
             }
 
@@ -66,6 +82,9 @@ class ClipboardMonitor extends EventDispatcher {
         intervalCallback();
     }
 
+    /**
+     * @returns {void}
+     */
     stop() {
         this._timerToken = null;
         this._previousText = null;
@@ -75,6 +94,9 @@ class ClipboardMonitor extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {?string} text
+     */
     setPreviousText(text) {
         this._previousText = text;
     }
diff --git a/ext/js/comm/clipboard-reader.js b/ext/js/comm/clipboard-reader.js
index 1ea507b87c..b6540389f2 100644
--- a/ext/js/comm/clipboard-reader.js
+++ b/ext/js/comm/clipboard-reader.js
@@ -26,17 +26,20 @@
 class ClipboardReader {
     /**
      * Creates a new instances of a clipboard reader.
-     * @param {object} details Details about how to set up the instance.
-     * @param {?Document} details.document The Document object to be used, or null for no support.
-     * @param {?string} details.pasteTargetSelector The selector for the paste target element.
-     * @param {?string} details.richContentPasteTargetSelector The selector for the rich content paste target element.
+     * @param {{document: ?Document, pasteTargetSelector: ?string, richContentPasteTargetSelector: ?string}} details Details about how to set up the instance.
      */
     constructor({document=null, pasteTargetSelector=null, richContentPasteTargetSelector=null}) {
+        /** @type {?Document} */
         this._document = document;
+        /** @type {?string} */
         this._browser = null;
+        /** @type {?HTMLTextAreaElement} */
         this._pasteTarget = null;
+        /** @type {?string} */
         this._pasteTargetSelector = pasteTargetSelector;
+        /** @type {?HTMLElement} */
         this._richContentPasteTarget = null;
+        /** @type {?string} */
         this._richContentPasteTargetSelector = richContentPasteTargetSelector;
     }
 
@@ -58,7 +61,7 @@ class ClipboardReader {
     /**
      * Gets the text in the clipboard.
      * @param {boolean} useRichText Whether or not to use rich text for pasting, when possible.
-     * @returns {string} A string containing the clipboard text.
+     * @returns {Promise<string>} A string containing the clipboard text.
      * @throws {Error} Error if not supported.
      */
     async getText(useRichText) {
@@ -92,7 +95,7 @@ class ClipboardReader {
             const target = this._getRichContentPasteTarget();
             target.focus();
             document.execCommand('paste');
-            const result = target.textContent;
+            const result = /** @type {string} */ (target.textContent);
             this._clearRichContent(target);
             return result;
         } else {
@@ -108,7 +111,7 @@ class ClipboardReader {
 
     /**
      * Gets the first image in the clipboard.
-     * @returns {string} A string containing a data URL of the image file, or null if no image was found.
+     * @returns {Promise<?string>} A string containing a data URL of the image file, or null if no image was found.
      * @throws {Error} Error if not supported.
      */
     async getImage() {
@@ -157,35 +160,62 @@ class ClipboardReader {
 
     // Private
 
+    /**
+     * @returns {boolean}
+     */
     _isFirefox() {
         return (this._browser === 'firefox' || this._browser === 'firefox-mobile');
     }
 
+    /**
+     * @param {Blob} file
+     * @returns {Promise<string>}
+     */
     _readFileAsDataURL(file) {
         return new Promise((resolve, reject) => {
             const reader = new FileReader();
-            reader.onload = () => resolve(reader.result);
+            reader.onload = () => resolve(/** @type {string} */ (reader.result));
             reader.onerror = () => reject(reader.error);
             reader.readAsDataURL(file);
         });
     }
 
+    /**
+     * @returns {HTMLTextAreaElement}
+     */
     _getPasteTarget() {
-        if (this._pasteTarget === null) { this._pasteTarget = this._findPasteTarget(this._pasteTargetSelector); }
+        if (this._pasteTarget === null) {
+            this._pasteTarget = /** @type {HTMLTextAreaElement} */ (this._findPasteTarget(this._pasteTargetSelector));
+        }
         return this._pasteTarget;
     }
 
+    /**
+     * @returns {HTMLElement}
+     */
     _getRichContentPasteTarget() {
-        if (this._richContentPasteTarget === null) { this._richContentPasteTarget = this._findPasteTarget(this._richContentPasteTargetSelector); }
+        if (this._richContentPasteTarget === null) {
+            this._richContentPasteTarget = /** @type {HTMLElement} */ (this._findPasteTarget(this._richContentPasteTargetSelector));
+        }
         return this._richContentPasteTarget;
     }
 
+    /**
+     * @template {Element} T
+     * @param {?string} selector
+     * @returns {T}
+     * @throws {Error}
+     */
     _findPasteTarget(selector) {
-        const target = this._document.querySelector(selector);
+        if (selector === null) { throw new Error('Invalid selector'); }
+        const target = this._document !== null ? this._document.querySelector(selector) : null;
         if (target === null) { throw new Error('Clipboard paste target does not exist'); }
-        return target;
+        return /** @type {T} */ (target);
     }
 
+    /**
+     * @param {HTMLElement} element
+     */
     _clearRichContent(element) {
         for (const image of element.querySelectorAll('img')) {
             image.removeAttribute('src');
diff --git a/ext/js/comm/cross-frame-api.js b/ext/js/comm/cross-frame-api.js
index 7892eb4cec..6c5ffa7723 100644
--- a/ext/js/comm/cross-frame-api.js
+++ b/ext/js/comm/cross-frame-api.js
@@ -16,31 +16,62 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/**
+ * @augments EventDispatcher<import('cross-frame-api').CrossFrameAPIPortEventType>
+ */
 class CrossFrameAPIPort extends EventDispatcher {
+    /**
+     * @param {?number} otherTabId
+     * @param {number} otherFrameId
+     * @param {chrome.runtime.Port} port
+     * @param {import('core').MessageHandlerMap} messageHandlers
+     */
     constructor(otherTabId, otherFrameId, port, messageHandlers) {
         super();
+        /** @type {?number} */
         this._otherTabId = otherTabId;
+        /** @type {number} */
         this._otherFrameId = otherFrameId;
+        /** @type {?chrome.runtime.Port} */
         this._port = port;
+        /** @type {import('core').MessageHandlerMap} */
         this._messageHandlers = messageHandlers;
+        /** @type {Map<number, import('cross-frame-api').Invocation>} */
         this._activeInvocations = new Map();
+        /** @type {number} */
         this._invocationId = 0;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
     }
 
+    /** @type {?number} */
     get otherTabId() {
         return this._otherTabId;
     }
 
+    /** @type {number} */
     get otherFrameId() {
         return this._otherFrameId;
     }
 
+    /**
+     * @throws {Error}
+     */
     prepare() {
+        if (this._port === null) { throw new Error('Invalid state'); }
         this._eventListeners.addListener(this._port.onDisconnect, this._onDisconnect.bind(this));
         this._eventListeners.addListener(this._port.onMessage, this._onMessage.bind(this));
     }
 
+    /**
+     * @template [TParams=import('core').SerializableObject]
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @param {number} ackTimeout
+     * @param {number} responseTimeout
+     * @returns {Promise<TReturn>}
+     */
     invoke(action, params, ackTimeout, responseTimeout) {
         return new Promise((resolve, reject) => {
             if (this._port === null) {
@@ -49,6 +80,7 @@ class CrossFrameAPIPort extends EventDispatcher {
             }
 
             const id = this._invocationId++;
+            /** @type {import('cross-frame-api').Invocation} */
             const invocation = {
                 id,
                 resolve,
@@ -70,19 +102,21 @@ class CrossFrameAPIPort extends EventDispatcher {
             }
 
             try {
-                this._port.postMessage({type: 'invoke', id, data: {action, params}});
+                this._port.postMessage(/** @type {import('cross-frame-api').InvokeMessage} */ ({type: 'invoke', id, data: {action, params}}));
             } catch (e) {
                 this._onError(id, e);
             }
         });
     }
 
+    /** */
     disconnect() {
         this._onDisconnect();
     }
 
     // Private
 
+    /** */
     _onDisconnect() {
         if (this._port === null) { return; }
         this._eventListeners.removeAllEventListeners();
@@ -93,22 +127,29 @@ class CrossFrameAPIPort extends EventDispatcher {
         this.trigger('disconnect', this);
     }
 
-    _onMessage({type, id, data}) {
+    /**
+     * @param {import('cross-frame-api').Message} details
+     */
+    _onMessage(details) {
+        const {type, id} = details;
         switch (type) {
             case 'invoke':
-                this._onInvoke(id, data);
+                this._onInvoke(id, details.data);
                 break;
             case 'ack':
                 this._onAck(id);
                 break;
             case 'result':
-                this._onResult(id, data);
+                this._onResult(id, details.data);
                 break;
         }
     }
 
     // Response handlers
 
+    /**
+     * @param {number} id
+     */
     _onAck(id) {
         const invocation = this._activeInvocations.get(id);
         if (typeof invocation === 'undefined') {
@@ -138,6 +179,10 @@ class CrossFrameAPIPort extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} id
+     * @param {import('core').Response<unknown>} data
+     */
     _onResult(id, data) {
         const invocation = this._activeInvocations.get(id);
         if (typeof invocation === 'undefined') {
@@ -159,17 +204,21 @@ class CrossFrameAPIPort extends EventDispatcher {
 
         const error = data.error;
         if (typeof error !== 'undefined') {
-            invocation.reject(deserializeError(error));
+            invocation.reject(ExtensionError.deserialize(error));
         } else {
             invocation.resolve(data.result);
         }
     }
 
+    /**
+     * @param {number} id
+     * @param {unknown} error
+     */
     _onError(id, error) {
         const invocation = this._activeInvocations.get(id);
         if (typeof invocation === 'undefined') { return; }
 
-        if (typeof error === 'string') {
+        if (!(error instanceof Error)) {
             error = new Error(`${error} (${invocation.action})`);
         }
 
@@ -183,6 +232,11 @@ class CrossFrameAPIPort extends EventDispatcher {
 
     // Invocation
 
+    /**
+     * @param {number} id
+     * @param {import('cross-frame-api').InvocationData} details
+     * @returns {boolean}
+     */
     _onInvoke(id, {action, params}) {
         const messageHandler = this._messageHandlers.get(action);
         this._sendAck(id);
@@ -191,10 +245,17 @@ class CrossFrameAPIPort extends EventDispatcher {
             return false;
         }
 
+        /**
+         * @param {import('core').Response<unknown>} data
+         * @returns {void}
+         */
         const callback = (data) => this._sendResult(id, data);
         return invokeMessageHandler(messageHandler, params, callback);
     }
 
+    /**
+     * @param {import('cross-frame-api').Message} data
+     */
     _sendResponse(data) {
         if (this._port === null) { return; }
         try {
@@ -204,42 +265,80 @@ class CrossFrameAPIPort extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} id
+     */
     _sendAck(id) {
         this._sendResponse({type: 'ack', id});
     }
 
+    /**
+     * @param {number} id
+     * @param {import('core').Response<unknown>} data
+     */
     _sendResult(id, data) {
         this._sendResponse({type: 'result', id, data});
     }
 
+    /**
+     * @param {number} id
+     * @param {Error} error
+     */
     _sendError(id, error) {
-        this._sendResponse({type: 'result', id, data: {error: serializeError(error)}});
+        this._sendResponse({type: 'result', id, data: {error: ExtensionError.serialize(error)}});
     }
 }
 
 class CrossFrameAPI {
     constructor() {
+        /** @type {number} */
         this._ackTimeout = 3000; // 3 seconds
+        /** @type {number} */
         this._responseTimeout = 10000; // 10 seconds
+        /** @type {Map<?number, Map<number, CrossFrameAPIPort>>} */
         this._commPorts = new Map();
+        /** @type {import('core').MessageHandlerMap} */
         this._messageHandlers = new Map();
+        /** @type {(port: CrossFrameAPIPort) => void} */
         this._onDisconnectBind = this._onDisconnect.bind(this);
     }
 
+    /** */
     prepare() {
         chrome.runtime.onConnect.addListener(this._onConnect.bind(this));
     }
 
-    invoke(targetFrameId, action, params={}) {
+    /**
+     * @template [TParams=import('core').SerializableObject]
+     * @template [TReturn=unknown]
+     * @param {number} targetFrameId
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn>}
+     */
+    invoke(targetFrameId, action, params) {
         return this.invokeTab(null, targetFrameId, action, params);
     }
 
-    async invokeTab(targetTabId, targetFrameId, action, params={}) {
+    /**
+     * @template [TParams=import('core').SerializableObject]
+     * @template [TReturn=unknown]
+     * @param {?number} targetTabId
+     * @param {number} targetFrameId
+     * @param {string} action
+     * @param {TParams} params
+     * @returns {Promise<TReturn>}
+     */
+    async invokeTab(targetTabId, targetFrameId, action, params) {
         if (typeof targetTabId !== 'number') { targetTabId = null; }
         const commPort = this._getOrCreateCommPort(targetTabId, targetFrameId);
         return await commPort.invoke(action, params, this._ackTimeout, this._responseTimeout);
     }
 
+    /**
+     * @param {import('core').MessageHandlerArray} messageHandlers
+     * @throws {Error}
+     */
     registerHandlers(messageHandlers) {
         for (const [key, value] of messageHandlers) {
             if (this._messageHandlers.has(key)) {
@@ -249,12 +348,19 @@ class CrossFrameAPI {
         }
     }
 
+    /**
+     * @param {string} key
+     * @returns {boolean}
+     */
     unregisterHandler(key) {
         return this._messageHandlers.delete(key);
     }
 
     // Private
 
+    /**
+     * @param {chrome.runtime.Port} port
+     */
     _onConnect(port) {
         try {
             let details;
@@ -274,6 +380,9 @@ class CrossFrameAPI {
         }
     }
 
+    /**
+     * @param {CrossFrameAPIPort} commPort
+     */
     _onDisconnect(commPort) {
         commPort.off('disconnect', this._onDisconnectBind);
         const {otherTabId, otherFrameId} = commPort;
@@ -286,6 +395,11 @@ class CrossFrameAPI {
         }
     }
 
+    /**
+     * @param {?number} otherTabId
+     * @param {number} otherFrameId
+     * @returns {CrossFrameAPIPort}
+     */
     _getOrCreateCommPort(otherTabId, otherFrameId) {
         const tabPorts = this._commPorts.get(otherTabId);
         if (typeof tabPorts !== 'undefined') {
@@ -297,6 +411,11 @@ class CrossFrameAPI {
         return this._createCommPort(otherTabId, otherFrameId);
     }
 
+    /**
+     * @param {?number} otherTabId
+     * @param {number} otherFrameId
+     * @returns {CrossFrameAPIPort}
+     */
     _createCommPort(otherTabId, otherFrameId) {
         const details = {
             name: 'background-cross-frame-communication-port',
@@ -307,6 +426,12 @@ class CrossFrameAPI {
         return this._setupCommPort(otherTabId, otherFrameId, port);
     }
 
+    /**
+     * @param {?number} otherTabId
+     * @param {number} otherFrameId
+     * @param {chrome.runtime.Port} port
+     * @returns {CrossFrameAPIPort}
+     */
     _setupCommPort(otherTabId, otherFrameId, port) {
         const commPort = new CrossFrameAPIPort(otherTabId, otherFrameId, port, this._messageHandlers);
         let tabPorts = this._commPorts.get(otherTabId);
diff --git a/ext/js/comm/frame-ancestry-handler.js b/ext/js/comm/frame-ancestry-handler.js
index c2e79733c3..6309eb0038 100644
--- a/ext/js/comm/frame-ancestry-handler.js
+++ b/ext/js/comm/frame-ancestry-handler.js
@@ -28,11 +28,17 @@ class FrameAncestryHandler {
      * @param {number} frameId The frame ID of the current frame the instance is instantiated in.
      */
     constructor(frameId) {
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {boolean} */
         this._isPrepared = false;
+        /** @type {string} */
         this._requestMessageId = 'FrameAncestryHandler.requestFrameInfo';
+        /** @type {string} */
         this._responseMessageIdBase = `${this._requestMessageId}.response.`;
+        /** @type {?Promise<number[]>} */
         this._getFrameAncestryInfoPromise = null;
+        /** @type {Map<number, {window: Window, frameElement: ?(undefined|Element)}>} */
         this._childFrameMap = new Map();
     }
 
@@ -65,7 +71,7 @@ class FrameAncestryHandler {
      * Gets the frame ancestry information for the current frame. If the frame is the
      * root frame, an empty array is returned. Otherwise, an array of frame IDs is returned,
      * starting from the nearest ancestor.
-     * @returns {number[]} An array of frame IDs corresponding to the ancestors of the current frame.
+     * @returns {Promise<number[]>} An array of frame IDs corresponding to the ancestors of the current frame.
      */
     async getFrameAncestryInfo() {
         if (this._getFrameAncestryInfoPromise === null) {
@@ -79,7 +85,7 @@ class FrameAncestryHandler {
      * For this function to work, the `getFrameAncestryInfo` function needs to have
      * been invoked previously.
      * @param {number} frameId The frame ID of the child frame to get.
-     * @returns {HTMLElement} The element corresponding to the frame with ID `frameId`, otherwise `null`.
+     * @returns {?Element} The element corresponding to the frame with ID `frameId`, otherwise `null`.
      */
     getChildFrameElement(frameId) {
         const frameInfo = this._childFrameMap.get(frameId);
@@ -96,6 +102,10 @@ class FrameAncestryHandler {
 
     // Private
 
+    /**
+     * @param {number} [timeout]
+     * @returns {Promise<number[]>}
+     */
     _getFrameAncestryInfo(timeout=5000) {
         return new Promise((resolve, reject) => {
             const targetWindow = window.parent;
@@ -107,7 +117,9 @@ class FrameAncestryHandler {
             const uniqueId = generateId(16);
             let nonce = generateId(16);
             const responseMessageId = `${this._responseMessageIdBase}${uniqueId}`;
+            /** @type {number[]} */
             const results = [];
+            /** @type {?number} */
             let timer = null;
 
             const cleanup = () => {
@@ -117,6 +129,10 @@ class FrameAncestryHandler {
                 }
                 yomichan.crossFrame.unregisterHandler(responseMessageId);
             };
+            /**
+             * @param {import('frame-ancestry-handler').RequestFrameInfoResponseParams} params
+             * @returns {?import('frame-ancestry-handler').RequestFrameInfoResponseReturn}
+             */
             const onMessage = (params) => {
                 if (params.nonce !== nonce) { return null; }
 
@@ -152,24 +168,35 @@ class FrameAncestryHandler {
         });
     }
 
+    /**
+     * @param {MessageEvent<unknown>} event
+     */
     _onWindowMessage(event) {
-        const {source} = event;
-        if (source === window || source.parent !== window) { return; }
+        const source = /** @type {?Window} */ (event.source);
+        if (source === null || source === window || source.parent !== window) { return; }
 
         const {data} = event;
-        if (
-            typeof data === 'object' &&
-            data !== null &&
-            data.action === this._requestMessageId
-        ) {
-            this._onRequestFrameInfo(data.params, source);
-        }
+        if (typeof data !== 'object' || data === null) { return; }
+
+        const {action} = /** @type {import('core').SerializableObject} */ (data);
+        if (action !== this._requestMessageId) { return; }
+
+        const {params} = /** @type {import('core').SerializableObject} */ (data);
+        if (typeof params !== 'object' || params === null) { return; }
+
+        this._onRequestFrameInfo(/** @type {import('core').SerializableObject} */ (params), source);
     }
 
+    /**
+     * @param {import('core').SerializableObject} params
+     * @param {Window} source
+     */
     async _onRequestFrameInfo(params, source) {
         try {
             let {originFrameId, childFrameId, uniqueId, nonce} = params;
             if (
+                typeof originFrameId !== 'number' ||
+                typeof childFrameId !== 'number' ||
                 !this._isNonNegativeInteger(originFrameId) ||
                 typeof uniqueId !== 'string' ||
                 typeof nonce !== 'string'
@@ -180,13 +207,17 @@ class FrameAncestryHandler {
             const frameId = this._frameId;
             const {parent} = window;
             const more = (window !== parent);
+            /** @type {import('frame-ancestry-handler').RequestFrameInfoResponseParams} */
             const responseParams = {frameId, nonce, more};
             const responseMessageId = `${this._responseMessageIdBase}${uniqueId}`;
 
             try {
+                /** @type {?import('frame-ancestry-handler').RequestFrameInfoResponseReturn} */
                 const response = await yomichan.crossFrame.invoke(originFrameId, responseMessageId, responseParams);
                 if (response === null) { return; }
-                nonce = response.nonce;
+                const nonce2 = response.nonce;
+                if (typeof nonce2 !== 'string') { return; }
+                nonce = nonce2;
             } catch (e) {
                 return;
             }
@@ -196,13 +227,20 @@ class FrameAncestryHandler {
             }
 
             if (more) {
-                this._requestFrameInfo(parent, originFrameId, frameId, uniqueId, nonce);
+                this._requestFrameInfo(parent, originFrameId, frameId, uniqueId, /** @type {string} */ (nonce));
             }
         } catch (e) {
             // NOP
         }
     }
 
+    /**
+     * @param {Window} targetWindow
+     * @param {number} originFrameId
+     * @param {number} childFrameId
+     * @param {string} uniqueId
+     * @param {string} nonce
+     */
     _requestFrameInfo(targetWindow, originFrameId, childFrameId, uniqueId, nonce) {
         targetWindow.postMessage({
             action: this._requestMessageId,
@@ -210,15 +248,22 @@ class FrameAncestryHandler {
         }, '*');
     }
 
+    /**
+     * @param {number} value
+     * @returns {boolean}
+     */
     _isNonNegativeInteger(value) {
         return (
-            typeof value === 'number' &&
             Number.isFinite(value) &&
             value >= 0 &&
             Math.floor(value) === value
         );
     }
 
+    /**
+     * @param {Window} contentWindow
+     * @returns {?Element}
+     */
     _findFrameElementWithContentWindow(contentWindow) {
         // Check frameElement, for non-null same-origin frames
         try {
@@ -229,9 +274,9 @@ class FrameAncestryHandler {
         }
 
         // Check frames
-        const frameTypes = ['iframe', 'frame', 'embed'];
+        const frameTypes = ['iframe', 'frame', 'object'];
         for (const frameType of frameTypes) {
-            for (const frame of document.getElementsByTagName(frameType)) {
+            for (const frame of /** @type {HTMLCollectionOf<import('extension').HtmlElementWithContentWindow>} */ (document.getElementsByTagName(frameType))) {
                 if (frame.contentWindow === contentWindow) {
                     return frame;
                 }
@@ -239,20 +284,24 @@ class FrameAncestryHandler {
         }
 
         // Check for shadow roots
+        /** @type {Node[]} */
         const rootElements = [document.documentElement];
         while (rootElements.length > 0) {
-            const rootElement = rootElements.shift();
+            const rootElement = /** @type {Node} */ (rootElements.shift());
             const walker = document.createTreeWalker(rootElement, NodeFilter.SHOW_ELEMENT);
             while (walker.nextNode()) {
-                const element = walker.currentNode;
+                const element = /** @type {Element} */ (walker.currentNode);
 
+                // @ts-ignore - this is more simple to elide any type checks or casting
                 if (element.contentWindow === contentWindow) {
                     return element;
                 }
 
+                /** @type {?ShadowRoot|undefined} */
                 const shadowRoot = (
                     element.shadowRoot ||
-                    element.openOrClosedShadowRoot // Available to Firefox 63+ for WebExtensions
+                    // @ts-ignore - openOrClosedShadowRoot is available to Firefox 63+ for WebExtensions
+                    element.openOrClosedShadowRoot
                 );
                 if (shadowRoot) {
                     rootElements.push(shadowRoot);
diff --git a/ext/js/comm/frame-client.js b/ext/js/comm/frame-client.js
index 46b1f50204..1eac2e10ea 100644
--- a/ext/js/comm/frame-client.js
+++ b/ext/js/comm/frame-client.js
@@ -18,47 +18,81 @@
 
 class FrameClient {
     constructor() {
+        /** @type {?string} */
         this._secret = null;
+        /** @type {?string} */
         this._token = null;
+        /** @type {?number} */
         this._frameId = null;
     }
 
+    /** @type {number} */
     get frameId() {
+        if (this._frameId === null) { throw new Error('Not connected'); }
         return this._frameId;
     }
 
+    /**
+     * @param {import('extension').HtmlElementWithContentWindow} frame
+     * @param {string} targetOrigin
+     * @param {number} hostFrameId
+     * @param {import('frame-client').SetupFrameFunction} setupFrame
+     * @param {number} [timeout]
+     */
     async connect(frame, targetOrigin, hostFrameId, setupFrame, timeout=10000) {
-        const {secret, token, frameId} = await this._connectIternal(frame, targetOrigin, hostFrameId, setupFrame, timeout);
+        const {secret, token, frameId} = await this._connectInternal(frame, targetOrigin, hostFrameId, setupFrame, timeout);
         this._secret = secret;
         this._token = token;
         this._frameId = frameId;
     }
 
+    /**
+     * @returns {boolean}
+     */
     isConnected() {
         return (this._secret !== null);
     }
 
+    /**
+     * @template T
+     * @param {T} data
+     * @returns {import('frame-client').Message<T>}
+     * @throws {Error}
+     */
     createMessage(data) {
         if (!this.isConnected()) {
             throw new Error('Not connected');
         }
         return {
-            token: this._token,
-            secret: this._secret,
+            token: /** @type {string} */ (this._token),
+            secret: /** @type {string} */ (this._secret),
             data
         };
     }
 
-    _connectIternal(frame, targetOrigin, hostFrameId, setupFrame, timeout) {
+    /**
+     * @param {import('extension').HtmlElementWithContentWindow} frame
+     * @param {string} targetOrigin
+     * @param {number} hostFrameId
+     * @param {(frame: import('extension').HtmlElementWithContentWindow) => void} setupFrame
+     * @param {number} timeout
+     * @returns {Promise<{secret: string, token: string, frameId: number}>}
+     */
+    _connectInternal(frame, targetOrigin, hostFrameId, setupFrame, timeout) {
         return new Promise((resolve, reject) => {
             const tokenMap = new Map();
+            /** @type {?number} */
             let timer = null;
-            let {
-                promise: frameLoadedPromise,
-                resolve: frameLoadedResolve,
-                reject: frameLoadedReject
-            } = deferPromise();
-
+            const deferPromiseDetails = /** @type {import('core').DeferredPromiseDetails<void>} */ (deferPromise());
+            const frameLoadedPromise = deferPromiseDetails.promise;
+            let frameLoadedResolve = /** @type {?() => void} */ (deferPromiseDetails.resolve);
+            let frameLoadedReject = /** @type {?(reason?: import('core').RejectionReason) => void} */ (deferPromiseDetails.reject);
+
+            /**
+             * @param {string} action
+             * @param {import('core').SerializableObject} params
+             * @throws {Error}
+             */
             const postMessage = (action, params) => {
                 const contentWindow = frame.contentWindow;
                 if (contentWindow === null) { throw new Error('Frame missing content window'); }
@@ -74,11 +108,15 @@ class FrameClient {
                 contentWindow.postMessage({action, params}, targetOrigin);
             };
 
+            /** @type {import('extension').ChromeRuntimeOnMessageCallback<import('extension').ChromeRuntimeMessageWithFrameId>} */
             const onMessage = (message) => {
                 onMessageInner(message);
                 return false;
             };
 
+            /**
+             * @param {import('extension').ChromeRuntimeMessageWithFrameId} message
+             */
             const onMessageInner = async (message) => {
                 try {
                     if (!isObject(message)) { return; }
@@ -90,7 +128,7 @@ class FrameClient {
                     switch (action) {
                         case 'frameEndpointReady':
                             {
-                                const {secret} = params;
+                                const {secret} = /** @type {import('frame-client').FrameEndpointReadyDetails} */ (params);
                                 const token = generateId(16);
                                 tokenMap.set(secret, token);
                                 postMessage('frameEndpointConnect', {secret, token, hostFrameId});
@@ -98,10 +136,10 @@ class FrameClient {
                             break;
                         case 'frameEndpointConnected':
                             {
-                                const {secret, token} = params;
+                                const {secret, token} = /** @type {import('frame-client').FrameEndpointConnectedDetails} */ (params);
                                 const frameId = message.frameId;
                                 const token2 = tokenMap.get(secret);
-                                if (typeof token2 !== 'undefined' && token === token2) {
+                                if (typeof token2 !== 'undefined' && token === token2 && typeof frameId === 'number') {
                                     cleanup();
                                     resolve({secret, token, frameId});
                                 }
@@ -166,6 +204,10 @@ class FrameClient {
         });
     }
 
+    /**
+     * @param {import('extension').HtmlElementWithContentWindow} frame
+     * @returns {boolean}
+     */
     static isFrameAboutBlank(frame) {
         try {
             const contentDocument = frame.contentDocument;
diff --git a/ext/js/comm/frame-endpoint.js b/ext/js/comm/frame-endpoint.js
index dad9f40e04..99245b15de 100644
--- a/ext/js/comm/frame-endpoint.js
+++ b/ext/js/comm/frame-endpoint.js
@@ -18,45 +18,68 @@
 
 class FrameEndpoint {
     constructor() {
+        /** @type {string} */
         this._secret = generateId(16);
+        /** @type {?string} */
         this._token = null;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {boolean} */
         this._eventListenersSetup = false;
     }
 
+    /**
+     * @returns {void}
+     */
     signal() {
         if (!this._eventListenersSetup) {
             this._eventListeners.addEventListener(window, 'message', this._onMessage.bind(this), false);
             this._eventListenersSetup = true;
         }
-        yomichan.api.broadcastTab('frameEndpointReady', {secret: this._secret});
+        /** @type {import('frame-client').FrameEndpointReadyDetails} */
+        const details = {secret: this._secret};
+        yomichan.api.broadcastTab('frameEndpointReady', details);
     }
 
+    /**
+     * @param {unknown} message
+     * @returns {boolean}
+     */
     authenticate(message) {
         return (
             this._token !== null &&
-            isObject(message) &&
-            this._token === message.token &&
-            this._secret === message.secret
+            typeof message === 'object' && message !== null &&
+            this._token === /** @type {import('core').SerializableObject} */ (message).token &&
+            this._secret === /** @type {import('core').SerializableObject} */ (message).secret
         );
     }
 
-    _onMessage(e) {
+    /**
+     * @param {MessageEvent<unknown>} event
+     */
+    _onMessage(event) {
         if (this._token !== null) { return; } // Already initialized
 
-        const data = e.data;
-        if (!isObject(data) || data.action !== 'frameEndpointConnect') { return; } // Invalid message
+        const {data} = event;
+        if (typeof data !== 'object' || data === null) { return; } // Invalid message
 
-        const params = data.params;
-        if (!isObject(params)) { return; } // Invalid data
+        const {action} = /** @type {import('core').SerializableObject} */ (data);
+        if (action !== 'frameEndpointConnect') { return; } // Invalid message
 
-        const secret = params.secret;
+        const {params} = /** @type {import('core').SerializableObject} */ (data);
+        if (typeof params !== 'object' || params === null) { return; } // Invalid data
+
+        const {secret} = /** @type {import('core').SerializableObject} */ (params);
         if (secret !== this._secret) { return; } // Invalid authentication
 
-        const {token, hostFrameId} = params;
+        const {token, hostFrameId} = /** @type {import('core').SerializableObject} */ (params);
+        if (typeof token !== 'string' || typeof hostFrameId !== 'number') { return; } // Invalid target
+
         this._token = token;
 
         this._eventListeners.removeAllEventListeners();
-        yomichan.api.sendMessageToFrame(hostFrameId, 'frameEndpointConnected', {secret, token});
+        /** @type {import('frame-client').FrameEndpointConnectedDetails} */
+        const details = {secret, token};
+        yomichan.api.sendMessageToFrame(hostFrameId, 'frameEndpointConnected', details);
     }
 }
diff --git a/ext/js/comm/frame-offset-forwarder.js b/ext/js/comm/frame-offset-forwarder.js
index 87c6a9cea6..e98c9962a0 100644
--- a/ext/js/comm/frame-offset-forwarder.js
+++ b/ext/js/comm/frame-offset-forwarder.js
@@ -21,11 +21,19 @@
  */
 
 class FrameOffsetForwarder {
+    /**
+     * @param {number} frameId
+     */
     constructor(frameId) {
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {FrameAncestryHandler} */
         this._frameAncestryHandler = new FrameAncestryHandler(frameId);
     }
 
+    /**
+     * @returns {void}
+     */
     prepare() {
         this._frameAncestryHandler.prepare();
         yomichan.crossFrame.registerHandlers([
@@ -33,6 +41,9 @@ class FrameOffsetForwarder {
         ]);
     }
 
+    /**
+     * @returns {Promise<?[x: number, y: number]>}
+     */
     async getOffset() {
         if (this._frameAncestryHandler.isRootFrame()) {
             return [0, 0];
@@ -42,6 +53,7 @@ class FrameOffsetForwarder {
             const ancestorFrameIds = await this._frameAncestryHandler.getFrameAncestryInfo();
 
             let childFrameId = this._frameId;
+            /** @type {Promise<?import('frame-offset-forwarder').ChildFrameRect>[]} */
             const promises = [];
             for (const frameId of ancestorFrameIds) {
                 promises.push(yomichan.crossFrame.invoke(frameId, 'FrameOffsetForwarder.getChildFrameRect', {frameId: childFrameId}));
@@ -65,6 +77,10 @@ class FrameOffsetForwarder {
 
     // Private
 
+    /**
+     * @param {{frameId: number}} event
+     * @returns {?import('frame-offset-forwarder').ChildFrameRect}
+     */
     _onMessageGetChildFrameRect({frameId}) {
         const frameElement = this._frameAncestryHandler.getChildFrameElement(frameId);
         if (frameElement === null) { return null; }
diff --git a/ext/js/comm/mecab.js b/ext/js/comm/mecab.js
index bdc8c588a3..2b9b469d63 100644
--- a/ext/js/comm/mecab.js
+++ b/ext/js/comm/mecab.js
@@ -21,33 +21,27 @@
  * used to parse text into individual terms.
  */
 class Mecab {
-    /**
-     * The resulting data from an invocation of `parseText`.
-     * @typedef {object} ParseResult
-     * @property {string} name The dictionary name for the parsed result.
-     * @property {ParseTerm[]} lines The resulting parsed terms.
-     */
-
-    /**
-     * A fragment of the parsed text.
-     * @typedef {object} ParseFragment
-     * @property {string} term The term.
-     * @property {string} reading The reading of the term.
-     * @property {string} source The source text.
-     */
-
     /**
      * Creates a new instance of the class.
      */
     constructor() {
+        /** @type {?chrome.runtime.Port} */
         this._port = null;
+        /** @type {number} */
         this._sequence = 0;
+        /** @type {Map<number, {resolve: (value: unknown) => void, reject: (reason?: unknown) => void, timer: number}>} */
         this._invocations = new Map();
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {number} */
         this._timeout = 5000;
+        /** @type {number} */
         this._version = 1;
+        /** @type {?number} */
         this._remoteVersion = null;
+        /** @type {boolean} */
         this._enabled = false;
+        /** @type {?Promise<void>} */
         this._setupPortPromise = null;
     }
 
@@ -105,7 +99,7 @@ class Mecab {
 
     /**
      * Gets the version of the MeCab component.
-     * @returns {?number} The version of the MeCab component, or `null` if the component was not found.
+     * @returns {Promise<?number>} The version of the MeCab component, or `null` if the component was not found.
      */
     async getVersion() {
         try {
@@ -133,17 +127,26 @@ class Mecab {
      * ]
      * ```
      * @param {string} text The string to parse.
-     * @returns {ParseResult[]} A collection of parsing results of the text.
+     * @returns {Promise<import('mecab').ParseResult[]>} A collection of parsing results of the text.
      */
     async parseText(text) {
         await this._setupPort();
         const rawResults = await this._invoke('parse_text', {text});
-        return this._convertParseTextResults(rawResults);
+        // Note: The format of rawResults is not validated
+        return this._convertParseTextResults(/** @type {import('mecab').ParseResultRaw} */ (rawResults));
     }
 
     // Private
 
-    _onMessage({sequence, data}) {
+    /**
+     * @param {unknown} message
+     */
+    _onMessage(message) {
+        if (typeof message !== 'object' || message === null) { return; }
+
+        const {sequence, data} = /** @type {import('core').SerializableObject} */ (message);
+        if (typeof sequence !== 'number') { return; }
+
         const invocation = this._invocations.get(sequence);
         if (typeof invocation === 'undefined') { return; }
 
@@ -153,6 +156,9 @@ class Mecab {
         this._invocations.delete(sequence);
     }
 
+    /**
+     * @returns {void}
+     */
     _onDisconnect() {
         if (this._port === null) { return; }
         const e = chrome.runtime.lastError;
@@ -164,10 +170,16 @@ class Mecab {
         this._clearPort();
     }
 
+    /**
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     * @returns {Promise<unknown>}
+     */
     _invoke(action, params) {
         return new Promise((resolve, reject) => {
             if (this._port === null) {
                 reject(new Error('Port disconnected'));
+                return;
             }
 
             const sequence = this._sequence++;
@@ -177,15 +189,21 @@ class Mecab {
                 reject(new Error(`MeCab invoke timed out after ${this._timeout}ms`));
             }, this._timeout);
 
-            this._invocations.set(sequence, {resolve, reject, timer}, this._timeout);
+            this._invocations.set(sequence, {resolve, reject, timer});
 
             this._port.postMessage({action, params, sequence});
         });
     }
 
+    /**
+     * @param {import('mecab').ParseResultRaw} rawResults
+     * @returns {import('mecab').ParseResult[]}
+     */
     _convertParseTextResults(rawResults) {
+        /** @type {import('mecab').ParseResult[]} */
         const results = [];
         for (const [name, rawLines] of Object.entries(rawResults)) {
+            /** @type {import('mecab').ParseFragment[][]} */
             const lines = [];
             for (const rawLine of rawLines) {
                 const line = [];
@@ -202,6 +220,9 @@ class Mecab {
         return results;
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _setupPort() {
         if (!this._enabled) {
             throw new Error('MeCab not enabled');
@@ -212,10 +233,13 @@ class Mecab {
         try {
             await this._setupPortPromise;
         } catch (e) {
-            throw new Error(e.message);
+            throw new Error(e instanceof Error ? e.message : `${e}`);
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _setupPort2() {
         const port = chrome.runtime.connectNative('yomichan_mecab');
         this._eventListeners.addListener(port.onMessage, this._onMessage.bind(this));
@@ -223,7 +247,14 @@ class Mecab {
         this._port = port;
 
         try {
-            const {version} = await this._invoke('get_version', {});
+            const data = await this._invoke('get_version', {});
+            if (typeof data !== 'object' || data === null) {
+                throw new Error('Invalid version');
+            }
+            const {version} = /** @type {import('core').SerializableObject} */ (data);
+            if (typeof version !== 'number') {
+                throw new Error('Invalid version');
+            }
             this._remoteVersion = version;
             if (version !== this._version) {
                 throw new Error(`Unsupported MeCab native messenger version ${version}. Yomichan supports version ${this._version}.`);
@@ -236,9 +267,14 @@ class Mecab {
         }
     }
 
+    /**
+     * @returns {void}
+     */
     _clearPort() {
-        this._port.disconnect();
-        this._port = null;
+        if (this._port !== null) {
+            this._port.disconnect();
+            this._port = null;
+        }
         this._invocations.clear();
         this._eventListeners.removeAllEventListeners();
         this._sequence = 0;
diff --git a/ext/js/core.js b/ext/js/core.js
index 5b064a363b..4e7757e116 100644
--- a/ext/js/core.js
+++ b/ext/js/core.js
@@ -16,54 +16,9 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-/**
- * Converts an `Error` object to a serializable JSON object.
- * @param {*} error An error object to convert.
- * @returns {{name: string, message: string, stack: string, data?: *}|{value: *, hasValue: boolean}} A simple object which can be serialized by `JSON.stringify()`.
- */
-function serializeError(error) {
-    try {
-        if (typeof error === 'object' && error !== null) {
-            const result = {
-                name: error.name,
-                message: error.message,
-                stack: error.stack
-            };
-            if (Object.prototype.hasOwnProperty.call(error, 'data')) {
-                result.data = error.data;
-            }
-            return result;
-        }
-    } catch (e) {
-        // NOP
-    }
-    return {
-        value: error,
-        hasValue: true
-    };
-}
-
-/**
- * Converts a serialized erorr into a standard `Error` object.
- * @param {{name: string, message: string, stack: string, data?: *}|{value: *, hasValue: boolean}} serializedError A simple object which was initially generated by serializeError.
- * @returns {Error|*} A new `Error` instance.
- */
-function deserializeError(serializedError) {
-    if (serializedError.hasValue) {
-        return serializedError.value;
-    }
-    const error = new Error(serializedError.message);
-    error.name = serializedError.name;
-    error.stack = serializedError.stack;
-    if (Object.prototype.hasOwnProperty.call(serializedError, 'data')) {
-        error.data = serializedError.data;
-    }
-    return error;
-}
-
 /**
  * Checks whether a given value is a non-array object.
- * @param {*} value The value to check.
+ * @param {unknown} value The value to check.
  * @returns {boolean} `true` if the value is an object and not an array, `false` otherwise.
  */
 function isObject(value) {
@@ -91,14 +46,20 @@ function stringReverse(string) {
 
 /**
  * Creates a deep clone of an object or value. This is similar to `JSON.parse(JSON.stringify(value))`.
- * @param {*} value The value to clone.
- * @returns {*} A new clone of the value.
+ * @template T
+ * @param {T} value The value to clone.
+ * @returns {T} A new clone of the value.
  * @throws An error if the value is circular and cannot be cloned.
  */
 const clone = (() => {
-    // eslint-disable-next-line no-shadow
+    /**
+     * @template T
+     * @param {T} value
+     * @returns {T}
+     */
+    // eslint-disable-next-line no-shadow, @typescript-eslint/no-shadow
     function clone(value) {
-        if (value === null) { return null; }
+        if (value === null) { return /** @type {T} */ (null); }
         switch (typeof value) {
             case 'boolean':
             case 'number':
@@ -112,8 +73,15 @@ const clone = (() => {
         }
     }
 
+    /**
+     * @template [T=unknown]
+     * @param {T} value
+     * @param {Set<unknown>} visited
+     * @returns {T}
+     * @throws {Error}
+     */
     function cloneInternal(value, visited) {
-        if (value === null) { return null; }
+        if (value === null) { return /** @type {T} */ (null); }
         switch (typeof value) {
             case 'boolean':
             case 'number':
@@ -122,13 +90,23 @@ const clone = (() => {
             case 'symbol':
             case 'undefined':
                 return value;
-            case 'function':
-                return cloneObject(value, visited);
             case 'object':
-                return Array.isArray(value) ? cloneArray(value, visited) : cloneObject(value, visited);
+                return /** @type {T} */ (
+                    Array.isArray(value) ?
+                    cloneArray(value, visited) :
+                    cloneObject(/** @type {import('core').SerializableObject} */ (value), visited)
+                );
+            default:
+                throw new Error(`Cannot clone object of type ${typeof value}`);
         }
     }
 
+    /**
+     * @param {unknown[]} value
+     * @param {Set<unknown>} visited
+     * @returns {unknown[]}
+     * @throws {Error}
+     */
     function cloneArray(value, visited) {
         if (visited.has(value)) { throw new Error('Circular'); }
         try {
@@ -143,10 +121,17 @@ const clone = (() => {
         }
     }
 
+    /**
+     * @param {import('core').SerializableObject} value
+     * @param {Set<unknown>} visited
+     * @returns {import('core').SerializableObject}
+     * @throws {Error}
+     */
     function cloneObject(value, visited) {
         if (visited.has(value)) { throw new Error('Circular'); }
         try {
             visited.add(value);
+            /** @type {import('core').SerializableObject} */
             const result = {};
             for (const key in value) {
                 if (Object.prototype.hasOwnProperty.call(value, key)) {
@@ -164,12 +149,17 @@ const clone = (() => {
 
 /**
  * Checks if an object or value is deeply equal to another object or value.
- * @param {*} value1 The first value to check.
- * @param {*} value2 The second value to check.
+ * @param {unknown} value1 The first value to check.
+ * @param {unknown} value2 The second value to check.
  * @returns {boolean} `true` if the values are the same object, or deeply equal without cycles. `false` otherwise.
  */
 const deepEqual = (() => {
-    // eslint-disable-next-line no-shadow
+    /**
+     * @param {unknown} value1
+     * @param {unknown} value2
+     * @returns {boolean}
+     */
+    // eslint-disable-next-line no-shadow, @typescript-eslint/no-shadow
     function deepEqual(value1, value2) {
         if (value1 === value2) { return true; }
 
@@ -185,6 +175,12 @@ const deepEqual = (() => {
         }
     }
 
+    /**
+     * @param {unknown} value1
+     * @param {unknown} value2
+     * @param {Set<unknown>} visited1
+     * @returns {boolean}
+     */
     function deepEqualInternal(value1, value2, visited1) {
         if (value1 === value2) { return true; }
 
@@ -200,13 +196,23 @@ const deepEqual = (() => {
                 if (array !== Array.isArray(value2)) { return false; }
                 if (visited1.has(value1)) { return false; }
                 visited1.add(value1);
-                return array ? areArraysEqual(value1, value2, visited1) : areObjectsEqual(value1, value2, visited1);
+                return (
+                    array ?
+                    areArraysEqual(/** @type {unknown[]} */ (value1), /** @type {unknown[]} */ (value2), visited1) :
+                    areObjectsEqual(/** @type {import('core').UnknownObject} */ (value1), /** @type {import('core').UnknownObject} */ (value2), visited1)
+                );
             }
             default:
                 return false;
         }
     }
 
+    /**
+     * @param {import('core').UnknownObject} value1
+     * @param {import('core').UnknownObject} value2
+     * @param {Set<unknown>} visited1
+     * @returns {boolean}
+     */
     function areObjectsEqual(value1, value2, visited1) {
         const keys1 = Object.keys(value1);
         const keys2 = Object.keys(value2);
@@ -220,6 +226,12 @@ const deepEqual = (() => {
         return true;
     }
 
+    /**
+     * @param {unknown[]} value1
+     * @param {unknown[]} value2
+     * @param {Set<unknown>} visited1
+     * @returns {boolean}
+     */
     function areArraysEqual(value1, value2, visited1) {
         const length = value1.length;
         if (length !== value2.length) { return false; }
@@ -251,76 +263,55 @@ function generateId(length) {
 
 /**
  * Creates an unresolved promise that can be resolved later, outside the promise's executor function.
- * @returns {{promise: Promise, resolve: Function, reject: Function}} An object `{promise, resolve, reject}`, containing the promise and the resolve/reject functions.
+ * @template T
+ * @returns {import('core').DeferredPromiseDetails<T>} An object `{promise, resolve, reject}`, containing the promise and the resolve/reject functions.
  */
 function deferPromise() {
+    /** @type {((value: T) => void)|undefined} */
     let resolve;
+    /** @type {((reason?: import('core').RejectionReason) => void)|undefined} */
     let reject;
     const promise = new Promise((resolve2, reject2) => {
         resolve = resolve2;
         reject = reject2;
     });
-    return {promise, resolve, reject};
+    return {
+        promise,
+        resolve: /** @type {(value: T) => void} */ (resolve),
+        reject: /** @type {(reason?: import('core').RejectionReason) => void} */ (reject)
+    };
 }
 
 /**
  * Creates a promise that is resolved after a set delay.
  * @param {number} delay How many milliseconds until the promise should be resolved. If 0, the promise is immediately resolved.
- * @param {*} [resolveValue] The value returned when the promise is resolved.
- * @returns {Promise} A promise with two additional properties: `resolve` and `reject`, which can be used to complete the promise early.
+ * @returns {Promise<void>} A promise with two additional properties: `resolve` and `reject`, which can be used to complete the promise early.
  */
-function promiseTimeout(delay, resolveValue) {
-    if (delay <= 0) {
-        const promise = Promise.resolve(resolveValue);
-        promise.resolve = () => {}; // NOP
-        promise.reject = () => {}; // NOP
-        return promise;
-    }
-
-    let timer = null;
-    let {promise, resolve, reject} = deferPromise();
-
-    const complete = (callback, value) => {
-        if (callback === null) { return; }
-        if (timer !== null) {
-            clearTimeout(timer);
-            timer = null;
-        }
-        resolve = null;
-        reject = null;
-        callback(value);
-    };
-
-    const resolveWrapper = (value) => complete(resolve, value);
-    const rejectWrapper = (value) => complete(reject, value);
-
-    timer = setTimeout(() => {
-        timer = null;
-        resolveWrapper(resolveValue);
-    }, delay);
-
-    promise.resolve = resolveWrapper;
-    promise.reject = rejectWrapper;
-
-    return promise;
+function promiseTimeout(delay) {
+    return delay <= 0 ? Promise.resolve() : new Promise((resolve) => { setTimeout(resolve, delay); });
 }
 
 /**
  * Creates a promise that will resolve after the next animation frame, using `requestAnimationFrame`.
  * @param {number} [timeout] A maximum duration (in milliseconds) to wait until the promise resolves. If null or omitted, no timeout is used.
- * @returns {Promise<{time: number, timeout: number}>} A promise that is resolved with `{time, timeout}`, where `time` is the timestamp from `requestAnimationFrame`,
- *  and `timeout` is a boolean indicating whether the cause was a timeout or not.
+ * @returns {Promise<{time: number, timeout: boolean}>} A promise that is resolved with `{time, timeout}`, where `time` is the timestamp from `requestAnimationFrame`,
+ *   and `timeout` is a boolean indicating whether the cause was a timeout or not.
  * @throws The promise throws an error if animation is not supported in this context, such as in a service worker.
  */
-function promiseAnimationFrame(timeout=null) {
+function promiseAnimationFrame(timeout) {
     return new Promise((resolve, reject) => {
         if (typeof cancelAnimationFrame !== 'function' || typeof requestAnimationFrame !== 'function') {
             reject(new Error('Animation not supported in this context'));
             return;
         }
 
+        /** @type {?number} */
         let timer = null;
+        /** @type {?number} */
         let frameRequest = null;
+        /**
+         * @param {number} time
+         */
         const onFrame = (time) => {
             frameRequest = null;
             if (timer !== null) {
@@ -350,14 +341,12 @@ function promiseAnimationFrame(timeout=null) {
 /**
  * Invokes a standard message handler. This function is used to react and respond
  * to communication messages within the extension.
- * @param {object} details Details about how to handle messages.
- * @param {Function} details.handler A handler function which is passed `params` and `...extraArgs` as arguments.
- * @param {boolean|string} details.async Whether or not the handler is async or not. Values include `false`, `true`, or `'dynamic'`.
- *   When the value is `'dynamic'`, the handler should return an object of the format `{async: boolean, result: any}`.
- * @param {object} params Information which was passed with the original message.
- * @param {Function} callback A callback function which is invoked after the handler has completed. The value passed
+ * @template {import('core').SafeAny} TParams
+ * @param {import('core').MessageHandlerDetails} details Details about how to handle messages.
+ * @param {TParams} params Information which was passed with the original message.
+ * @param {(response: import('core').Response) => void} callback A callback function which is invoked after the handler has completed. The value passed
  *   to the function is in the format:
- *   - `{result: any}` if the handler invoked successfully.
+ *   - `{result: unknown}` if the handler invoked successfully.
  *   - `{error: object}` if the handler thew an error. The error is serialized.
  * @param {...*} extraArgs Additional arguments which are passed to the `handler` function.
  * @returns {boolean} `true` if the function is invoked asynchronously, `false` otherwise.
@@ -369,9 +358,9 @@ function invokeMessageHandler({handler, async}, params, callback, ...extraArgs)
             ({async, result: promiseOrResult} = promiseOrResult);
         }
         if (async) {
-            promiseOrResult.then(
+            /** @type {Promise<any>} */ (promiseOrResult).then(
                 (result) => { callback({result}); },
-                (error) => { callback({error: serializeError(error)}); }
+                (error) => { callback({error: ExtensionError.serialize(error)}); }
             );
             return true;
         } else {
@@ -379,12 +368,13 @@ function invokeMessageHandler({handler, async}, params, callback, ...extraArgs)
             return false;
         }
     } catch (error) {
-        callback({error: serializeError(error)});
+        callback({error: ExtensionError.serialize(error)});
         return false;
     }
 }
 
 /**
+ * @template {string} TEventName
  * Base class controls basic event dispatching.
  */
 class EventDispatcher {
@@ -392,13 +382,14 @@ class EventDispatcher {
      * Creates a new instance.
      */
     constructor() {
+        /** @type {Map<string, ((details: import('core').SafeAny) => void)[]>} */
         this._eventMap = new Map();
     }
 
     /**
      * Triggers an event with the given name and specified argument.
-     * @param {string} eventName The string representing the event's name.
-     * @param {*} [details] The argument passed to the callback functions.
+     * @param {TEventName} eventName The string representing the event's name.
+     * @param {unknown} [details] The argument passed to the callback functions.
      * @returns {boolean} `true` if any callbacks were registered, `false` otherwise.
      */
     trigger(eventName, details) {
@@ -413,8 +404,8 @@ class EventDispatcher {
 
     /**
      * Adds a single event listener to a specific event.
-     * @param {string} eventName The string representing the event's name.
-     * @param {Function} callback The event listener callback to add.
+     * @param {TEventName} eventName The string representing the event's name.
+     * @param {(details: import('core').SafeAny) => void} callback The event listener callback to add.
      */
     on(eventName, callback) {
         let callbacks = this._eventMap.get(eventName);
@@ -427,8 +418,8 @@ class EventDispatcher {
 
     /**
      * Removes a single event listener from a specific event.
-     * @param {string} eventName The string representing the event's name.
-     * @param {Function} callback The event listener callback to add.
+     * @param {TEventName} eventName The string representing the event's name.
+     * @param {(details: import('core').SafeAny) => void} callback The event listener callback to add.
      * @returns {boolean} `true` if the callback was removed, `false` otherwise.
      */
     off(eventName, callback) {
@@ -450,7 +441,7 @@ class EventDispatcher {
 
     /**
      * Checks if an event has any listeners.
-     * @param {string} eventName The string representing the event's name.
+     * @param {TEventName} eventName The string representing the event's name.
      * @returns {boolean} `true` if the event has listeners, `false` otherwise.
      */
     hasListeners(eventName) {
@@ -467,6 +458,7 @@ class EventListenerCollection {
      * Creates a new instance.
      */
     constructor() {
+        /** @type {import('event-listener-collection').EventListenerDetails[]} */
         this._eventListeners = [];
     }
 
@@ -478,51 +470,41 @@ class EventListenerCollection {
         return this._eventListeners.length;
     }
 
-    /**
-     * Adds an event listener of a generic type.
-     * @param {string} type The type of event listener, which can be 'addEventListener', 'addListener', or 'on'.
-     * @param {object} object The object to add the event listener to.
-     * @param {...*} args The argument array passed to the object's event listener adding function.
-     * @returns {void}
-     * @throws An error if type is not an expected value.
-     */
-    addGeneric(type, object, ...args) {
-        switch (type) {
-            case 'addEventListener': return this.addEventListener(object, ...args);
-            case 'addListener': return this.addListener(object, ...args);
-            case 'on': return this.on(object, ...args);
-            default: throw new Error(`Invalid type: ${type}`);
-        }
-    }
-
     /**
      * Adds an event listener using `object.addEventListener`. The listener will later be removed using `object.removeEventListener`.
-     * @param {object} object The object to add the event listener to.
-     * @param {...*} args The argument array passed to the `addEventListener`/`removeEventListener` functions.
+     * @param {import('event-listener-collection').EventTarget} target The object to add the event listener to.
+     * @param {string} type The name of the event.
+     * @param {EventListener | EventListenerObject | import('event-listener-collection').EventListenerFunction} listener The callback listener.
+     * @param {AddEventListenerOptions | boolean} [options] Options for the event.
      */
-    addEventListener(object, ...args) {
-        object.addEventListener(...args);
-        this._eventListeners.push(['removeEventListener', object, ...args]);
+    addEventListener(target, type, listener, options) {
+        target.addEventListener(type, listener, options);
+        this._eventListeners.push({type: 'removeEventListener', target, eventName: type, listener, options});
     }
 
     /**
      * Adds an event listener using `object.addListener`. The listener will later be removed using `object.removeListener`.
-     * @param {object} object The object to add the event listener to.
-     * @param {...*} args The argument array passed to the `addListener`/`removeListener` function.
+     * @template {import('event-listener-collection').EventListenerFunction} TCallback
+     * @template [TArgs=unknown]
+     * @param {import('event-listener-collection').ExtensionEvent<TCallback, TArgs>} target The object to add the event listener to.
+     * @param {TCallback} callback The callback.
+     * @param {TArgs[]} args The extra argument array passed to the `addListener`/`removeListener` function.
      */
-    addListener(object, ...args) {
-        object.addListener(...args);
-        this._eventListeners.push(['removeListener', object, ...args]);
+    addListener(target, callback, ...args) {
+        target.addListener(callback, ...args);
+        this._eventListeners.push({type: 'removeListener', target, callback, args});
     }
 
     /**
      * Adds an event listener using `object.on`. The listener will later be removed using `object.off`.
-     * @param {object} object The object to add the event listener to.
-     * @param {...*} args The argument array passed to the `on`/`off` function.
+     * @template {string} TEventName
+     * @param {EventDispatcher<TEventName>} target The object to add the event listener to.
+     * @param {TEventName} eventName The string representing the event's name.
+     * @param {(details: import('core').SafeAny) => void} callback The event listener callback to add.
      */
-    on(object, ...args) {
-        object.on(...args);
-        this._eventListeners.push(['off', object, ...args]);
+    on(target, eventName, callback) {
+        target.on(eventName, callback);
+        this._eventListeners.push({type: 'off', eventName, target, callback});
     }
 
     /**
@@ -530,16 +512,16 @@ class EventListenerCollection {
      */
     removeAllEventListeners() {
         if (this._eventListeners.length === 0) { return; }
-        for (const [removeFunctionName, object, ...args] of this._eventListeners) {
-            switch (removeFunctionName) {
+        for (const item of this._eventListeners) {
+            switch (item.type) {
                 case 'removeEventListener':
-                    object.removeEventListener(...args);
+                    item.target.removeEventListener(item.eventName, item.listener, item.options);
                     break;
                 case 'removeListener':
-                    object.removeListener(...args);
+                    item.target.removeListener(item.callback, ...item.args);
                     break;
                 case 'off':
-                    object.off(...args);
+                    item.target.off(item.eventName, item.callback);
                     break;
             }
         }
@@ -550,23 +532,28 @@ class EventListenerCollection {
 /**
  * Class representing a generic value with an override stack.
  * Changes can be observed by listening to the 'change' event.
+ * @template T
+ * @augments EventDispatcher<import('dynamic-property').EventType>
  */
 class DynamicProperty extends EventDispatcher {
     /**
      * Creates a new instance with the specified value.
-     * @param {*} value The value to assign.
+     * @param {T} value The value to assign.
      */
     constructor(value) {
         super();
+        /** @type {T} */
         this._value = value;
+        /** @type {T} */
         this._defaultValue = value;
+        /** @type {{value: T, priority: number, token: string}[]} */
         this._overrides = [];
     }
 
     /**
      * Gets the default value for the property, which is assigned to the
      * public value property when no overrides are present.
-     * @type {*}
+     * @type {T}
      */
     get defaultValue() {
         return this._defaultValue;
@@ -576,7 +563,7 @@ class DynamicProperty extends EventDispatcher {
      * Assigns the default value for the property. If no overrides are present
      * and if the value is different than the current default value,
      * the 'change' event will be triggered.
-     * @param {*} value The value to assign.
+     * @param {T} value The value to assign.
      */
     set defaultValue(value) {
         this._defaultValue = value;
@@ -585,7 +572,7 @@ class DynamicProperty extends EventDispatcher {
 
     /**
      * Gets the current value for the property, taking any overrides into account.
-     * @type {*}
+     * @type {T}
      */
     get value() {
         return this._value;
@@ -593,7 +580,7 @@ class DynamicProperty extends EventDispatcher {
 
     /**
      * Gets the number of overrides added to the property.
-     * @type {*}
+     * @type {number}
      */
     get overrideCount() {
         return this._overrides.length;
@@ -606,10 +593,10 @@ class DynamicProperty extends EventDispatcher {
      * If the newly added override has the highest priority of all overrides
      * and if the override value is different from the current value,
      * the 'change' event will be fired.
-     * @param {*} value The override value to assign.
+     * @param {T} value The override value to assign.
      * @param {number} [priority] The priority value to use, as a number.
-     * @returns {string} A string token which can be passed to the clearOverride function
-     *  to remove the override.
+     * @returns {import('core').TokenString} A string token which can be passed to the clearOverride function
+     *   to remove the override.
      */
     setOverride(value, priority=0) {
         const overridesCount = this._overrides.length;
@@ -627,7 +614,7 @@ class DynamicProperty extends EventDispatcher {
      * Removes a specific override value. If the removed override
      * had the highest priority, and the new value is different from
      * the previous value, the 'change' event will be fired.
-     * @param {string} token The token for the corresponding override which is to be removed.
+     * @param {import('core').TokenString} token The token for the corresponding override which is to be removed.
      * @returns {boolean} `true` if an override was returned, `false` otherwise.
      */
     clearOverride(token) {
@@ -649,13 +636,14 @@ class DynamicProperty extends EventDispatcher {
         const value = this._overrides.length > 0 ? this._overrides[0].value : this._defaultValue;
         if (this._value === value) { return; }
         this._value = value;
-        this.trigger('change', {value});
+        this.trigger('change', /** @type {import('dynamic-property').ChangeEventDetails<T>} */ ({value}));
     }
 }
 
 /**
  * This class handles logging of messages to the console and triggering
  * an event for log calls.
+ * @augments EventDispatcher<import('log').LoggerEventType>
  */
 class Logger extends EventDispatcher {
     /**
@@ -663,6 +651,7 @@ class Logger extends EventDispatcher {
      */
     constructor() {
         super();
+        /** @type {string} */
         this._extensionName = 'Yomichan';
         try {
             const {name, version} = chrome.runtime.getManifest();
@@ -674,13 +663,13 @@ class Logger extends EventDispatcher {
 
     /**
      * Logs a generic error. This will trigger the 'log' event with the same arguments as the function invocation.
-     * @param {Error|object|*} error The error to log. This is typically an `Error` or `Error`-like object.
-     * @param {string} level The level to log at. Values include `'info'`, `'debug'`, `'warn'`, and `'error'`.
+     * @param {unknown} error The error to log. This is typically an `Error` or `Error`-like object.
+     * @param {import('log').LogLevel} level The level to log at. Values include `'info'`, `'debug'`, `'warn'`, and `'error'`.
      *   Other values will be logged at a non-error level.
-     * @param {?object} [context] An optional context object for the error which should typically include a `url` field.
+     * @param {?import('log').LogContext} [context] An optional context object for the error which should typically include a `url` field.
      */
     log(error, level, context=null) {
-        if (!isObject(context)) {
+        if (typeof context !== 'object' || context === null) {
             context = {url: location.href};
         }
 
@@ -689,7 +678,11 @@ class Logger extends EventDispatcher {
             if (typeof error === 'string') {
                 errorString = error;
             } else {
-                errorString = error.toString();
+                errorString = (
+                    typeof error === 'object' && error !== null ?
+                    error.toString() :
+                    `${error}`
+                );
                 if (/^\[object \w+\]$/.test(errorString)) {
                     errorString = JSON.stringify(error);
                 }
@@ -700,14 +693,20 @@ class Logger extends EventDispatcher {
 
         let errorStack;
         try {
-            errorStack = (typeof error.stack === 'string' ? error.stack.trimRight() : '');
+            errorStack = (
+                error instanceof Error ?
+                (typeof error.stack === 'string' ? error.stack.trimEnd() : '') :
+                ''
+            );
         } catch (e) {
             errorStack = '';
         }
 
         let errorData;
         try {
-            errorData = error.data;
+            if (error instanceof ExtensionError) {
+                errorData = error.data;
+            }
         } catch (e) {
             // NOP
         }
@@ -739,8 +738,8 @@ class Logger extends EventDispatcher {
 
     /**
      * Logs a warning. This function invokes `log` internally.
-     * @param {Error|object|*} error The error to log. This is typically an `Error` or `Error`-like object.
-     * @param {?object} context An optional context object for the error which should typically include a `url` field.
+     * @param {unknown} error The error to log. This is typically an `Error` or `Error`-like object.
+     * @param {?import('log').LogContext} context An optional context object for the error which should typically include a `url` field.
      */
     warn(error, context=null) {
         this.log(error, 'warn', context);
@@ -748,8 +747,8 @@ class Logger extends EventDispatcher {
 
     /**
      * Logs an error. This function invokes `log` internally.
-     * @param {Error|object|*} error The error to log. This is typically an `Error` or `Error`-like object.
-     * @param {?object} context An optional context object for the error which should typically include a `url` field.
+     * @param {unknown} error The error to log. This is typically an `Error` or `Error`-like object.
+     * @param {?import('log').LogContext} context An optional context object for the error which should typically include a `url` field.
      */
     error(error, context=null) {
         this.log(error, 'error', context);
diff --git a/ext/js/core/extension-error.js b/ext/js/core/extension-error.js
new file mode 100644
index 0000000000..1739f435fe
--- /dev/null
+++ b/ext/js/core/extension-error.js
@@ -0,0 +1,85 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Custom error class for the extension which can contain extra data.
+ * This works around an issue where assigning the `DOMException.data` field can fail on Firefox.
+ * @see https://bugzilla.mozilla.org/show_bug.cgi?id=1776555
+ */
+class ExtensionError extends Error {
+    /**
+     * @param {string} message
+     */
+    constructor(message) {
+        super(message);
+        /** @type {unknown} */
+        this._data = void 0;
+    }
+
+    /** @type {unknown} */
+    get data() { return this._data; }
+    set data(value) { this._data = value; }
+
+    /**
+     * Converts an `Error` object to a serializable JSON object.
+     * @param {unknown} error An error object to convert.
+     * @returns {import('core').SerializedError} A simple object which can be serialized by `JSON.stringify()`.
+     */
+    static serialize(error) {
+        try {
+            if (typeof error === 'object' && error !== null) {
+                const {name, message, stack} = /** @type {import('core').SerializableObject} */ (error);
+                /** @type {import('core').SerializedError1} */
+                const result = {
+                    name: typeof name === 'string' ? name : '',
+                    message: typeof message === 'string' ? message : '',
+                    stack: typeof stack === 'string' ? stack : ''
+                };
+                if (error instanceof ExtensionError) {
+                    result.data = error.data;
+                }
+                return result;
+            }
+        } catch (e) {
+            // NOP
+        }
+        return /** @type {import('core').SerializedError2} */ ({
+            value: error,
+            hasValue: true
+        });
+    }
+
+    /**
+     * Converts a serialized error into a standard `Error` object.
+     * @param {import('core').SerializedError} serializedError A simple object which was initially generated by the `serialize` function.
+     * @returns {ExtensionError} A new `Error` instance.
+     */
+    static deserialize(serializedError) {
+        if (serializedError.hasValue) {
+            const {value} = serializedError;
+            return new ExtensionError(`Error of type ${typeof value}: ${value}`);
+        }
+        const {message, name, stack, data} = serializedError;
+        const error = new ExtensionError(message);
+        error.name = name;
+        error.stack = stack;
+        if (typeof data !== 'undefined') {
+            error.data = data;
+        }
+        return error;
+    }
+}
diff --git a/ext/js/data/anki-note-builder.js b/ext/js/data/anki-note-builder.js
index c1b58cc256..e98064117d 100644
--- a/ext/js/data/anki-note-builder.js
+++ b/ext/js/data/anki-note-builder.js
@@ -22,14 +22,26 @@
  */
 
 class AnkiNoteBuilder {
+    /**
+     * @param {{japaneseUtil: JapaneseUtil}} details
+     */
     constructor({japaneseUtil}) {
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
+        /** @type {RegExp} */
         this._markerPattern = AnkiUtil.cloneFieldMarkerPattern(true);
+        /** @type {TemplateRendererProxy} */
         this._templateRenderer = new TemplateRendererProxy();
+        /** @type {import('anki-note-builder').BatchedRequestGroup[]} */
         this._batchedRequests = [];
+        /** @type {boolean} */
         this._batchedRequestsQueued = false;
     }
 
+    /**
+     * @param {import('anki-note-builder').CreateNoteDetails} details
+     * @returns {Promise<import('anki-note-builder').CreateNoteResult>}
+     */
     async createNote({
         dictionaryEntry,
         mode,
@@ -56,16 +68,15 @@ class AnkiNoteBuilder {
             duplicateScopeCheckChildren = true;
         }
 
+        /** @type {Error[]} */
         const allErrors = [];
         let media;
         if (requirements.length > 0 && mediaOptions !== null) {
             let errors;
             ({media, errors} = await this._injectMedia(dictionaryEntry, requirements, mediaOptions));
             for (const error of errors) {
-                allErrors.push(deserializeError(error));
+                allErrors.push(ExtensionError.deserialize(error));
             }
-        } else {
-            media = {};
         }
 
         const commonData = this._createData(dictionaryEntry, mode, context, resultOutputMode, glossaryLayoutMode, compactTags, media);
@@ -77,6 +88,7 @@ class AnkiNoteBuilder {
 
         const formattedFieldValues = await Promise.all(formattedFieldValuePromises);
         const uniqueRequirements = new Map();
+        /** @type {import('anki').NoteFields} */
         const noteFields = {};
         for (let i = 0, ii = fields.length; i < ii; ++i) {
             const fieldName = fields[i][0];
@@ -90,6 +102,7 @@ class AnkiNoteBuilder {
             }
         }
 
+        /** @type {import('anki').Note} */
         const note = {
             fields: noteFields,
             tags,
@@ -108,6 +121,10 @@ class AnkiNoteBuilder {
         return {note, errors: allErrors, requirements: [...uniqueRequirements.values()]};
     }
 
+    /**
+     * @param {import('anki-note-builder').GetRenderingDataDetails} details
+     * @returns {Promise<import('anki-templates').NoteData>}
+     */
     async getRenderingData({
         dictionaryEntry,
         mode,
@@ -115,12 +132,16 @@ class AnkiNoteBuilder {
         resultOutputMode='split',
         glossaryLayoutMode='default',
         compactTags=false,
-        marker=null
+        marker
     }) {
-        const commonData = this._createData(dictionaryEntry, mode, context, resultOutputMode, glossaryLayoutMode, compactTags, {});
+        const commonData = this._createData(dictionaryEntry, mode, context, resultOutputMode, glossaryLayoutMode, compactTags, void 0);
         return await this._templateRenderer.getModifiedData({marker, commonData}, 'ankiNote');
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @returns {import('api').InjectAnkiNoteMediaDefinitionDetails}
+     */
     getDictionaryEntryDetailsForNote(dictionaryEntry) {
         const {type} = dictionaryEntry;
         if (type === 'kanji') {
@@ -150,6 +171,16 @@ class AnkiNoteBuilder {
 
     // Private
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @param {import('anki-templates-internal').CreateMode} mode
+     * @param {import('anki-templates-internal').Context} context
+     * @param {import('settings').ResultOutputMode} resultOutputMode
+     * @param {import('settings').GlossaryLayoutMode} glossaryLayoutMode
+     * @param {boolean} compactTags
+     * @param {import('anki-templates').Media|undefined} media
+     * @returns {import('anki-note-builder').CommonData}
+     */
     _createData(dictionaryEntry, mode, context, resultOutputMode, glossaryLayoutMode, compactTags, media) {
         return {
             dictionaryEntry,
@@ -162,16 +193,25 @@ class AnkiNoteBuilder {
         };
     }
 
+    /**
+     * @param {string} field
+     * @param {import('anki-note-builder').CommonData} commonData
+     * @param {string} template
+     * @returns {Promise<{value: string, errors: ExtensionError[], requirements: import('anki-note-builder').Requirement[]}>}
+     */
     async _formatField(field, commonData, template) {
+        /** @type {ExtensionError[]} */
         const errors = [];
+        /** @type {import('anki-note-builder').Requirement[]} */
         const requirements = [];
-        const value = await this._stringReplaceAsync(field, this._markerPattern, async (g0, marker) => {
+        const value = await this._stringReplaceAsync(field, this._markerPattern, async (match) => {
+            const marker = match[1];
             try {
                 const {result, requirements: fieldRequirements} = await this._renderTemplateBatched(template, commonData, marker);
                 requirements.push(...fieldRequirements);
                 return result;
             } catch (e) {
-                const error = new Error(`Template render error for {${marker}}`);
+                const error = new ExtensionError(`Template render error for {${marker}}`);
                 error.data = {error: e};
                 errors.push(error);
                 return `{${marker}-render-error}`;
@@ -180,12 +220,19 @@ class AnkiNoteBuilder {
         return {value, errors, requirements};
     }
 
+    /**
+     * @param {string} str
+     * @param {RegExp} regex
+     * @param {(match: RegExpExecArray, index: number, str: string) => (string|Promise<string>)} replacer
+     * @returns {Promise<string>}
+     */
     async _stringReplaceAsync(str, regex, replacer) {
         let match;
         let index = 0;
+        /** @type {(Promise<string>|string)[]} */
         const parts = [];
         while ((match = regex.exec(str)) !== null) {
-            parts.push(str.substring(index, match.index), replacer(...match, match.index, str));
+            parts.push(str.substring(index, match.index), replacer(match, match.index, str));
             index = regex.lastIndex;
         }
         if (parts.length === 0) {
@@ -195,6 +242,10 @@ class AnkiNoteBuilder {
         return (await Promise.all(parts)).join('');
     }
 
+    /**
+     * @param {string} template
+     * @returns {import('anki-note-builder').BatchedRequestGroup}
+     */
     _getBatchedTemplateGroup(template) {
         for (const item of this._batchedRequests) {
             if (item.template === template) {
@@ -207,7 +258,14 @@ class AnkiNoteBuilder {
         return result;
     }
 
+    /**
+     * @param {string} template
+     * @param {import('anki-note-builder').CommonData} commonData
+     * @param {string} marker
+     * @returns {Promise<import('template-renderer').RenderResult>}
+     */
     _renderTemplateBatched(template, commonData, marker) {
+        /** @type {import('core').DeferredPromiseDetails<import('template-renderer').RenderResult>} */
         const {promise, resolve, reject} = deferPromise();
         const {commonDataRequestsMap} = this._getBatchedTemplateGroup(template);
         let requests = commonDataRequestsMap.get(commonData);
@@ -220,6 +278,9 @@ class AnkiNoteBuilder {
         return promise;
     }
 
+    /**
+     * @returns {void}
+     */
     _runBatchedRequestsDelayed() {
         if (this._batchedRequestsQueued) { return; }
         this._batchedRequestsQueued = true;
@@ -229,20 +290,30 @@ class AnkiNoteBuilder {
         });
     }
 
+    /**
+     * @returns {void}
+     */
     _runBatchedRequests() {
         if (this._batchedRequests.length === 0) { return; }
 
         const allRequests = [];
+        /** @type {import('template-renderer').RenderMultiItem[]} */
         const items = [];
         for (const {template, commonDataRequestsMap} of this._batchedRequests) {
+            /** @type {import('template-renderer').RenderMultiTemplateItem[]} */
             const templateItems = [];
             for (const [commonData, requests] of commonDataRequestsMap.entries()) {
+                /** @type {import('template-renderer').PartialOrCompositeRenderData[]} */
                 const datas = [];
                 for (const {marker} of requests) {
-                    datas.push(marker);
+                    datas.push({marker});
                 }
                 allRequests.push(...requests);
-                templateItems.push({type: 'ankiNote', commonData, datas});
+                templateItems.push({
+                    type: /** @type {import('anki-templates').RenderMode} */ ('ankiNote'),
+                    commonData,
+                    datas
+                });
             }
             items.push({template, templateItems});
         }
@@ -252,6 +323,10 @@ class AnkiNoteBuilder {
         this._resolveBatchedRequests(items, allRequests);
     }
 
+    /**
+     * @param {import('template-renderer').RenderMultiItem[]} items
+     * @param {import('anki-note-builder').BatchedRequestData[]} requests
+     */
     async _resolveBatchedRequests(items, requests) {
         let responses;
         try {
@@ -269,7 +344,7 @@ class AnkiNoteBuilder {
                 const response = responses[i];
                 const {error} = response;
                 if (typeof error !== 'undefined') {
-                    throw deserializeError(error);
+                    throw ExtensionError.deserialize(error);
                 } else {
                     request.resolve(response.result);
                 }
@@ -279,6 +354,12 @@ class AnkiNoteBuilder {
         }
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @param {import('anki-note-builder').Requirement[]} requirements
+     * @param {import('anki-note-builder').MediaOptions} mediaOptions
+     * @returns {Promise<{media: import('anki-templates').Media, errors: import('core').SerializedError[]}>}
+     */
     async _injectMedia(dictionaryEntry, requirements, mediaOptions) {
         const timestamp = Date.now();
 
@@ -288,7 +369,9 @@ class AnkiNoteBuilder {
         let injectClipboardImage = false;
         let injectClipboardText = false;
         let injectSelectionText = false;
+        /** @type {import('anki-note-builder').TextFuriganaDetails[]} */
         const textFuriganaDetails = [];
+        /** @type {import('api').InjectAnkiNoteMediaDictionaryMediaDetails[]} */
         const dictionaryMediaDetails = [];
         for (const requirement of requirements) {
             const {type} = requirement;
@@ -315,8 +398,11 @@ class AnkiNoteBuilder {
 
         // Generate request data
         const dictionaryEntryDetails = this.getDictionaryEntryDetailsForNote(dictionaryEntry);
+        /** @type {?import('api').InjectAnkiNoteMediaAudioDetails} */
         let audioDetails = null;
+        /** @type {?import('api').InjectAnkiNoteMediaScreenshotDetails} */
         let screenshotDetails = null;
+        /** @type {import('api').InjectAnkiNoteMediaClipboardDetails} */
         const clipboardDetails = {image: injectClipboardImage, text: injectClipboardText};
         if (injectAudio && dictionaryEntryDetails.type !== 'kanji') {
             const audioOptions = mediaOptions.audio;
@@ -357,6 +443,7 @@ class AnkiNoteBuilder {
         const textFurigana = textFuriganaPromise !== null ? await textFuriganaPromise : [];
 
         // Format results
+        /** @type {import('anki-templates').DictionaryMedia} */
         const dictionaryMedia = {};
         for (const {dictionary, path, fileName} of dictionaryMediaArray) {
             if (fileName === null) { continue; }
@@ -368,21 +455,31 @@ class AnkiNoteBuilder {
             dictionaryMedia2[path] = {value: fileName};
         }
         const media = {
-            audio: (typeof audioFileName === 'string' ? {value: audioFileName} : null),
-            screenshot: (typeof screenshotFileName === 'string' ? {value: screenshotFileName} : null),
-            clipboardImage: (typeof clipboardImageFileName === 'string' ? {value: clipboardImageFileName} : null),
-            clipboardText: (typeof clipboardText === 'string' ? {value: clipboardText} : null),
-            selectionText: (typeof selectionText === 'string' ? {value: selectionText} : null),
+            audio: (typeof audioFileName === 'string' ? {value: audioFileName} : void 0),
+            screenshot: (typeof screenshotFileName === 'string' ? {value: screenshotFileName} : void 0),
+            clipboardImage: (typeof clipboardImageFileName === 'string' ? {value: clipboardImageFileName} : void 0),
+            clipboardText: (typeof clipboardText === 'string' ? {value: clipboardText} : void 0),
+            selectionText: (typeof selectionText === 'string' ? {value: selectionText} : void 0),
             textFurigana,
             dictionaryMedia
         };
         return {media, errors};
     }
 
+    /**
+     * @returns {string}
+     */
     _getSelectionText() {
-        return document.getSelection().toString();
+        const selection = document.getSelection();
+        return selection !== null ? selection.toString() : '';
     }
 
+    /**
+     * @param {import('anki-note-builder').TextFuriganaDetails[]} entries
+     * @param {import('settings').OptionsContext} optionsContext
+     * @param {number} scanLength
+     * @returns {Promise<import('anki-templates').TextFuriganaSegment[]>}
+     */
     async _getTextFurigana(entries, optionsContext, scanLength) {
         const results = [];
         for (const {text, readingMode} of entries) {
@@ -401,6 +498,11 @@ class AnkiNoteBuilder {
         return results;
     }
 
+    /**
+     * @param {import('api').ParseTextLine[]} data
+     * @param {?import('anki-templates').TextFuriganaReadingMode} readingMode
+     * @returns {string}
+     */
     _createFuriganaHtml(data, readingMode) {
         let result = '';
         for (const term of data) {
@@ -418,6 +520,11 @@ class AnkiNoteBuilder {
         return result;
     }
 
+    /**
+     * @param {string} reading
+     * @param {?import('anki-templates').TextFuriganaReadingMode} readingMode
+     * @returns {string}
+     */
     _convertReading(reading, readingMode) {
         switch (readingMode) {
             case 'hiragana':
diff --git a/ext/js/data/anki-util.js b/ext/js/data/anki-util.js
index 3b433dc9db..a146565b7e 100644
--- a/ext/js/data/anki-util.js
+++ b/ext/js/data/anki-util.js
@@ -69,7 +69,7 @@ class AnkiUtil {
 
     /**
      * Checks whether or not a note object is valid.
-     * @param {*} note A note object to check.
+     * @param {import('anki').Note} note A note object to check.
      * @returns {boolean} `true` if the note is valid, `false` otherwise.
      */
     static isNoteDataValid(note) {
diff --git a/ext/js/data/database.js b/ext/js/data/database.js
index 205f638534..9ead61ad20 100644
--- a/ext/js/data/database.js
+++ b/ext/js/data/database.js
@@ -16,12 +16,22 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/**
+ * @template {string} TObjectStoreName
+ */
 class Database {
     constructor() {
+        /** @type {?IDBDatabase} */
         this._db = null;
+        /** @type {boolean} */
         this._isOpening = false;
     }
 
+    /**
+     * @param {string} databaseName
+     * @param {number} version
+     * @param {import('database').StructureDefinition<TObjectStoreName>[]} structure
+     */
     async open(databaseName, version, structure) {
         if (this._db !== null) {
             throw new Error('Database already open');
@@ -40,6 +50,9 @@ class Database {
         }
     }
 
+    /**
+     * @throws {Error}
+     */
     close() {
         if (this._db === null) {
             throw new Error('Database is not open');
@@ -49,14 +62,26 @@ class Database {
         this._db = null;
     }
 
+    /**
+     * @returns {boolean}
+     */
     isOpening() {
         return this._isOpening;
     }
 
+    /**
+     * @returns {boolean}
+     */
     isOpen() {
         return this._db !== null;
     }
 
+    /**
+     * @param {string[]} storeNames
+     * @param {IDBTransactionMode} mode
+     * @returns {IDBTransaction}
+     * @throws {Error}
+     */
     transaction(storeNames, mode) {
         if (this._db === null) {
             throw new Error(this._isOpening ? 'Database not ready' : 'Database not open');
@@ -64,6 +89,13 @@ class Database {
         return this._db.transaction(storeNames, mode);
     }
 
+    /**
+     * @param {TObjectStoreName} objectStoreName
+     * @param {unknown[]} items
+     * @param {number} start
+     * @param {number} count
+     * @returns {Promise<void>}
+     */
     bulkAdd(objectStoreName, items, start, count) {
         return new Promise((resolve, reject) => {
             if (start + count > items.length) {
@@ -84,6 +116,15 @@ class Database {
         });
     }
 
+    /**
+     * @template [TData=unknown]
+     * @template [TResult=unknown]
+     * @param {IDBObjectStore|IDBIndex} objectStoreOrIndex
+     * @param {?IDBValidKey|IDBKeyRange} query
+     * @param {(results: TResult[], data: TData) => void} onSuccess
+     * @param {(reason: unknown, data: TData) => void} onError
+     * @param {TData} data
+     */
     getAll(objectStoreOrIndex, query, onSuccess, onError, data) {
         if (typeof objectStoreOrIndex.getAll === 'function') {
             this._getAllFast(objectStoreOrIndex, query, onSuccess, onError, data);
@@ -92,6 +133,12 @@ class Database {
         }
     }
 
+    /**
+     * @param {IDBObjectStore|IDBIndex} objectStoreOrIndex
+     * @param {IDBValidKey|IDBKeyRange} query
+     * @param {(value: IDBValidKey[]) => void} onSuccess
+     * @param {(reason?: unknown) => void} onError
+     */
     getAllKeys(objectStoreOrIndex, query, onSuccess, onError) {
         if (typeof objectStoreOrIndex.getAllKeys === 'function') {
             this._getAllKeysFast(objectStoreOrIndex, query, onSuccess, onError);
@@ -100,6 +147,18 @@ class Database {
         }
     }
 
+    /**
+     * @template TPredicateArg
+     * @template [TResult=unknown]
+     * @template [TResultDefault=unknown]
+     * @param {TObjectStoreName} objectStoreName
+     * @param {?string} indexName
+     * @param {?IDBValidKey|IDBKeyRange} query
+     * @param {?((value: TResult|TResultDefault, predicateArg: TPredicateArg) => boolean)} predicate
+     * @param {TPredicateArg} predicateArg
+     * @param {TResultDefault} defaultValue
+     * @returns {Promise<TResult|TResultDefault>}
+     */
     find(objectStoreName, indexName, query, predicate, predicateArg, defaultValue) {
         return new Promise((resolve, reject) => {
             const transaction = this.transaction([objectStoreName], 'readonly');
@@ -109,12 +168,26 @@ class Database {
         });
     }
 
+    /**
+     * @template TData
+     * @template TPredicateArg
+     * @template [TResult=unknown]
+     * @template [TResultDefault=unknown]
+     * @param {IDBObjectStore|IDBIndex} objectStoreOrIndex
+     * @param {?IDBValidKey|IDBKeyRange} query
+     * @param {(value: TResult|TResultDefault, data: TData) => void} resolve
+     * @param {(reason: unknown, data: TData) => void} reject
+     * @param {TData} data
+     * @param {?((value: TResult, predicateArg: TPredicateArg) => boolean)} predicate
+     * @param {TPredicateArg} predicateArg
+     * @param {TResultDefault} defaultValue
+     */
     findFirst(objectStoreOrIndex, query, resolve, reject, data, predicate, predicateArg, defaultValue) {
         const noPredicate = (typeof predicate !== 'function');
         const request = objectStoreOrIndex.openCursor(query, 'next');
-        request.onerror = (e) => reject(e.target.error, data);
+        request.onerror = (e) => reject(/** @type {IDBRequest<?IDBCursorWithValue>} */ (e.target).error, data);
         request.onsuccess = (e) => {
-            const cursor = e.target.result;
+            const cursor = /** @type {IDBRequest<?IDBCursorWithValue>} */ (e.target).result;
             if (cursor) {
                 const {value} = cursor;
                 if (noPredicate || predicate(value, predicateArg)) {
@@ -128,19 +201,33 @@ class Database {
         };
     }
 
+    /**
+     * @param {import('database').CountTarget[]} targets
+     * @param {(results: number[]) => void} resolve
+     * @param {(reason?: unknown) => void} reject
+     */
     bulkCount(targets, resolve, reject) {
         const targetCount = targets.length;
         if (targetCount <= 0) {
-            resolve();
+            resolve([]);
             return;
         }
 
         let completedCount = 0;
+        /** @type {number[]} */
         const results = new Array(targetCount).fill(null);
 
-        const onError = (e) => reject(e.target.error);
+        /**
+         * @param {Event} e
+         * @returns {void}
+         */
+        const onError = (e) => reject(/** @type {IDBRequest<number>} */ (e.target).error);
+        /**
+         * @param {Event} e
+         * @param {number} index
+         */
         const onSuccess = (e, index) => {
-            const count = e.target.result;
+            const count = /** @type {IDBRequest<number>} */ (e.target).result;
             results[index] = count;
             if (++completedCount >= targetCount) {
                 resolve(results);
@@ -156,6 +243,11 @@ class Database {
         }
     }
 
+    /**
+     * @param {TObjectStoreName} objectStoreName
+     * @param {IDBValidKey|IDBKeyRange} key
+     * @returns {Promise<void>}
+     */
     delete(objectStoreName, key) {
         return new Promise((resolve, reject) => {
             const transaction = this._readWriteTransaction([objectStoreName], resolve, reject);
@@ -165,12 +257,23 @@ class Database {
         });
     }
 
+    /**
+     * @param {TObjectStoreName} objectStoreName
+     * @param {?string} indexName
+     * @param {IDBKeyRange} query
+     * @param {?(keys: IDBValidKey[]) => IDBValidKey[]} filterKeys
+     * @param {?(completedCount: number, totalCount: number) => void} onProgress
+     * @returns {Promise<void>}
+     */
     bulkDelete(objectStoreName, indexName, query, filterKeys=null, onProgress=null) {
         return new Promise((resolve, reject) => {
             const transaction = this._readWriteTransaction([objectStoreName], resolve, reject);
             const objectStore = transaction.objectStore(objectStoreName);
             const objectStoreOrIndex = indexName !== null ? objectStore.index(indexName) : objectStore;
 
+            /**
+             * @param {IDBValidKey[]} keys
+             */
             const onGetKeys = (keys) => {
                 try {
                     if (typeof filterKeys === 'function') {
@@ -187,10 +290,14 @@ class Database {
         });
     }
 
+    /**
+     * @param {string} databaseName
+     * @returns {Promise<void>}
+     */
     static deleteDatabase(databaseName) {
         return new Promise((resolve, reject) => {
             const request = indexedDB.deleteDatabase(databaseName);
-            request.onerror = (e) => reject(e.target.error);
+            request.onerror = (e) => reject(/** @type {IDBRequest} */ (e.target).error);
             request.onsuccess = () => resolve();
             request.onblocked = () => reject(new Error('Database deletion blocked'));
         });
@@ -198,24 +305,37 @@ class Database {
 
     // Private
 
+    /**
+     * @param {string} name
+     * @param {number} version
+     * @param {import('database').UpdateFunction} onUpgradeNeeded
+     * @returns {Promise<IDBDatabase>}
+     */
     _open(name, version, onUpgradeNeeded) {
         return new Promise((resolve, reject) => {
             const request = indexedDB.open(name, version);
 
             request.onupgradeneeded = (event) => {
                 try {
-                    request.transaction.onerror = (e) => reject(e.target.error);
-                    onUpgradeNeeded(request.result, request.transaction, event.oldVersion, event.newVersion);
+                    const transaction = /** @type {IDBTransaction} */ (request.transaction);
+                    transaction.onerror = (e) => reject(/** @type {IDBRequest} */ (e.target).error);
+                    onUpgradeNeeded(request.result, transaction, event.oldVersion, event.newVersion);
                 } catch (e) {
                     reject(e);
                 }
             };
 
-            request.onerror = (e) => reject(e.target.error);
+            request.onerror = (e) => reject(/** @type {IDBRequest} */ (e.target).error);
             request.onsuccess = () => resolve(request.result);
         });
     }
 
+    /**
+     * @param {IDBDatabase} db
+     * @param {IDBTransaction} transaction
+     * @param {number} oldVersion
+     * @param {import('database').StructureDefinition<TObjectStoreName>[]} upgrades
+     */
     _upgrade(db, transaction, oldVersion, upgrades) {
         for (const {version, stores} of upgrades) {
             if (oldVersion >= version) { continue; }
@@ -238,6 +358,11 @@ class Database {
         }
     }
 
+    /**
+     * @param {DOMStringList} list
+     * @param {string} value
+     * @returns {boolean}
+     */
     _listContains(list, value) {
         for (let i = 0, ii = list.length; i < ii; ++i) {
             if (list[i] === value) { return true; }
@@ -245,18 +370,37 @@ class Database {
         return false;
     }
 
+    /**
+     * @template [TData=unknown]
+     * @template [TResult=unknown]
+     * @param {IDBObjectStore|IDBIndex} objectStoreOrIndex
+     * @param {?IDBValidKey|IDBKeyRange} query
+     * @param {(results: TResult[], data: TData) => void} onSuccess
+     * @param {(reason: unknown, data: TData) => void} onReject
+     * @param {TData} data
+     */
     _getAllFast(objectStoreOrIndex, query, onSuccess, onReject, data) {
         const request = objectStoreOrIndex.getAll(query);
-        request.onerror = (e) => onReject(e.target.error, data);
-        request.onsuccess = (e) => onSuccess(e.target.result, data);
+        request.onerror = (e) => onReject(/** @type {IDBRequest<import('core').SafeAny[]>} */ (e.target).error, data);
+        request.onsuccess = (e) => onSuccess(/** @type {IDBRequest<import('core').SafeAny[]>} */ (e.target).result, data);
     }
 
+    /**
+     * @template [TData=unknown]
+     * @template [TResult=unknown]
+     * @param {IDBObjectStore|IDBIndex} objectStoreOrIndex
+     * @param {?IDBValidKey|IDBKeyRange} query
+     * @param {(results: TResult[], data: TData) => void} onSuccess
+     * @param {(reason: unknown, data: TData) => void} onReject
+     * @param {TData} data
+     */
     _getAllUsingCursor(objectStoreOrIndex, query, onSuccess, onReject, data) {
+        /** @type {TResult[]} */
         const results = [];
         const request = objectStoreOrIndex.openCursor(query, 'next');
-        request.onerror = (e) => onReject(e.target.error, data);
+        request.onerror = (e) => onReject(/** @type {IDBRequest<?IDBCursorWithValue>} */ (e.target).error, data);
         request.onsuccess = (e) => {
-            const cursor = e.target.result;
+            const cursor = /** @type {IDBRequest<?IDBCursorWithValue>} */ (e.target).result;
             if (cursor) {
                 results.push(cursor.value);
                 cursor.continue();
@@ -266,18 +410,31 @@ class Database {
         };
     }
 
+    /**
+     * @param {IDBObjectStore|IDBIndex} objectStoreOrIndex
+     * @param {IDBValidKey|IDBKeyRange} query
+     * @param {(value: IDBValidKey[]) => void} onSuccess
+     * @param {(reason?: unknown) => void} onError
+     */
     _getAllKeysFast(objectStoreOrIndex, query, onSuccess, onError) {
         const request = objectStoreOrIndex.getAllKeys(query);
-        request.onerror = (e) => onError(e.target.error);
-        request.onsuccess = (e) => onSuccess(e.target.result);
+        request.onerror = (e) => onError(/** @type {IDBRequest<IDBValidKey[]>} */ (e.target).error);
+        request.onsuccess = (e) => onSuccess(/** @type {IDBRequest<IDBValidKey[]>} */ (e.target).result);
     }
 
+    /**
+     * @param {IDBObjectStore|IDBIndex} objectStoreOrIndex
+     * @param {IDBValidKey|IDBKeyRange} query
+     * @param {(value: IDBValidKey[]) => void} onSuccess
+     * @param {(reason?: unknown) => void} onError
+     */
     _getAllKeysUsingCursor(objectStoreOrIndex, query, onSuccess, onError) {
+        /** @type {IDBValidKey[]} */
         const results = [];
         const request = objectStoreOrIndex.openKeyCursor(query, 'next');
-        request.onerror = (e) => onError(e.target.error);
+        request.onerror = (e) => onError(/** @type {IDBRequest<?IDBCursor>} */ (e.target).error);
         request.onsuccess = (e) => {
-            const cursor = e.target.result;
+            const cursor = /** @type {IDBRequest<?IDBCursor>} */ (e.target).result;
             if (cursor) {
                 results.push(cursor.primaryKey);
                 cursor.continue();
@@ -287,6 +444,11 @@ class Database {
         };
     }
 
+    /**
+     * @param {IDBObjectStore} objectStore
+     * @param {IDBValidKey[]} keys
+     * @param {?(completedCount: number, totalCount: number) => void} onProgress
+     */
     _bulkDeleteInternal(objectStore, keys, onProgress) {
         const count = keys.length;
         if (count === 0) { return; }
@@ -295,7 +457,7 @@ class Database {
         const onSuccess = () => {
             ++completedCount;
             try {
-                onProgress(completedCount, count);
+                /** @type {(completedCount: number, totalCount: number) => void}} */ (onProgress)(completedCount, count);
             } catch (e) {
                 // NOP
             }
@@ -310,9 +472,15 @@ class Database {
         }
     }
 
+    /**
+     * @param {string[]} storeNames
+     * @param {() => void} resolve
+     * @param {(reason?: unknown) => void} reject
+     * @returns {IDBTransaction}
+     */
     _readWriteTransaction(storeNames, resolve, reject) {
         const transaction = this.transaction(storeNames, 'readwrite');
-        transaction.onerror = (e) => reject(e.target.error);
+        transaction.onerror = (e) => reject(/** @type {IDBTransaction} */ (e.target).error);
         transaction.onabort = () => reject(new Error('Transaction aborted'));
         transaction.oncomplete = () => resolve();
         return transaction;
diff --git a/ext/js/data/json-schema.js b/ext/js/data/json-schema.js
index c22a0e1ab9..90652845c3 100644
--- a/ext/js/data/json-schema.js
+++ b/ext/js/data/json-schema.js
@@ -20,31 +20,70 @@
  * CacheMap
  */
 
+class JsonSchemaError extends Error {
+    /**
+     * @param {string} message
+     * @param {import('json-schema').ValueStackItem[]} valueStack
+     * @param {import('json-schema').SchemaStackItem[]} schemaStack
+     */
+    constructor(message, valueStack, schemaStack) {
+        super(message);
+        /** @type {import('json-schema').ValueStackItem[]} */
+        this._valueStack = valueStack;
+        /** @type {import('json-schema').SchemaStackItem[]} */
+        this._schemaStack = schemaStack;
+    }
+
+    /** @type {unknown|undefined} */
+    get value() { return this._valueStack.length > 0 ? this._valueStack[this._valueStack.length - 1].value : void 0; }
+
+    /** @type {import('json-schema').Schema|import('json-schema').Schema[]|undefined} */
+    get schema() { return this._schemaStack.length > 0 ? this._schemaStack[this._schemaStack.length - 1].schema : void 0; }
+
+    /** @type {import('json-schema').ValueStackItem[]} */
+    get valueStack() { return this._valueStack; }
+
+    /** @type {import('json-schema').SchemaStackItem[]} */
+    get schemaStack() { return this._schemaStack; }
+}
+
 class JsonSchema {
+    /**
+     * @param {import('json-schema').Schema} schema
+     * @param {import('json-schema').Schema} [rootSchema]
+     */
     constructor(schema, rootSchema) {
-        this._schema = null;
+        /** @type {import('json-schema').Schema} */
         this._startSchema = schema;
+        /** @type {import('json-schema').Schema} */
         this._rootSchema = typeof rootSchema !== 'undefined' ? rootSchema : schema;
+        /** @type {?CacheMap<string, RegExp>} */
         this._regexCache = null;
+        /** @type {?Map<string, {schema: import('json-schema').Schema, stack: import('json-schema').SchemaStackItem[]}>} */
         this._refCache = null;
+        /** @type {import('json-schema').ValueStackItem[]} */
         this._valueStack = [];
+        /** @type {import('json-schema').SchemaStackItem[]} */
         this._schemaStack = [];
+        /** @type {?(jsonSchema: JsonSchema) => void} */
         this._progress = null;
+        /** @type {number} */
         this._progressCounter = 0;
+        /** @type {number} */
         this._progressInterval = 1;
-
-        this._schemaPush(null, null);
-        this._valuePush(null, null);
     }
 
+    /** @type {import('json-schema').Schema} */
     get schema() {
         return this._startSchema;
     }
 
+    /** @type {import('json-schema').Schema} */
     get rootSchema() {
         return this._rootSchema;
     }
 
+    /** @type {?(jsonSchema: JsonSchema) => void} */
     get progress() {
         return this._progress;
     }
@@ -53,6 +92,7 @@ class JsonSchema {
         this._progress = value;
     }
 
+    /** @type {number} */
     get progressInterval() {
         return this._progressInterval;
     }
@@ -61,6 +101,10 @@ class JsonSchema {
         this._progressInterval = value;
     }
 
+    /**
+     * @param {import('json-schema').Value} value
+     * @returns {import('json-schema').Value}
+     */
     createProxy(value) {
         return (
             typeof value === 'object' && value !== null ?
@@ -69,6 +113,10 @@ class JsonSchema {
         );
     }
 
+    /**
+     * @param {unknown} value
+     * @returns {boolean}
+     */
     isValid(value) {
         try {
             this.validate(value);
@@ -78,123 +126,203 @@ class JsonSchema {
         }
     }
 
+    /**
+     * @param {unknown} value
+     */
     validate(value) {
-        this._schemaPush(this._startSchema, null);
+        const schema = this._startSchema;
+        this._schemaPush(schema, null);
         this._valuePush(value, null);
         try {
-            this._validate(value);
+            this._validate(schema, value);
         } finally {
             this._valuePop();
             this._schemaPop();
         }
     }
 
+    /**
+     * @param {unknown} [value]
+     * @returns {import('json-schema').Value}
+     */
     getValidValueOrDefault(value) {
-        return this._getValidValueOrDefault(null, value, {schema: this._startSchema, path: null});
+        const schema = this._startSchema;
+        return this._getValidValueOrDefault(schema, null, value, [{schema, path: null}]);
     }
 
+    /**
+     * @param {string} property
+     * @returns {?JsonSchema}
+     */
     getObjectPropertySchema(property) {
-        const startSchemaInfo = this._getResolveSchemaInfo({schema: this._startSchema, path: null});
-        this._schemaPush(startSchemaInfo.schema, startSchemaInfo.path);
+        const schema = this._startSchema;
+        const {schema: schema2, stack} = this._getResolvedSchemaInfo(schema, [{schema, path: null}]);
+        this._schemaPushMultiple(stack);
         try {
-            const schemaInfo = this._getObjectPropertySchemaInfo(property);
-            return schemaInfo !== null ? new JsonSchema(schemaInfo.schema, this._rootSchema) : null;
+            const {schema: propertySchema} = this._getObjectPropertySchemaInfo(schema2, property);
+            return propertySchema !== false ? new JsonSchema(propertySchema, this._rootSchema) : null;
         } finally {
-            this._schemaPop();
+            this._schemaPopMultiple(stack.length);
         }
     }
 
+    /**
+     * @param {number} index
+     * @returns {?JsonSchema}
+     */
     getArrayItemSchema(index) {
-        const startSchemaInfo = this._getResolveSchemaInfo({schema: this._startSchema, path: null});
-        this._schemaPush(startSchemaInfo.schema, startSchemaInfo.path);
+        const schema = this._startSchema;
+        const {schema: schema2, stack} = this._getResolvedSchemaInfo(schema, [{schema, path: null}]);
+        this._schemaPushMultiple(stack);
         try {
-            const schemaInfo = this._getArrayItemSchemaInfo(index);
-            return schemaInfo !== null ? new JsonSchema(schemaInfo.schema, this._rootSchema) : null;
+            const {schema: itemSchema} = this._getArrayItemSchemaInfo(schema2, index);
+            return itemSchema !== false ? new JsonSchema(itemSchema, this._rootSchema) : null;
         } finally {
-            this._schemaPop();
+            this._schemaPopMultiple(stack.length);
         }
     }
 
+    /**
+     * @param {string} property
+     * @returns {boolean}
+     */
     isObjectPropertyRequired(property) {
-        const {required} = this._startSchema;
+        const schema = this._startSchema;
+        if (typeof schema === 'boolean') { return false; }
+        const {required} = schema;
         return Array.isArray(required) && required.includes(property);
     }
 
     // Internal state functions for error construction and progress callback
 
+    /**
+     * @returns {import('json-schema').ValueStackItem[]}
+     */
     getValueStack() {
-        const valueStack = [];
-        for (let i = 1, ii = this._valueStack.length; i < ii; ++i) {
-            const {value, path} = this._valueStack[i];
-            valueStack.push({value, path});
+        const result = [];
+        for (const {value, path} of this._valueStack) {
+            result.push({value, path});
         }
-        return valueStack;
+        return result;
     }
 
+    /**
+     * @returns {import('json-schema').SchemaStackItem[]}
+     */
     getSchemaStack() {
-        const schemaStack = [];
-        for (let i = 1, ii = this._schemaStack.length; i < ii; ++i) {
-            const {schema, path} = this._schemaStack[i];
-            schemaStack.push({schema, path});
+        const result = [];
+        for (const {schema, path} of this._schemaStack) {
+            result.push({schema, path});
         }
-        return schemaStack;
+        return result;
     }
 
+    /**
+     * @returns {number}
+     */
     getValueStackLength() {
         return this._valueStack.length - 1;
     }
 
+    /**
+     * @param {number} index
+     * @returns {import('json-schema').ValueStackItem}
+     */
     getValueStackItem(index) {
         const {value, path} = this._valueStack[index + 1];
         return {value, path};
     }
 
+    /**
+     * @returns {number}
+     */
     getSchemaStackLength() {
         return this._schemaStack.length - 1;
     }
 
+    /**
+     * @param {number} index
+     * @returns {import('json-schema').SchemaStackItem}
+     */
     getSchemaStackItem(index) {
         const {schema, path} = this._schemaStack[index + 1];
         return {schema, path};
     }
 
+    /**
+     * @template T
+     * @param {T} value
+     * @returns {T}
+     */
+    static clone(value) {
+        return clone(value);
+    }
+
     // Stack
 
+    /**
+     * @param {unknown} value
+     * @param {string|number|null} path
+     */
     _valuePush(value, path) {
         this._valueStack.push({value, path});
     }
 
+    /**
+     * @returns {void}
+     */
     _valuePop() {
         this._valueStack.pop();
     }
 
+    /**
+     * @param {import('json-schema').Schema|import('json-schema').Schema[]} schema
+     * @param {string|number|null} path
+     */
     _schemaPush(schema, path) {
         this._schemaStack.push({schema, path});
-        this._schema = schema;
     }
 
+    /**
+     * @param {import('json-schema').SchemaStackItem[]} items
+     */
+    _schemaPushMultiple(items) {
+        this._schemaStack.push(...items);
+    }
+
+    /**
+     * @returns {void}
+     */
     _schemaPop() {
         this._schemaStack.pop();
-        this._schema = this._schemaStack[this._schemaStack.length - 1].schema;
+    }
+
+    /**
+     * @param {number} count
+     */
+    _schemaPopMultiple(count) {
+        for (let i = 0; i < count; ++i) {
+            this._schemaStack.pop();
+        }
     }
 
     // Private
 
+    /**
+     * @param {string} message
+     * @returns {JsonSchemaError}
+     */
     _createError(message) {
         const valueStack = this.getValueStack();
         const schemaStack = this.getSchemaStack();
-        const error = new Error(message);
-        error.value = valueStack[valueStack.length - 1].value;
-        error.schema = schemaStack[schemaStack.length - 1].schema;
-        error.valueStack = valueStack;
-        error.schemaStack = schemaStack;
-        return error;
-    }
-
-    _isObject(value) {
-        return typeof value === 'object' && value !== null && !Array.isArray(value);
+        return new JsonSchemaError(message, valueStack, schemaStack);
     }
 
+    /**
+     * @param {string} pattern
+     * @param {string} flags
+     * @returns {RegExp}
+     */
     _getRegex(pattern, flags) {
         if (this._regexCache === null) {
             this._regexCache = new CacheMap(100);
@@ -209,81 +337,125 @@ class JsonSchema {
         return regex;
     }
 
-    _getUnconstrainedSchema() {
-        return {};
-    }
-
-    _getObjectPropertySchemaInfo(property) {
-        const {properties} = this._schema;
-        if (this._isObject(properties)) {
+    /**
+     * @param {import('json-schema').Schema} schema
+     * @param {string} property
+     * @returns {{schema: import('json-schema').Schema, stack: import('json-schema').SchemaStackItem[]}}
+     */
+    _getObjectPropertySchemaInfo(schema, property) {
+        if (typeof schema === 'boolean') {
+            return {schema, stack: [{schema, path: null}]};
+        }
+        const {properties} = schema;
+        if (typeof properties !== 'undefined' && Object.prototype.hasOwnProperty.call(properties, property)) {
             const propertySchema = properties[property];
-            if (this._isObject(propertySchema)) {
-                return {schema: propertySchema, path: ['properties', property]};
+            if (typeof propertySchema !== 'undefined') {
+                return {
+                    schema: propertySchema,
+                    stack: [
+                        {schema: properties, path: 'properties'},
+                        {schema: propertySchema, path: property}
+                    ]
+                };
             }
         }
-
-        const {additionalProperties} = this._schema;
-        if (additionalProperties === false) {
-            return null;
-        } else if (this._isObject(additionalProperties)) {
-            return {schema: additionalProperties, path: 'additionalProperties'};
-        } else {
-            const result = this._getUnconstrainedSchema();
-            return {schema: result, path: null};
-        }
-    }
-
-    _getArrayItemSchemaInfo(index) {
-        const {items} = this._schema;
-        if (this._isObject(items)) {
-            return {schema: items, path: 'items'};
-        }
-        if (Array.isArray(items)) {
-            if (index >= 0 && index < items.length) {
-                const propertySchema = items[index];
-                if (this._isObject(propertySchema)) {
-                    return {schema: propertySchema, path: ['items', index]};
+        return this._getOptionalSchemaInfo(schema.additionalProperties, 'additionalProperties');
+    }
+
+    /**
+     * @param {import('json-schema').Schema} schema
+     * @param {number} index
+     * @returns {{schema: import('json-schema').Schema, stack: import('json-schema').SchemaStackItem[]}}
+     */
+    _getArrayItemSchemaInfo(schema, index) {
+        if (typeof schema === 'boolean') {
+            return {schema, stack: [{schema, path: null}]};
+        }
+        const {prefixItems} = schema;
+        if (typeof prefixItems !== 'undefined') {
+            if (index >= 0 && index < prefixItems.length) {
+                const itemSchema = prefixItems[index];
+                if (typeof itemSchema !== 'undefined') {
+                    return {
+                        schema: itemSchema,
+                        stack: [
+                            {schema: prefixItems, path: 'prefixItems'},
+                            {schema: itemSchema, path: index}
+                        ]
+                    };
                 }
             }
         }
-
-        const {additionalItems} = this._schema;
-        if (additionalItems === false) {
-            return null;
-        } else if (this._isObject(additionalItems)) {
-            return {schema: additionalItems, path: 'additionalItems'};
-        } else {
-            const result = this._getUnconstrainedSchema();
-            return {schema: result, path: null};
-        }
-    }
-
-    _getSchemaOrValueType(value) {
-        const {type} = this._schema;
-
-        if (Array.isArray(type)) {
-            if (typeof value !== 'undefined') {
-                const valueType = this._getValueType(value);
-                if (type.indexOf(valueType) >= 0) {
-                    return valueType;
+        const {items} = schema;
+        if (typeof items !== 'undefined') {
+            if (Array.isArray(items)) { // Legacy schema format
+                if (index >= 0 && index < items.length) {
+                    const itemSchema = items[index];
+                    if (typeof itemSchema !== 'undefined') {
+                        return {
+                            schema: itemSchema,
+                            stack: [
+                                {schema: items, path: 'items'},
+                                {schema: itemSchema, path: index}
+                            ]
+                        };
+                    }
                 }
+            } else {
+                return {
+                    schema: items,
+                    stack: [{schema: items, path: 'items'}]
+                };
             }
-            return null;
         }
+        return this._getOptionalSchemaInfo(schema.additionalItems, 'additionalItems');
+    }
 
-        if (typeof type !== 'undefined') { return type; }
-        return (typeof value !== 'undefined') ? this._getValueType(value) : null;
+    /**
+     * @param {import('json-schema').Schema|undefined} schema
+     * @param {string|number|null} path
+     * @returns {{schema: import('json-schema').Schema, stack: import('json-schema').SchemaStackItem[]}}
+     */
+    _getOptionalSchemaInfo(schema, path) {
+        switch (typeof schema) {
+            case 'boolean':
+            case 'object':
+                break;
+            default:
+                schema = true;
+                path = null;
+                break;
+        }
+        return {schema, stack: [{schema, path}]};
     }
 
+    /**
+     * @param {unknown} value
+     * @returns {?import('json-schema').Type}
+     * @throws {Error}
+     */
     _getValueType(value) {
         const type = typeof value;
-        if (type === 'object') {
-            if (value === null) { return 'null'; }
-            if (Array.isArray(value)) { return 'array'; }
+        switch (type) {
+            case 'object':
+                if (value === null) { return 'null'; }
+                if (Array.isArray(value)) { return 'array'; }
+                return 'object';
+            case 'string':
+            case 'number':
+            case 'boolean':
+                return type;
+            default:
+                return null;
         }
-        return type;
     }
 
+    /**
+     * @param {unknown} value
+     * @param {?import('json-schema').Type} type
+     * @param {import('json-schema').Type|import('json-schema').Type[]|undefined} schemaTypes
+     * @returns {boolean}
+     */
     _isValueTypeAny(value, type, schemaTypes) {
         if (typeof schemaTypes === 'string') {
             return this._isValueType(value, type, schemaTypes);
@@ -298,13 +470,24 @@ class JsonSchema {
         return true;
     }
 
+    /**
+     * @param {unknown} value
+     * @param {?import('json-schema').Type} type
+     * @param {import('json-schema').Type} schemaType
+     * @returns {boolean}
+     */
     _isValueType(value, type, schemaType) {
         return (
             type === schemaType ||
-            (schemaType === 'integer' && Math.floor(value) === value)
+            (schemaType === 'integer' && typeof value === 'number' && Math.floor(value) === value)
         );
     }
 
+    /**
+     * @param {unknown} value1
+     * @param {import('json-schema').Value[]} valueList
+     * @returns {boolean}
+     */
     _valuesAreEqualAny(value1, valueList) {
         for (const value2 of valueList) {
             if (this._valuesAreEqual(value1, value2)) {
@@ -314,29 +497,45 @@ class JsonSchema {
         return false;
     }
 
+    /**
+     * @param {unknown} value1
+     * @param {import('json-schema').Value} value2
+     * @returns {boolean}
+     */
     _valuesAreEqual(value1, value2) {
         return value1 === value2;
     }
 
-    _getResolveSchemaInfo(schemaInfo) {
-        const ref = schemaInfo.schema.$ref;
-        if (typeof ref !== 'string') { return schemaInfo; }
-
-        const {path: basePath} = schemaInfo;
-        const {schema, path} = this._getReference(ref);
-        if (Array.isArray(basePath)) {
-            path.unshift(...basePath);
-        } else {
-            path.unshift(basePath);
+    /**
+     * @param {import('json-schema').Schema} schema
+     * @param {import('json-schema').SchemaStackItem[]} stack
+     * @returns {{schema: import('json-schema').Schema, stack: import('json-schema').SchemaStackItem[]}}
+     */
+    _getResolvedSchemaInfo(schema, stack) {
+        if (typeof schema !== 'boolean') {
+            const ref = schema.$ref;
+            if (typeof ref === 'string') {
+                const {schema: schema2, stack: stack2} = this._getReference(ref);
+                return {
+                    schema: schema2,
+                    stack: [...stack, ...stack2]
+                };
+            }
         }
-        return {schema, path};
+        return {schema, stack};
     }
 
+    /**
+     * @param {string} ref
+     * @returns {{schema: import('json-schema').Schema, stack: import('json-schema').SchemaStackItem[]}}
+     * @throws {Error}
+     */
     _getReference(ref) {
         if (!ref.startsWith('#/')) {
             throw this._createError(`Unsupported reference path: ${ref}`);
         }
 
+        /** @type {{schema: import('json-schema').Schema, stack: import('json-schema').SchemaStackItem[]}|undefined} */
         let info;
         if (this._refCache !== null) {
             info = this._refCache.get(ref);
@@ -349,12 +548,20 @@ class JsonSchema {
             this._refCache.set(ref, info);
         }
 
-        return {schema: info.schema, path: [...info.path]};
+        info.stack = this._copySchemaStack(info.stack);
+        return info;
     }
 
+    /**
+     * @param {string} ref
+     * @returns {{schema: import('json-schema').Schema, stack: import('json-schema').SchemaStackItem[]}}
+     * @throws {Error}
+     */
     _getReferenceUncached(ref) {
+        /** @type {Set<string>} */
         const visited = new Set();
-        const path = [];
+        /** @type {import('json-schema').SchemaStackItem[]} */
+        const stack = [];
         while (true) {
             if (visited.has(ref)) {
                 throw this._createError(`Recursive reference: ${ref}`);
@@ -363,106 +570,139 @@ class JsonSchema {
 
             const pathParts = ref.substring(2).split('/');
             let schema = this._rootSchema;
-            try {
-                for (const pathPart of pathParts) {
-                    schema = schema[pathPart];
+            stack.push({schema, path: null});
+            for (const pathPart of pathParts) {
+                if (!(typeof schema === 'object' && schema !== null && Object.prototype.hasOwnProperty.call(schema, pathPart))) {
+                    throw this._createError(`Invalid reference: ${ref}`);
                 }
-            } catch (e) {
-                throw this._createError(`Invalid reference: ${ref}`);
+                const schemaNext = /** @type {import('core').UnknownObject} */ (schema)[pathPart];
+                if (!(typeof schemaNext === 'boolean' || (typeof schemaNext === 'object' && schemaNext !== null))) {
+                    throw this._createError(`Invalid reference: ${ref}`);
+                }
+                schema = schemaNext;
+                stack.push({schema, path: pathPart});
             }
-            if (!this._isObject(schema)) {
+            if (Array.isArray(schema)) {
                 throw this._createError(`Invalid reference: ${ref}`);
             }
 
-            path.push(null, ...pathParts);
-
-            ref = schema.$ref;
-            if (typeof ref !== 'string') {
-                return {schema, path};
+            const refNext = typeof schema === 'object' && schema !== null ? schema.$ref : void 0;
+            if (typeof refNext !== 'string') {
+                return {schema, stack};
             }
+            ref = refNext;
+        }
+    }
+
+    /**
+     * @param {import('json-schema').SchemaStackItem[]} schemaStack
+     * @returns {import('json-schema').SchemaStackItem[]}
+     */
+    _copySchemaStack(schemaStack) {
+        /** @type {import('json-schema').SchemaStackItem[]} */
+        const results = [];
+        for (const {schema, path} of schemaStack) {
+            results.push({schema, path});
         }
+        return results;
     }
 
     // Validation
 
-    _isValidCurrent(value) {
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {unknown} value
+     * @returns {boolean}
+     */
+    _isValidCurrent(schema, value) {
         try {
-            this._validate(value);
+            this._validate(schema, value);
             return true;
         } catch (e) {
             return false;
         }
     }
 
-    _validate(value) {
+    /**
+     * @param {import('json-schema').Schema} schema
+     * @param {unknown} value
+     */
+    _validate(schema, value) {
         if (this._progress !== null) {
             const counter = (this._progressCounter + 1) % this._progressInterval;
             this._progressCounter = counter;
             if (counter === 0) { this._progress(this); }
         }
 
-        const ref = this._schema.$ref;
-        const schemaInfo = (typeof ref === 'string') ? this._getReference(ref) : null;
-
-        if (schemaInfo === null) {
-            this._validateInner(value);
-        } else {
-            this._schemaPush(schemaInfo.schema, schemaInfo.path);
-            try {
-                this._validateInner(value);
-            } finally {
-                this._schemaPop();
-            }
-        }
-    }
-
-    _validateInner(value) {
-        this._validateSingleSchema(value);
-        this._validateConditional(value);
-        this._validateAllOf(value);
-        this._validateAnyOf(value);
-        this._validateOneOf(value);
-        this._validateNoneOf(value);
-    }
-
-    _validateConditional(value) {
-        const ifSchema = this._schema.if;
-        if (!this._isObject(ifSchema)) { return; }
+        const {schema: schema2, stack} = this._getResolvedSchemaInfo(schema, []);
+        this._schemaPushMultiple(stack);
+        try {
+            this._validateInner(schema2, value);
+        } finally {
+            this._schemaPopMultiple(stack.length);
+        }
+    }
+
+    /**
+     * @param {import('json-schema').Schema} schema
+     * @param {unknown} value
+     * @throws {Error}
+     */
+    _validateInner(schema, value) {
+        if (schema === true) { return; }
+        if (schema === false) { throw this._createError('False schema'); }
+        this._validateSingleSchema(schema, value);
+        this._validateConditional(schema, value);
+        this._validateAllOf(schema, value);
+        this._validateAnyOf(schema, value);
+        this._validateOneOf(schema, value);
+        this._validateNot(schema, value);
+    }
+
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {unknown} value
+     */
+    _validateConditional(schema, value) {
+        const ifSchema = schema.if;
+        if (typeof ifSchema === 'undefined') { return; }
 
         let okay = true;
         this._schemaPush(ifSchema, 'if');
         try {
-            this._validate(value);
+            this._validate(ifSchema, value);
         } catch (e) {
             okay = false;
         } finally {
             this._schemaPop();
         }
 
-        const nextSchema = okay ? this._schema.then : this._schema.else;
-        if (this._isObject(nextSchema)) { return; }
+        const nextSchema = okay ? schema.then : schema.else;
+        if (typeof nextSchema === 'undefined') { return; }
 
         this._schemaPush(nextSchema, okay ? 'then' : 'else');
         try {
-            this._validate(value);
+            this._validate(nextSchema, value);
         } finally {
             this._schemaPop();
         }
     }
 
-    _validateAllOf(value) {
-        const subSchemas = this._schema.allOf;
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {unknown} value
+     */
+    _validateAllOf(schema, value) {
+        const subSchemas = schema.allOf;
         if (!Array.isArray(subSchemas)) { return; }
 
         this._schemaPush(subSchemas, 'allOf');
         try {
             for (let i = 0, ii = subSchemas.length; i < ii; ++i) {
                 const subSchema = subSchemas[i];
-                if (!this._isObject(subSchema)) { continue; }
-
                 this._schemaPush(subSchema, i);
                 try {
-                    this._validate(value);
+                    this._validate(subSchema, value);
                 } finally {
                     this._schemaPop();
                 }
@@ -472,19 +712,21 @@ class JsonSchema {
         }
     }
 
-    _validateAnyOf(value) {
-        const subSchemas = this._schema.anyOf;
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {unknown} value
+     */
+    _validateAnyOf(schema, value) {
+        const subSchemas = schema.anyOf;
         if (!Array.isArray(subSchemas)) { return; }
 
         this._schemaPush(subSchemas, 'anyOf');
         try {
             for (let i = 0, ii = subSchemas.length; i < ii; ++i) {
                 const subSchema = subSchemas[i];
-                if (!this._isObject(subSchema)) { continue; }
-
                 this._schemaPush(subSchema, i);
                 try {
-                    this._validate(value);
+                    this._validate(subSchema, value);
                     return;
                 } catch (e) {
                     // NOP
@@ -499,8 +741,12 @@ class JsonSchema {
         }
     }
 
-    _validateOneOf(value) {
-        const subSchemas = this._schema.oneOf;
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {unknown} value
+     */
+    _validateOneOf(schema, value) {
+        const subSchemas = schema.oneOf;
         if (!Array.isArray(subSchemas)) { return; }
 
         this._schemaPush(subSchemas, 'oneOf');
@@ -508,11 +754,9 @@ class JsonSchema {
             let count = 0;
             for (let i = 0, ii = subSchemas.length; i < ii; ++i) {
                 const subSchema = subSchemas[i];
-                if (!this._isObject(subSchema)) { continue; }
-
                 this._schemaPush(subSchema, i);
                 try {
-                    this._validate(value);
+                    this._validate(subSchema, value);
                     ++count;
                 } catch (e) {
                     // NOP
@@ -529,33 +773,37 @@ class JsonSchema {
         }
     }
 
-    _validateNoneOf(value) {
-        const subSchemas = this._schema.not;
-        if (!Array.isArray(subSchemas)) { return; }
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {unknown} value
+     * @throws {Error}
+     */
+    _validateNot(schema, value) {
+        const notSchema = schema.not;
+        if (typeof notSchema === 'undefined') { return; }
 
-        this._schemaPush(subSchemas, 'not');
-        try {
-            for (let i = 0, ii = subSchemas.length; i < ii; ++i) {
-                const subSchema = subSchemas[i];
-                if (!this._isObject(subSchema)) { continue; }
+        if (Array.isArray(notSchema)) {
+            throw this._createError('not schema is an array');
+        }
 
-                this._schemaPush(subSchema, i);
-                try {
-                    this._validate(value);
-                } catch (e) {
-                    continue;
-                } finally {
-                    this._schemaPop();
-                }
-                throw this._createError(`not[${i}] schema matched`);
-            }
+        this._schemaPush(notSchema, 'not');
+        try {
+            this._validate(notSchema, value);
+        } catch (e) {
+            return;
         } finally {
             this._schemaPop();
         }
+        throw this._createError('not schema matched');
     }
 
-    _validateSingleSchema(value) {
-        const {type: schemaType, const: schemaConst, enum: schemaEnum} = this._schema;
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {unknown} value
+     * @throws {Error}
+     */
+    _validateSingleSchema(schema, value) {
+        const {type: schemaType, const: schemaConst, enum: schemaEnum} = schema;
         const type = this._getValueType(value);
         if (!this._isValueTypeAny(value, type, schemaType)) {
             throw this._createError(`Value type ${type} does not match schema type ${schemaType}`);
@@ -571,22 +819,27 @@ class JsonSchema {
 
         switch (type) {
             case 'number':
-                this._validateNumber(value);
+                this._validateNumber(schema, /** @type {number} */ (value));
                 break;
             case 'string':
-                this._validateString(value);
+                this._validateString(schema, /** @type {string} */ (value));
                 break;
             case 'array':
-                this._validateArray(value);
+                this._validateArray(schema, /** @type {import('json-schema').Value[]} */ (value));
                 break;
             case 'object':
-                this._validateObject(value);
+                this._validateObject(schema, /** @type {import('json-schema').ValueObject} */ (value));
                 break;
         }
     }
 
-    _validateNumber(value) {
-        const {multipleOf, minimum, exclusiveMinimum, maximum, exclusiveMaximum} = this._schema;
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {number} value
+     * @throws {Error}
+     */
+    _validateNumber(schema, value) {
+        const {multipleOf, minimum, exclusiveMinimum, maximum, exclusiveMaximum} = schema;
         if (typeof multipleOf === 'number' && Math.floor(value / multipleOf) * multipleOf !== value) {
             throw this._createError(`Number is not a multiple of ${multipleOf}`);
         }
@@ -608,8 +861,13 @@ class JsonSchema {
         }
     }
 
-    _validateString(value) {
-        const {minLength, maxLength, pattern} = this._schema;
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {string} value
+     * @throws {Error}
+     */
+    _validateString(schema, value) {
+        const {minLength, maxLength, pattern} = schema;
         if (typeof minLength === 'number' && value.length < minLength) {
             throw this._createError('String length too short');
         }
@@ -619,14 +877,14 @@ class JsonSchema {
         }
 
         if (typeof pattern === 'string') {
-            let {patternFlags} = this._schema;
+            let {patternFlags} = schema;
             if (typeof patternFlags !== 'string') { patternFlags = ''; }
 
             let regex;
             try {
                 regex = this._getRegex(pattern, patternFlags);
             } catch (e) {
-                throw this._createError(`Pattern is invalid (${e.message})`);
+                throw this._createError(`Pattern is invalid (${e instanceof Error ? e.message : `${e}`})`);
             }
 
             if (!regex.test(value)) {
@@ -635,8 +893,13 @@ class JsonSchema {
         }
     }
 
-    _validateArray(value) {
-        const {minItems, maxItems} = this._schema;
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {unknown[]} value
+     * @throws {Error}
+     */
+    _validateArray(schema, value) {
+        const {minItems, maxItems} = schema;
         const {length} = value;
 
         if (typeof minItems === 'number' && length < minItems) {
@@ -647,30 +910,35 @@ class JsonSchema {
             throw this._createError('Array length too long');
         }
 
-        this._validateArrayContains(value);
+        this._validateArrayContains(schema, value);
 
         for (let i = 0; i < length; ++i) {
-            const schemaInfo = this._getArrayItemSchemaInfo(i);
-            if (schemaInfo === null) {
+            const {schema: itemSchema, stack} = this._getArrayItemSchemaInfo(schema, i);
+            if (itemSchema === false) {
                 throw this._createError(`No schema found for array[${i}]`);
             }
 
             const propertyValue = value[i];
 
-            this._schemaPush(schemaInfo.schema, schemaInfo.path);
+            this._schemaPushMultiple(stack);
             this._valuePush(propertyValue, i);
             try {
-                this._validate(propertyValue);
+                this._validate(itemSchema, propertyValue);
             } finally {
                 this._valuePop();
-                this._schemaPop();
+                this._schemaPopMultiple(stack.length);
             }
         }
     }
 
-    _validateArrayContains(value) {
-        const containsSchema = this._schema.contains;
-        if (!this._isObject(containsSchema)) { return; }
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {unknown[]} value
+     * @throws {Error}
+     */
+    _validateArrayContains(schema, value) {
+        const containsSchema = schema.contains;
+        if (typeof containsSchema === 'undefined') { return; }
 
         this._schemaPush(containsSchema, 'contains');
         try {
@@ -678,7 +946,7 @@ class JsonSchema {
                 const propertyValue = value[i];
                 this._valuePush(propertyValue, i);
                 try {
-                    this._validate(propertyValue);
+                    this._validate(containsSchema, propertyValue);
                     return;
                 } catch (e) {
                     // NOP
@@ -692,8 +960,13 @@ class JsonSchema {
         }
     }
 
-    _validateObject(value) {
-        const {required, minProperties, maxProperties} = this._schema;
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {import('json-schema').ValueObject} value
+     * @throws {Error}
+     */
+    _validateObject(schema, value) {
+        const {required, minProperties, maxProperties} = schema;
         const properties = Object.getOwnPropertyNames(value);
         const {length} = properties;
 
@@ -715,27 +988,32 @@ class JsonSchema {
 
         for (let i = 0; i < length; ++i) {
             const property = properties[i];
-            const schemaInfo = this._getObjectPropertySchemaInfo(property);
-            if (schemaInfo === null) {
+            const {schema: propertySchema, stack} = this._getObjectPropertySchemaInfo(schema, property);
+            if (propertySchema === false) {
                 throw this._createError(`No schema found for ${property}`);
             }
 
             const propertyValue = value[property];
 
-            this._schemaPush(schemaInfo.schema, schemaInfo.path);
+            this._schemaPushMultiple(stack);
             this._valuePush(propertyValue, property);
             try {
-                this._validate(propertyValue);
+                this._validate(propertySchema, propertyValue);
             } finally {
                 this._valuePop();
-                this._schemaPop();
+                this._schemaPopMultiple(stack.length);
             }
         }
     }
 
     // Creation
 
+    /**
+     * @param {import('json-schema').Type|import('json-schema').Type[]|undefined} type
+     * @returns {import('json-schema').Value}
+     */
     _getDefaultTypeValue(type) {
+        if (Array.isArray(type)) { type = type[0]; }
         if (typeof type === 'string') {
             switch (type) {
                 case 'null':
@@ -756,95 +1034,122 @@ class JsonSchema {
         return null;
     }
 
-    _getDefaultSchemaValue() {
-        const {type: schemaType, default: schemaDefault} = this._schema;
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @returns {import('json-schema').Value}
+     */
+    _getDefaultSchemaValue(schema) {
+        const {type: schemaType, default: schemaDefault} = schema;
         return (
             typeof schemaDefault !== 'undefined' &&
             this._isValueTypeAny(schemaDefault, this._getValueType(schemaDefault), schemaType) ?
-            clone(schemaDefault) :
+            JsonSchema.clone(schemaDefault) :
             this._getDefaultTypeValue(schemaType)
         );
     }
 
-    _getValidValueOrDefault(path, value, schemaInfo) {
-        schemaInfo = this._getResolveSchemaInfo(schemaInfo);
-        this._schemaPush(schemaInfo.schema, schemaInfo.path);
+    /**
+     * @param {import('json-schema').Schema} schema
+     * @param {string|number|null} path
+     * @param {unknown} value
+     * @param {import('json-schema').SchemaStackItem[]} stack
+     * @returns {import('json-schema').Value}
+     */
+    _getValidValueOrDefault(schema, path, value, stack) {
+        ({schema, stack} = this._getResolvedSchemaInfo(schema, stack));
+        this._schemaPushMultiple(stack);
         this._valuePush(value, path);
         try {
-            return this._getValidValueOrDefaultInner(value);
+            return this._getValidValueOrDefaultInner(schema, value);
         } finally {
             this._valuePop();
-            this._schemaPop();
+            this._schemaPopMultiple(stack.length);
         }
     }
 
-    _getValidValueOrDefaultInner(value) {
+    /**
+     * @param {import('json-schema').Schema} schema
+     * @param {unknown} value
+     * @returns {import('json-schema').Value}
+     */
+    _getValidValueOrDefaultInner(schema, value) {
         let type = this._getValueType(value);
-        if (typeof value === 'undefined' || !this._isValueTypeAny(value, type, this._schema.type)) {
-            value = this._getDefaultSchemaValue();
+        if (typeof schema === 'boolean') {
+            return type !== null ? /** @type {import('json-schema').ValueObject} */ (value) : null;
+        }
+        if (typeof value === 'undefined' || !this._isValueTypeAny(value, type, schema.type)) {
+            value = this._getDefaultSchemaValue(schema);
             type = this._getValueType(value);
         }
 
         switch (type) {
             case 'object':
-                value = this._populateObjectDefaults(value);
-                break;
+                return this._populateObjectDefaults(schema, /** @type {import('json-schema').ValueObject} */ (value));
             case 'array':
-                value = this._populateArrayDefaults(value);
-                break;
+                return this._populateArrayDefaults(schema, /** @type {import('json-schema').Value[]} */ (value));
             default:
-                if (!this._isValidCurrent(value)) {
-                    const schemaDefault = this._getDefaultSchemaValue();
-                    if (this._isValidCurrent(schemaDefault)) {
-                        value = schemaDefault;
+                if (!this._isValidCurrent(schema, value)) {
+                    const schemaDefault = this._getDefaultSchemaValue(schema);
+                    if (this._isValidCurrent(schema, schemaDefault)) {
+                        return schemaDefault;
                     }
                 }
                 break;
         }
 
-        return value;
+        return /** @type {import('json-schema').ValueObject} */ (value);
     }
 
-    _populateObjectDefaults(value) {
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {import('json-schema').ValueObject} value
+     * @returns {import('json-schema').ValueObject}
+     */
+    _populateObjectDefaults(schema, value) {
         const properties = new Set(Object.getOwnPropertyNames(value));
 
-        const {required} = this._schema;
+        const {required} = schema;
         if (Array.isArray(required)) {
             for (const property of required) {
                 properties.delete(property);
-                const schemaInfo = this._getObjectPropertySchemaInfo(property);
-                if (schemaInfo === null) { continue; }
+                const {schema: propertySchema, stack} = this._getObjectPropertySchemaInfo(schema, property);
+                if (propertySchema === false) { continue; }
                 const propertyValue = Object.prototype.hasOwnProperty.call(value, property) ? value[property] : void 0;
-                value[property] = this._getValidValueOrDefault(property, propertyValue, schemaInfo);
+                value[property] = this._getValidValueOrDefault(propertySchema, property, propertyValue, stack);
             }
         }
 
         for (const property of properties) {
-            const schemaInfo = this._getObjectPropertySchemaInfo(property);
-            if (schemaInfo === null) {
+            const {schema: propertySchema, stack} = this._getObjectPropertySchemaInfo(schema, property);
+            if (propertySchema === false) {
                 Reflect.deleteProperty(value, property);
             } else {
-                value[property] = this._getValidValueOrDefault(property, value[property], schemaInfo);
+                value[property] = this._getValidValueOrDefault(propertySchema, property, value[property], stack);
             }
         }
 
         return value;
     }
 
-    _populateArrayDefaults(value) {
+    /**
+     * @param {import('json-schema').SchemaObject} schema
+     * @param {import('json-schema').Value[]} value
+     * @returns {import('json-schema').Value[]}
+     */
+    _populateArrayDefaults(schema, value) {
         for (let i = 0, ii = value.length; i < ii; ++i) {
-            const schemaInfo = this._getArrayItemSchemaInfo(i);
-            if (schemaInfo === null) { continue; }
+            const {schema: itemSchema, stack} = this._getArrayItemSchemaInfo(schema, i);
+            if (itemSchema === false) { continue; }
             const propertyValue = value[i];
-            value[i] = this._getValidValueOrDefault(i, propertyValue, schemaInfo);
+            value[i] = this._getValidValueOrDefault(itemSchema, i, propertyValue, stack);
         }
 
-        const {minItems, maxItems} = this._schema;
+        const {minItems, maxItems} = schema;
         if (typeof minItems === 'number' && value.length < minItems) {
             for (let i = value.length; i < minItems; ++i) {
-                const schemaInfo = this._getArrayItemSchemaInfo(i);
-                if (schemaInfo === null) { break; }
-                const item = this._getValidValueOrDefault(i, void 0, schemaInfo);
+                const {schema: itemSchema, stack} = this._getArrayItemSchemaInfo(schema, i);
+                if (itemSchema === false) { break; }
+                const item = this._getValidValueOrDefault(itemSchema, i, void 0, stack);
                 value.push(item);
             }
         }
@@ -857,115 +1162,187 @@ class JsonSchema {
     }
 }
 
+/**
+ * @implements {ProxyHandler<import('json-schema').ValueObjectOrArray>}
+ */
 class JsonSchemaProxyHandler {
-    constructor(schema) {
-        this._schema = schema;
+    /**
+     * @param {JsonSchema} schemaValidator
+     */
+    constructor(schemaValidator) {
+        /** @type {JsonSchema} */
+        this._schemaValidator = schemaValidator;
+        /** @type {RegExp} */
         this._numberPattern = /^(?:0|[1-9]\d*)$/;
     }
 
+    /**
+     * @param {import('json-schema').ValueObjectOrArray} target
+     * @returns {?import('core').UnknownObject}
+     */
     getPrototypeOf(target) {
         return Object.getPrototypeOf(target);
     }
 
+    /**
+     * @type {(target: import('json-schema').ValueObjectOrArray, newPrototype: ?unknown) => boolean}
+     */
     setPrototypeOf() {
         throw new Error('setPrototypeOf not supported');
     }
 
+    /**
+     * @param {import('json-schema').ValueObjectOrArray} target
+     * @returns {boolean}
+     */
     isExtensible(target) {
         return Object.isExtensible(target);
     }
 
+    /**
+     * @param {import('json-schema').ValueObjectOrArray} target
+     * @returns {boolean}
+     */
     preventExtensions(target) {
         Object.preventExtensions(target);
         return true;
     }
 
+    /**
+     * @param {import('json-schema').ValueObjectOrArray} target
+     * @param {string|symbol} property
+     * @returns {PropertyDescriptor|undefined}
+     */
     getOwnPropertyDescriptor(target, property) {
         return Object.getOwnPropertyDescriptor(target, property);
     }
 
+    /**
+     * @type {(target: import('json-schema').ValueObjectOrArray, property: string|symbol, attributes: PropertyDescriptor) => boolean}
+     */
     defineProperty() {
         throw new Error('defineProperty not supported');
     }
 
+    /**
+     * @param {import('json-schema').ValueObjectOrArray} target
+     * @param {string|symbol} property
+     * @returns {boolean}
+     */
     has(target, property) {
         return property in target;
     }
 
-    get(target, property) {
-        if (typeof property === 'symbol') { return target[property]; }
+    /**
+     * @param {import('json-schema').ValueObjectOrArray} target
+     * @param {string|symbol} property
+     * @param {import('core').SafeAny} _receiver
+     * @returns {import('core').SafeAny}
+     */
+    get(target, property, _receiver) {
+        if (typeof property === 'symbol') { return /** @type {import('core').UnknownObject} */ (target)[property]; }
 
         let propertySchema;
         if (Array.isArray(target)) {
             const index = this._getArrayIndex(property);
             if (index === null) {
                 // Note: this does not currently wrap mutating functions like push, pop, shift, unshift, splice
-                return target[property];
+                return /** @type {import('core').SafeAny} */ (target)[property];
             }
-            property = index;
-            propertySchema = this._schema.getArrayItemSchema(property);
+            property = `${index}`;
+            propertySchema = this._schemaValidator.getArrayItemSchema(index);
         } else {
-            propertySchema = this._schema.getObjectPropertySchema(property);
+            propertySchema = this._schemaValidator.getObjectPropertySchema(property);
         }
 
         if (propertySchema === null) { return void 0; }
 
-        const value = target[property];
-        return value !== null && typeof value === 'object' ? propertySchema.createProxy(value) : value;
+        const value = /** @type {import('core').UnknownObject} */ (target)[property];
+        return value !== null && typeof value === 'object' ? propertySchema.createProxy(/** @type {import('json-schema').Value} */ (value)) : value;
     }
 
+    /**
+     * @param {import('json-schema').ValueObjectOrArray} target
+     * @param {string|number|symbol} property
+     * @param {import('core').SafeAny} value
+     * @returns {boolean}
+     * @throws {Error}
+     */
     set(target, property, value) {
-        if (typeof property === 'symbol') { throw new Error(`Cannot assign symbol property ${property}`); }
+        if (typeof property === 'symbol') { throw new Error(`Cannot assign symbol property ${typeof property === 'symbol' ? '<symbol>' : property}`); }
 
         let propertySchema;
         if (Array.isArray(target)) {
             const index = this._getArrayIndex(property);
             if (index === null) {
-                target[property] = value;
+                /** @type {import('core').SafeAny} */ (target)[property] = value;
                 return true;
             }
             if (index > target.length) { throw new Error('Array index out of range'); }
             property = index;
-            propertySchema = this._schema.getArrayItemSchema(property);
+            propertySchema = this._schemaValidator.getArrayItemSchema(property);
         } else {
-            propertySchema = this._schema.getObjectPropertySchema(property);
+            if (typeof property !== 'string') {
+                property = `${property}`;
+            }
+            propertySchema = this._schemaValidator.getObjectPropertySchema(property);
         }
 
         if (propertySchema === null) { throw new Error(`Property ${property} not supported`); }
 
-        value = clone(value);
+        value = JsonSchema.clone(value);
         propertySchema.validate(value);
 
-        target[property] = value;
+        /** @type {import('core').UnknownObject} */ (target)[property] = value;
         return true;
     }
 
+    /**
+     * @param {import('json-schema').ValueObjectOrArray} target
+     * @param {string|symbol} property
+     * @returns {boolean}
+     * @throws {Error}
+     */
     deleteProperty(target, property) {
         const required = (
             (typeof target === 'object' && target !== null) ?
-            (!Array.isArray(target) && this._schema.isObjectPropertyRequired(property)) :
+            (!Array.isArray(target) && typeof property === 'string' && this._schemaValidator.isObjectPropertyRequired(property)) :
             true
         );
         if (required) {
-            throw new Error(`${property} cannot be deleted`);
+            throw new Error(`${typeof property === 'symbol' ? '<symbol>' : property} cannot be deleted`);
         }
         return Reflect.deleteProperty(target, property);
     }
 
+    /**
+     * @param {import('json-schema').ValueObjectOrArray} target
+     * @returns {ArrayLike<string|symbol>}
+     */
     ownKeys(target) {
         return Reflect.ownKeys(target);
     }
 
+    /**
+     * @type {(target: import('json-schema').ValueObjectOrArray, thisArg: import('core').SafeAny, argArray: import('core').SafeAny[]) => import('core').SafeAny}
+     */
     apply() {
         throw new Error('apply not supported');
     }
 
+    /**
+     * @type {(target: import('json-schema').ValueObjectOrArray, argArray: import('core').SafeAny[], newTarget: import('core').SafeFunction) => import('json-schema').ValueObjectOrArray}
+     */
     construct() {
         throw new Error('construct not supported');
     }
 
     // Private
 
+    /**
+     * @param {string|symbol|number} property
+     * @returns {?number}
+     */
     _getArrayIndex(property) {
         if (typeof property === 'string' && this._numberPattern.test(property)) {
             return Number.parseInt(property, 10);
diff --git a/ext/js/data/options-util.js b/ext/js/data/options-util.js
index 2674701f3f..30bf1be024 100644
--- a/ext/js/data/options-util.js
+++ b/ext/js/data/options-util.js
@@ -23,20 +23,29 @@
 
 class OptionsUtil {
     constructor() {
+        /** @type {?TemplatePatcher} */
         this._templatePatcher = null;
+        /** @type {?JsonSchema} */
         this._optionsSchema = null;
     }
 
+    /** */
     async prepare() {
-        const schema = await this._fetchAsset('/data/schemas/options-schema.json', true);
+        const schema = /** @type {import('json-schema').Schema} */ (await this._fetchJson('/data/schemas/options-schema.json'));
         this._optionsSchema = new JsonSchema(schema);
     }
 
-    async update(options, targetVersion=null) {
+    /**
+     * @param {unknown} optionsInput
+     * @param {?number} [targetVersion]
+     * @returns {Promise<import('settings').Options>}
+     */
+    async update(optionsInput, targetVersion=null) {
         // Invalid options
-        if (!isObject(options)) {
-            options = {};
-        }
+        let options = /** @type {{[key: string]: unknown}} */ (
+            typeof optionsInput === 'object' && optionsInput !== null && !Array.isArray(optionsInput) ?
+            optionsInput : {}
+        );
 
         // Check for legacy options
         let defaultProfileOptions = {};
@@ -51,7 +60,7 @@ class OptionsUtil {
         }
 
         // Remove invalid profiles
-        const profiles = options.profiles;
+        const profiles = /** @type {unknown[]} */ (options.profiles);
         for (let i = profiles.length - 1; i >= 0; --i) {
             if (!isObject(profiles[i])) {
                 profiles.splice(i, 1);
@@ -88,12 +97,12 @@ class OptionsUtil {
         options = await this._applyUpdates(options, this._getVersionUpdates(targetVersion));
 
         // Validation
-        options = this._optionsSchema.getValidValueOrDefault(options);
-
-        // Result
-        return options;
+        return /** @type {import('settings').Options} */ (/** @type {JsonSchema} */ (this._optionsSchema).getValidValueOrDefault(options));
     }
 
+    /**
+     * @returns {Promise<import('settings').Options>}
+     */
     async load() {
         let options;
         try {
@@ -121,6 +130,10 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @param {import('settings').Options} options
+     * @returns {Promise<void>}
+     */
     save(options) {
         return new Promise((resolve, reject) => {
             chrome.storage.local.set({options: JSON.stringify(options)}, () => {
@@ -134,23 +147,36 @@ class OptionsUtil {
         });
     }
 
+    /**
+     * @returns {import('settings').Options}
+     */
     getDefault() {
-        const optionsVersion = this._getVersionUpdates().length;
-        const options = this._optionsSchema.getValidValueOrDefault();
+        const optionsVersion = this._getVersionUpdates(null).length;
+        const options = /** @type {import('settings').Options} */ (/** @type {JsonSchema} */ (this._optionsSchema).getValidValueOrDefault());
         options.version = optionsVersion;
         return options;
     }
 
+    /**
+     * @param {import('settings').Options} options
+     * @returns {import('settings').Options}
+     */
     createValidatingProxy(options) {
-        return this._optionsSchema.createProxy(options);
+        return /** @type {import('settings').Options} */ (/** @type {JsonSchema} */ (this._optionsSchema).createProxy(options));
     }
 
+    /**
+     * @param {import('settings').Options} options
+     */
     validate(options) {
-        return this._optionsSchema.validate(options);
+        /** @type {JsonSchema} */ (this._optionsSchema).validate(options);
     }
 
     // Legacy profile updating
 
+    /**
+     * @returns {(?import('options-util').LegacyUpdateFunction)[]}
+     */
     _legacyProfileUpdateGetUpdates() {
         return [
             null,
@@ -242,6 +268,9 @@ class OptionsUtil {
         ];
     }
 
+    /**
+     * @returns {import('options-util').LegacyOptions}
+     */
     _legacyProfileUpdateGetDefaults() {
         return {
             general: {
@@ -341,9 +370,17 @@ class OptionsUtil {
         };
     }
 
+    /**
+     * @param {import('options-util').IntermediateOptions} options
+     * @returns {import('options-util').IntermediateOptions}
+     */
     _legacyProfileUpdateAssignDefaults(options) {
         const defaults = this._legacyProfileUpdateGetDefaults();
 
+        /**
+         * @param {import('options-util').IntermediateOptions} target
+         * @param {import('core').UnknownObject} source
+         */
         const combine = (target, source) => {
             for (const key in source) {
                 if (!Object.prototype.hasOwnProperty.call(target, key)) {
@@ -362,6 +399,10 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @param {import('options-util').IntermediateOptions} options
+     * @returns {import('options-util').IntermediateOptions}
+     */
     _legacyProfileUpdateUpdateVersion(options) {
         const updates = this._legacyProfileUpdateGetUpdates();
         this._legacyProfileUpdateAssignDefaults(options);
@@ -384,6 +425,10 @@ class OptionsUtil {
 
     // Private
 
+    /**
+     * @param {import('options-util').IntermediateOptions} options
+     * @param {string} modificationsUrl
+     */
     async _applyAnkiFieldTemplatesPatch(options, modificationsUrl) {
         let patch = null;
         for (const {options: profileOptions} of options.profiles) {
@@ -391,18 +436,22 @@ class OptionsUtil {
             if (fieldTemplates === null) { continue; }
 
             if (patch === null) {
-                const content = await this._fetchAsset(modificationsUrl);
+                const content = await this._fetchText(modificationsUrl);
                 if (this._templatePatcher === null) {
                     this._templatePatcher = new TemplatePatcher();
                 }
                 patch = this._templatePatcher.parsePatch(content);
             }
 
-            profileOptions.anki.fieldTemplates = this._templatePatcher.applyPatch(fieldTemplates, patch);
+            profileOptions.anki.fieldTemplates = /** @type {TemplatePatcher} */ (this._templatePatcher).applyPatch(fieldTemplates, patch);
         }
     }
 
-    async _fetchAsset(url, json=false) {
+    /**
+     * @param {string} url
+     * @returns {Promise<Response>}
+     */
+    async _fetchGeneric(url) {
         url = chrome.runtime.getURL(url);
         const response = await fetch(url, {
             method: 'GET',
@@ -415,9 +464,31 @@ class OptionsUtil {
         if (!response.ok) {
             throw new Error(`Failed to fetch ${url}: ${response.status}`);
         }
-        return await (json ? response.json() : response.text());
+        return response;
+    }
+
+    /**
+     * @param {string} url
+     * @returns {Promise<string>}
+     */
+    async _fetchText(url) {
+        const response = await this._fetchGeneric(url);
+        return await response.text();
+    }
+
+    /**
+     * @param {string} url
+     * @returns {Promise<unknown>}
+     */
+    async _fetchJson(url) {
+        const response = await this._fetchGeneric(url);
+        return await response.json();
     }
 
+    /**
+     * @param {string} string
+     * @returns {number}
+     */
     _getStringHashCode(string) {
         let hashCode = 0;
 
@@ -431,6 +502,11 @@ class OptionsUtil {
         return hashCode;
     }
 
+    /**
+     * @param {import('options-util').IntermediateOptions} options
+     * @param {import('options-util').ModernUpdate[]} updates
+     * @returns {Promise<import('settings').Options>}
+     */
     async _applyUpdates(options, updates) {
         const targetVersion = updates.length;
         let currentVersion = options.version;
@@ -449,6 +525,10 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @param {?number} targetVersion
+     * @returns {import('options-util').ModernUpdate[]}
+     */
     _getVersionUpdates(targetVersion) {
         const result = [
             {async: false, update: this._updateVersion1.bind(this)},
@@ -478,6 +558,9 @@ class OptionsUtil {
         return result;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion1(options) {
         // Version 1 changes:
         //  Added options.global.database.prefixWildcardsSupported = false.
@@ -489,6 +572,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion2(options) {
         // Version 2 changes:
         //  Legacy profile update process moved into this upgrade function.
@@ -501,6 +587,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionAsync}
+     */
     async _updateVersion3(options) {
         // Version 3 changes:
         //  Pitch accent Anki field templates added.
@@ -508,6 +597,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionAsync}
+     */
     async _updateVersion4(options) {
         // Version 4 changes:
         //  Options conditions converted to string representations.
@@ -593,6 +685,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion5(options) {
         // Version 5 changes:
         //  Removed legacy version number from profile options.
@@ -602,6 +697,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionAsync}
+     */
     async _updateVersion6(options) {
         // Version 6 changes:
         //  Updated handlebars templates to include "conjugation" definition.
@@ -624,6 +722,10 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @param {string} templates
+     * @returns {string}
+     */
     _updateVersion6AnkiTemplatesCompactTags(templates) {
         const rawPattern1 = '{{~#if definitionTags~}}<i>({{#each definitionTags}}{{name}}{{#unless @last}}, {{/unless}}{{/each}})</i> {{/if~}}';
         const pattern1 = new RegExp(`((\r?\n)?[ \t]*)${escapeRegExp(rawPattern1)}`, 'g');
@@ -648,6 +750,9 @@ class OptionsUtil {
         return templates;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion7(options) {
         // Version 7 changes:
         //  Added general.maximumClipboardSearchLength.
@@ -665,6 +770,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionAsync}
+     */
     async _updateVersion8(options) {
         // Version 8 changes:
         //  Added translation.textReplacements.
@@ -754,6 +862,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion9(options) {
         // Version 9 changes:
         //  Added general.frequencyDisplayMode.
@@ -765,6 +876,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionAsync}
+     */
     async _updateVersion10(options) {
         // Version 10 changes:
         //  Removed global option useSettingsV2.
@@ -802,6 +916,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion11(options) {
         // Version 11 changes:
         //  Changed dictionaries to an array.
@@ -826,6 +943,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionAsync}
+     */
     async _updateVersion12(options) {
         // Version 12 changes:
         //  Changed sentenceParsing.enableTerminationCharacters to sentenceParsing.terminationCharacterMode.
@@ -840,7 +960,7 @@ class OptionsUtil {
             delete sentenceParsing.enableTerminationCharacters;
 
             const {sources, customSourceUrl, customSourceType, textToSpeechVoice} = audio;
-            audio.sources = sources.map((type) => {
+            audio.sources = /** @type {string[]} */ (sources).map((type) => {
                 switch (type) {
                     case 'text-to-speech':
                     case 'text-to-speech-reading':
@@ -858,6 +978,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionAsync}
+     */
     async _updateVersion13(options) {
         // Version 13 changes:
         //  Handlebars templates updated to use formatGlossary.
@@ -873,6 +996,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion14(options) {
         // Version 14 changes:
         //  Added accessibility options.
@@ -884,6 +1010,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion15(options) {
         // Version 15 changes:
         //  Added general.sortFrequencyDictionary.
@@ -895,6 +1024,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion16(options) {
         // Version 16 changes:
         //  Added scanning.matchTypePrefix.
@@ -904,12 +1036,16 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion17(options) {
         // Version 17 changes:
         //  Added vertical sentence punctuation to terminationCharacters.
         const additions = ['︒', '︕', '︖', '︙'];
         for (const profile of options.profiles) {
-            const {terminationCharacters} = profile.options.sentenceParsing;
+            /** @type {import('settings').SentenceParsingTerminationCharacterOption[]} */
+            const terminationCharacters = profile.options.sentenceParsing.terminationCharacters;
             const newAdditions = [];
             for (const character of additions) {
                 if (terminationCharacters.findIndex((value) => (value.character1 === character && value.character2 === null)) < 0) {
@@ -929,6 +1065,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion18(options) {
         // Version 18 changes:
         //  general.popupTheme's 'default' value changed to 'light'
@@ -951,6 +1090,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion19(options) {
         // Version 19 changes:
         //  Added anki.noteGuiMode.
@@ -978,6 +1120,9 @@ class OptionsUtil {
         return options;
     }
 
+    /**
+     * @type {import('options-util').ModernUpdateFunctionSync}
+     */
     _updateVersion20(options) {
         // Version 20 changes:
         //  Added anki.downloadTimeout.
diff --git a/ext/js/data/permissions-util.js b/ext/js/data/permissions-util.js
index afec470c96..6ba9ba6c9c 100644
--- a/ext/js/data/permissions-util.js
+++ b/ext/js/data/permissions-util.js
@@ -22,12 +22,17 @@
 
 class PermissionsUtil {
     constructor() {
+        /** @type {Set<string>} */
         this._ankiFieldMarkersRequiringClipboardPermission = new Set([
             'clipboard-image',
             'clipboard-text'
         ]);
     }
 
+    /**
+     * @param {chrome.permissions.Permissions} permissions
+     * @returns {Promise<boolean>}
+     */
     hasPermissions(permissions) {
         return new Promise((resolve, reject) => chrome.permissions.contains(permissions, (result) => {
             const e = chrome.runtime.lastError;
@@ -39,6 +44,11 @@ class PermissionsUtil {
         }));
     }
 
+    /**
+     * @param {chrome.permissions.Permissions} permissions
+     * @param {boolean} shouldHave
+     * @returns {Promise<boolean>}
+     */
     setPermissionsGranted(permissions, shouldHave) {
         return (
             shouldHave ?
@@ -61,6 +71,9 @@ class PermissionsUtil {
         );
     }
 
+    /**
+     * @returns {Promise<chrome.permissions.Permissions>}
+     */
     getAllPermissions() {
         return new Promise((resolve, reject) => chrome.permissions.getAll((result) => {
             const e = chrome.runtime.lastError;
@@ -72,6 +85,10 @@ class PermissionsUtil {
         }));
     }
 
+    /**
+     * @param {string} fieldValue
+     * @returns {string[]}
+     */
     getRequiredPermissionsForAnkiFieldValue(fieldValue) {
         const markers = AnkiUtil.getFieldMarkers(fieldValue);
         const markerPermissions = this._ankiFieldMarkersRequiringClipboardPermission;
@@ -83,6 +100,11 @@ class PermissionsUtil {
         return [];
     }
 
+    /**
+     * @param {chrome.permissions.Permissions} permissions
+     * @param {import('settings').ProfileOptions} options
+     * @returns {boolean}
+     */
     hasRequiredPermissionsForOptions(permissions, options) {
         const permissionsSet = new Set(permissions.permissions);
 
diff --git a/ext/js/data/sandbox/anki-note-data-creator.js b/ext/js/data/sandbox/anki-note-data-creator.js
index 33b4af6fb5..4e3ad426d1 100644
--- a/ext/js/data/sandbox/anki-note-data-creator.js
+++ b/ext/js/data/sandbox/anki-note-data-creator.js
@@ -30,21 +30,15 @@ class AnkiNoteDataCreator {
      * @param {JapaneseUtil} japaneseUtil An instance of `JapaneseUtil`.
      */
     constructor(japaneseUtil) {
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
     }
 
     /**
      * Creates a compatibility representation of the specified data.
      * @param {string} marker The marker that is being used for template rendering.
-     * @param {object} details Information which is used to generate the data.
-     * @param {Translation.DictionaryEntry} details.dictionaryEntry The dictionary entry.
-     * @param {string} details.resultOutputMode The result output mode.
-     * @param {string} details.mode The mode being used to generate the Anki data.
-     * @param {string} details.glossaryLayoutMode The glossary layout mode.
-     * @param {boolean} details.compactTags Whether or not compact tags mode is enabled.
-     * @param {{documentTitle: string, query: string, fullQuery: string}} details.context Contextual information about the source of the dictionary entry.
-     * @param {object} details.media Media data.
-     * @returns {object} An object used for rendering Anki templates.
+     * @param {import('anki-templates-internal').CreateDetails} details Information which is used to generate the data.
+     * @returns {import('anki-templates').NoteData} An object used for rendering Anki templates.
      */
     create(marker, {
         dictionaryEntry,
@@ -55,6 +49,7 @@ class AnkiNoteDataCreator {
         context,
         media
     }) {
+        // eslint-disable-next-line @typescript-eslint/no-this-alias
         const self = this;
         const definition = this.createCachedValue(this._getDefinition.bind(this, dictionaryEntry, context, resultOutputMode));
         const uniqueExpressions = this.createCachedValue(this._getUniqueExpressions.bind(this, dictionaryEntry));
@@ -62,7 +57,18 @@ class AnkiNoteDataCreator {
         const context2 = this.createCachedValue(this._getPublicContext.bind(this, context));
         const pitches = this.createCachedValue(this._getPitches.bind(this, dictionaryEntry));
         const pitchCount = this.createCachedValue(this._getPitchCount.bind(this, pitches));
-        if (typeof media !== 'object' || media === null || Array.isArray(media)) { media = {}; }
+        if (typeof media !== 'object' || media === null || Array.isArray(media)) {
+            media = {
+                audio: void 0,
+                screenshot: void 0,
+                clipboardImage: void 0,
+                clipboardText: void 0,
+                selectionText: void 0,
+                textFurigana: [],
+                dictionaryMedia: {}
+            };
+        }
+        /** @type {import('anki-templates').NoteData} */
         const result = {
             marker,
             get definition() { return self.getCachedValue(definition); },
@@ -79,7 +85,8 @@ class AnkiNoteDataCreator {
             get pitches() { return self.getCachedValue(pitches); },
             get pitchCount() { return self.getCachedValue(pitchCount); },
             get context() { return self.getCachedValue(context2); },
-            media
+            media,
+            dictionaryEntry
         };
         Object.defineProperty(result, 'dictionaryEntry', {
             configurable: false,
@@ -92,8 +99,9 @@ class AnkiNoteDataCreator {
 
     /**
      * Creates a deferred-evaluation value.
-     * @param {Function} getter The function to invoke to get the return value.
-     * @returns {{getter: Function, hasValue: false, value: undefined}} An object which can be passed into `getCachedValue`.
+     * @template [T=unknown]
+     * @param {() => T} getter The function to invoke to get the return value.
+     * @returns {import('anki-templates-internal').CachedValue<T>} An object which can be passed into `getCachedValue`.
      */
     createCachedValue(getter) {
         return {getter, hasValue: false, value: void 0};
@@ -101,11 +109,12 @@ class AnkiNoteDataCreator {
 
     /**
      * Gets the value of a cached object.
-     * @param {{getter: Function, hasValue: boolean, value: *}} item An object that was returned from `createCachedValue`.
-     * @returns {*} The result of evaluating the getter, which is cached after the first invocation.
+     * @template [T=unknown]
+     * @param {import('anki-templates-internal').CachedValue<T>} item An object that was returned from `createCachedValue`.
+     * @returns {T} The result of evaluating the getter, which is cached after the first invocation.
      */
     getCachedValue(item) {
-        if (item.hasValue) { return item.value; }
+        if (item.hasValue) { return /** @type {T} */ (item.value); }
         const value = item.getter();
         item.value = value;
         item.hasValue = true;
@@ -114,10 +123,10 @@ class AnkiNoteDataCreator {
 
     // Private
 
-    _asObject(value) {
-        return (typeof value === 'object' && value !== null ? value : {});
-    }
-
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {?import('dictionary').TermSource}
+     */
     _getPrimarySource(dictionaryEntry) {
         for (const headword of dictionaryEntry.headwords) {
             for (const source of headword.sources) {
@@ -127,6 +136,10 @@ class AnkiNoteDataCreator {
         return null;
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @returns {string[]}
+     */
     _getUniqueExpressions(dictionaryEntry) {
         if (dictionaryEntry.type === 'term') {
             const results = new Set();
@@ -139,6 +152,10 @@ class AnkiNoteDataCreator {
         }
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @returns {string[]}
+     */
     _getUniqueReadings(dictionaryEntry) {
         if (dictionaryEntry.type === 'term') {
             const results = new Set();
@@ -151,8 +168,12 @@ class AnkiNoteDataCreator {
         }
     }
 
+    /**
+     * @param {import('anki-templates-internal').Context} context
+     * @returns {import('anki-templates').Context}
+     */
     _getPublicContext(context) {
-        let {documentTitle, query, fullQuery} = this._asObject(context);
+        let {documentTitle, query, fullQuery} = context;
         if (typeof documentTitle !== 'string') { documentTitle = ''; }
         return {
             query,
@@ -163,10 +184,16 @@ class AnkiNoteDataCreator {
         };
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @returns {import('anki-templates').PitchGroup[]}
+     */
     _getPitches(dictionaryEntry) {
+        /** @type {import('anki-templates').PitchGroup[]} */
         const results = [];
         if (dictionaryEntry.type === 'term') {
             for (const {dictionary, pronunciations} of DictionaryDataUtil.getGroupedPronunciations(dictionaryEntry)) {
+                /** @type {import('anki-templates').Pitch[]} */
                 const pitches = [];
                 for (const {terms, reading, position, nasalPositions, devoicePositions, tags, exclusiveTerms, exclusiveReadings} of pronunciations) {
                     pitches.push({
@@ -175,7 +202,7 @@ class AnkiNoteDataCreator {
                         position,
                         nasalPositions,
                         devoicePositions,
-                        tags,
+                        tags: this._convertPitchTags(tags),
                         exclusiveExpressions: exclusiveTerms,
                         exclusiveReadings
                     });
@@ -186,11 +213,21 @@ class AnkiNoteDataCreator {
         return results;
     }
 
+    /**
+     * @param {import('anki-templates-internal').CachedValue<import('anki-templates').PitchGroup[]>} cachedPitches
+     * @returns {number}
+     */
     _getPitchCount(cachedPitches) {
         const pitches = this.getCachedValue(cachedPitches);
         return pitches.reduce((i, v) => i + v.pitches.length, 0);
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @param {import('anki-templates-internal').Context} context
+     * @param {import('settings').ResultOutputMode} resultOutputMode
+     * @returns {import('anki-templates').DictionaryEntry}
+     */
     _getDefinition(dictionaryEntry, context, resultOutputMode) {
         switch (dictionaryEntry.type) {
             case 'term':
@@ -198,16 +235,22 @@ class AnkiNoteDataCreator {
             case 'kanji':
                 return this._getKanjiDefinition(dictionaryEntry, context);
             default:
-                return {};
+                return /** @type {import('anki-templates').UnknownDictionaryEntry} */ ({});
         }
     }
 
+    /**
+     * @param {import('dictionary').KanjiDictionaryEntry} dictionaryEntry
+     * @param {import('anki-templates-internal').Context} context
+     * @returns {import('anki-templates').KanjiDictionaryEntry}
+     */
     _getKanjiDefinition(dictionaryEntry, context) {
+        // eslint-disable-next-line @typescript-eslint/no-this-alias
         const self = this;
 
         const {character, dictionary, onyomi, kunyomi, definitions} = dictionaryEntry;
 
-        let {url} = this._asObject(context);
+        let {url} = context;
         if (typeof url !== 'string') { url = ''; }
 
         const stats = this.createCachedValue(this._getKanjiStats.bind(this, dictionaryEntry));
@@ -230,14 +273,24 @@ class AnkiNoteDataCreator {
         };
     }
 
+    /**
+     * @param {import('dictionary').KanjiDictionaryEntry} dictionaryEntry
+     * @returns {import('anki-templates').KanjiStatGroups}
+     */
     _getKanjiStats(dictionaryEntry) {
+        /** @type {import('anki-templates').KanjiStatGroups} */
         const results = {};
+        const convertKanjiStatBind = this._convertKanjiStat.bind(this);
         for (const [key, value] of Object.entries(dictionaryEntry.stats)) {
-            results[key] = value.map(this._convertKanjiStat.bind(this));
+            results[key] = value.map(convertKanjiStatBind);
         }
         return results;
     }
 
+    /**
+     * @param {import('dictionary').KanjiStat} kanjiStat
+     * @returns {import('anki-templates').KanjiStat}
+     */
     _convertKanjiStat({name, category, content, order, score, dictionary, value}) {
         return {
             name,
@@ -250,7 +303,12 @@ class AnkiNoteDataCreator {
         };
     }
 
+    /**
+     * @param {import('dictionary').KanjiDictionaryEntry} dictionaryEntry
+     * @returns {import('anki-templates').KanjiFrequency[]}
+     */
     _getKanjiFrequencies(dictionaryEntry) {
+        /** @type {import('anki-templates').KanjiFrequency[]} */
         const results = [];
         for (const {index, dictionary, dictionaryIndex, dictionaryPriority, character, frequency, displayValue} of dictionaryEntry.frequencies) {
             results.push({
@@ -267,9 +325,17 @@ class AnkiNoteDataCreator {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @param {import('anki-templates-internal').Context} context
+     * @param {import('settings').ResultOutputMode} resultOutputMode
+     * @returns {import('anki-templates').TermDictionaryEntry}
+     */
     _getTermDefinition(dictionaryEntry, context, resultOutputMode) {
+        // eslint-disable-next-line @typescript-eslint/no-this-alias
         const self = this;
 
+        /** @type {import('anki-templates').TermDictionaryEntryType} */
         let type = 'term';
         switch (resultOutputMode) {
             case 'group': type = 'termGrouped'; break;
@@ -278,7 +344,7 @@ class AnkiNoteDataCreator {
 
         const {inflections, score, dictionaryIndex, dictionaryPriority, sourceTermExactMatchCount, definitions} = dictionaryEntry;
 
-        let {url} = this._asObject(context);
+        let {url} = context;
         if (typeof url !== 'string') { url = ''; }
 
         const primarySource = this._getPrimarySource(dictionaryEntry);
@@ -332,6 +398,10 @@ class AnkiNoteDataCreator {
         };
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {string[]}
+     */
     _getTermDictionaryNames(dictionaryEntry) {
         const dictionaryNames = new Set();
         for (const {dictionary} of dictionaryEntry.definitions) {
@@ -340,11 +410,18 @@ class AnkiNoteDataCreator {
         return [...dictionaryNames];
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @param {import('anki-templates').TermDictionaryEntryType} type
+     * @returns {import('anki-templates').TermDictionaryEntryCommonInfo}
+     */
     _getTermDictionaryEntryCommonInfo(dictionaryEntry, type) {
         const merged = (type === 'termMerged');
         const hasDefinitions = (type !== 'term');
 
+        /** @type {Set<string>} */
         const allTermsSet = new Set();
+        /** @type {Set<string>} */
         const allReadingsSet = new Set();
         for (const {term, reading} of dictionaryEntry.headwords) {
             allTermsSet.add(term);
@@ -353,7 +430,9 @@ class AnkiNoteDataCreator {
         const uniqueTerms = [...allTermsSet];
         const uniqueReadings = [...allReadingsSet];
 
+        /** @type {import('anki-templates').TermDefinition[]} */
         const definitions = [];
+        /** @type {import('anki-templates').Tag[]} */
         const definitionTags = [];
         for (const {tags, headwordIndices, entries, dictionary, sequences} of dictionaryEntry.definitions) {
             const definitionTags2 = [];
@@ -380,6 +459,10 @@ class AnkiNoteDataCreator {
         };
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {import('anki-templates').TermFrequency[]}
+     */
     _getTermFrequencies(dictionaryEntry) {
         const results = [];
         const {headwords} = dictionaryEntry;
@@ -402,7 +485,12 @@ class AnkiNoteDataCreator {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {import('anki-templates').TermPronunciation[]}
+     */
     _getTermPitches(dictionaryEntry) {
+        // eslint-disable-next-line @typescript-eslint/no-this-alias
         const self = this;
         const results = [];
         const {headwords} = dictionaryEntry;
@@ -425,7 +513,12 @@ class AnkiNoteDataCreator {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').TermPitch[]} pitches
+     * @returns {import('anki-templates').TermPitch[]}
+     */
     _getTermPitchesInner(pitches) {
+        // eslint-disable-next-line @typescript-eslint/no-this-alias
         const self = this;
         const results = [];
         for (const {position, tags} of pitches) {
@@ -438,7 +531,12 @@ class AnkiNoteDataCreator {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {import('anki-templates').TermHeadword[]}
+     */
     _getTermExpressions(dictionaryEntry) {
+        // eslint-disable-next-line @typescript-eslint/no-this-alias
         const self = this;
         const results = [];
         const {headwords} = dictionaryEntry;
@@ -465,6 +563,11 @@ class AnkiNoteDataCreator {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @param {number} i
+     * @returns {import('anki-templates').TermFrequency[]}
+     */
     _getTermExpressionFrequencies(dictionaryEntry, i) {
         const results = [];
         const {headwords, frequencies} = dictionaryEntry;
@@ -488,7 +591,13 @@ class AnkiNoteDataCreator {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @param {number} i
+     * @returns {import('anki-templates').TermPronunciation[]}
+     */
     _getTermExpressionPitches(dictionaryEntry, i) {
+        // eslint-disable-next-line @typescript-eslint/no-this-alias
         const self = this;
         const results = [];
         const {headwords, pronunciations} = dictionaryEntry;
@@ -512,11 +621,20 @@ class AnkiNoteDataCreator {
         return results;
     }
 
+    /**
+     * @param {import('anki-templates-internal').CachedValue<import('anki-templates').Tag[]>} cachedTermTags
+     * @returns {import('anki-templates').TermFrequencyType}
+     */
     _getTermExpressionTermFrequency(cachedTermTags) {
         const termTags = this.getCachedValue(cachedTermTags);
         return DictionaryDataUtil.getTermFrequency(termTags);
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @param {import('anki-templates').TermDictionaryEntryType} type
+     * @returns {import('dictionary-data').TermGlossary[]|undefined}
+     */
     _getTermGlossaryArray(dictionaryEntry, type) {
         if (type === 'term') {
             const results = [];
@@ -528,6 +646,11 @@ class AnkiNoteDataCreator {
         return void 0;
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @param {import('anki-templates').TermDictionaryEntryType} type
+     * @returns {import('anki-templates').Tag[]|undefined}
+     */
     _getTermTags(dictionaryEntry, type) {
         if (type !== 'termMerged') {
             const results = [];
@@ -539,6 +662,10 @@ class AnkiNoteDataCreator {
         return void 0;
     }
 
+    /**
+     * @param {import('dictionary').Tag[]} tags
+     * @returns {import('anki-templates').Tag[]}
+     */
     _convertTags(tags) {
         const results = [];
         for (const tag of tags) {
@@ -547,6 +674,10 @@ class AnkiNoteDataCreator {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').Tag} tag
+     * @returns {import('anki-templates').Tag}
+     */
     _convertTag({name, category, content, order, score, dictionaries, redundant}) {
         return {
             name,
@@ -559,6 +690,39 @@ class AnkiNoteDataCreator {
         };
     }
 
+    /**
+     * @param {import('dictionary').Tag[]} tags
+     * @returns {import('anki-templates').PitchTag[]}
+     */
+    _convertPitchTags(tags) {
+        const results = [];
+        for (const tag of tags) {
+            results.push(this._convertPitchTag(tag));
+        }
+        return results;
+    }
+
+    /**
+     * @param {import('dictionary').Tag} tag
+     * @returns {import('anki-templates').PitchTag}
+     */
+    _convertPitchTag({name, category, content, order, score, dictionaries, redundant}) {
+        return {
+            name,
+            category,
+            order,
+            score,
+            content: [...content],
+            dictionaries: [...dictionaries],
+            redundant
+        };
+    }
+
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @param {import('anki-templates-internal').Context} context
+     * @returns {import('anki-templates').Cloze}
+     */
     _getCloze(dictionaryEntry, context) {
         let originalText = '';
         switch (dictionaryEntry.type) {
@@ -573,8 +737,12 @@ class AnkiNoteDataCreator {
                 break;
         }
 
-        const {sentence} = this._asObject(context);
-        let {text, offset} = this._asObject(sentence);
+        const {sentence} = context;
+        let text;
+        let offset;
+        if (typeof sentence === 'object' && sentence !== null) {
+            ({text, offset} = sentence);
+        }
         if (typeof text !== 'string') { text = ''; }
         if (typeof offset !== 'number') { offset = 0; }
 
@@ -586,6 +754,11 @@ class AnkiNoteDataCreator {
         };
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @param {import('anki-templates').TermDictionaryEntryType} type
+     * @returns {import('anki-templates').FuriganaSegment[]|undefined}
+     */
     _getTermFuriganaSegments(dictionaryEntry, type) {
         if (type === 'term') {
             for (const {term, reading} of dictionaryEntry.headwords) {
@@ -595,7 +768,13 @@ class AnkiNoteDataCreator {
         return void 0;
     }
 
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @returns {import('anki-templates').FuriganaSegment[]}
+     */
     _getTermHeadwordFuriganaSegments(term, reading) {
+        /** @type {import('anki-templates').FuriganaSegment[]} */
         const result = [];
         for (const {text, reading: reading2} of this._japaneseUtil.distributeFurigana(term, reading)) {
             result.push({text, furigana: reading2});
@@ -603,11 +782,15 @@ class AnkiNoteDataCreator {
         return result;
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {number}
+     */
     _getTermDictionaryEntrySequence(dictionaryEntry) {
         let hasSequence = false;
         let mainSequence = -1;
-        for (const {sequences, isPrimary} of dictionaryEntry.definitions) {
-            if (!isPrimary) { continue; }
+        if (!dictionaryEntry.isPrimary) { return mainSequence; }
+        for (const {sequences} of dictionaryEntry.definitions) {
             const sequence = sequences[0];
             if (!hasSequence) {
                 mainSequence = sequence;
diff --git a/ext/js/debug/timer.js b/ext/js/debug/timer.js
index f57e9e796a..3c9a1f4424 100644
--- a/ext/js/debug/timer.js
+++ b/ext/js/debug/timer.js
@@ -17,8 +17,13 @@
  */
 
 class Timer {
+    /**
+     * @param {string} name
+     */
     constructor(name) {
+        /** @type {{name: string, time: number, children: Timer[]}[]} */
         this.samples = [];
+        /** @type {?Timer} */
         this.parent = null;
 
         this.sample(name);
@@ -30,6 +35,9 @@ class Timer {
         Timer.current = this;
     }
 
+    /**
+     * @param {string} name
+     */
     sample(name) {
         const time = performance.now();
         this.samples.push({
@@ -39,6 +47,9 @@ class Timer {
         });
     }
 
+    /**
+     * @param {boolean} skip
+     */
     complete(skip) {
         this.sample('complete');
 
@@ -55,13 +66,20 @@ class Timer {
         }
     }
 
+    /**
+     * @param {number} sampleIndex
+     * @returns {number}
+     */
     duration(sampleIndex) {
         const sampleIndexIsValid = (typeof sampleIndex === 'number');
         const startIndex = (sampleIndexIsValid ? sampleIndex : 0);
-        const endIndex = (sampleIndexIsValid ? sampleIndex + 1 : this.times.length - 1);
-        return (this.times[endIndex].time - this.times[startIndex].time);
+        const endIndex = (sampleIndexIsValid ? sampleIndex + 1 : this.samples.length - 1);
+        return (this.samples[endIndex].time - this.samples[startIndex].time);
     }
 
+    /**
+     * @returns {string}
+     */
     toString() {
         const indent = '  ';
         const name = this.samples[0].name;
@@ -70,6 +88,9 @@ class Timer {
         return `${name} took ${duration.toFixed(8)}ms  [${extensionName}]` + this._indentString(this.getSampleString(), indent);
     }
 
+    /**
+     * @returns {string}
+     */
     getSampleString() {
         const indent = '  ';
         const duration = this.samples[this.samples.length - 1].time - this.samples[0].time;
@@ -87,9 +108,15 @@ class Timer {
         return message;
     }
 
+    /**
+     * @param {string} message
+     * @param {string} indent
+     * @returns {string}
+     */
     _indentString(message, indent) {
         return message.replace(/\n/g, `\n${indent}`);
     }
 }
 
+/** @type {?Timer} */
 Timer.current = null;
diff --git a/ext/js/display/display-anki.js b/ext/js/display/display-anki.js
index 9a1aae231f..42ca4ad990 100644
--- a/ext/js/display/display-anki.js
+++ b/ext/js/display/display-anki.js
@@ -23,47 +23,88 @@
  */
 
 class DisplayAnki {
+    /**
+     * @param {Display} display
+     * @param {DisplayAudio} displayAudio
+     * @param {JapaneseUtil} japaneseUtil
+     */
     constructor(display, displayAudio, japaneseUtil) {
+        /** @type {Display} */
         this._display = display;
+        /** @type {DisplayAudio} */
         this._displayAudio = displayAudio;
+        /** @type {?string} */
         this._ankiFieldTemplates = null;
+        /** @type {?string} */
         this._ankiFieldTemplatesDefault = null;
+        /** @type {AnkiNoteBuilder} */
         this._ankiNoteBuilder = new AnkiNoteBuilder({japaneseUtil});
+        /** @type {?DisplayNotification} */
         this._errorNotification = null;
+        /** @type {?EventListenerCollection} */
         this._errorNotificationEventListeners = null;
+        /** @type {?DisplayNotification} */
         this._tagsNotification = null;
-        this._updateAdderButtonsPromise = Promise.resolve();
+        /** @type {?Promise<void>} */
+        this._updateAdderButtonsPromise = null;
+        /** @type {?import('core').TokenObject} */
         this._updateDictionaryEntryDetailsToken = null;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?import('display-anki').DictionaryEntryDetails[]} */
         this._dictionaryEntryDetails = null;
+        /** @type {?import('anki-templates-internal').Context} */
         this._noteContext = null;
+        /** @type {boolean} */
         this._checkForDuplicates = false;
+        /** @type {boolean} */
         this._suspendNewCards = false;
+        /** @type {boolean} */
         this._compactTags = false;
+        /** @type {import('settings').ResultOutputMode} */
         this._resultOutputMode = 'split';
+        /** @type {import('settings').GlossaryLayoutMode} */
         this._glossaryLayoutMode = 'default';
+        /** @type {import('settings').AnkiDisplayTags} */
         this._displayTags = 'never';
+        /** @type {import('settings').AnkiDuplicateScope} */
         this._duplicateScope = 'collection';
+        /** @type {boolean} */
         this._duplicateScopeCheckAllModels = false;
+        /** @type {import('settings').AnkiScreenshotFormat} */
         this._screenshotFormat = 'png';
+        /** @type {number} */
         this._screenshotQuality = 100;
+        /** @type {number} */
         this._scanLength = 10;
+        /** @type {import('settings').AnkiNoteGuiMode} */
         this._noteGuiMode = 'browse';
+        /** @type {?number} */
         this._audioDownloadIdleTimeout = null;
+        /** @type {string[]} */
         this._noteTags = [];
+        /** @type {Map<import('display-anki').CreateMode, import('settings').AnkiNoteOptions>} */
         this._modeOptions = new Map();
+        /** @type {Map<import('dictionary').DictionaryEntryType, import('display-anki').CreateMode[]>} */
         this._dictionaryEntryTypeModeMap = new Map([
             ['kanji', ['kanji']],
             ['term', ['term-kanji', 'term-kana']]
         ]);
-        this._menuContainer = document.querySelector('#popup-menus');
+        /** @type {HTMLElement} */
+        this._menuContainer = /** @type {HTMLElement} */ (document.querySelector('#popup-menus'));
+        /** @type {(event: MouseEvent) => void} */
         this._onShowTagsBind = this._onShowTags.bind(this);
+        /** @type {(event: MouseEvent) => void} */
         this._onNoteAddBind = this._onNoteAdd.bind(this);
+        /** @type {(event: MouseEvent) => void} */
         this._onViewNoteButtonClickBind = this._onViewNoteButtonClick.bind(this);
+        /** @type {(event: MouseEvent) => void} */
         this._onViewNoteButtonContextMenuBind = this._onViewNoteButtonContextMenu.bind(this);
+        /** @type {(event: import('popup-menu').MenuCloseEvent) => void} */
         this._onViewNoteButtonMenuCloseBind = this._onViewNoteButtonMenuClose.bind(this);
     }
 
+    /** */
     prepare() {
         this._noteContext = this._getNoteContext();
         this._display.hotkeyHandler.registerActions([
@@ -80,13 +121,16 @@ class DisplayAnki {
         this._display.on('logDictionaryEntryData', this._onLogDictionaryEntryData.bind(this));
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @returns {Promise<import('display-anki').LogData>}
+     */
     async getLogData(dictionaryEntry) {
-        const result = {};
-
         // Anki note data
         let ankiNoteData;
         let ankiNoteDataException;
         try {
+            if (this._noteContext === null) { throw new Error('Note context not initialized'); }
             ankiNoteData = await this._ankiNoteBuilder.getRenderingData({
                 dictionaryEntry,
                 mode: 'test',
@@ -99,12 +143,9 @@ class DisplayAnki {
         } catch (e) {
             ankiNoteDataException = e;
         }
-        result.ankiNoteData = ankiNoteData;
-        if (typeof ankiNoteDataException !== 'undefined') {
-            result.ankiNoteDataException = ankiNoteDataException;
-        }
 
         // Anki notes
+        /** @type {import('display-anki').AnkiNoteLogData[]} */
         const ankiNotes = [];
         const modes = this._getModes(dictionaryEntry.type === 'term');
         for (const mode of modes) {
@@ -114,8 +155,9 @@ class DisplayAnki {
             try {
                 ({note: note, errors, requirements} = await this._createNote(dictionaryEntry, mode, []));
             } catch (e) {
-                errors = [e];
+                errors = [e instanceof Error ? e : new Error(`${e}`)];
             }
+            /** @type {import('display-anki').AnkiNoteLogData} */
             const entry = {mode, note};
             if (Array.isArray(errors) && errors.length > 0) {
                 entry.errors = errors;
@@ -125,13 +167,19 @@ class DisplayAnki {
             }
             ankiNotes.push(entry);
         }
-        result.ankiNotes = ankiNotes;
 
-        return result;
+        return {
+            ankiNoteData,
+            ankiNoteDataException: ankiNoteDataException instanceof Error ? ankiNoteDataException : new Error(`${ankiNoteDataException}`),
+            ankiNotes
+        };
     }
 
     // Private
 
+    /**
+     * @param {import('display').OptionsUpdatedEvent} details
+     */
     _onOptionsUpdated({options}) {
         const {
             general: {resultOutputMode, glossaryLayoutMode, compactTags},
@@ -173,16 +221,21 @@ class DisplayAnki {
         this._updateAnkiFieldTemplates(options);
     }
 
+    /** */
     _onContentClear() {
         this._updateDictionaryEntryDetailsToken = null;
         this._dictionaryEntryDetails = null;
         this._hideErrorNotification(false);
     }
 
+    /** */
     _onContentUpdateStart() {
         this._noteContext = this._getNoteContext();
     }
 
+    /**
+     * @param {import('display').ContentUpdateEntryEvent} details
+     */
     _onContentUpdateEntry({element}) {
         const eventListeners = this._eventListeners;
         for (const node of element.querySelectorAll('.action-button[data-action=view-tags]')) {
@@ -198,45 +251,77 @@ class DisplayAnki {
         }
     }
 
+    /** */
     _onContentUpdateComplete() {
         this._updateDictionaryEntryDetails();
     }
 
+    /**
+     * @param {import('display').LogDictionaryEntryDataEvent} details
+     */
     _onLogDictionaryEntryData({dictionaryEntry, promises}) {
         promises.push(this.getLogData(dictionaryEntry));
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onNoteAdd(e) {
         e.preventDefault();
-        const node = e.currentTarget;
-        const index = this._display.getElementDictionaryEntryIndex(node);
-        this._addAnkiNote(index, node.dataset.mode);
+        const element = /** @type {HTMLElement} */ (e.currentTarget);
+        const mode = this._getValidCreateMode(element.dataset.mode);
+        if (mode === null) { return; }
+        const index = this._display.getElementDictionaryEntryIndex(element);
+        this._addAnkiNote(index, mode);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onShowTags(e) {
         e.preventDefault();
-        const tags = e.currentTarget.title;
+        const element = /** @type {HTMLElement} */ (e.currentTarget);
+        const tags = element.title;
         this._showTagsNotification(tags);
     }
 
+    /**
+     * @param {number} index
+     * @param {import('display-anki').CreateMode} mode
+     * @returns {?HTMLButtonElement}
+     */
     _adderButtonFind(index, mode) {
         const entry = this._getEntry(index);
         return entry !== null ? entry.querySelector(`.action-button[data-action=add-note][data-mode="${mode}"]`) : null;
     }
 
+    /**
+     * @param {number} index
+     * @returns {?HTMLButtonElement}
+     */
     _tagsIndicatorFind(index) {
         const entry = this._getEntry(index);
         return entry !== null ? entry.querySelector('.action-button[data-action=view-tags]') : null;
     }
 
+    /**
+     * @param {number} index
+     * @returns {?HTMLElement}
+     */
     _getEntry(index) {
         const entries = this._display.dictionaryEntryNodes;
         return index >= 0 && index < entries.length ? entries[index] : null;
     }
 
+    /**
+     * @returns {?import('anki-templates-internal').Context}
+     */
     _getNoteContext() {
         const {state} = this._display.history;
-        let {documentTitle, url, sentence} = (isObject(state) ? state : {});
+        let documentTitle, url, sentence;
+        if (typeof state === 'object' && state !== null) {
+            ({documentTitle, url, sentence} = state);
+        }
         if (typeof documentTitle !== 'string') {
             documentTitle = document.title;
         }
@@ -254,8 +339,10 @@ class DisplayAnki {
         };
     }
 
+    /** */
     async _updateDictionaryEntryDetails() {
         const {dictionaryEntries} = this._display;
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._updateDictionaryEntryDetailsToken = token;
         if (this._updateAdderButtonsPromise !== null) {
@@ -263,13 +350,13 @@ class DisplayAnki {
         }
         if (this._updateDictionaryEntryDetailsToken !== token) { return; }
 
-        const {promise, resolve} = deferPromise();
+        const {promise, resolve} = /** @type {import('core').DeferredPromiseDetails<void>} */ (deferPromise());
         try {
             this._updateAdderButtonsPromise = promise;
             const dictionaryEntryDetails = await this._getDictionaryEntryDetails(dictionaryEntries);
             if (this._updateDictionaryEntryDetailsToken !== token) { return; }
             this._dictionaryEntryDetails = dictionaryEntryDetails;
-            this._updateAdderButtons();
+            this._updateAdderButtons(dictionaryEntryDetails);
         } finally {
             resolve();
             if (this._updateAdderButtonsPromise === promise) {
@@ -278,9 +365,11 @@ class DisplayAnki {
         }
     }
 
-    _updateAdderButtons() {
+    /**
+     * @param {import('display-anki').DictionaryEntryDetails[]} dictionaryEntryDetails
+     */
+    _updateAdderButtons(dictionaryEntryDetails) {
         const displayTags = this._displayTags;
-        const dictionaryEntryDetails = this._dictionaryEntryDetails;
         for (let i = 0, ii = dictionaryEntryDetails.length; i < ii; ++i) {
             let allNoteIds = null;
             for (const {mode, canAdd, noteIds, noteInfos, ankiError} of dictionaryEntryDetails[i].modeMap.values()) {
@@ -303,6 +392,10 @@ class DisplayAnki {
         }
     }
 
+    /**
+     * @param {number} i
+     * @param {(?import('anki').NoteInfo)[]} noteInfos
+     */
     _setupTagsIndicator(i, noteInfos) {
         const tagsIndicator = this._tagsIndicatorFind(i);
         if (tagsIndicator === null) {
@@ -310,8 +403,9 @@ class DisplayAnki {
         }
 
         const displayTags = new Set();
-        for (const {tags} of noteInfos) {
-            for (const tag of tags) {
+        for (const item of noteInfos) {
+            if (item === null) { continue; }
+            for (const tag of item.tags) {
                 displayTags.add(tag);
             }
         }
@@ -328,6 +422,9 @@ class DisplayAnki {
         }
     }
 
+    /**
+     * @param {string} message
+     */
     _showTagsNotification(message) {
         if (this._tagsNotification === null) {
             this._tagsNotification = this._display.createNotification(true);
@@ -337,11 +434,18 @@ class DisplayAnki {
         this._tagsNotification.open();
     }
 
+    /**
+     * @param {import('display-anki').CreateMode} mode
+     */
     _tryAddAnkiNoteForSelectedEntry(mode) {
         const index = this._display.selectedIndex;
         this._addAnkiNote(index, mode);
     }
 
+    /**
+     * @param {number} dictionaryEntryIndex
+     * @param {import('display-anki').CreateMode} mode
+     */
     async _addAnkiNote(dictionaryEntryIndex, mode) {
         const dictionaryEntries = this._display.dictionaryEntries;
         const dictionaryEntryDetails = this._dictionaryEntryDetails;
@@ -364,6 +468,7 @@ class DisplayAnki {
 
         this._hideErrorNotification(true);
 
+        /** @type {Error[]} */
         const allErrors = [];
         const progressIndicatorVisible = this._display.progressIndicatorVisible;
         const overrideToken = progressIndicatorVisible.setOverride(true);
@@ -381,7 +486,7 @@ class DisplayAnki {
                 addNoteOkay = true;
             } catch (e) {
                 allErrors.length = 0;
-                allErrors.push(e);
+                allErrors.push(e instanceof Error ? e : new Error(`${e}`));
             }
 
             if (addNoteOkay) {
@@ -392,7 +497,7 @@ class DisplayAnki {
                         try {
                             await yomichan.api.suspendAnkiCardsForNote(noteId);
                         } catch (e) {
-                            allErrors.push(e);
+                            allErrors.push(e instanceof Error ? e : new Error(`${e}`));
                         }
                     }
                     button.disabled = true;
@@ -400,7 +505,7 @@ class DisplayAnki {
                 }
             }
         } catch (e) {
-            allErrors.push(e);
+            allErrors.push(e instanceof Error ? e : new Error(`${e}`));
         } finally {
             progressIndicatorVisible.clearOverride(overrideToken);
         }
@@ -412,6 +517,11 @@ class DisplayAnki {
         }
     }
 
+    /**
+     * @param {import('anki-note-builder').Requirement[]} requirements
+     * @param {import('anki-note-builder').Requirement[]} outputRequirements
+     * @returns {?DisplayAnkiError}
+     */
     _getAddNoteRequirementsError(requirements, outputRequirements) {
         if (outputRequirements.length === 0) { return null; }
 
@@ -429,12 +539,16 @@ class DisplayAnki {
         }
         if (count === 0) { return null; }
 
-        const error = new Error('The created card may not have some content');
+        const error = new DisplayAnkiError('The created card may not have some content');
         error.requirements = requirements;
         error.outputRequirements = outputRequirements;
         return error;
     }
 
+    /**
+     * @param {Error[]} errors
+     * @param {(DocumentFragment|Node|Error)[]} [displayErrors]
+     */
     _showErrorNotification(errors, displayErrors) {
         if (typeof displayErrors === 'undefined') { displayErrors = errors; }
 
@@ -449,7 +563,7 @@ class DisplayAnki {
 
         const content = this._display.displayGenerator.createAnkiNoteErrorsNotificationContent(displayErrors);
         for (const node of content.querySelectorAll('.anki-note-error-log-link')) {
-            this._errorNotificationEventListeners.addEventListener(node, 'click', () => {
+            /** @type {EventListenerCollection} */ (this._errorNotificationEventListeners).addEventListener(node, 'click', () => {
                 console.log({ankiNoteErrors: errors});
             }, false);
         }
@@ -458,16 +572,26 @@ class DisplayAnki {
         this._errorNotification.open();
     }
 
+    /**
+     * @param {boolean} animate
+     */
     _hideErrorNotification(animate) {
         if (this._errorNotification === null) { return; }
         this._errorNotification.close(animate);
-        this._errorNotificationEventListeners.removeAllEventListeners();
+        /** @type {EventListenerCollection} */ (this._errorNotificationEventListeners).removeAllEventListeners();
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     async _updateAnkiFieldTemplates(options) {
         this._ankiFieldTemplates = await this._getAnkiFieldTemplates(options);
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     * @returns {Promise<string>}
+     */
     async _getAnkiFieldTemplates(options) {
         let templates = options.anki.fieldTemplates;
         if (typeof templates === 'string') { return templates; }
@@ -480,6 +604,10 @@ class DisplayAnki {
         return templates;
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry[]} dictionaryEntries
+     * @returns {Promise<import('display-anki').DictionaryEntryDetails[]>}
+     */
     async _getDictionaryEntryDetails(dictionaryEntries) {
         const forceCanAddValue = (this._checkForDuplicates ? null : true);
         const fetchAdditionalInfo = (this._displayTags !== 'never');
@@ -514,9 +642,10 @@ class DisplayAnki {
             }
         } catch (e) {
             infos = this._getAnkiNoteInfoForceValue(notes, false);
-            ankiError = e;
+            ankiError = e instanceof Error ? e : new Error(`${e}`);
         }
 
+        /** @type {import('display-anki').DictionaryEntryDetails[]} */
         const results = [];
         for (let i = 0, ii = dictionaryEntries.length; i < ii; ++i) {
             results.push({
@@ -533,6 +662,11 @@ class DisplayAnki {
         return results;
     }
 
+    /**
+     * @param {import('anki').Note[]} notes
+     * @param {boolean} canAdd
+     * @returns {import('anki').NoteInfoWrapper[]}
+     */
     _getAnkiNoteInfoForceValue(notes, canAdd) {
         const results = [];
         for (const note of notes) {
@@ -542,11 +676,19 @@ class DisplayAnki {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @param {import('display-anki').CreateMode} mode
+     * @param {import('anki-note-builder').Requirement[]} requirements
+     * @returns {Promise<import('display-anki').CreateNoteResult>}
+     */
     async _createNote(dictionaryEntry, mode, requirements) {
         const context = this._noteContext;
+        if (context === null) { throw new Error('Note context not initialized'); }
         const modeOptions = this._modeOptions.get(mode);
         if (typeof modeOptions === 'undefined') { throw new Error(`Unsupported note type: ${mode}`); }
         const template = this._ankiFieldTemplates;
+        if (typeof template !== 'string') { throw new Error('Invalid template'); }
         const {deck: deckName, model: modelName} = modeOptions;
         const fields = Object.entries(modeOptions.fields);
         const contentOrigin = this._display.getContentOrigin();
@@ -586,12 +728,26 @@ class DisplayAnki {
         return {note, errors, requirements: outputRequirements};
     }
 
+    /**
+     * @param {boolean} isTerms
+     * @returns {import('display-anki').CreateMode[]}
+     */
     _getModes(isTerms) {
         return isTerms ? ['term-kanji', 'term-kana'] : ['kanji'];
     }
 
+    /**
+     * @param {unknown} sentence
+     * @param {string} fallback
+     * @param {number} fallbackOffset
+     * @returns {import('anki-templates-internal').ContextSentence}
+     */
     _getValidSentenceData(sentence, fallback, fallbackOffset) {
-        let {text, offset} = (isObject(sentence) ? sentence : {});
+        let text;
+        let offset;
+        if (typeof sentence === 'object' && sentence !== null) {
+            ({text, offset} = /** @type {import('core').UnknownObject} */ (sentence));
+        }
         if (typeof text !== 'string') {
             text = fallback;
             offset = fallbackOffset;
@@ -601,6 +757,10 @@ class DisplayAnki {
         return {text, offset};
     }
 
+    /**
+     * @param {import('api').InjectAnkiNoteMediaDefinitionDetails} details
+     * @returns {?import('anki-note-builder').AudioMediaOptions}
+     */
     _getAnkiNoteMediaAudioDetails(details) {
         if (details.type !== 'term') { return null; }
         const {sources, preferredAudioIndex} = this._displayAudio.getAnkiNoteMediaAudioDetails(details.term, details.reading);
@@ -609,56 +769,79 @@ class DisplayAnki {
 
     // View note functions
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onViewNoteButtonClick(e) {
+        const element = /** @type {HTMLElement} */ (e.currentTarget);
         e.preventDefault();
         if (e.shiftKey) {
-            this._showViewNoteMenu(e.currentTarget);
+            this._showViewNoteMenu(element);
         } else {
-            this._viewNote(e.currentTarget);
+            this._viewNote(element);
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onViewNoteButtonContextMenu(e) {
+        const element = /** @type {HTMLElement} */ (e.currentTarget);
         e.preventDefault();
-        this._showViewNoteMenu(e.currentTarget);
+        this._showViewNoteMenu(element);
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onViewNoteButtonMenuClose(e) {
         const {detail: {action, item}} = e;
         switch (action) {
             case 'viewNote':
-                this._viewNote(item);
+                if (item !== null) {
+                    this._viewNote(item);
+                }
                 break;
         }
     }
 
+    /**
+     * @param {number} index
+     * @param {number[]} noteIds
+     * @param {boolean} prepend
+     */
     _updateViewNoteButton(index, noteIds, prepend) {
         const button = this._getViewNoteButton(index);
         if (button === null) { return; }
+        /** @type {(number|string)[]} */
+        let allNoteIds = noteIds;
         if (prepend) {
             const currentNoteIds = button.dataset.noteIds;
             if (typeof currentNoteIds === 'string' && currentNoteIds.length > 0) {
-                noteIds = [...noteIds, currentNoteIds.split(' ')];
+                allNoteIds = [...allNoteIds, ...currentNoteIds.split(' ')];
             }
         }
-        const disabled = (noteIds.length === 0);
+        const disabled = (allNoteIds.length === 0);
         button.disabled = disabled;
         button.hidden = disabled;
-        button.dataset.noteIds = noteIds.join(' ');
+        button.dataset.noteIds = allNoteIds.join(' ');
 
-        const badge = button.querySelector('.action-button-badge');
+        const badge = /** @type {?HTMLElement} */ (button.querySelector('.action-button-badge'));
         if (badge !== null) {
             const badgeData = badge.dataset;
-            if (noteIds.length > 1) {
+            if (allNoteIds.length > 1) {
                 badgeData.icon = 'plus-thick';
-                badgeData.hidden = false;
+                badge.hidden = false;
             } else {
                 delete badgeData.icon;
-                badgeData.hidden = true;
+                badge.hidden = true;
             }
         }
     }
 
+    /**
+     * @param {HTMLElement} node
+     */
     async _viewNote(node) {
         const noteIds = this._getNodeNoteIds(node);
         if (noteIds.length === 0) { return; }
@@ -666,26 +849,30 @@ class DisplayAnki {
             await yomichan.api.noteView(noteIds[0], this._noteGuiMode, false);
         } catch (e) {
             const displayErrors = (
-                e.message === 'Mode not supported' ?
+                e instanceof Error && e.message === 'Mode not supported' ?
                 [this._display.displayGenerator.instantiateTemplateFragment('footer-notification-anki-view-note-error')] :
                 void 0
             );
-            this._showErrorNotification([e], displayErrors);
+            this._showErrorNotification([e instanceof Error ? e : new Error(`${e}`)], displayErrors);
             return;
         }
     }
 
+    /**
+     * @param {HTMLElement} node
+     */
     _showViewNoteMenu(node) {
         const noteIds = this._getNodeNoteIds(node);
         if (noteIds.length === 0) { return; }
 
-        const menuContainerNode = this._display.displayGenerator.instantiateTemplate('view-note-button-popup-menu');
-        const menuBodyNode = menuContainerNode.querySelector('.popup-menu-body');
+        const menuContainerNode = /** @type {HTMLElement} */ (this._display.displayGenerator.instantiateTemplate('view-note-button-popup-menu'));
+        const menuBodyNode = /** @type {HTMLElement} */ (menuContainerNode.querySelector('.popup-menu-body'));
 
         for (let i = 0, ii = noteIds.length; i < ii; ++i) {
             const noteId = noteIds[i];
-            const item = this._display.displayGenerator.instantiateTemplate('view-note-button-popup-menu-item');
-            item.querySelector('.popup-menu-item-label').textContent = `Note ${i + 1}: ${noteId}`;
+            const item = /** @type {HTMLElement} */ (this._display.displayGenerator.instantiateTemplate('view-note-button-popup-menu-item'));
+            const label = /** @type {Element} */ (item.querySelector('.popup-menu-item-label'));
+            label.textContent = `Note ${i + 1}: ${noteId}`;
             item.dataset.menuAction = 'viewNote';
             item.dataset.noteIds = `${noteId}`;
             menuBodyNode.appendChild(item);
@@ -696,6 +883,10 @@ class DisplayAnki {
         popupMenu.prepare();
     }
 
+    /**
+     * @param {HTMLElement} node
+     * @returns {number[]}
+     */
     _getNodeNoteIds(node) {
         const {noteIds} = node.dataset;
         const results = [];
@@ -710,11 +901,16 @@ class DisplayAnki {
         return results;
     }
 
+    /**
+     * @param {number} index
+     * @returns {?HTMLButtonElement}
+     */
     _getViewNoteButton(index) {
         const entry = this._getEntry(index);
         return entry !== null ? entry.querySelector('.action-button[data-action=view-note]') : null;
     }
 
+    /** */
     _viewNoteForSelectedEntry() {
         const index = this._display.selectedIndex;
         const button = this._getViewNoteButton(index);
@@ -722,4 +918,40 @@ class DisplayAnki {
             this._viewNote(button);
         }
     }
+
+    /**
+     * @param {string|undefined} value
+     * @returns {?import('display-anki').CreateMode}
+     */
+    _getValidCreateMode(value) {
+        switch (value) {
+            case 'kanji':
+            case 'term-kanji':
+            case 'term-kana':
+                return value;
+            default:
+                return null;
+        }
+    }
+}
+
+class DisplayAnkiError extends Error {
+    /**
+     * @param {string} message
+     */
+    constructor(message) {
+        super(message);
+        /** @type {?import('anki-note-builder').Requirement[]} */
+        this._requirements = null;
+        /** @type {?import('anki-note-builder').Requirement[]} */
+        this._outputRequirements = null;
+    }
+
+    /** @type {?import('anki-note-builder').Requirement[]} */
+    get requirements() { return this._requirements; }
+    set requirements(value) { this._requirements = value; }
+
+    /** @type {?import('anki-note-builder').Requirement[]} */
+    get outputRequirements() { return this._outputRequirements; }
+    set outputRequirements(value) { this._outputRequirements = value; }
 }
diff --git a/ext/js/display/display-audio.js b/ext/js/display/display-audio.js
index c0b3859d5c..0ad33972d4 100644
--- a/ext/js/display/display-audio.js
+++ b/ext/js/display/display-audio.js
@@ -22,20 +22,37 @@
  */
 
 class DisplayAudio {
+    /**
+     * @param {Display} display
+     */
     constructor(display) {
+        /** @type {Display} */
         this._display = display;
+        /** @type {?import('display-audio').GenericAudio} */
         this._audioPlaying = null;
+        /** @type {AudioSystem} */
         this._audioSystem = new AudioSystem();
+        /** @type {number} */
         this._playbackVolume = 1.0;
+        /** @type {boolean} */
         this._autoPlay = false;
+        /** @type {?number} */
         this._autoPlayAudioTimer = null;
+        /** @type {number} */
         this._autoPlayAudioDelay = 400;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {Map<string, import('display-audio').CacheItem>} */
         this._cache = new Map();
-        this._menuContainer = document.querySelector('#popup-menus');
+        /** @type {Element} */
+        this._menuContainer = /** @type {Element} */ (document.querySelector('#popup-menus'));
+        /** @type {import('core').TokenObject} */
         this._entriesToken = {};
+        /** @type {Set<PopupMenu>} */
         this._openMenus = new Set();
+        /** @type {import('display-audio').AudioSource[]} */
         this._audioSources = [];
+        /** @type {Map<import('settings').AudioSourceType, string>} */
         this._audioSourceTypeNames = new Map([
             ['jpod101', 'JapanesePod101'],
             ['jpod101-alternate', 'JapanesePod101 (Alternate)'],
@@ -45,11 +62,15 @@ class DisplayAudio {
             ['custom', 'Custom URL'],
             ['custom-json', 'Custom URL (JSON)']
         ]);
+        /** @type {(event: MouseEvent) => void} */
         this._onAudioPlayButtonClickBind = this._onAudioPlayButtonClick.bind(this);
+        /** @type {(event: MouseEvent) => void} */
         this._onAudioPlayButtonContextMenuBind = this._onAudioPlayButtonContextMenu.bind(this);
+        /** @type {(event: import('popup-menu').MenuCloseEvent) => void} */
         this._onAudioPlayMenuCloseClickBind = this._onAudioPlayMenuCloseClick.bind(this);
     }
 
+    /** @type {number} */
     get autoPlayAudioDelay() {
         return this._autoPlayAudioDelay;
     }
@@ -58,6 +79,7 @@ class DisplayAudio {
         this._autoPlayAudioDelay = value;
     }
 
+    /** */
     prepare() {
         this._audioSystem.prepare();
         this._display.hotkeyHandler.registerActions([
@@ -72,21 +94,31 @@ class DisplayAudio {
         this._display.on('contentUpdateEntry', this._onContentUpdateEntry.bind(this));
         this._display.on('contentUpdateComplete', this._onContentUpdateComplete.bind(this));
         this._display.on('frameVisibilityChange', this._onFrameVisibilityChange.bind(this));
-        this._onOptionsUpdated({options: this._display.getOptions()});
+        const options = this._display.getOptions();
+        if (options !== null) {
+            this._onOptionsUpdated({options});
+        }
     }
 
+    /** */
     clearAutoPlayTimer() {
         if (this._autoPlayAudioTimer === null) { return; }
         clearTimeout(this._autoPlayAudioTimer);
         this._autoPlayAudioTimer = null;
     }
 
+    /** */
     stopAudio() {
         if (this._audioPlaying === null) { return; }
         this._audioPlaying.pause();
         this._audioPlaying = null;
     }
 
+    /**
+     * @param {number} dictionaryEntryIndex
+     * @param {number} headwordIndex
+     * @param {?string} [sourceType]
+     */
     async playAudio(dictionaryEntryIndex, headwordIndex, sourceType=null) {
         let sources = this._audioSources;
         if (sourceType !== null) {
@@ -100,7 +132,13 @@ class DisplayAudio {
         await this._playAudio(dictionaryEntryIndex, headwordIndex, sources, null);
     }
 
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @returns {import('display-audio').AudioMediaOptions}
+     */
     getAnkiNoteMediaAudioDetails(term, reading) {
+        /** @type {import('display-audio').AudioSourceShort[]} */
         const sources = [];
         let preferredAudioIndex = null;
         const primaryCardAudio = this._getPrimaryCardAudio(term, reading);
@@ -120,17 +158,21 @@ class DisplayAudio {
 
     // Private
 
+    /**
+     * @param {import('display').OptionsUpdatedEvent} details
+     */
     _onOptionsUpdated({options}) {
-        if (options === null) { return; }
         const {enabled, autoPlay, volume, sources} = options.audio;
         this._autoPlay = enabled && autoPlay;
         this._playbackVolume = Number.isFinite(volume) ? Math.max(0.0, Math.min(1.0, volume / 100.0)) : 1.0;
 
+        /** @type {Set<import('settings').AudioSourceType>} */
         const requiredAudioSources = new Set([
             'jpod101',
             'jpod101-alternate',
             'jisho'
         ]);
+        /** @type {Map<string, import('display-audio').AudioSource[]>} */
         const nameMap = new Map();
         this._audioSources.length = 0;
         for (const {type, url, voice} of sources) {
@@ -147,6 +189,7 @@ class DisplayAudio {
         this._cache.clear();
     }
 
+    /** */
     _onContentClear() {
         this._entriesToken = {};
         this._cache.clear();
@@ -154,6 +197,9 @@ class DisplayAudio {
         this._eventListeners.removeAllEventListeners();
     }
 
+    /**
+     * @param {import('display').ContentUpdateEntryEvent} details
+     */
     _onContentUpdateEntry({element}) {
         const eventListeners = this._eventListeners;
         for (const button of element.querySelectorAll('.action-button[data-action=play-audio]')) {
@@ -163,6 +209,7 @@ class DisplayAudio {
         }
     }
 
+    /** */
     _onContentUpdateComplete() {
         if (!this._autoPlay || !this._display.frameVisible) { return; }
 
@@ -186,6 +233,9 @@ class DisplayAudio {
         }
     }
 
+    /**
+     * @param {import('display').FrameVisibilityChangeEvent} details
+     */
     _onFrameVisibilityChange({value}) {
         if (!value) {
             // The auto-play timer is stopped, but any audio that has already started playing
@@ -194,18 +244,31 @@ class DisplayAudio {
         }
     }
 
+    /** */
     _onHotkeyActionPlayAudio() {
         this.playAudio(this._display.selectedIndex, 0);
     }
 
+    /**
+     * @param {unknown} source
+     */
     _onHotkeyActionPlayAudioFromSource(source) {
+        if (!(typeof source === 'string' || typeof source === 'undefined' || source === null)) { return; }
         this.playAudio(this._display.selectedIndex, 0, source);
     }
 
+    /** */
     _onMessageClearAutoPlayTimer() {
         this.clearAutoPlayTimer();
     }
 
+    /**
+     * @param {import('settings').AudioSourceType} type
+     * @param {string} url
+     * @param {string} voice
+     * @param {boolean} isInOptions
+     * @param {Map<string, import('display-audio').AudioSource[]>} nameMap
+     */
     _addAudioSourceInfo(type, url, voice, isInOptions, nameMap) {
         const index = this._audioSources.length;
         const downloadable = this._sourceIsDownloadable(type);
@@ -222,6 +285,7 @@ class DisplayAudio {
             entries[0].nameUnique = false;
         }
 
+        /** @type {import('display-audio').AudioSource} */
         const source = {
             index,
             type,
@@ -238,32 +302,41 @@ class DisplayAudio {
         this._audioSources.push(source);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onAudioPlayButtonClick(e) {
         e.preventDefault();
 
-        const button = e.currentTarget;
+        const button = /** @type {HTMLButtonElement} */ (e.currentTarget);
         const headwordIndex = this._getAudioPlayButtonHeadwordIndex(button);
         const dictionaryEntryIndex = this._display.getElementDictionaryEntryIndex(button);
 
         if (e.shiftKey) {
-            this._showAudioMenu(e.currentTarget, dictionaryEntryIndex, headwordIndex);
+            this._showAudioMenu(button, dictionaryEntryIndex, headwordIndex);
         } else {
             this.playAudio(dictionaryEntryIndex, headwordIndex);
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onAudioPlayButtonContextMenu(e) {
         e.preventDefault();
 
-        const button = e.currentTarget;
+        const button = /** @type {HTMLButtonElement} */ (e.currentTarget);
         const headwordIndex = this._getAudioPlayButtonHeadwordIndex(button);
         const dictionaryEntryIndex = this._display.getElementDictionaryEntryIndex(button);
 
-        this._showAudioMenu(e.currentTarget, dictionaryEntryIndex, headwordIndex);
+        this._showAudioMenu(button, dictionaryEntryIndex, headwordIndex);
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onAudioPlayMenuCloseClick(e) {
-        const button = e.currentTarget;
+        const button = /** @type {Element} */ (e.currentTarget);
         const headwordIndex = this._getAudioPlayButtonHeadwordIndex(button);
         const dictionaryEntryIndex = this._display.getElementDictionaryEntryIndex(button);
 
@@ -282,6 +355,12 @@ class DisplayAudio {
         }
     }
 
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @param {boolean} create
+     * @returns {import('display-audio').CacheItem|undefined}
+     */
     _getCacheItem(term, reading, create) {
         const key = this._getTermReadingKey(term, reading);
         let cacheEntry = this._cache.get(key);
@@ -295,31 +374,41 @@ class DisplayAudio {
         return cacheEntry;
     }
 
+    /**
+     * @param {Element} item
+     * @returns {import('display-audio').SourceInfo}
+     */
     _getMenuItemSourceInfo(item) {
-        const group = item.closest('.popup-menu-item-group');
+        const group = /** @type {?HTMLElement} */ (item.closest('.popup-menu-item-group'));
         if (group !== null) {
-            let {index, subIndex} = group.dataset;
-            index = Number.parseInt(index, 10);
-            if (index >= 0 && index < this._audioSources.length) {
-                const source = this._audioSources[index];
-                if (typeof subIndex === 'string') {
-                    subIndex = Number.parseInt(subIndex, 10);
-                } else {
-                    subIndex = null;
+            const {index, subIndex} = group.dataset;
+            if (typeof index === 'string') {
+                const indexNumber = Number.parseInt(index, 10);
+                if (indexNumber >= 0 && indexNumber < this._audioSources.length) {
+                    return {
+                        source: this._audioSources[indexNumber],
+                        subIndex: typeof subIndex === 'string' ? Number.parseInt(subIndex, 10) : null
+                    };
                 }
-                return {source, subIndex};
             }
         }
         return {source: null, subIndex: null};
     }
 
+    /**
+     * @param {number} dictionaryEntryIndex
+     * @param {number} headwordIndex
+     * @param {import('display-audio').AudioSource[]} sources
+     * @param {?number} audioInfoListIndex
+     * @returns {Promise<import('display-audio').PlayAudioResult>}
+     */
     async _playAudio(dictionaryEntryIndex, headwordIndex, sources, audioInfoListIndex) {
         this.stopAudio();
         this.clearAutoPlayTimer();
 
         const headword = this._getHeadword(dictionaryEntryIndex, headwordIndex);
         if (headword === null) {
-            return {audio: null, source: null, valid: false};
+            return {audio: null, source: null, subIndex: 0, valid: false};
         }
 
         const buttons = this._getAudioPlayButtons(dictionaryEntryIndex, headwordIndex);
@@ -377,7 +466,13 @@ class DisplayAudio {
         }
     }
 
+    /**
+     * @param {number} dictionaryEntryIndex
+     * @param {number} headwordIndex
+     * @param {?HTMLElement} item
+     */
     async _playAudioFromSource(dictionaryEntryIndex, headwordIndex, item) {
+        if (item === null) { return; }
         const {source, subIndex} = this._getMenuItemSourceInfo(item);
         if (source === null) { return; }
 
@@ -392,7 +487,15 @@ class DisplayAudio {
         }
     }
 
+    /**
+     * @param {number} dictionaryEntryIndex
+     * @param {number} headwordIndex
+     * @param {?HTMLElement} item
+     * @param {?PopupMenu} menu
+     * @param {boolean} canToggleOff
+     */
     _setPrimaryAudio(dictionaryEntryIndex, headwordIndex, item, menu, canToggleOff) {
+        if (item === null) { return; }
         const {source, subIndex} = this._getMenuItemSourceInfo(item);
         if (source === null || !source.downloadable) { return; }
 
@@ -402,6 +505,7 @@ class DisplayAudio {
         const {index} = source;
         const {term, reading} = headword;
         const cacheEntry = this._getCacheItem(term, reading, true);
+        if (typeof cacheEntry === 'undefined') { return; }
 
         let {primaryCardAudio} = cacheEntry;
         primaryCardAudio = (
@@ -417,39 +521,59 @@ class DisplayAudio {
         }
     }
 
+    /**
+     * @param {Element} button
+     * @returns {number}
+     */
     _getAudioPlayButtonHeadwordIndex(button) {
-        const headwordNode = button.closest('.headword');
+        const headwordNode = /** @type {?HTMLElement} */ (button.closest('.headword'));
         if (headwordNode !== null) {
-            const headwordIndex = parseInt(headwordNode.dataset.index, 10);
-            if (Number.isFinite(headwordIndex)) { return headwordIndex; }
+            const {index} = headwordNode.dataset;
+            if (typeof index === 'string') {
+                const headwordIndex = parseInt(index, 10);
+                if (Number.isFinite(headwordIndex)) { return headwordIndex; }
+            }
         }
         return 0;
     }
 
+    /**
+     * @param {number} dictionaryEntryIndex
+     * @param {number} headwordIndex
+     * @returns {HTMLButtonElement[]}
+     */
     _getAudioPlayButtons(dictionaryEntryIndex, headwordIndex) {
         const results = [];
         const {dictionaryEntryNodes} = this._display;
         if (dictionaryEntryIndex >= 0 && dictionaryEntryIndex < dictionaryEntryNodes.length) {
             const node = dictionaryEntryNodes[dictionaryEntryIndex];
-            const button1 = (headwordIndex === 0 ? node.querySelector('.action-button[data-action=play-audio]') : null);
-            const button2 = node.querySelector(`.headword:nth-of-type(${headwordIndex + 1}) .action-button[data-action=play-audio]`);
+            const button1 = /** @type {?HTMLButtonElement} */ ((headwordIndex === 0 ? node.querySelector('.action-button[data-action=play-audio]') : null));
+            const button2 = /** @type {?HTMLButtonElement} */ (node.querySelector(`.headword:nth-of-type(${headwordIndex + 1}) .action-button[data-action=play-audio]`));
             if (button1 !== null) { results.push(button1); }
             if (button2 !== null) { results.push(button2); }
         }
         return results;
     }
 
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @param {import('display-audio').AudioSource[]} sources
+     * @param {?number} audioInfoListIndex
+     * @returns {Promise<?import('display-audio').TermAudio>}
+     */
     async _createTermAudio(term, reading, sources, audioInfoListIndex) {
-        const {sourceMap} = this._getCacheItem(term, reading, true);
+        const cacheItem = this._getCacheItem(term, reading, true);
+        if (typeof cacheItem === 'undefined') { return null; }
+        const {sourceMap} = cacheItem;
 
         for (const source of sources) {
             const {index} = source;
 
             let cacheUpdated = false;
-            let infoListPromise;
             let sourceInfo = sourceMap.get(index);
             if (typeof sourceInfo === 'undefined') {
-                infoListPromise = this._getTermAudioInfoList(source, term, reading);
+                const infoListPromise = this._getTermAudioInfoList(source, term, reading);
                 sourceInfo = {infoListPromise, infoList: null};
                 sourceMap.set(index, sourceInfo);
                 cacheUpdated = true;
@@ -457,7 +581,7 @@ class DisplayAudio {
 
             let {infoList} = sourceInfo;
             if (infoList === null) {
-                infoList = await infoListPromise;
+                infoList = await sourceInfo.infoListPromise;
                 sourceInfo.infoList = infoList;
             }
 
@@ -471,6 +595,12 @@ class DisplayAudio {
         return null;
     }
 
+    /**
+     * @param {import('display-audio').AudioSource} source
+     * @param {import('display-audio').AudioInfoList} infoList
+     * @param {?number} audioInfoListIndex
+     * @returns {Promise<import('display-audio').CreateAudioResult>}
+     */
     async _createAudioFromInfoList(source, infoList, audioInfoListIndex) {
         let start = 0;
         let end = infoList.length;
@@ -479,6 +609,7 @@ class DisplayAudio {
             end = Math.max(0, Math.min(end, audioInfoListIndex + 1));
         }
 
+        /** @type {import('display-audio').CreateAudioResult} */
         const result = {
             audio: null,
             index: -1,
@@ -518,6 +649,11 @@ class DisplayAudio {
         return result;
     }
 
+    /**
+     * @param {import('audio-downloader').Info} info
+     * @param {import('display-audio').AudioSource} source
+     * @returns {Promise<import('display-audio').GenericAudio>}
+     */
     async _createAudioFromInfo(info, source) {
         switch (info.type) {
             case 'url':
@@ -525,16 +661,27 @@ class DisplayAudio {
             case 'tts':
                 return this._audioSystem.createTextToSpeechAudio(info.text, info.voice);
             default:
-                throw new Error(`Unsupported type: ${info.type}`);
+                throw new Error(`Unsupported type: ${/** @type {import('core').SafeAny} */ (info).type}`);
         }
     }
 
+    /**
+     * @param {import('display-audio').AudioSource} source
+     * @param {string} term
+     * @param {string} reading
+     * @returns {Promise<import('display-audio').AudioInfoList>}
+     */
     async _getTermAudioInfoList(source, term, reading) {
         const sourceData = this._getSourceData(source);
         const infoList = await yomichan.api.getTermAudioInfoList(sourceData, term, reading);
         return infoList.map((info) => ({info, audioPromise: null, audioResolved: false, audio: null}));
     }
 
+    /**
+     * @param {number} dictionaryEntryIndex
+     * @param {number} headwordIndex
+     * @returns {?import('dictionary').TermHeadword}
+     */
     _getHeadword(dictionaryEntryIndex, headwordIndex) {
         const {dictionaryEntries} = this._display;
         if (dictionaryEntryIndex < 0 || dictionaryEntryIndex >= dictionaryEntries.length) { return null; }
@@ -548,10 +695,19 @@ class DisplayAudio {
         return headwords[headwordIndex];
     }
 
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @returns {string}
+     */
     _getTermReadingKey(term, reading) {
         return JSON.stringify([term, reading]);
     }
 
+    /**
+     * @param {HTMLButtonElement} button
+     * @param {?number} potentialAvailableAudioCount
+     */
     _updateAudioPlayButtonBadge(button, potentialAvailableAudioCount) {
         if (potentialAvailableAudioCount === null) {
             delete button.dataset.potentialAvailableAudioCount;
@@ -559,27 +715,32 @@ class DisplayAudio {
             button.dataset.potentialAvailableAudioCount = `${potentialAvailableAudioCount}`;
         }
 
-        const badge = button.querySelector('.action-button-badge');
+        const badge = /** @type {?HTMLElement} */ (button.querySelector('.action-button-badge'));
         if (badge === null) { return; }
 
         const badgeData = badge.dataset;
         switch (potentialAvailableAudioCount) {
             case 0:
                 badgeData.icon = 'cross';
-                badgeData.hidden = false;
+                badge.hidden = false;
                 break;
             case 1:
             case null:
                 delete badgeData.icon;
-                badgeData.hidden = true;
+                badge.hidden = true;
                 break;
             default:
                 badgeData.icon = 'plus-thick';
-                badgeData.hidden = false;
+                badge.hidden = false;
                 break;
         }
     }
 
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @returns {?number}
+     */
     _getPotentialAvailableAudioCount(term, reading) {
         const cacheEntry = this._getCacheItem(term, reading, false);
         if (typeof cacheEntry === 'undefined') { return null; }
@@ -597,6 +758,11 @@ class DisplayAudio {
         return count;
     }
 
+    /**
+     * @param {HTMLButtonElement} button
+     * @param {number} dictionaryEntryIndex
+     * @param {number} headwordIndex
+     */
     _showAudioMenu(button, dictionaryEntryIndex, headwordIndex) {
         const headword = this._getHeadword(dictionaryEntryIndex, headwordIndex);
         if (headword === null) { return; }
@@ -608,10 +774,17 @@ class DisplayAudio {
         popupMenu.on('close', this._onPopupMenuClose.bind(this));
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEventDetails} details
+     */
     _onPopupMenuClose({menu}) {
         this._openMenus.delete(menu);
     }
 
+    /**
+     * @param {import('settings').AudioSourceType} source
+     * @returns {boolean}
+     */
     _sourceIsDownloadable(source) {
         switch (source) {
             case 'text-to-speech':
@@ -622,10 +795,16 @@ class DisplayAudio {
         }
     }
 
+    /**
+     * @param {HTMLButtonElement} sourceButton
+     * @param {string} term
+     * @param {string} reading
+     * @returns {PopupMenu}
+     */
     _createMenu(sourceButton, term, reading) {
         // Create menu
-        const menuContainerNode = this._display.displayGenerator.instantiateTemplate('audio-button-popup-menu');
-        const menuBodyNode = menuContainerNode.querySelector('.popup-menu-body');
+        const menuContainerNode = /** @type {HTMLElement} */ (this._display.displayGenerator.instantiateTemplate('audio-button-popup-menu'));
+        const menuBodyNode = /** @type {HTMLElement} */ (menuContainerNode.querySelector('.popup-menu-body'));
         menuContainerNode.dataset.term = term;
         menuContainerNode.dataset.reading = reading;
 
@@ -640,6 +819,12 @@ class DisplayAudio {
         return new PopupMenu(sourceButton, menuContainerNode);
     }
 
+    /**
+     * @param {HTMLElement} menuContainerNode
+     * @param {HTMLElement} menuItemContainer
+     * @param {string} term
+     * @param {string} reading
+     */
     _createMenuItems(menuContainerNode, menuItemContainer, term, reading) {
         const {displayGenerator} = this._display;
         let showIcons = false;
@@ -649,12 +834,10 @@ class DisplayAudio {
             const entries = this._getMenuItemEntries(source, term, reading);
             for (let i = 0, ii = entries.length; i < ii; ++i) {
                 const {valid, index: subIndex, name: subName} = entries[i];
-                let node = this._getOrCreateMenuItem(currentItems, index, subIndex);
-                if (node === null) {
-                    node = displayGenerator.instantiateTemplate('audio-button-popup-menu-item');
-                }
+                const existingNode = this._getOrCreateMenuItem(currentItems, index, subIndex);
+                const node = existingNode !== null ? existingNode : /** @type {HTMLElement} */ (displayGenerator.instantiateTemplate('audio-button-popup-menu-item'));
 
-                const labelNode = node.querySelector('.popup-menu-item-audio-button .popup-menu-item-label');
+                const labelNode = /** @type {HTMLElement} */ (node.querySelector('.popup-menu-item-audio-button .popup-menu-item-label'));
                 let label = name;
                 if (!nameUnique) {
                     label = `${label} ${nameIndex + 1}`;
@@ -664,11 +847,11 @@ class DisplayAudio {
                 if (typeof subName === 'string' && subName.length > 0) { label += `: ${subName}`; }
                 labelNode.textContent = label;
 
-                const cardButton = node.querySelector('.popup-menu-item-set-primary-audio-button');
+                const cardButton = /** @type {HTMLElement} */ (node.querySelector('.popup-menu-item-set-primary-audio-button'));
                 cardButton.hidden = !downloadable;
 
                 if (valid !== null) {
-                    const icon = node.querySelector('.popup-menu-item-audio-button .popup-menu-item-icon');
+                    const icon = /** @type {HTMLElement} */ (node.querySelector('.popup-menu-item-audio-button .popup-menu-item-icon'));
                     icon.dataset.icon = valid ? 'checkmark' : 'cross';
                     showIcons = true;
                 }
@@ -691,16 +874,22 @@ class DisplayAudio {
         menuContainerNode.dataset.showIcons = `${showIcons}`;
     }
 
+    /**
+     * @param {Element[]} currentItems
+     * @param {number} index
+     * @param {?number} subIndex
+     * @returns {?HTMLElement}
+     */
     _getOrCreateMenuItem(currentItems, index, subIndex) {
-        index = `${index}`;
-        subIndex = `${subIndex !== null ? subIndex : 0}`;
+        const indexNumber = `${index}`;
+        const subIndexNumber = `${subIndex !== null ? subIndex : 0}`;
         for (let i = 0, ii = currentItems.length; i < ii; ++i) {
             const node = currentItems[i];
-            if (index !== node.dataset.index) { continue; }
+            if (!(node instanceof HTMLElement) || indexNumber !== node.dataset.index) { continue; }
 
             let subIndex2 = node.dataset.subIndex;
             if (typeof subIndex2 === 'undefined') { subIndex2 = '0'; }
-            if (subIndex !== subIndex2) { continue; }
+            if (subIndexNumber !== subIndex2) { continue; }
 
             currentItems.splice(i, 1);
             return node;
@@ -708,6 +897,12 @@ class DisplayAudio {
         return null;
     }
 
+    /**
+     * @param {import('display-audio').AudioSource} source
+     * @param {string} term
+     * @param {string} reading
+     * @returns {import('display-audio').MenuItemEntry[]}
+     */
     _getMenuItemEntries(source, term, reading) {
         const cacheEntry = this._getCacheItem(term, reading, false);
         if (typeof cacheEntry !== 'undefined') {
@@ -721,11 +916,12 @@ class DisplayAudio {
                         return [{valid: false, index: null, name: null}];
                     }
 
+                    /** @type {import('display-audio').MenuItemEntry[]} */
                     const results = [];
                     for (let i = 0; i < ii; ++i) {
                         const {audio, audioResolved, info: {name}} = infoList[i];
                         const valid = audioResolved ? (audio !== null) : null;
-                        const entry = {valid, index: i, name};
+                        const entry = {valid, index: i, name: typeof name === 'string' ? name : null};
                         results.push(entry);
                     }
                     return results;
@@ -735,34 +931,52 @@ class DisplayAudio {
         return [{valid: null, index: null, name: null}];
     }
 
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @returns {?import('display-audio').PrimaryCardAudio}
+     */
     _getPrimaryCardAudio(term, reading) {
         const cacheEntry = this._getCacheItem(term, reading, false);
         return typeof cacheEntry !== 'undefined' ? cacheEntry.primaryCardAudio : null;
     }
 
+    /**
+     * @param {HTMLElement} menuBodyNode
+     * @param {string} term
+     * @param {string} reading
+     */
     _updateMenuPrimaryCardAudio(menuBodyNode, term, reading) {
         const primaryCardAudio = this._getPrimaryCardAudio(term, reading);
         const primaryCardAudioIndex = (primaryCardAudio !== null ? primaryCardAudio.index : null);
         const primaryCardAudioSubIndex = (primaryCardAudio !== null ? primaryCardAudio.subIndex : null);
-        const itemGroups = menuBodyNode.querySelectorAll('.popup-menu-item-group');
+        const itemGroups = /** @type {NodeListOf<HTMLElement>} */ (menuBodyNode.querySelectorAll('.popup-menu-item-group'));
         for (const node of itemGroups) {
-            let {index, subIndex} = node.dataset;
-            index = Number.parseInt(index, 10);
-            subIndex = typeof subIndex === 'string' ? Number.parseInt(subIndex, 10) : null;
-            const isPrimaryCardAudio = (index === primaryCardAudioIndex && subIndex === primaryCardAudioSubIndex);
+            const {index, subIndex} = node.dataset;
+            if (typeof index !== 'string') { continue; }
+            const indexNumber = Number.parseInt(index, 10);
+            const subIndexNumber = typeof subIndex === 'string' ? Number.parseInt(subIndex, 10) : null;
+            const isPrimaryCardAudio = (indexNumber === primaryCardAudioIndex && subIndexNumber === primaryCardAudioSubIndex);
             node.dataset.isPrimaryCardAudio = `${isPrimaryCardAudio}`;
         }
     }
 
+    /** */
     _updateOpenMenu() {
         for (const menu of this._openMenus) {
             const menuContainerNode = menu.containerNode;
             const {term, reading} = menuContainerNode.dataset;
-            this._createMenuItems(menuContainerNode, menu.bodyNode, term, reading);
+            if (typeof term === 'string' && typeof reading === 'string') {
+                this._createMenuItems(menuContainerNode, menu.bodyNode, term, reading);
+            }
             menu.updatePosition();
         }
     }
 
+    /**
+     * @param {import('display-audio').AudioSource} source
+     * @returns {import('display-audio').AudioSourceShort}
+     */
     _getSourceData(source) {
         const {type, url, voice} = source;
         return {type, url, voice};
diff --git a/ext/js/display/display-content-manager.js b/ext/js/display/display-content-manager.js
index 2abff98a84..0000bf7292 100644
--- a/ext/js/display/display-content-manager.js
+++ b/ext/js/display/display-content-manager.js
@@ -20,18 +20,6 @@
  * ArrayBufferUtil
  */
 
-/**
- * A callback used when a media file has been loaded.
- * @callback DisplayContentManager.OnLoadCallback
- * @param {string} url The URL of the media that was loaded.
- */
-
-/**
- * A callback used when a media file should be unloaded.
- * @callback DisplayContentManager.OnUnloadCallback
- * @param {boolean} fullyLoaded Whether or not the media was fully loaded.
- */
-
 /**
  * The content manager which is used when generating HTML display content.
  */
@@ -41,10 +29,15 @@ class DisplayContentManager {
      * @param {Display} display The display instance that owns this object.
      */
     constructor(display) {
+        /** @type {Display} */
         this._display = display;
+        /** @type {import('core').TokenObject} */
         this._token = {};
+        /** @type {Map<string, Map<string, Promise<?import('display-content-manager').CachedMediaDataLoaded>>>} */
         this._mediaCache = new Map();
+        /** @type {import('display-content-manager').LoadMediaDataInfo[]} */
         this._loadMediaData = [];
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
     }
 
@@ -52,9 +45,9 @@ class DisplayContentManager {
      * Attempts to load the media file from a given dictionary.
      * @param {string} path The path to the media file in the dictionary.
      * @param {string} dictionary The name of the dictionary.
-     * @param {DisplayContentManager.OnLoadCallback} onLoad The callback that is executed if the media was loaded successfully.
+     * @param {import('display-content-manager').OnLoadCallback} onLoad The callback that is executed if the media was loaded successfully.
      *   No assumptions should be made about the synchronicity of this callback.
-     * @param {DisplayContentManager.OnUnloadCallback} onUnload The callback that is executed when the media should be unloaded.
+     * @param {import('display-content-manager').OnUnloadCallback} onUnload The callback that is executed when the media should be unloaded.
      */
     loadMedia(path, dictionary, onLoad, onUnload) {
         this._loadMedia(path, dictionary, onLoad, onUnload);
@@ -72,10 +65,8 @@ class DisplayContentManager {
         this._loadMediaData = [];
 
         for (const map of this._mediaCache.values()) {
-            for (const {url} of map.values()) {
-                if (url !== null) {
-                    URL.revokeObjectURL(url);
-                }
+            for (const result of map.values()) {
+                this._revokeUrl(result);
             }
         }
         this._mediaCache.clear();
@@ -87,7 +78,7 @@ class DisplayContentManager {
 
     /**
      * Sets up attributes and events for a link element.
-     * @param {Element} element The link element.
+     * @param {HTMLAnchorElement} element The link element.
      * @param {string} href The URL.
      * @param {boolean} internal Whether or not the URL is an internal or external link.
      */
@@ -100,57 +91,71 @@ class DisplayContentManager {
         this._eventListeners.addEventListener(element, 'click', this._onLinkClick.bind(this));
     }
 
+    /**
+     * @param {string} path
+     * @param {string} dictionary
+     * @param {import('display-content-manager').OnLoadCallback} onLoad
+     * @param {import('display-content-manager').OnUnloadCallback} onUnload
+     */
     async _loadMedia(path, dictionary, onLoad, onUnload) {
         const token = this._token;
-        const data = {onUnload, loaded: false};
-
-        this._loadMediaData.push(data);
-
         const media = await this._getMedia(path, dictionary);
-        if (token !== this._token) { return; }
+        if (token !== this._token || media === null) { return; }
 
+        /** @type {import('display-content-manager').LoadMediaDataInfo} */
+        const data = {onUnload, loaded: false};
+        this._loadMediaData.push(data);
         onLoad(media.url);
         data.loaded = true;
     }
 
-    async _getMedia(path, dictionary) {
-        let cachedData;
+    /**
+     * @param {string} path
+     * @param {string} dictionary
+     * @returns {Promise<?import('display-content-manager').CachedMediaDataLoaded>}
+     */
+    _getMedia(path, dictionary) {
+        /** @type {Promise<?import('display-content-manager').CachedMediaDataLoaded>|undefined} */
+        let promise;
         let dictionaryCache = this._mediaCache.get(dictionary);
         if (typeof dictionaryCache !== 'undefined') {
-            cachedData = dictionaryCache.get(path);
+            promise = dictionaryCache.get(path);
         } else {
             dictionaryCache = new Map();
             this._mediaCache.set(dictionary, dictionaryCache);
         }
 
-        if (typeof cachedData === 'undefined') {
-            cachedData = {
-                promise: null,
-                data: null,
-                url: null
-            };
-            dictionaryCache.set(path, cachedData);
-            cachedData.promise = this._getMediaData(path, dictionary, cachedData);
+        if (typeof promise === 'undefined') {
+            promise = this._getMediaData(path, dictionary);
+            dictionaryCache.set(path, promise);
         }
 
-        return cachedData.promise;
+        return promise;
     }
 
-    async _getMediaData(path, dictionary, cachedData) {
+    /**
+     * @param {string} path
+     * @param {string} dictionary
+     * @returns {Promise<?import('display-content-manager').CachedMediaDataLoaded>}
+     */
+    async _getMediaData(path, dictionary) {
         const token = this._token;
-        const data = (await yomichan.api.getMedia([{path, dictionary}]))[0];
-        if (token === this._token && data !== null) {
+        const datas = await yomichan.api.getMedia([{path, dictionary}]);
+        if (token === this._token && datas.length > 0) {
+            const data = datas[0];
             const buffer = ArrayBufferUtil.base64ToArrayBuffer(data.content);
             const blob = new Blob([buffer], {type: data.mediaType});
             const url = URL.createObjectURL(blob);
-            cachedData.data = data;
-            cachedData.url = url;
+            return {data, url};
         }
-        return cachedData;
+        return null;
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onLinkClick(e) {
-        const {href} = e.currentTarget;
+        const {href} = /** @type {HTMLAnchorElement} */ (e.currentTarget);
         if (typeof href !== 'string') { return; }
 
         const baseUrl = new URL(location.href);
@@ -160,6 +165,7 @@ class DisplayContentManager {
 
         e.preventDefault();
 
+        /** @type {import('display').HistoryParams} */
         const params = {};
         for (const [key, value] of url.searchParams.entries()) {
             params[key] = value;
@@ -172,4 +178,13 @@ class DisplayContentManager {
             content: null
         });
     }
+
+    /**
+     * @param {Promise<?import('display-content-manager').CachedMediaDataLoaded>} data
+     */
+    async _revokeUrl(data) {
+        const result = await data;
+        if (result === null) { return; }
+        URL.revokeObjectURL(result.url);
+    }
 }
diff --git a/ext/js/display/display-generator.js b/ext/js/display/display-generator.js
index 293cb72572..f61f4dce7b 100644
--- a/ext/js/display/display-generator.js
+++ b/ext/js/display/display-generator.js
@@ -24,21 +24,32 @@
  */
 
 class DisplayGenerator {
+    /**
+     * @param {import('display').DisplayGeneratorConstructorDetails} details
+     */
     constructor({japaneseUtil, contentManager, hotkeyHelpController=null}) {
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
+        /** @type {DisplayContentManager} */
         this._contentManager = contentManager;
+        /** @type {?HotkeyHelpController} */
         this._hotkeyHelpController = hotkeyHelpController;
-        this._templates = null;
+        /** @type {HtmlTemplateCollection} */
+        this._templates = new HtmlTemplateCollection();
+        /** @type {StructuredContentGenerator} */
         this._structuredContentGenerator = new StructuredContentGenerator(this._contentManager, japaneseUtil, document);
+        /** @type {PronunciationGenerator} */
         this._pronunciationGenerator = new PronunciationGenerator(japaneseUtil);
     }
 
+    /** */
     async prepare() {
         const html = await yomichan.api.getDisplayTemplatesHtml();
-        this._templates = new HtmlTemplateCollection(html);
+        this._templates.load(html);
         this.updateHotkeys();
     }
 
+    /** */
     updateHotkeys() {
         const hotkeyHelpController = this._hotkeyHelpController;
         if (hotkeyHelpController === null) { return; }
@@ -47,15 +58,19 @@ class DisplayGenerator {
         }
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {HTMLElement}
+     */
     createTermEntry(dictionaryEntry) {
-        const node = this._templates.instantiate('term-entry');
+        const node = this._instantiate('term-entry');
 
-        const headwordsContainer = node.querySelector('.headword-list');
-        const inflectionsContainer = node.querySelector('.inflection-list');
-        const groupedPronunciationsContainer = node.querySelector('.pronunciation-group-list');
-        const frequencyGroupListContainer = node.querySelector('.frequency-group-list');
-        const definitionsContainer = node.querySelector('.definition-list');
-        const headwordTagsContainer = node.querySelector('.headword-list-tag-list');
+        const headwordsContainer = this._querySelector(node, '.headword-list');
+        const inflectionsContainer = this._querySelector(node, '.inflection-list');
+        const groupedPronunciationsContainer = this._querySelector(node, '.pronunciation-group-list');
+        const frequencyGroupListContainer = this._querySelector(node, '.frequency-group-list');
+        const definitionsContainer = this._querySelector(node, '.definition-list');
+        const headwordTagsContainer = this._querySelector(node, '.headword-list-tag-list');
 
         const {headwords, type, inflections, definitions, frequencies, pronunciations} = dictionaryEntry;
         const groupedPronunciations = DictionaryDataUtil.getGroupedPronunciations(dictionaryEntry);
@@ -63,8 +78,11 @@ class DisplayGenerator {
         const groupedFrequencies = DictionaryDataUtil.groupTermFrequencies(dictionaryEntry);
         const termTags = DictionaryDataUtil.groupTermTags(dictionaryEntry);
 
+        /** @type {Set<string>} */
         const uniqueTerms = new Set();
+        /** @type {Set<string>} */
         const uniqueReadings = new Set();
+        /** @type {Set<import('dictionary').TermSourceMatchType>} */
         const primaryMatchTypes = new Set();
         for (const {term, reading, sources} of headwords) {
             uniqueTerms.add(term);
@@ -107,16 +125,16 @@ class DisplayGenerator {
         }
 
         // Add definitions
-        const dictionaryTag = this._createDictionaryTag(null);
+        const dictionaryTag = this._createDictionaryTag('');
         for (let i = 0, ii = definitions.length; i < ii; ++i) {
             const definition = definitions[i];
             const {dictionary} = definition;
 
-            if (dictionaryTag.dictionary === dictionary) {
+            if (dictionaryTag.dictionaries.includes(dictionary)) {
                 dictionaryTag.redundant = true;
             } else {
                 dictionaryTag.redundant = false;
-                dictionaryTag.dictionary = dictionary;
+                dictionaryTag.dictionaries.push(dictionary);
                 dictionaryTag.name = dictionary;
             }
 
@@ -129,19 +147,23 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {import('dictionary').KanjiDictionaryEntry} dictionaryEntry
+     * @returns {HTMLElement}
+     */
     createKanjiEntry(dictionaryEntry) {
-        const node = this._templates.instantiate('kanji-entry');
-
-        const glyphContainer = node.querySelector('.kanji-glyph');
-        const frequencyGroupListContainer = node.querySelector('.frequency-group-list');
-        const tagContainer = node.querySelector('.kanji-tag-list');
-        const definitionsContainer = node.querySelector('.kanji-gloss-list');
-        const chineseReadingsContainer = node.querySelector('.kanji-readings-chinese');
-        const japaneseReadingsContainer = node.querySelector('.kanji-readings-japanese');
-        const statisticsContainer = node.querySelector('.kanji-statistics');
-        const classificationsContainer = node.querySelector('.kanji-classifications');
-        const codepointsContainer = node.querySelector('.kanji-codepoints');
-        const dictionaryIndicesContainer = node.querySelector('.kanji-dictionary-indices');
+        const node = this._instantiate('kanji-entry');
+
+        const glyphContainer = this._querySelector(node, '.kanji-glyph');
+        const frequencyGroupListContainer = this._querySelector(node, '.frequency-group-list');
+        const tagContainer = this._querySelector(node, '.kanji-tag-list');
+        const definitionsContainer = this._querySelector(node, '.kanji-gloss-list');
+        const chineseReadingsContainer = this._querySelector(node, '.kanji-readings-chinese');
+        const japaneseReadingsContainer = this._querySelector(node, '.kanji-readings-japanese');
+        const statisticsContainer = this._querySelector(node, '.kanji-statistics');
+        const classificationsContainer = this._querySelector(node, '.kanji-classifications');
+        const codepointsContainer = this._querySelector(node, '.kanji-codepoints');
+        const dictionaryIndicesContainer = this._querySelector(node, '.kanji-dictionary-indices');
 
         this._setTextContent(glyphContainer, dictionaryEntry.character, 'ja');
         const groupedFrequencies = DictionaryDataUtil.groupKanjiFrequencies(dictionaryEntry.frequencies);
@@ -162,27 +184,36 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @returns {HTMLElement}
+     */
     createEmptyFooterNotification() {
-        return this._templates.instantiate('footer-notification');
+        return this._instantiate('footer-notification');
     }
 
+    /**
+     * @param {HTMLElement} tagNode
+     * @param {?import('dictionary').DictionaryEntry} dictionaryEntry
+     * @returns {DocumentFragment}
+     */
     createTagFooterNotificationDetails(tagNode, dictionaryEntry) {
         const node = this._templates.instantiateFragment('footer-notification-tag-details');
 
         let details = tagNode.dataset.details;
         if (typeof details !== 'string') {
             const label = tagNode.querySelector('.tag-label-content');
-            details = label !== null ? label.textContent : '';
+            details = label !== null && label.textContent !== null ? label.textContent : '';
         }
-        this._setTextContent(node.querySelector('.tag-details'), details);
+        const tagDetails = this._querySelector(node, '.tag-details');
+        this._setTextContent(tagDetails, details);
 
-        if (dictionaryEntry !== null) {
+        if (dictionaryEntry !== null && dictionaryEntry.type === 'term') {
             const {headwords} = dictionaryEntry;
             const disambiguationHeadwords = [];
             const {headwords: headwordIndices} = tagNode.dataset;
             if (typeof headwordIndices === 'string' && headwordIndices.length > 0) {
-                for (let headwordIndex of headwordIndices.split(' ')) {
-                    headwordIndex = Number.parseInt(headwordIndex, 10);
+                for (const headwordIndexString of headwordIndices.split(' ')) {
+                    const headwordIndex = Number.parseInt(headwordIndexString, 10);
                     if (!Number.isNaN(headwordIndex) && headwordIndex >= 0 && headwordIndex < headwords.length) {
                         disambiguationHeadwords.push(headwords[headwordIndex]);
                     }
@@ -190,7 +221,7 @@ class DisplayGenerator {
             }
 
             if (disambiguationHeadwords.length > 0 && disambiguationHeadwords.length < headwords.length) {
-                const disambiguationContainer = node.querySelector('.tag-details-disambiguation-list');
+                const disambiguationContainer = this._querySelector(node, '.tag-details-disambiguation-list');
                 const copyAttributes = ['totalHeadwordCount', 'matchedHeadwordCount', 'unmatchedHeadwordCount'];
                 for (const attribute of copyAttributes) {
                     const value = tagNode.dataset[attribute];
@@ -211,13 +242,17 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {(DocumentFragment|Node|Error)[]} errors
+     * @returns {HTMLElement}
+     */
     createAnkiNoteErrorsNotificationContent(errors) {
-        const content = this._templates.instantiate('footer-notification-anki-errors-content');
+        const content = this._instantiate('footer-notification-anki-errors-content');
 
-        const header = content.querySelector('.anki-note-error-header');
+        const header = this._querySelector(content, '.anki-note-error-header');
         this._setTextContent(header, (errors.length === 1 ? 'An error occurred:' : `${errors.length} errors occurred:`), 'en');
 
-        const list = content.querySelector('.anki-note-error-list');
+        const list = this._querySelector(content, '.anki-note-error-list');
         for (const error of errors) {
             const div = document.createElement('li');
             div.className = 'anki-note-error-message';
@@ -226,11 +261,11 @@ class DisplayGenerator {
             } else {
                 let message = isObject(error) && typeof error.message === 'string' ? error.message : `${error}`;
                 let link = null;
-                if (isObject(error) && isObject(error.data)) {
-                    const {referenceUrl} = error.data;
+                if (error instanceof ExtensionError && error.data !== null && typeof error.data === 'object') {
+                    const {referenceUrl} = /** @type {import('core').UnknownObject} */ (error.data);
                     if (typeof referenceUrl === 'string') {
                         message = message.trimEnd();
-                        if (!/[.!?]^/.test()) { message += '.'; }
+                        if (!/[.!?]^/.test(message)) { message += '.'; }
                         message += ' ';
                         link = document.createElement('a');
                         link.href = referenceUrl;
@@ -248,20 +283,37 @@ class DisplayGenerator {
         return content;
     }
 
+    /**
+     * @returns {HTMLElement}
+     */
     createProfileListItem() {
-        return this._templates.instantiate('profile-list-item');
+        return this._instantiate('profile-list-item');
     }
 
+    /**
+     * @param {string} name
+     * @returns {HTMLElement}
+     */
     instantiateTemplate(name) {
-        return this._templates.instantiate(name);
+        return this._instantiate(name);
     }
 
+    /**
+     * @param {string} name
+     * @returns {DocumentFragment}
+     */
     instantiateTemplateFragment(name) {
         return this._templates.instantiateFragment(name);
     }
 
     // Private
 
+    /**
+     * @param {import('dictionary').TermHeadword} headword
+     * @param {number} headwordIndex
+     * @param {import('dictionary').TermPronunciation[]} pronunciations
+     * @returns {HTMLElement}
+     */
     _createTermHeadword(headword, headwordIndex, pronunciations) {
         const {term, reading, tags, sources} = headword;
 
@@ -276,9 +328,9 @@ class DisplayGenerator {
             matchSources.add(matchSource);
         }
 
-        const node = this._templates.instantiate('headword');
+        const node = this._instantiate('headword');
 
-        const termContainer = node.querySelector('.headword-term');
+        const termContainer = this._querySelector(node, '.headword-term');
 
         node.dataset.isPrimary = `${isPrimaryAny}`;
         node.dataset.readingIsSame = `${reading === term}`;
@@ -295,30 +347,43 @@ class DisplayGenerator {
             node.dataset.wordClasses = wordClasses.join(' ');
         }
 
-        this._setTextContent(node.querySelector('.headword-reading'), reading);
+        const headwordReading = this._querySelector(node, '.headword-reading');
+        this._setTextContent(headwordReading, reading);
 
         this._appendFurigana(termContainer, term, reading, this._appendKanjiLinks.bind(this));
 
         return node;
     }
 
+    /**
+     * @param {string} inflection
+     * @returns {DocumentFragment}
+     */
     _createTermInflection(inflection) {
         const fragment = this._templates.instantiateFragment('inflection');
-        const node = fragment.querySelector('.inflection');
+        const node = this._querySelector(fragment, '.inflection');
         this._setTextContent(node, inflection);
         node.dataset.reason = inflection;
         return fragment;
     }
 
+    /**
+     * @param {import('dictionary').TermDefinition} definition
+     * @param {import('dictionary').Tag} dictionaryTag
+     * @param {import('dictionary').TermHeadword[]} headwords
+     * @param {Set<string>} uniqueTerms
+     * @param {Set<string>} uniqueReadings
+     * @returns {HTMLElement}
+     */
     _createTermDefinition(definition, dictionaryTag, headwords, uniqueTerms, uniqueReadings) {
         const {dictionary, tags, headwordIndices, entries} = definition;
         const disambiguations = DictionaryDataUtil.getDisambiguations(headwords, headwordIndices, uniqueTerms, uniqueReadings);
 
-        const node = this._templates.instantiate('definition-item');
+        const node = this._instantiate('definition-item');
 
-        const tagListContainer = node.querySelector('.definition-tag-list');
-        const onlyListContainer = node.querySelector('.definition-disambiguation-list');
-        const entriesContainer = node.querySelector('.gloss-list');
+        const tagListContainer = this._querySelector(node, '.definition-tag-list');
+        const onlyListContainer = this._querySelector(node, '.definition-disambiguation-list');
+        const entriesContainer = this._querySelector(node, '.gloss-list');
 
         node.dataset.dictionary = dictionary;
 
@@ -329,6 +394,11 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {import('dictionary-data').TermGlossary} entry
+     * @param {string} dictionary
+     * @returns {?HTMLElement}
+     */
     _createTermDefinitionEntry(entry, dictionary) {
         if (typeof entry === 'string') {
             return this._createTermDefinitionEntryText(entry);
@@ -344,25 +414,34 @@ class DisplayGenerator {
         return null;
     }
 
+    /**
+     * @param {string} text
+     * @returns {HTMLElement}
+     */
     _createTermDefinitionEntryText(text) {
-        const node = this._templates.instantiate('gloss-item');
-        const container = node.querySelector('.gloss-content');
+        const node = this._instantiate('gloss-item');
+        const container = this._querySelector(node, '.gloss-content');
         this._setMultilineTextContent(container, text);
         return node;
     }
 
+    /**
+     * @param {import('dictionary-data').TermGlossaryImage} data
+     * @param {string} dictionary
+     * @returns {HTMLElement}
+     */
     _createTermDefinitionEntryImage(data, dictionary) {
         const {description} = data;
 
-        const node = this._templates.instantiate('gloss-item');
+        const node = this._instantiate('gloss-item');
 
-        const contentContainer = node.querySelector('.gloss-content');
+        const contentContainer = this._querySelector(node, '.gloss-content');
         const image = this._structuredContentGenerator.createDefinitionImage(data, dictionary);
         contentContainer.appendChild(image);
 
         if (typeof description === 'string') {
             const fragment = this._templates.instantiateFragment('gloss-item-image-description');
-            const container = fragment.querySelector('.gloss-image-description');
+            const container = this._querySelector(fragment, '.gloss-image-description');
             this._setMultilineTextContent(container, description);
             contentContainer.appendChild(fragment);
         }
@@ -370,20 +449,33 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {import('structured-content').Content} content
+     * @param {string} dictionary
+     * @returns {HTMLElement}
+     */
     _createTermDefinitionEntryStructuredContent(content, dictionary) {
-        const node = this._templates.instantiate('gloss-item');
-        const contentContainer = node.querySelector('.gloss-content');
+        const node = this._instantiate('gloss-item');
+        const contentContainer = this._querySelector(node, '.gloss-content');
         this._structuredContentGenerator.appendStructuredContent(contentContainer, content, dictionary);
         return node;
     }
 
+    /**
+     * @param {string} disambiguation
+     * @returns {HTMLElement}
+     */
     _createTermDisambiguation(disambiguation) {
-        const node = this._templates.instantiate('definition-disambiguation');
+        const node = this._instantiate('definition-disambiguation');
         node.dataset.term = disambiguation;
         this._setTextContent(node, disambiguation, 'ja');
         return node;
     }
 
+    /**
+     * @param {string} character
+     * @returns {HTMLAnchorElement}
+     */
     _createKanjiLink(character) {
         const node = document.createElement('a');
         node.className = 'headword-kanji-link';
@@ -391,22 +483,34 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {string} text
+     * @returns {HTMLElement}
+     */
     _createKanjiDefinition(text) {
-        const node = this._templates.instantiate('kanji-gloss-item');
-        const container = node.querySelector('.kanji-gloss-content');
+        const node = this._instantiate('kanji-gloss-item');
+        const container = this._querySelector(node, '.kanji-gloss-content');
         this._setMultilineTextContent(container, text);
         return node;
     }
 
+    /**
+     * @param {string} reading
+     * @returns {HTMLElement}
+     */
     _createKanjiReading(reading) {
-        const node = this._templates.instantiate('kanji-reading');
+        const node = this._instantiate('kanji-reading');
         this._setTextContent(node, reading, 'ja');
         return node;
     }
 
+    /**
+     * @param {import('dictionary').KanjiStat[]} details
+     * @returns {HTMLElement}
+     */
     _createKanjiInfoTable(details) {
-        const node = this._templates.instantiate('kanji-info-table');
-        const container = node.querySelector('.kanji-info-table-body');
+        const node = this._instantiate('kanji-info-table');
+        const container = this._querySelector(node, '.kanji-info-table-body');
 
         const count = this._appendMultiple(container, this._createKanjiInfoTableItem.bind(this), details);
         if (count === 0) {
@@ -417,25 +521,36 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {import('dictionary').KanjiStat} details
+     * @returns {HTMLElement}
+     */
     _createKanjiInfoTableItem(details) {
         const {content, name, value} = details;
-        const node = this._templates.instantiate('kanji-info-table-item');
-        const nameNode = node.querySelector('.kanji-info-table-item-header');
-        const valueNode = node.querySelector('.kanji-info-table-item-value');
+        const node = this._instantiate('kanji-info-table-item');
+        const nameNode = this._querySelector(node, '.kanji-info-table-item-header');
+        const valueNode = this._querySelector(node, '.kanji-info-table-item-value');
         this._setTextContent(nameNode, content.length > 0 ? content : name);
-        this._setTextContent(valueNode, value);
+        this._setTextContent(valueNode, typeof value === 'string' ? value : `${value}`);
         return node;
     }
 
+    /**
+     * @returns {HTMLElement}
+     */
     _createKanjiInfoTableItemEmpty() {
-        return this._templates.instantiate('kanji-info-table-empty');
+        return this._instantiate('kanji-info-table-empty');
     }
 
+    /**
+     * @param {import('dictionary').Tag} tag
+     * @returns {HTMLElement}
+     */
     _createTag(tag) {
         const {content, name, category, redundant} = tag;
-        const node = this._templates.instantiate('tag');
+        const node = this._instantiate('tag');
 
-        const inner = node.querySelector('.tag-label-content');
+        const inner = this._querySelector(node, '.tag-label-content');
 
         const contentString = content.join('\n');
 
@@ -448,6 +563,11 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {import('dictionary-data-util').TagGroup} tagInfo
+     * @param {number} totalHeadwordCount
+     * @returns {HTMLElement}
+     */
     _createTermTag(tagInfo, totalHeadwordCount) {
         const {tag, headwordIndices} = tagInfo;
         const node = this._createTag(tag);
@@ -458,6 +578,11 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {string} name
+     * @param {string} category
+     * @returns {import('dictionary').Tag}
+     */
     _createTagData(name, category) {
         return {
             name,
@@ -470,20 +595,29 @@ class DisplayGenerator {
         };
     }
 
+    /**
+     * @param {string} text
+     * @returns {HTMLElement}
+     */
     _createSearchTag(text) {
         return this._createTag(this._createTagData(text, 'search'));
     }
 
+    /**
+     * @param {import('dictionary-data-util').DictionaryGroupedPronunciations} details
+     * @returns {HTMLElement}
+     */
     _createGroupedPronunciation(details) {
         const {dictionary, pronunciations} = details;
 
-        const node = this._templates.instantiate('pronunciation-group');
+        const node = this._instantiate('pronunciation-group');
         node.dataset.dictionary = dictionary;
         node.dataset.pronunciationsMulti = 'true';
         node.dataset.pronunciationsCount = `${pronunciations.length}`;
 
+        const n1 = this._querySelector(node, '.pronunciation-group-tag-list');
         const tag = this._createTag(this._createTagData(dictionary, 'pronunciation-dictionary'));
-        node.querySelector('.pronunciation-group-tag-list').appendChild(tag);
+        n1.appendChild(tag);
 
         let hasTags = false;
         for (const {tags} of pronunciations) {
@@ -493,54 +627,64 @@ class DisplayGenerator {
             }
         }
 
-        const n = node.querySelector('.pronunciation-list');
+        const n = this._querySelector(node, '.pronunciation-list');
         n.dataset.hasTags = `${hasTags}`;
         this._appendMultiple(n, this._createPronunciation.bind(this), pronunciations);
 
         return node;
     }
 
+    /**
+     * @param {import('dictionary-data-util').GroupedPronunciation} details
+     * @returns {HTMLElement}
+     */
     _createPronunciation(details) {
         const jp = this._japaneseUtil;
         const {reading, position, nasalPositions, devoicePositions, tags, exclusiveTerms, exclusiveReadings} = details;
         const morae = jp.getKanaMorae(reading);
 
-        const node = this._templates.instantiate('pronunciation');
+        const node = this._instantiate('pronunciation');
 
         node.dataset.pitchAccentDownstepPosition = `${position}`;
         if (nasalPositions.length > 0) { node.dataset.nasalMoraPosition = nasalPositions.join(' '); }
         if (devoicePositions.length > 0) { node.dataset.devoiceMoraPosition = devoicePositions.join(' '); }
         node.dataset.tagCount = `${tags.length}`;
 
-        let n = node.querySelector('.pronunciation-tag-list');
+        let n = this._querySelector(node, '.pronunciation-tag-list');
         this._appendMultiple(n, this._createTag.bind(this), tags);
 
-        n = node.querySelector('.pronunciation-disambiguation-list');
+        n = this._querySelector(node, '.pronunciation-disambiguation-list');
         this._createPronunciationDisambiguations(n, exclusiveTerms, exclusiveReadings);
 
-        n = node.querySelector('.pronunciation-downstep-notation-container');
+        n = this._querySelector(node, '.pronunciation-downstep-notation-container');
         n.appendChild(this._pronunciationGenerator.createPronunciationDownstepPosition(position));
 
-        n = node.querySelector('.pronunciation-text-container');
+        n = this._querySelector(node, '.pronunciation-text-container');
         n.lang = 'ja';
         n.appendChild(this._pronunciationGenerator.createPronunciationText(morae, position, nasalPositions, devoicePositions));
 
-        node.querySelector('.pronunciation-graph-container').appendChild(this._pronunciationGenerator.createPronunciationGraph(morae, position));
+        n = this._querySelector(node, '.pronunciation-graph-container');
+        n.appendChild(this._pronunciationGenerator.createPronunciationGraph(morae, position));
 
         return node;
     }
 
+    /**
+     * @param {HTMLElement} container
+     * @param {string[]} exclusiveTerms
+     * @param {string[]} exclusiveReadings
+     */
     _createPronunciationDisambiguations(container, exclusiveTerms, exclusiveReadings) {
         const templateName = 'pronunciation-disambiguation';
         for (const term of exclusiveTerms) {
-            const node = this._templates.instantiate(templateName);
+            const node = this._instantiate(templateName);
             node.dataset.type = 'term';
             this._setTextContent(node, term, 'ja');
             container.appendChild(node);
         }
 
         for (const exclusiveReading of exclusiveReadings) {
-            const node = this._templates.instantiate(templateName);
+            const node = this._instantiate(templateName);
             node.dataset.type = 'reading';
             this._setTextContent(node, exclusiveReading, 'ja');
             container.appendChild(node);
@@ -551,19 +695,29 @@ class DisplayGenerator {
         container.dataset.readingCount = `${exclusiveReadings.length}`;
     }
 
+    /**
+     * @param {import('dictionary-data-util').DictionaryFrequency<import('dictionary-data-util').TermFrequency>|import('dictionary-data-util').DictionaryFrequency<import('dictionary-data-util').KanjiFrequency>} details
+     * @param {boolean} kanji
+     * @returns {HTMLElement}
+     */
     _createFrequencyGroup(details, kanji) {
         const {dictionary, frequencies} = details;
 
-        const node = this._templates.instantiate('frequency-group-item');
-        const body = node.querySelector('.tag-body-content');
+        const node = this._instantiate('frequency-group-item');
+        const body = this._querySelector(node, '.tag-body-content');
 
-        this._setTextContent(node.querySelector('.tag-label-content'), dictionary);
+        const tagLabel = this._querySelector(node, '.tag-label-content');
+        this._setTextContent(tagLabel, dictionary);
         node.dataset.details = dictionary;
 
         const ii = frequencies.length;
         for (let i = 0; i < ii; ++i) {
             const item = frequencies[i];
-            const itemNode = (kanji ? this._createKanjiFrequency(item, dictionary) : this._createTermFrequency(item, dictionary));
+            const itemNode = (
+                kanji ?
+                this._createKanjiFrequency(/** @type {import('dictionary-data-util').KanjiFrequency} */ (item), dictionary) :
+                this._createTermFrequency(/** @type {import('dictionary-data-util').TermFrequency} */ (item), dictionary)
+            );
             itemNode.dataset.index = `${i}`;
             body.appendChild(itemNode);
         }
@@ -575,18 +729,28 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {import('dictionary-data-util').TermFrequency} details
+     * @param {string} dictionary
+     * @returns {HTMLElement}
+     */
     _createTermFrequency(details, dictionary) {
         const {term, reading, values} = details;
-        const node = this._templates.instantiate('term-frequency-item');
+        const node = this._instantiate('term-frequency-item');
+        const tagLabel = this._querySelector(node, '.tag-label-content');
+        const disambiguationTerm = this._querySelector(node, '.frequency-disambiguation-term');
+        const disambiguationReading = this._querySelector(node, '.frequency-disambiguation-reading');
+        const frequencyValueList = this._querySelector(node, '.frequency-value-list');
 
-        this._setTextContent(node.querySelector('.tag-label-content'), dictionary);
-
-        this._setTextContent(node.querySelector('.frequency-disambiguation-term'), term, 'ja');
-        this._setTextContent(node.querySelector('.frequency-disambiguation-reading'), (reading !== null ? reading : ''), 'ja');
-        this._populateFrequencyValueList(node.querySelector('.frequency-value-list'), values);
+        this._setTextContent(tagLabel, dictionary);
+        this._setTextContent(disambiguationTerm, term, 'ja');
+        this._setTextContent(disambiguationReading, (reading !== null ? reading : ''), 'ja');
+        this._populateFrequencyValueList(frequencyValueList, values);
 
         node.dataset.term = term;
-        node.dataset.reading = reading;
+        if (typeof reading === 'string') {
+            node.dataset.reading = reading;
+        }
         node.dataset.hasReading = `${reading !== null}`;
         node.dataset.readingIsSame = `${reading === term}`;
         node.dataset.dictionary = dictionary;
@@ -595,12 +759,19 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {import('dictionary-data-util').KanjiFrequency} details
+     * @param {string} dictionary
+     * @returns {HTMLElement}
+     */
     _createKanjiFrequency(details, dictionary) {
         const {character, values} = details;
-        const node = this._templates.instantiate('kanji-frequency-item');
+        const node = this._instantiate('kanji-frequency-item');
+        const tagLabel = this._querySelector(node, '.tag-label-content');
+        const frequencyValueList = this._querySelector(node, '.frequency-value-list');
 
-        this._setTextContent(node.querySelector('.tag-label-content'), dictionary);
-        this._populateFrequencyValueList(node.querySelector('.frequency-value-list'), values);
+        this._setTextContent(tagLabel, dictionary);
+        this._populateFrequencyValueList(frequencyValueList, values);
 
         node.dataset.character = character;
         node.dataset.dictionary = dictionary;
@@ -609,12 +780,16 @@ class DisplayGenerator {
         return node;
     }
 
+    /**
+     * @param {HTMLElement} node
+     * @param {import('dictionary-data-util').FrequencyData[]} values
+     */
     _populateFrequencyValueList(node, values) {
         let fullFrequency = '';
         for (let i = 0, ii = values.length; i < ii; ++i) {
             const {frequency, displayValue} = values[i];
             const frequencyString = `${frequency}`;
-            const text = displayValue !== null ? displayValue : frequency;
+            const text = displayValue !== null ? displayValue : `${frequency}`;
 
             if (i > 0) {
                 const node2 = document.createElement('span');
@@ -643,11 +818,15 @@ class DisplayGenerator {
         node.dataset.frequency = fullFrequency;
     }
 
+    /**
+     * @param {HTMLElement} container
+     * @param {string} text
+     */
     _appendKanjiLinks(container, text) {
         const jp = this._japaneseUtil;
         let part = '';
         for (const c of text) {
-            if (jp.isCodePointKanji(c.codePointAt(0))) {
+            if (jp.isCodePointKanji(/** @type {number} */ (c.codePointAt(0)))) {
                 if (part.length > 0) {
                     container.appendChild(document.createTextNode(part));
                     part = '';
@@ -664,16 +843,25 @@ class DisplayGenerator {
         }
     }
 
-    _appendMultiple(container, createItem, detailsArray, ...args) {
+    /**
+     * @template TItem
+     * @template [TExtraArg=void]
+     * @param {HTMLElement} container
+     * @param {(item: TItem, arg: TExtraArg) => ?Node} createItem
+     * @param {TItem[]} detailsArray
+     * @param {TExtraArg} [arg]
+     * @returns {number}
+     */
+    _appendMultiple(container, createItem, detailsArray, arg) {
         let count = 0;
         const {ELEMENT_NODE} = Node;
         if (Array.isArray(detailsArray)) {
             for (const details of detailsArray) {
-                const item = createItem(details, ...args);
+                const item = createItem(details, /** @type {TExtraArg} */ (arg));
                 if (item === null) { continue; }
                 container.appendChild(item);
                 if (item.nodeType === ELEMENT_NODE) {
-                    item.dataset.index = `${count}`;
+                    /** @type {HTMLElement} */ (item).dataset.index = `${count}`;
                 }
                 ++count;
             }
@@ -684,6 +872,12 @@ class DisplayGenerator {
         return count;
     }
 
+    /**
+     * @param {HTMLElement} container
+     * @param {string} term
+     * @param {string} reading
+     * @param {(element: HTMLElement, text: string) => void} addText
+     */
     _appendFurigana(container, term, reading, addText) {
         container.lang = 'ja';
         const segments = this._japaneseUtil.distributeFurigana(term, reading);
@@ -701,10 +895,19 @@ class DisplayGenerator {
         }
     }
 
+    /**
+     * @param {string} dictionary
+     * @returns {import('dictionary').Tag}
+     */
     _createDictionaryTag(dictionary) {
         return this._createTagData(dictionary, 'dictionary');
     }
 
+    /**
+     * @param {HTMLElement} node
+     * @param {string} value
+     * @param {string} [language]
+     */
     _setTextContent(node, value, language) {
         if (typeof language === 'string') {
             node.lang = language;
@@ -715,6 +918,11 @@ class DisplayGenerator {
         node.textContent = value;
     }
 
+    /**
+     * @param {HTMLElement} node
+     * @param {string} value
+     * @param {string} [language]
+     */
     _setMultilineTextContent(node, value, language) {
         // This can't just call _setTextContent because the lack of <br> elements will
         // cause the text to not copy correctly.
@@ -738,9 +946,17 @@ class DisplayGenerator {
         }
     }
 
+    /**
+     * @param {string} reading
+     * @param {import('dictionary').TermPronunciation[]} pronunciations
+     * @param {string[]} wordClasses
+     * @param {number} headwordIndex
+     * @returns {?string}
+     */
     _getPronunciationCategories(reading, pronunciations, wordClasses, headwordIndex) {
         if (pronunciations.length === 0) { return null; }
         const isVerbOrAdjective = DictionaryDataUtil.isNonNounVerbOrAdjective(wordClasses);
+        /** @type {Set<import('japanese-util').PitchCategory>} */
         const categories = new Set();
         for (const pronunciation of pronunciations) {
             if (pronunciation.headwordIndex !== headwordIndex) { continue; }
@@ -753,4 +969,23 @@ class DisplayGenerator {
         }
         return categories.size > 0 ? [...categories].join(' ') : null;
     }
+
+    /**
+     * @template {HTMLElement} T
+     * @param {string} name
+     * @returns {T}
+     */
+    _instantiate(name) {
+        return /** @type {T} */ (this._templates.instantiate(name));
+    }
+
+    /**
+     * @template {HTMLElement} T
+     * @param {Element|DocumentFragment} element
+     * @param {string} selector
+     * @returns {T}
+     */
+    _querySelector(element, selector) {
+        return /** @type {T} */ (element.querySelector(selector));
+    }
 }
diff --git a/ext/js/display/display-history.js b/ext/js/display/display-history.js
index 71882ca357..e7268d368e 100644
--- a/ext/js/display/display-history.js
+++ b/ext/js/display/display-history.js
@@ -16,26 +16,39 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/**
+ * @augments EventDispatcher<import('display-history').EventType>
+ */
 class DisplayHistory extends EventDispatcher {
+    /**
+     * @param {{clearable?: boolean, useBrowserHistory?: boolean}} details
+     */
     constructor({clearable=true, useBrowserHistory=false}) {
         super();
+        /** @type {boolean} */
         this._clearable = clearable;
+        /** @type {boolean} */
         this._useBrowserHistory = useBrowserHistory;
+        /** @type {Map<string, import('display-history').Entry>} */
         this._historyMap = new Map();
 
         const historyState = history.state;
         const {id, state} = isObject(historyState) ? historyState : {id: null, state: null};
+        /** @type {import('display-history').Entry} */
         this._current = this._createHistoryEntry(id, location.href, state, null, null);
     }
 
+    /** @type {?import('display-history').EntryState} */
     get state() {
         return this._current.state;
     }
 
+    /** @type {?import('display-history').EntryContent} */
     get content() {
         return this._current.content;
     }
 
+    /** @type {boolean} */
     get useBrowserHistory() {
         return this._useBrowserHistory;
     }
@@ -44,31 +57,54 @@ class DisplayHistory extends EventDispatcher {
         this._useBrowserHistory = value;
     }
 
+    /** @type {boolean} */
+    get clearable() { return this._clearable; }
+    set clearable(value) { this._clearable = value; }
+
+    /** */
     prepare() {
         window.addEventListener('popstate', this._onPopState.bind(this), false);
     }
 
+    /**
+     * @returns {boolean}
+     */
     hasNext() {
         return this._current.next !== null;
     }
 
+    /**
+     * @returns {boolean}
+     */
     hasPrevious() {
         return this._current.previous !== null;
     }
 
+    /** */
     clear() {
         if (!this._clearable) { return; }
         this._clear();
     }
 
+    /**
+     * @returns {boolean}
+     */
     back() {
         return this._go(false);
     }
 
+    /**
+     * @returns {boolean}
+     */
     forward() {
         return this._go(true);
     }
 
+    /**
+     * @param {?import('display-history').EntryState} state
+     * @param {?import('display-history').EntryContent} content
+     * @param {string} [url]
+     */
     pushState(state, content, url) {
         if (typeof url === 'undefined') { url = location.href; }
 
@@ -78,6 +114,11 @@ class DisplayHistory extends EventDispatcher {
         this._updateHistoryFromCurrent(!this._useBrowserHistory);
     }
 
+    /**
+     * @param {?import('display-history').EntryState} state
+     * @param {?import('display-history').EntryContent} content
+     * @param {string} [url]
+     */
     replaceState(state, content, url) {
         if (typeof url === 'undefined') { url = location.href; }
 
@@ -87,11 +128,16 @@ class DisplayHistory extends EventDispatcher {
         this._updateHistoryFromCurrent(true);
     }
 
+    /** */
     _onPopState() {
         this._updateStateFromHistory();
         this._triggerStateChanged(false);
     }
 
+    /**
+     * @param {boolean} forward
+     * @returns {boolean}
+     */
     _go(forward) {
         if (this._useBrowserHistory) {
             if (forward) {
@@ -109,10 +155,16 @@ class DisplayHistory extends EventDispatcher {
         return true;
     }
 
+    /**
+     * @param {boolean} synthetic
+     */
     _triggerStateChanged(synthetic) {
-        this.trigger('stateChanged', {synthetic});
+        this.trigger('stateChanged', /** @type {import('display-history').StateChangedEvent} */ ({synthetic}));
     }
 
+    /**
+     * @param {boolean} replace
+     */
     _updateHistoryFromCurrent(replace) {
         const {id, state, url} = this._current;
         if (replace) {
@@ -123,6 +175,7 @@ class DisplayHistory extends EventDispatcher {
         this._triggerStateChanged(true);
     }
 
+    /** */
     _updateStateFromHistory() {
         let state = history.state;
         let id = null;
@@ -149,24 +202,36 @@ class DisplayHistory extends EventDispatcher {
         this._clear();
     }
 
+    /**
+     * @param {unknown} id
+     * @param {string} url
+     * @param {?import('display-history').EntryState} state
+     * @param {?import('display-history').EntryContent} content
+     * @param {?import('display-history').Entry} previous
+     * @returns {import('display-history').Entry}
+     */
     _createHistoryEntry(id, url, state, content, previous) {
-        if (typeof id !== 'string') { id = this._generateId(); }
+        /** @type {import('display-history').Entry} */
         const entry = {
-            id,
+            id: typeof id === 'string' ? id : this._generateId(),
             url,
             next: null,
             previous,
             state,
             content
         };
-        this._historyMap.set(id, entry);
+        this._historyMap.set(entry.id, entry);
         return entry;
     }
 
+    /**
+     * @returns {string}
+     */
     _generateId() {
         return generateId(16);
     }
 
+    /** */
     _clear() {
         this._historyMap.clear();
         this._historyMap.set(this._current.id, this._current);
diff --git a/ext/js/display/display-notification.js b/ext/js/display/display-notification.js
index d5c77b0431..2ed90a0e14 100644
--- a/ext/js/display/display-notification.js
+++ b/ext/js/display/display-notification.js
@@ -17,23 +17,36 @@
  */
 
 class DisplayNotification {
+    /**
+     * @param {HTMLElement} container
+     * @param {HTMLElement} node
+     */
     constructor(container, node) {
+        /** @type {HTMLElement} */
         this._container = container;
+        /** @type {HTMLElement} */
         this._node = node;
-        this._body = node.querySelector('.footer-notification-body');
-        this._closeButton = node.querySelector('.footer-notification-close-button');
+        /** @type {HTMLElement} */
+        this._body = /** @type {HTMLElement} */ (node.querySelector('.footer-notification-body'));
+        /** @type {HTMLElement} */
+        this._closeButton = /** @type {HTMLElement} */ (node.querySelector('.footer-notification-close-button'));
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?number} */
         this._closeTimer = null;
     }
 
+    /** @type {HTMLElement} */
     get container() {
         return this._container;
     }
 
+    /** @type {HTMLElement} */
     get node() {
         return this._node;
     }
 
+    /** */
     open() {
         if (!this.isClosed()) { return; }
 
@@ -48,6 +61,9 @@ class DisplayNotification {
         this._eventListeners.addEventListener(this._closeButton, 'click', this._onCloseButtonClick.bind(this), false);
     }
 
+    /**
+     * @param {boolean} [animate]
+     */
     close(animate=false) {
         if (this.isClosed()) { return; }
 
@@ -67,6 +83,9 @@ class DisplayNotification {
         }
     }
 
+    /**
+     * @param {string|Node} value
+     */
     setContent(value) {
         if (typeof value === 'string') {
             this._body.textContent = value;
@@ -76,25 +95,34 @@ class DisplayNotification {
         }
     }
 
+    /**
+     * @returns {boolean}
+     */
     isClosing() {
         return this._closeTimer !== null;
     }
 
+    /**
+     * @returns {boolean}
+     */
     isClosed() {
         return this._node.parentNode === null;
     }
 
     // Private
 
+    /** */
     _onCloseButtonClick() {
         this.close(true);
     }
 
+    /** */
     _onDelayClose() {
         this._closeTimer = null;
         this.close(false);
     }
 
+    /** */
     _clearTimer() {
         if (this._closeTimer !== null) {
             clearTimeout(this._closeTimer);
diff --git a/ext/js/display/display-profile-selection.js b/ext/js/display/display-profile-selection.js
index b14b4d8bc6..d139d60473 100644
--- a/ext/js/display/display-profile-selection.js
+++ b/ext/js/display/display-profile-selection.js
@@ -21,19 +21,30 @@
  */
 
 class DisplayProfileSelection {
+    /**
+     * @param {Display} display
+     */
     constructor(display) {
+        /** @type {Display} */
         this._display = display;
-        this._profielList = document.querySelector('#profile-list');
-        this._profileButton = document.querySelector('#profile-button');
+        /** @type {HTMLElement} */
+        this._profielList = /** @type {HTMLElement} */ (document.querySelector('#profile-list'));
+        /** @type {HTMLButtonElement} */
+        this._profileButton = /** @type {HTMLButtonElement} */ (document.querySelector('#profile-button'));
+        /** @type {PanelElement} */
         this._profilePanel = new PanelElement({
-            node: document.querySelector('#profile-panel'),
+            node: /** @type {HTMLElement} */ (document.querySelector('#profile-panel')),
             closingAnimationDuration: 375 // Milliseconds; includes buffer
         });
+        /** @type {boolean} */
         this._profileListNeedsUpdate = false;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {string} */
         this._source = generateId(16);
     }
 
+    /** */
     async prepare() {
         yomichan.on('optionsUpdated', this._onOptionsUpdated.bind(this));
         this._profileButton.addEventListener('click', this._onProfileButtonClick.bind(this), false);
@@ -42,6 +53,9 @@ class DisplayProfileSelection {
 
     // Private
 
+    /**
+     * @param {{source: string}} details
+     */
     _onOptionsUpdated({source}) {
         if (source === this._source) { return; }
         this._profileListNeedsUpdate = true;
@@ -50,12 +64,18 @@ class DisplayProfileSelection {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onProfileButtonClick(e) {
         e.preventDefault();
         e.stopPropagation();
         this._setProfilePanelVisible(!this._profilePanel.isVisible());
     }
 
+    /**
+     * @param {boolean} visible
+     */
     _setProfilePanelVisible(visible) {
         this._profilePanel.setVisible(visible);
         this._profileButton.classList.toggle('sidebar-button-highlight', visible);
@@ -65,6 +85,7 @@ class DisplayProfileSelection {
         }
     }
 
+    /** */
     async _updateProfileList() {
         this._profileListNeedsUpdate = false;
         const options = await yomichan.api.optionsGetFull();
@@ -77,9 +98,9 @@ class DisplayProfileSelection {
         for (let i = 0, ii = profiles.length; i < ii; ++i) {
             const {name} = profiles[i];
             const entry = displayGenerator.createProfileListItem();
-            const radio = entry.querySelector('.profile-entry-is-default-radio');
+            const radio = /** @type {HTMLInputElement} */ (entry.querySelector('.profile-entry-is-default-radio'));
             radio.checked = (i === profileCurrent);
-            const nameNode = entry.querySelector('.profile-list-item-name');
+            const nameNode = /** @type {Element} */ (entry.querySelector('.profile-list-item-name'));
             nameNode.textContent = name;
             fragment.appendChild(entry);
             this._eventListeners.addEventListener(radio, 'change', this._onProfileRadioChange.bind(this, i), false);
@@ -88,19 +109,30 @@ class DisplayProfileSelection {
         this._profielList.appendChild(fragment);
     }
 
+    /**
+     * @param {number} index
+     * @param {Event} e
+     */
     _onProfileRadioChange(index, e) {
-        if (e.currentTarget.checked) {
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        if (element.checked) {
             this._setProfileCurrent(index);
         }
     }
 
+    /**
+     * @param {number} index
+     */
     async _setProfileCurrent(index) {
-        await yomichan.api.modifySettings([{
+        /** @type {import('settings-modifications').ScopedModificationSet} */
+        const modification = {
             action: 'set',
             path: 'profileCurrent',
             value: index,
-            scope: 'global'
-        }], this._source);
+            scope: 'global',
+            optionsContext: null
+        };
+        await yomichan.api.modifySettings([modification], this._source);
         this._setProfilePanelVisible(false);
     }
 }
diff --git a/ext/js/display/display-resizer.js b/ext/js/display/display-resizer.js
index 1356c0a717..44148d59ca 100644
--- a/ext/js/display/display-resizer.js
+++ b/ext/js/display/display-resizer.js
@@ -17,16 +17,27 @@
  */
 
 class DisplayResizer {
+    /**
+     * @param {Display} display
+     */
     constructor(display) {
+        /** @type {Display} */
         this._display = display;
+        /** @type {?import('core').TokenObject} */
         this._token = null;
+        /** @type {?HTMLElement} */
         this._handle = null;
+        /** @type {?number} */
         this._touchIdentifier = null;
+        /** @type {?{width: number, height: number}} */
         this._startSize = null;
+        /** @type {?{x: number, y: number}} */
         this._startOffset = null;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
     }
 
+    /** */
     prepare() {
         this._handle = document.querySelector('#frame-resizer-handle');
         if (this._handle === null) { return; }
@@ -37,6 +48,9 @@ class DisplayResizer {
 
     // Private
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onFrameResizerMouseDown(e) {
         if (e.button !== 0) { return; }
         // Don't do e.preventDefault() here; this allows mousemove events to be processed
@@ -44,19 +58,27 @@ class DisplayResizer {
         this._startFrameResize(e);
     }
 
+    /**
+     * @param {TouchEvent} e
+     */
     _onFrameResizerTouchStart(e) {
         e.preventDefault();
         this._startFrameResizeTouch(e);
     }
 
+    /** */
     _onFrameResizerMouseUp() {
         this._stopFrameResize();
     }
 
+    /** */
     _onFrameResizerWindowBlur() {
         this._stopFrameResize();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onFrameResizerMouseMove(e) {
         if ((e.buttons & 0x1) === 0x0) {
             this._stopFrameResize();
@@ -67,16 +89,25 @@ class DisplayResizer {
         }
     }
 
+    /**
+     * @param {TouchEvent} e
+     */
     _onFrameResizerTouchEnd(e) {
         if (this._getTouch(e.changedTouches, this._touchIdentifier) === null) { return; }
         this._stopFrameResize();
     }
 
+    /**
+     * @param {TouchEvent} e
+     */
     _onFrameResizerTouchCancel(e) {
         if (this._getTouch(e.changedTouches, this._touchIdentifier) === null) { return; }
         this._stopFrameResize();
     }
 
+    /**
+     * @param {TouchEvent} e
+     */
     _onFrameResizerTouchMove(e) {
         if (this._startSize === null) { return; }
         const primaryTouch = this._getTouch(e.changedTouches, this._touchIdentifier);
@@ -85,10 +116,14 @@ class DisplayResizer {
         this._updateFrameSize(x, y);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _startFrameResize(e) {
         if (this._token !== null) { return; }
 
         const {clientX: x, clientY: y} = e;
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._token = token;
         this._startOffset = {x, y};
@@ -104,10 +139,14 @@ class DisplayResizer {
         this._initializeFrameResize(token);
     }
 
+    /**
+     * @param {TouchEvent} e
+     */
     _startFrameResizeTouch(e) {
         if (this._token !== null) { return; }
 
         const {clientX: x, clientY: y, identifier} = e.changedTouches[0];
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._token = token;
         this._startOffset = {x, y};
@@ -125,15 +164,21 @@ class DisplayResizer {
         this._initializeFrameResize(token);
     }
 
+    /**
+     * @param {import('core').TokenObject} token
+     */
     async _initializeFrameResize(token) {
         const {parentPopupId} = this._display;
         if (parentPopupId === null) { return; }
 
+        /** @type {import('popup').ValidSize} */
         const size = await this._display.invokeParentFrame('PopupFactory.getFrameSize', {id: parentPopupId});
         if (this._token !== token) { return; }
-        this._startSize = size;
+        const {width, height} = size;
+        this._startSize = {width, height};
     }
 
+    /** */
     _stopFrameResize() {
         if (this._token === null) { return; }
 
@@ -149,9 +194,13 @@ class DisplayResizer {
         }
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     */
     async _updateFrameSize(x, y) {
         const {parentPopupId} = this._display;
-        if (parentPopupId === null) { return; }
+        if (parentPopupId === null || this._handle === null || this._startOffset === null || this._startSize === null) { return; }
 
         const handleSize = this._handle.getBoundingClientRect();
         let {width, height} = this._startSize;
@@ -162,6 +211,11 @@ class DisplayResizer {
         await this._display.invokeParentFrame('PopupFactory.setFrameSize', {id: parentPopupId, width, height});
     }
 
+    /**
+     * @param {TouchList} touchList
+     * @param {?number} identifier
+     * @returns {?Touch}
+     */
     _getTouch(touchList, identifier) {
         for (const touch of touchList) {
             if (touch.identifier === identifier) {
diff --git a/ext/js/display/display.js b/ext/js/display/display.js
index 693bd2012d..a4684cfe43 100644
--- a/ext/js/display/display.js
+++ b/ext/js/display/display.js
@@ -35,132 +35,164 @@
  * dynamicLoader
  */
 
+/**
+ * @augments EventDispatcher<import('display').DisplayEventType>
+ */
 class Display extends EventDispatcher {
     /**
-     * Information about how popup content should be shown, specifically related to the inner popup content.
-     * @typedef {object} ContentDetails
-     * @property {boolean} focus Whether or not the frame should be `focus()`'d.
-     * @property {HistoryParams} params An object containing key-value pairs representing the URL search params.
-     * @property {?HistoryState} state The semi-persistent state assigned to the navigation entry.
-     * @property {?HistoryContent} content The non-persistent content assigned to the navigation entry.
-     * @property {'clear'|'overwrite'|'new'} historyMode How the navigation history should be modified.
-     */
-
-    /**
-     * An object containing key-value pairs representing the URL search params.
-     * @typedef {object} HistoryParams
-     * @property {'terms'|'kanji'|'unloaded'|'clear'} [type] The type of content that is being shown.
-     * @property {string} [query] The search query.
-     * @property {'on'|'off'} [wildcards] Whether or not wildcards can be used for the search query.
-     * @property {string} [offset] The start position of the `query` string as an index into the `full` query string.
-     * @property {string} [full] The full search text. If absent, `query` is the full search text.
-     * @property {'true'|'false'} [full-visible] Whether or not the full search query should be forced to be visible.
-     * @property {'true'|'false'} [lookup] Whether or not the query should be looked up. If it is not looked up,
-     *   the content should be provided.
-     */
-
-    /**
-     * The semi-persistent state assigned to the navigation entry.
-     * @typedef {object} HistoryState
-     * @property {'queryParser'} [cause] What was the cause of the navigation.
-     * @property {object} [sentence] The sentence context.
-     * @property {string} sentence.text The full string.
-     * @property {number} sentence.offset The offset from the start of `text` to the full search query.
-     * @property {number} [focusEntry] The index of the dictionary entry to focus.
-     * @property {number} [scrollX] The horizontal scroll position.
-     * @property {number} [scrollY] The vertical scroll position.
-     * @property {object} [optionsContext] The options context which should be used for lookups.
-     * @property {string} [url] The originating URL of the content.
-     * @property {string} [documentTitle] The originating document title of the content.
-     */
-
-    /**
-     * The non-persistent content assigned to the navigation entry.
-     * @typedef {object} HistoryContent
-     * @property {boolean} [animate] Whether or not any CSS animations should occur.
-     * @property {object[]} [dictionaryEntries] An array of dictionary entries to display as content.
-     * @property {object} [contentOrigin] The identifying information for the frame the content originated from.
-     * @property {number} [contentOrigin.tabId] The tab id.
-     * @property {number} [contentOrigin.frameId] The frame id within the tab.
+     * @param {number|undefined} tabId
+     * @param {number|undefined} frameId
+     * @param {import('display').DisplayPageType} pageType
+     * @param {JapaneseUtil} japaneseUtil
+     * @param {DocumentFocusController} documentFocusController
+     * @param {HotkeyHandler} hotkeyHandler
      */
-
     constructor(tabId, frameId, pageType, japaneseUtil, documentFocusController, hotkeyHandler) {
         super();
+        /** @type {number|undefined} */
         this._tabId = tabId;
+        /** @type {number|undefined} */
         this._frameId = frameId;
+        /** @type {import('display').DisplayPageType} */
         this._pageType = pageType;
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
+        /** @type {DocumentFocusController} */
         this._documentFocusController = documentFocusController;
+        /** @type {HotkeyHandler} */
         this._hotkeyHandler = hotkeyHandler;
-        this._container = document.querySelector('#dictionary-entries');
+        /** @type {HTMLElement} */
+        this._container = /** @type {HTMLElement} */ (document.querySelector('#dictionary-entries'));
+        /** @type {import('dictionary').DictionaryEntry[]} */
         this._dictionaryEntries = [];
+        /** @type {HTMLElement[]} */
         this._dictionaryEntryNodes = [];
+        /** @type {import('settings').OptionsContext} */
         this._optionsContext = {depth: 0, url: window.location.href};
+        /** @type {?import('settings').ProfileOptions} */
         this._options = null;
+        /** @type {number} */
         this._index = 0;
+        /** @type {?HTMLStyleElement} */
         this._styleNode = null;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?import('core').TokenObject} */
         this._setContentToken = null;
+        /** @type {DisplayContentManager} */
         this._contentManager = new DisplayContentManager(this);
+        /** @type {HotkeyHelpController} */
         this._hotkeyHelpController = new HotkeyHelpController();
+        /** @type {DisplayGenerator} */
         this._displayGenerator = new DisplayGenerator({
             japaneseUtil,
             contentManager: this._contentManager,
             hotkeyHelpController: this._hotkeyHelpController
         });
+        /** @type {import('core').MessageHandlerMap} */
         this._messageHandlers = new Map();
+        /** @type {import('core').MessageHandlerMap} */
         this._directMessageHandlers = new Map();
+        /** @type {import('core').MessageHandlerMap} */
         this._windowMessageHandlers = new Map();
+        /** @type {DisplayHistory} */
         this._history = new DisplayHistory({clearable: true, useBrowserHistory: false});
+        /** @type {boolean} */
         this._historyChangeIgnore = false;
+        /** @type {boolean} */
         this._historyHasChanged = false;
+        /** @type {?Element} */
         this._navigationHeader = document.querySelector('#navigation-header');
+        /** @type {import('display').PageType} */
         this._contentType = 'clear';
+        /** @type {string} */
         this._defaultTitle = document.title;
+        /** @type {number} */
         this._titleMaxLength = 1000;
+        /** @type {string} */
         this._query = '';
+        /** @type {string} */
         this._fullQuery = '';
+        /** @type {number} */
         this._queryOffset = 0;
-        this._progressIndicator = document.querySelector('#progress-indicator');
+        /** @type {HTMLElement} */
+        this._progressIndicator = /** @type {HTMLElement} */ (document.querySelector('#progress-indicator'));
+        /** @type {?number} */
         this._progressIndicatorTimer = null;
+        /** @type {DynamicProperty<boolean>} */
         this._progressIndicatorVisible = new DynamicProperty(false);
+        /** @type {boolean} */
         this._queryParserVisible = false;
+        /** @type {?boolean} */
         this._queryParserVisibleOverride = null;
-        this._queryParserContainer = document.querySelector('#query-parser-container');
+        /** @type {HTMLElement} */
+        this._queryParserContainer = /** @type {HTMLElement} */ (document.querySelector('#query-parser-container'));
+        /** @type {QueryParser} */
         this._queryParser = new QueryParser({
             getSearchContext: this._getSearchContext.bind(this),
             japaneseUtil
         });
-        this._contentScrollElement = document.querySelector('#content-scroll');
-        this._contentScrollBodyElement = document.querySelector('#content-body');
+        /** @type {HTMLElement} */
+        this._contentScrollElement = /** @type {HTMLElement} */ (document.querySelector('#content-scroll'));
+        /** @type {HTMLElement} */
+        this._contentScrollBodyElement = /** @type {HTMLElement} */ (document.querySelector('#content-body'));
+        /** @type {ScrollElement} */
         this._windowScroll = new ScrollElement(this._contentScrollElement);
-        this._closeButton = document.querySelector('#close-button');
-        this._navigationPreviousButton = document.querySelector('#navigate-previous-button');
-        this._navigationNextButton = document.querySelector('#navigate-next-button');
+        /** @type {HTMLButtonElement} */
+        this._closeButton = /** @type {HTMLButtonElement} */ (document.querySelector('#close-button'));
+        /** @type {HTMLButtonElement} */
+        this._navigationPreviousButton = /** @type {HTMLButtonElement} */ (document.querySelector('#navigate-previous-button'));
+        /** @type {HTMLButtonElement} */
+        this._navigationNextButton = /** @type {HTMLButtonElement} */ (document.querySelector('#navigate-next-button'));
+        /** @type {?Frontend} */
         this._frontend = null;
+        /** @type {?Promise<void>} */
         this._frontendSetupPromise = null;
+        /** @type {number} */
         this._depth = 0;
+        /** @type {?string} */
         this._parentPopupId = null;
+        /** @type {?number} */
         this._parentFrameId = null;
+        /** @type {number|undefined} */
         this._contentOriginTabId = tabId;
+        /** @type {number|undefined} */
         this._contentOriginFrameId = frameId;
+        /** @type {boolean} */
         this._childrenSupported = true;
+        /** @type {?FrameEndpoint} */
         this._frameEndpoint = (pageType === 'popup' ? new FrameEndpoint() : null);
+        /** @type {?import('environment').Browser} */
         this._browser = null;
+        /** @type {?HTMLTextAreaElement} */
         this._copyTextarea = null;
+        /** @type {?TextScanner} */
         this._contentTextScanner = null;
+        /** @type {?DisplayNotification} */
         this._tagNotification = null;
-        this._footerNotificationContainer = document.querySelector('#content-footer');
+        /** @type {HTMLElement} */
+        this._footerNotificationContainer = /** @type {HTMLElement} */ (document.querySelector('#content-footer'));
+        /** @type {OptionToggleHotkeyHandler} */
         this._optionToggleHotkeyHandler = new OptionToggleHotkeyHandler(this);
+        /** @type {ElementOverflowController} */
         this._elementOverflowController = new ElementOverflowController();
+        /** @type {boolean} */
         this._frameVisible = (pageType === 'search');
-        this._menuContainer = document.querySelector('#popup-menus');
+        /** @type {HTMLElement} */
+        this._menuContainer = /** @type {HTMLElement} */ (document.querySelector('#popup-menus'));
+        /** @type {(event: MouseEvent) => void} */
         this._onEntryClickBind = this._onEntryClick.bind(this);
+        /** @type {(event: MouseEvent) => void} */
         this._onKanjiLookupBind = this._onKanjiLookup.bind(this);
+        /** @type {(event: MouseEvent) => void} */
         this._onDebugLogClickBind = this._onDebugLogClick.bind(this);
+        /** @type {(event: MouseEvent) => void} */
         this._onTagClickBind = this._onTagClick.bind(this);
+        /** @type {(event: MouseEvent) => void} */
         this._onMenuButtonClickBind = this._onMenuButtonClick.bind(this);
+        /** @type {(event: import('popup-menu').MenuCloseEvent) => void} */
         this._onMenuButtonMenuCloseBind = this._onMenuButtonMenuClose.bind(this);
+        /** @type {ThemeController} */
         this._themeController = new ThemeController(document.documentElement);
 
         this._hotkeyHandler.registerActions([
@@ -188,10 +220,12 @@ class Display extends EventDispatcher {
         ]);
     }
 
+    /** @type {DisplayGenerator} */
     get displayGenerator() {
         return this._displayGenerator;
     }
 
+    /** @type {boolean} */
     get queryParserVisible() {
         return this._queryParserVisible;
     }
@@ -201,58 +235,72 @@ class Display extends EventDispatcher {
         this._updateQueryParser();
     }
 
+    /** @type {JapaneseUtil} */
     get japaneseUtil() {
         return this._japaneseUtil;
     }
 
+    /** @type {number} */
     get depth() {
         return this._depth;
     }
 
+    /** @type {HotkeyHandler} */
     get hotkeyHandler() {
         return this._hotkeyHandler;
     }
 
+    /** @type {import('dictionary').DictionaryEntry[]} */
     get dictionaryEntries() {
         return this._dictionaryEntries;
     }
 
+    /** @type {HTMLElement[]} */
     get dictionaryEntryNodes() {
         return this._dictionaryEntryNodes;
     }
 
+    /** @type {DynamicProperty<boolean>} */
     get progressIndicatorVisible() {
         return this._progressIndicatorVisible;
     }
 
+    /** @type {?string} */
     get parentPopupId() {
         return this._parentPopupId;
     }
 
+    /** @type {number} */
     get selectedIndex() {
         return this._index;
     }
 
+    /** @type {DisplayHistory} */
     get history() {
         return this._history;
     }
 
+    /** @type {string} */
     get query() {
         return this._query;
     }
 
+    /** @type {string} */
     get fullQuery() {
         return this._fullQuery;
     }
 
+    /** @type {number} */
     get queryOffset() {
         return this._queryOffset;
     }
 
+    /** @type {boolean} */
     get frameVisible() {
         return this._frameVisible;
     }
 
+    /** */
     async prepare() {
         // Theme
         this._themeController.siteTheme = 'light';
@@ -302,6 +350,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @returns {import('extension').ContentOrigin}
+     */
     getContentOrigin() {
         return {
             tabId: this._contentOriginTabId,
@@ -309,6 +360,7 @@ class Display extends EventDispatcher {
         };
     }
 
+    /** */
     initializeState() {
         this._onStateChanged();
         if (this._frameEndpoint !== null) {
@@ -316,6 +368,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {{clearable?: boolean, useBrowserHistory?: boolean}} details
+     */
     setHistorySettings({clearable, useBrowserHistory}) {
         if (typeof clearable !== 'undefined') {
             this._history.clearable = clearable;
@@ -325,24 +380,37 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {Error} error
+     */
     onError(error) {
         if (yomichan.isExtensionUnloaded) { return; }
         log.error(error);
     }
 
+    /**
+     * @returns {?import('settings').ProfileOptions}
+     */
     getOptions() {
         return this._options;
     }
 
+    /**
+     * @returns {import('settings').OptionsContext}
+     */
     getOptionsContext() {
         return this._optionsContext;
     }
 
+    /**
+     * @param {import('settings').OptionsContext} optionsContext
+     */
     async setOptionsContext(optionsContext) {
         this._optionsContext = optionsContext;
         await this.updateOptions();
     }
 
+    /** */
     async updateOptions() {
         const options = await yomichan.api.optionsGet(this.getOptionsContext());
         const {scanning: scanningOptions, sentenceParsing: sentenceParsingOptions} = options;
@@ -381,12 +449,14 @@ class Display extends EventDispatcher {
         this._updateNestedFrontend(options);
         this._updateContentTextScanner(options);
 
-        this.trigger('optionsUpdated', {options});
+        /** @type {import('display').OptionsUpdatedEvent} */
+        const event = {options};
+        this.trigger('optionsUpdated', event);
     }
 
     /**
      * Updates the content of the display.
-     * @param {ContentDetails} details Information about the content to show.
+     * @param {import('display').ContentDetails} details Information about the content to show.
      */
     setContent(details) {
         const {focus, params, state, content} = details;
@@ -398,6 +468,7 @@ class Display extends EventDispatcher {
 
         const urlSearchParams = new URLSearchParams();
         for (const [key, value] of Object.entries(params)) {
+            if (typeof value !== 'string') { continue; }
             urlSearchParams.append(key, value);
         }
         const url = `${location.protocol}//${location.host}${location.pathname}?${urlSearchParams.toString()}`;
@@ -417,6 +488,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} css
+     */
     setCustomCss(css) {
         if (this._styleNode === null) {
             if (css.length === 0) { return; }
@@ -431,18 +505,25 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('core').MessageHandlerArray} handlers
+     */
     registerDirectMessageHandlers(handlers) {
         for (const [name, handlerInfo] of handlers) {
             this._directMessageHandlers.set(name, handlerInfo);
         }
     }
 
+    /**
+     * @param {import('core').MessageHandlerArray} handlers
+     */
     registerWindowMessageHandlers(handlers) {
         for (const [name, handlerInfo] of handlers) {
             this._windowMessageHandlers.set(name, handlerInfo);
         }
     }
 
+    /** */
     close() {
         switch (this._pageType) {
             case 'popup':
@@ -454,49 +535,72 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {HTMLElement} element
+     */
     blurElement(element) {
         this._documentFocusController.blurElement(element);
     }
 
+    /**
+     * @param {boolean} updateOptionsContext
+     */
     searchLast(updateOptionsContext) {
         const type = this._contentType;
         if (type === 'clear') { return; }
         const query = this._query;
-        const hasState = this._historyHasState();
-        const state = (
+        const {state} = this._history;
+        const hasState = typeof state === 'object' && state !== null;
+        /** @type {import('display').HistoryState} */
+        const newState = (
             hasState ?
-            clone(this._history.state) :
+            clone(state) :
             {
                 focusEntry: 0,
-                optionsContext: null,
+                optionsContext: void 0,
                 url: window.location.href,
                 sentence: {text: query, offset: 0},
                 documentTitle: document.title
             }
         );
         if (!hasState || updateOptionsContext) {
-            state.optionsContext = clone(this._optionsContext);
+            newState.optionsContext = clone(this._optionsContext);
         }
+        /** @type {import('display').ContentDetails} */
         const details = {
             focus: false,
             historyMode: 'clear',
             params: this._createSearchParams(type, query, false, this._queryOffset),
-            state,
+            state: newState,
             content: {
-                dictionaryEntries: null,
                 contentOrigin: this.getContentOrigin()
             }
         };
         this.setContent(details);
     }
 
+    /**
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {import('core').SerializableObject} [params]
+     * @returns {Promise<TReturn>}
+     */
     async invokeContentOrigin(action, params={}) {
         if (this._contentOriginTabId === this._tabId && this._contentOriginFrameId === this._frameId) {
             throw new Error('Content origin is same page');
         }
+        if (typeof this._contentOriginTabId !== 'number' || typeof this._contentOriginFrameId !== 'number') {
+            throw new Error('No content origin is assigned');
+        }
         return await yomichan.crossFrame.invokeTab(this._contentOriginTabId, this._contentOriginFrameId, action, params);
     }
 
+    /**
+     * @template [TReturn=unknown]
+     * @param {string} action
+     * @param {import('core').SerializableObject} [params]
+     * @returns {Promise<TReturn>}
+     */
     async invokeParentFrame(action, params={}) {
         if (this._parentFrameId === null || this._parentFrameId === this._frameId) {
             throw new Error('Invalid parent frame');
@@ -504,11 +608,17 @@ class Display extends EventDispatcher {
         return await yomichan.crossFrame.invoke(this._parentFrameId, action, params);
     }
 
+    /**
+     * @param {Element} element
+     * @returns {number}
+     */
     getElementDictionaryEntryIndex(element) {
-        const node = element.closest('.entry');
+        const node = /** @type {?HTMLElement} */ (element.closest('.entry'));
         if (node === null) { return -1; }
-        const index = parseInt(node.dataset.index, 10);
-        return Number.isFinite(index) ? index : -1;
+        const {index} = node.dataset;
+        if (typeof index !== 'string') { return -1; }
+        const indexNumber = parseInt(index, 10);
+        return Number.isFinite(indexNumber) ? indexNumber : -1;
     }
 
     /**
@@ -526,9 +636,13 @@ class Display extends EventDispatcher {
 
     // Message handlers
 
+    /**
+     * @param {import('frame-client').Message<import('display').MessageDetails>} data
+     * @returns {import('core').MessageHandlerAsyncResult}
+     * @throws {Error}
+     */
     _onDirectMessage(data) {
-        data = this._authenticateMessageData(data);
-        const {action, params} = data;
+        const {action, params} = this._authenticateMessageData(data);
         const handlerInfo = this._directMessageHandlers.get(action);
         if (typeof handlerInfo === 'undefined') {
             throw new Error(`Invalid action: ${action}`);
@@ -536,17 +650,24 @@ class Display extends EventDispatcher {
 
         const {async, handler} = handlerInfo;
         const result = handler(params);
-        return {async, result};
+        return {
+            async: typeof async === 'boolean' && async,
+            result
+        };
     }
 
+    /**
+     * @param {MessageEvent<import('frame-client').Message<import('display').MessageDetails>>} details
+     */
     _onWindowMessage({data}) {
+        let data2;
         try {
-            data = this._authenticateMessageData(data);
+            data2 = this._authenticateMessageData(data);
         } catch (e) {
             return;
         }
 
-        const {action, params} = data;
+        const {action, params} = data2;
         const messageHandler = this._windowMessageHandlers.get(action);
         if (typeof messageHandler === 'undefined') { return; }
 
@@ -554,23 +675,38 @@ class Display extends EventDispatcher {
         invokeMessageHandler(messageHandler, params, callback);
     }
 
+    /**
+     * @param {{optionsContext: import('settings').OptionsContext}} details
+     */
     async _onMessageSetOptionsContext({optionsContext}) {
         await this.setOptionsContext(optionsContext);
         this.searchLast(true);
     }
 
+    /**
+     * @param {{details: import('display').ContentDetails}} details
+     */
     _onMessageSetContent({details}) {
         this.setContent(details);
     }
 
+    /**
+     * @param {{css: string}} details
+     */
     _onMessageSetCustomCss({css}) {
         this.setCustomCss(css);
     }
 
+    /**
+     * @param {{scale: number}} details
+     */
     _onMessageSetContentScale({scale}) {
         this._setContentScale(scale);
     }
 
+    /**
+     * @param {import('display').ConfigureMessageDetails} details
+     */
     async _onMessageConfigure({depth, parentPopupId, parentFrameId, childrenSupported, scale, optionsContext}) {
         this._depth = depth;
         this._parentPopupId = parentPopupId;
@@ -580,11 +716,17 @@ class Display extends EventDispatcher {
         await this.setOptionsContext(optionsContext);
     }
 
+    /**
+     * @param {{value: boolean}} details
+     */
     _onMessageVisibilityChanged({value}) {
         this._frameVisible = value;
-        this.trigger('frameVisibilityChange', {value});
+        /** @type {import('display').FrameVisibilityChangeEvent} */
+        const event = {value};
+        this.trigger('frameVisibilityChange', event);
     }
 
+    /** */
     _onMessageExtensionUnloaded() {
         if (yomichan.isExtensionUnloaded) { return; }
         yomichan.triggerExtensionUnloaded();
@@ -592,19 +734,27 @@ class Display extends EventDispatcher {
 
     // Private
 
+    /**
+     * @template [T=unknown]
+     * @param {T|import('frame-client').Message<T>} data
+     * @returns {T}
+     * @throws {Error}
+     */
     _authenticateMessageData(data) {
         if (this._frameEndpoint === null) {
-            return data;
+            return /** @type {T} */ (data);
         }
         if (!this._frameEndpoint.authenticate(data)) {
             throw new Error('Invalid authentication');
         }
-        return data.data;
+        return /** @type {import('frame-client').Message<T>} */ (data).data;
     }
 
+    /** */
     async _onStateChanged() {
         if (this._historyChangeIgnore) { return; }
 
+        /** @type {?import('core').TokenObject} */
         const token = {}; // Unique identifier token
         this._setContentToken = token;
         try {
@@ -628,15 +778,16 @@ class Display extends EventDispatcher {
             this._queryParserVisibleOverride = (fullVisible === null ? null : (fullVisible !== 'false'));
 
             this._historyHasChanged = true;
-            this._contentType = type;
 
             // Set content
             switch (type) {
                 case 'terms':
                 case 'kanji':
+                    this._contentType = type;
                     await this._setContentTermsOrKanji(type, urlSearchParams, token);
                     break;
                 case 'unloaded':
+                    this._contentType = type;
                     this._setContentExtensionUnloaded();
                     break;
                 default:
@@ -645,18 +796,22 @@ class Display extends EventDispatcher {
                     break;
             }
         } catch (e) {
-            this.onError(e);
+            this.onError(e instanceof Error ? e : new Error(`${e}`));
         }
     }
 
+    /**
+     * @param {import('display').QueryParserSearchedEvent} details
+     */
     _onQueryParserSearch({type, dictionaryEntries, sentence, inputInfo: {eventType}, textSource, optionsContext, sentenceOffset}) {
         const query = textSource.text();
         const historyState = this._history.state;
         const historyMode = (
             eventType === 'click' ||
-            !isObject(historyState) ||
+            !(typeof historyState === 'object' && historyState !== null) ||
             historyState.cause !== 'queryParser'
         ) ? 'new' : 'overwrite';
+        /** @type {import('display').ContentDetails} */
         const details = {
             focus: false,
             historyMode,
@@ -674,9 +829,11 @@ class Display extends EventDispatcher {
         this.setContent(details);
     }
 
+    /** */
     _onExtensionUnloaded() {
         const type = 'unloaded';
         if (this._contentType === type) { return; }
+        /** @type {import('display').ContentDetails} */
         const details = {
             focus: false,
             historyMode: 'clear',
@@ -692,21 +849,33 @@ class Display extends EventDispatcher {
         this.setContent(details);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onCloseButtonClick(e) {
         e.preventDefault();
         this.close();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onSourceTermView(e) {
         e.preventDefault();
         this._sourceTermView();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onNextTermView(e) {
         e.preventDefault();
         this._nextTermView();
     }
 
+    /**
+     * @param {import('dynamic-property').ChangeEventDetails<boolean>} details
+     */
     _onProgressIndicatorVisibleChanged({value}) {
         if (this._progressIndicatorTimer !== null) {
             clearTimeout(this._progressIndicatorTimer);
@@ -726,17 +895,24 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     async _onKanjiLookup(e) {
         try {
             e.preventDefault();
-            if (!this._historyHasState()) { return; }
+            const {state} = this._history;
+            if (!(typeof state === 'object' && state !== null)) { return; }
 
-            let {state: {sentence, url, documentTitle}} = this._history;
+            let {sentence, url, documentTitle} = state;
             if (typeof url !== 'string') { url = window.location.href; }
             if (typeof documentTitle !== 'string') { documentTitle = document.title; }
             const optionsContext = this.getOptionsContext();
-            const query = e.currentTarget.textContent;
+            const element = /** @type {Element} */ (e.currentTarget);
+            let query = element.textContent;
+            if (query === null) { query = ''; }
             const dictionaryEntries = await yomichan.api.kanjiFind(query, optionsContext);
+            /** @type {import('display').ContentDetails} */
             const details = {
                 focus: false,
                 historyMode: 'new',
@@ -755,10 +931,13 @@ class Display extends EventDispatcher {
             };
             this.setContent(details);
         } catch (error) {
-            this.onError(error);
+            this.onError(error instanceof Error ? error : new Error(`${error}`));
         }
     }
 
+    /**
+     * @param {WheelEvent} e
+     */
     _onWheel(e) {
         if (e.altKey) {
             if (e.deltaY !== 0) {
@@ -770,6 +949,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {WheelEvent} e
+     */
     _onHistoryWheel(e) {
         if (e.altKey) { return; }
         const delta = -e.deltaX || e.deltaY;
@@ -784,12 +966,18 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onDebugLogClick(e) {
-        const link = e.currentTarget;
+        const link = /** @type {HTMLElement} */ (e.currentTarget);
         const index = this.getElementDictionaryEntryIndex(link);
         this._logDictionaryEntryData(index);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onDocumentElementMouseUp(e) {
         switch (e.button) {
             case 3: // Back
@@ -805,6 +993,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onDocumentElementClick(e) {
         switch (e.button) {
             case 3: // Back
@@ -822,27 +1013,43 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onEntryClick(e) {
         if (e.button !== 0) { return; }
-        const node = e.currentTarget;
-        const index = parseInt(node.dataset.index, 10);
-        if (!Number.isFinite(index)) { return; }
-        this._entrySetCurrent(index);
+        const node = /** @type {HTMLElement} */ (e.currentTarget);
+        const {index} = node.dataset;
+        if (typeof index !== 'string') { return; }
+        const indexNumber = parseInt(index, 10);
+        if (!Number.isFinite(indexNumber)) { return; }
+        this._entrySetCurrent(indexNumber);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onTagClick(e) {
-        this._showTagNotification(e.currentTarget);
+        const node = /** @type {HTMLElement} */ (e.currentTarget);
+        this._showTagNotification(node);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMenuButtonClick(e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLElement} */ (e.currentTarget);
 
-        const menuContainerNode = this._displayGenerator.instantiateTemplate('dictionary-entry-popup-menu');
-        const menuBodyNode = menuContainerNode.querySelector('.popup-menu-body');
+        const menuContainerNode = /** @type {HTMLElement} */ (this._displayGenerator.instantiateTemplate('dictionary-entry-popup-menu'));
+        const menuBodyNode = /** @type {HTMLElement} */ (menuContainerNode.querySelector('.popup-menu-body'));
 
+        /**
+         * @param {string} menuAction
+         * @param {string} label
+         */
         const addItem = (menuAction, label) => {
-            const item = this._displayGenerator.instantiateTemplate('dictionary-entry-popup-menu-item');
-            item.querySelector('.popup-menu-item-label').textContent = label;
+            const item = /** @type {HTMLElement} */ (this._displayGenerator.instantiateTemplate('dictionary-entry-popup-menu-item'));
+            /** @type {HTMLElement} */ (item.querySelector('.popup-menu-item-label')).textContent = label;
             item.dataset.menuAction = menuAction;
             menuBodyNode.appendChild(item);
         };
@@ -854,8 +1061,12 @@ class Display extends EventDispatcher {
         popupMenu.prepare();
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuButtonMenuClose(e) {
-        const {currentTarget: node, detail: {action}} = e;
+        const node = /** @type {HTMLElement} */ (e.currentTarget);
+        const {action} = e.detail;
         switch (action) {
             case 'log-debug-info':
                 this._logDictionaryEntryData(this.getElementDictionaryEntryIndex(node));
@@ -863,27 +1074,36 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {Element} tagNode
+     */
     _showTagNotification(tagNode) {
-        tagNode = tagNode.parentNode;
-        if (tagNode === null) { return; }
+        const parent = tagNode.parentNode;
+        if (parent === null || !(parent instanceof HTMLElement)) { return; }
 
         if (this._tagNotification === null) {
             this._tagNotification = this.createNotification(true);
         }
 
-        const index = this.getElementDictionaryEntryIndex(tagNode);
+        const index = this.getElementDictionaryEntryIndex(parent);
         const dictionaryEntry = (index >= 0 && index < this._dictionaryEntries.length ? this._dictionaryEntries[index] : null);
 
-        const content = this._displayGenerator.createTagFooterNotificationDetails(tagNode, dictionaryEntry);
+        const content = this._displayGenerator.createTagFooterNotificationDetails(parent, dictionaryEntry);
         this._tagNotification.setContent(content);
         this._tagNotification.open();
     }
 
+    /**
+     * @param {boolean} animate
+     */
     _hideTagNotification(animate) {
         if (this._tagNotification === null) { return; }
         this._tagNotification.close(animate);
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     _updateDocumentOptions(options) {
         const data = document.documentElement.dataset;
         data.ankiEnabled = `${options.anki.enable}`;
@@ -903,6 +1123,9 @@ class Display extends EventDispatcher {
         data.popupActionBarLocation = `${options.general.popupActionBarLocation}`;
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     _setTheme(options) {
         const {general} = options;
         const {popupTheme} = general;
@@ -912,11 +1135,19 @@ class Display extends EventDispatcher {
         this.setCustomCss(general.customPopupCss);
     }
 
+    /**
+     * @param {boolean} isKanji
+     * @param {string} source
+     * @param {boolean} wildcardsEnabled
+     * @param {import('settings').OptionsContext} optionsContext
+     * @returns {Promise<import('dictionary').DictionaryEntry[]>}
+     */
     async _findDictionaryEntries(isKanji, source, wildcardsEnabled, optionsContext) {
         if (isKanji) {
             const dictionaryEntries = await yomichan.api.kanjiFind(source, optionsContext);
             return dictionaryEntries;
         } else {
+            /** @type {import('api').FindTermsDetails} */
             const findDetails = {};
             if (wildcardsEnabled) {
                 const match = /^([*\uff0a]*)([\w\W]*?)([*\uff0a]*)$/.exec(source);
@@ -937,6 +1168,11 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} type
+     * @param {URLSearchParams} urlSearchParams
+     * @param {import('core').TokenObject} token
+     */
     async _setContentTermsOrKanji(type, urlSearchParams, token) {
         const lookup = (urlSearchParams.get('lookup') !== 'false');
         const wildcardsEnabled = (urlSearchParams.get('wildcards') !== 'off');
@@ -946,20 +1182,21 @@ class Display extends EventDispatcher {
         if (query === null) { query = ''; }
         let queryFull = urlSearchParams.get('full');
         queryFull = (queryFull !== null ? queryFull : query);
-        let queryOffset = urlSearchParams.get('offset');
-        if (queryOffset !== null) {
-            queryOffset = Number.parseInt(queryOffset, 10);
-            queryOffset = Number.isFinite(queryOffset) ? Math.max(0, Math.min(queryFull.length - query.length, queryOffset)) : null;
+        const queryOffsetString = urlSearchParams.get('offset');
+        let queryOffset = 0;
+        if (queryOffsetString !== null) {
+            queryOffset = Number.parseInt(queryOffsetString, 10);
+            queryOffset = Number.isFinite(queryOffset) ? Math.max(0, Math.min(queryFull.length - query.length, queryOffset)) : 0;
         }
         this._setQuery(query, queryFull, queryOffset);
 
         let {state, content} = this._history;
         let changeHistory = false;
-        if (!isObject(content)) {
+        if (!(typeof content === 'object' && content !== null)) {
             content = {};
             changeHistory = true;
         }
-        if (!isObject(state)) {
+        if (!(typeof state === 'object' && state !== null)) {
             state = {};
             changeHistory = true;
         }
@@ -1052,8 +1289,9 @@ class Display extends EventDispatcher {
         this._triggerContentUpdateComplete();
     }
 
+    /** */
     _setContentExtensionUnloaded() {
-        const errorExtensionUnloaded = document.querySelector('#error-extension-unloaded');
+        const errorExtensionUnloaded = /** @type {?HTMLElement} */ (document.querySelector('#error-extension-unloaded'));
 
         if (this._container !== null) {
             this._container.hidden = true;
@@ -1071,6 +1309,7 @@ class Display extends EventDispatcher {
         this._triggerContentUpdateComplete();
     }
 
+    /** */
     _clearContent() {
         this._container.textContent = '';
         this._updateNavigationAuto();
@@ -1080,14 +1319,22 @@ class Display extends EventDispatcher {
         this._triggerContentUpdateComplete();
     }
 
+    /**
+     * @param {boolean} visible
+     */
     _setNoContentVisible(visible) {
-        const noResults = document.querySelector('#no-results');
+        const noResults = /** @type {?HTMLElement} */ (document.querySelector('#no-results'));
 
         if (noResults !== null) {
             noResults.hidden = !visible;
         }
     }
 
+    /**
+     * @param {string} query
+     * @param {string} fullQuery
+     * @param {number} queryOffset
+     */
     _setQuery(query, fullQuery, queryOffset) {
         this._query = query;
         this._fullQuery = fullQuery;
@@ -1096,6 +1343,7 @@ class Display extends EventDispatcher {
         this._setTitleText(query);
     }
 
+    /** */
     _updateQueryParser() {
         const text = this._fullQuery;
         const visible = this._isQueryParserVisible();
@@ -1105,6 +1353,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} text
+     */
     async _setQueryParserText(text) {
         const overrideToken = this._progressIndicatorVisible.setOverride(true);
         try {
@@ -1114,6 +1365,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} text
+     */
     _setTitleText(text) {
         let title = this._defaultTitle;
         if (text.length > 0) {
@@ -1130,10 +1384,15 @@ class Display extends EventDispatcher {
         document.title = title;
     }
 
+    /** */
     _updateNavigationAuto() {
         this._updateNavigation(this._history.hasPrevious(), this._history.hasNext());
     }
 
+    /**
+     * @param {boolean} previous
+     * @param {boolean} next
+     */
     _updateNavigation(previous, next) {
         const {documentElement} = document;
         if (documentElement !== null) {
@@ -1148,6 +1407,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} index
+     */
     _entrySetCurrent(index) {
         const entryPre = this._getEntry(this._index);
         if (entryPre !== null) {
@@ -1162,6 +1424,11 @@ class Display extends EventDispatcher {
         this._index = index;
     }
 
+    /**
+     * @param {number} index
+     * @param {number} definitionIndex
+     * @param {boolean} smooth
+     */
     _focusEntry(index, definitionIndex, smooth) {
         index = Math.max(Math.min(index, this._dictionaryEntries.length - 1), 0);
 
@@ -1188,6 +1455,11 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} offset
+     * @param {boolean} smooth
+     * @returns {boolean}
+     */
     _focusEntryWithDifferentDictionary(offset, smooth) {
         const sign = Math.sign(offset);
         if (sign === 0) { return false; }
@@ -1200,18 +1472,22 @@ class Display extends EventDispatcher {
         const visibleDefinitionIndex = this._getDictionaryEntryVisibleDefinitionIndex(index, sign);
         if (visibleDefinitionIndex === null) { return false; }
 
-        const {dictionary} = dictionaryEntry.definitions[visibleDefinitionIndex];
         let focusDefinitionIndex = null;
-        for (let i = index; i >= 0 && i < count; i += sign) {
-            const {definitions} = this._dictionaryEntries[i];
-            const jj = definitions.length;
-            let j = (i === index ? visibleDefinitionIndex + sign : (sign > 0 ? 0 : jj - 1));
-            for (; j >= 0 && j < jj; j += sign) {
-                if (definitions[j].dictionary !== dictionary) {
-                    focusDefinitionIndex = j;
-                    index = i;
-                    i = -2; // Terminate outer loop
-                    break;
+        if (dictionaryEntry.type === 'term') {
+            const {dictionary} = dictionaryEntry.definitions[visibleDefinitionIndex];
+            for (let i = index; i >= 0 && i < count; i += sign) {
+                const otherDictionaryEntry = this._dictionaryEntries[i];
+                if (otherDictionaryEntry.type !== 'term') { continue; }
+                const {definitions} = otherDictionaryEntry;
+                const jj = definitions.length;
+                let j = (i === index ? visibleDefinitionIndex + sign : (sign > 0 ? 0 : jj - 1));
+                for (; j >= 0 && j < jj; j += sign) {
+                    if (definitions[j].dictionary !== dictionary) {
+                        focusDefinitionIndex = j;
+                        index = i;
+                        i = -2; // Terminate outer loop
+                        break;
+                    }
                 }
             }
         }
@@ -1222,6 +1498,11 @@ class Display extends EventDispatcher {
         return true;
     }
 
+    /**
+     * @param {number} index
+     * @param {number} sign
+     * @returns {?number}
+     */
     _getDictionaryEntryVisibleDefinitionIndex(index, sign) {
         const {top: scrollTop, bottom: scrollBottom} = this._windowScroll.getRect();
 
@@ -1247,18 +1528,28 @@ class Display extends EventDispatcher {
         return visibleIndex !== null ? visibleIndex : (sign > 0 ? definitionCount - 1 : 0);
     }
 
+    /**
+     * @param {number} index
+     * @returns {NodeListOf<HTMLElement>}
+     */
     _getDictionaryEntryDefinitionNodes(index) {
         return this._dictionaryEntryNodes[index].querySelectorAll('.definition-item');
     }
 
+    /** */
     _sourceTermView() {
         this._relativeTermView(false);
     }
 
+    /** */
     _nextTermView() {
         this._relativeTermView(true);
     }
 
+    /**
+     * @param {boolean} next
+     * @returns {boolean}
+     */
     _relativeTermView(next) {
         if (next) {
             return this._history.hasNext() && this._history.forward();
@@ -1267,24 +1558,29 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} index
+     * @returns {?HTMLElement}
+     */
     _getEntry(index) {
         const entries = this._dictionaryEntryNodes;
         return index >= 0 && index < entries.length ? entries[index] : null;
     }
 
+    /**
+     * @param {Element} element
+     * @returns {number}
+     */
     _getElementTop(element) {
         const elementRect = element.getBoundingClientRect();
         const documentRect = this._contentScrollBodyElement.getBoundingClientRect();
         return elementRect.top - documentRect.top;
     }
 
-    _historyHasState() {
-        return isObject(this._history.state);
-    }
-
+    /** */
     _updateHistoryState() {
         const {state, content} = this._history;
-        if (!isObject(state)) { return; }
+        if (!(typeof state === 'object' && state !== null)) { return; }
 
         state.focusEntry = this._index;
         state.scrollX = this._windowScroll.x;
@@ -1292,6 +1588,10 @@ class Display extends EventDispatcher {
         this._replaceHistoryStateNoNavigate(state, content);
     }
 
+    /**
+     * @param {import('display-history').EntryState} state
+     * @param {?import('display-history').EntryContent} content
+     */
     _replaceHistoryStateNoNavigate(state, content) {
         const historyChangeIgnorePre = this._historyChangeIgnore;
         try {
@@ -1302,7 +1602,15 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('display').PageType} type
+     * @param {string} query
+     * @param {boolean} wildcards
+     * @param {?number} sentenceOffset
+     * @returns {import('display').HistoryParams}
+     */
     _createSearchParams(type, query, wildcards, sentenceOffset) {
+        /** @type {import('display').HistoryParams} */
         const params = {};
         const fullQuery = this._fullQuery;
         const includeFull = (query.length < fullQuery.length);
@@ -1325,6 +1633,9 @@ class Display extends EventDispatcher {
         return params;
     }
 
+    /**
+     * @returns {boolean}
+     */
     _isQueryParserVisible() {
         return (
             this._queryParserVisibleOverride !== null ?
@@ -1333,22 +1644,34 @@ class Display extends EventDispatcher {
         );
     }
 
+    /** */
     _closePopups() {
         yomichan.trigger('closePopups');
     }
 
+    /**
+     * @param {import('settings').OptionsContext} optionsContext
+     */
     async _setOptionsContextIfDifferent(optionsContext) {
         if (deepEqual(this._optionsContext, optionsContext)) { return; }
         await this.setOptionsContext(optionsContext);
     }
 
+    /**
+     * @param {number} scale
+     */
     _setContentScale(scale) {
         const body = document.body;
         if (body === null) { return; }
         body.style.fontSize = `${scale}em`;
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     async _updateNestedFrontend(options) {
+        if (typeof this._frameId !== 'number') { return; }
+
         const isSearchPage = (this._pageType === 'search');
         const isEnabled = (
             this._childrenSupported &&
@@ -1376,15 +1699,18 @@ class Display extends EventDispatcher {
             }
         }
 
-        this._frontend.setDisabledOverride(!isEnabled);
+        /** @type {Frontend} */ (this._frontend).setDisabledOverride(!isEnabled);
     }
 
+    /** */
     async _setupNestedFrontend() {
-        const setupNestedPopupsOptions = {
-            useProxyPopup: this._parentFrameId !== null,
-            parentPopupId: this._parentPopupId,
-            parentFrameId: this._parentFrameId
-        };
+        if (typeof this._frameId !== 'number') {
+            throw new Error('No frameId assigned');
+        }
+
+        const useProxyPopup = this._parentFrameId !== null;
+        const parentPopupId = this._parentPopupId;
+        const parentFrameId = this._parentFrameId;
 
         await dynamicLoader.loadScripts([
             '/js/language/text-scanner.js',
@@ -1401,7 +1727,11 @@ class Display extends EventDispatcher {
         const popupFactory = new PopupFactory(this._frameId);
         popupFactory.prepare();
 
-        Object.assign(setupNestedPopupsOptions, {
+        /** @type {import('frontend').ConstructorDetails} */
+        const setupNestedPopupsOptions = {
+            useProxyPopup,
+            parentPopupId,
+            parentFrameId,
             depth: this._depth + 1,
             tabId: this._tabId,
             frameId: this._frameId,
@@ -1410,19 +1740,25 @@ class Display extends EventDispatcher {
             allowRootFramePopupProxy: true,
             childrenSupported: this._childrenSupported,
             hotkeyHandler: this._hotkeyHandler
-        });
+        };
 
         const frontend = new Frontend(setupNestedPopupsOptions);
         this._frontend = frontend;
         await frontend.prepare();
     }
 
+    /**
+     * @returns {boolean}
+     */
     _copyHostSelection() {
-        if (this._contentOriginFrameId === null || window.getSelection().toString()) { return false; }
+        if (typeof this._contentOriginFrameId !== 'number') { return false; }
+        const selection = window.getSelection();
+        if (selection !== null && selection.toString().length > 0) { return false; }
         this._copyHostSelectionSafe();
         return true;
     }
 
+    /** */
     async _copyHostSelectionSafe() {
         try {
             await this._copyHostSelectionInner();
@@ -1431,11 +1767,13 @@ class Display extends EventDispatcher {
         }
     }
 
+    /** */
     async _copyHostSelectionInner() {
         switch (this._browser) {
             case 'firefox':
             case 'firefox-mobile':
                 {
+                    /** @type {string} */
                     let text;
                     try {
                         text = await this.invokeContentOrigin('Frontend.getSelectionText');
@@ -1451,6 +1789,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} text
+     */
     _copyText(text) {
         const parent = document.body;
         if (parent === null) { return; }
@@ -1468,6 +1809,9 @@ class Display extends EventDispatcher {
         parent.removeChild(textarea);
     }
 
+    /**
+     * @param {HTMLElement} entry
+     */
     _addEntryEventListeners(entry) {
         const eventListeners = this._eventListeners;
         eventListeners.addEventListener(entry, 'click', this._onEntryClickBind);
@@ -1483,6 +1827,9 @@ class Display extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     _updateContentTextScanner(options) {
         if (!options.scanning.enablePopupSearch) {
             if (this._contentTextScanner !== null) {
@@ -1544,10 +1891,14 @@ class Display extends EventDispatcher {
         this._contentTextScanner.setEnabled(true);
     }
 
+    /** */
     _onContentTextScannerClear() {
-        this._contentTextScanner.clearSelection();
+        /** @type {TextScanner} */ (this._contentTextScanner).clearSelection();
     }
 
+    /**
+     * @param {import('text-scanner').SearchedEventDetails} details
+     */
     _onContentTextScannerSearched({type, dictionaryEntries, sentence, textSource, optionsContext, error}) {
         if (error !== null && !yomichan.isExtensionUnloaded) {
             log.error(error);
@@ -1558,6 +1909,7 @@ class Display extends EventDispatcher {
         const query = textSource.text();
         const url = window.location.href;
         const documentTitle = document.title;
+        /** @type {import('display').ContentDetails} */
         const details = {
             focus: false,
             historyMode: 'new',
@@ -1568,28 +1920,35 @@ class Display extends EventDispatcher {
             },
             state: {
                 focusEntry: 0,
-                optionsContext,
+                optionsContext: optionsContext !== null ? optionsContext : void 0,
                 url,
-                sentence,
+                sentence: sentence !== null ? sentence : void 0,
                 documentTitle
             },
             content: {
-                dictionaryEntries,
+                dictionaryEntries: dictionaryEntries !== null ? dictionaryEntries : void 0,
                 contentOrigin: this.getContentOrigin()
             }
         };
-        this._contentTextScanner.clearSelection();
+        /** @type {TextScanner} */ (this._contentTextScanner).clearSelection();
         this.setContent(details);
     }
 
+    /**
+     * @type {import('display').GetSearchContextCallback}
+     */
     _getSearchContext() {
         return {optionsContext: this.getOptionsContext()};
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     _updateHotkeys(options) {
         this._hotkeyHandler.setHotkeys(this._pageType, options.inputs.hotkeys);
     }
 
+    /** */
     async _closeTab() {
         const tab = await new Promise((resolve, reject) => {
             chrome.tabs.getCurrent((result) => {
@@ -1602,7 +1961,7 @@ class Display extends EventDispatcher {
             });
         });
         const tabId = tab.id;
-        await new Promise((resolve, reject) => {
+        await /** @type {Promise<void>} */ (new Promise((resolve, reject) => {
             chrome.tabs.remove(tabId, () => {
                 const e = chrome.runtime.lastError;
                 if (e) {
@@ -1611,27 +1970,36 @@ class Display extends EventDispatcher {
                     resolve();
                 }
             });
-        });
+        }));
     }
 
+    /** */
     _onHotkeyClose() {
         if (this._closeSinglePopupMenu()) { return; }
         this.close();
     }
 
+    /**
+     * @param {number} sign
+     * @param {unknown} argument
+     */
     _onHotkeyActionMoveRelative(sign, argument) {
-        let count = Number.parseInt(argument, 10);
+        let count = typeof argument === 'number' ? argument : (typeof argument === 'string' ? Number.parseInt(argument, 10) : 0);
         if (!Number.isFinite(count)) { count = 1; }
         count = Math.max(0, Math.floor(count));
         this._focusEntry(this._index + count * sign, 0, true);
     }
 
+    /** */
     _closeAllPopupMenus() {
         for (const popupMenu of PopupMenu.openMenus) {
             popupMenu.close();
         }
     }
 
+    /**
+     * @returns {boolean}
+     */
     _closeSinglePopupMenu() {
         for (const popupMenu of PopupMenu.openMenus) {
             popupMenu.close();
@@ -1640,13 +2008,19 @@ class Display extends EventDispatcher {
         return false;
     }
 
+    /**
+     * @param {number} index
+     */
     async _logDictionaryEntryData(index) {
         if (index < 0 || index >= this._dictionaryEntries.length) { return; }
         const dictionaryEntry = this._dictionaryEntries[index];
         const result = {dictionaryEntry};
 
+        /** @type {Promise<unknown>[]} */
         const promises = [];
-        this.trigger('logDictionaryEntryData', {dictionaryEntry, promises});
+        /** @type {import('display').LogDictionaryEntryDataEvent} */
+        const event = {dictionaryEntry, promises};
+        this.trigger('logDictionaryEntryData', event);
         if (promises.length > 0) {
             for (const result2 of await Promise.all(promises)) {
                 Object.assign(result, result2);
@@ -1656,19 +2030,33 @@ class Display extends EventDispatcher {
         console.log(result);
     }
 
+    /** */
     _triggerContentClear() {
         this.trigger('contentClear', {});
     }
 
+    /** */
     _triggerContentUpdateStart() {
-        this.trigger('contentUpdateStart', {type: this._contentType, query: this._query});
+        /** @type {import('display').ContentUpdateStartEvent} */
+        const event = {type: this._contentType, query: this._query};
+        this.trigger('contentUpdateStart', event);
     }
 
+    /**
+     * @param {import('dictionary').DictionaryEntry} dictionaryEntry
+     * @param {Element} element
+     * @param {number} index
+     */
     _triggerContentUpdateEntry(dictionaryEntry, element, index) {
-        this.trigger('contentUpdateEntry', {dictionaryEntry, element, index});
+        /** @type {import('display').ContentUpdateEntryEvent} */
+        const event = {dictionaryEntry, element, index};
+        this.trigger('contentUpdateEntry', event);
     }
 
+    /** */
     _triggerContentUpdateComplete() {
-        this.trigger('contentUpdateComplete', {type: this._contentType});
+        /** @type {import('display').ContentUpdateCompleteEvent} */
+        const event = {type: this._contentType};
+        this.trigger('contentUpdateComplete', event);
     }
 }
diff --git a/ext/js/display/element-overflow-controller.js b/ext/js/display/element-overflow-controller.js
index 9fb3d26f0a..3556da9383 100644
--- a/ext/js/display/element-overflow-controller.js
+++ b/ext/js/display/element-overflow-controller.js
@@ -18,16 +18,27 @@
 
 class ElementOverflowController {
     constructor() {
+        /** @type {Element[]} */
         this._elements = [];
+        /** @type {?number} */
         this._checkTimer = null;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {EventListenerCollection} */
         this._windowEventListeners = new EventListenerCollection();
+        /** @type {Map<string, {collapsed: boolean, force: boolean}>} */
         this._dictionaries = new Map();
+        /** @type {() => void} */
         this._updateBind = this._update.bind(this);
+        /** @type {() => void} */
         this._onWindowResizeBind = this._onWindowResize.bind(this);
+        /** @type {(event: MouseEvent) => void} */
         this._onToggleButtonClickBind = this._onToggleButtonClick.bind(this);
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     setOptions(options) {
         this._dictionaries.clear();
         for (const {name, definitionsCollapsible} of options.dictionaries) {
@@ -57,12 +68,18 @@ class ElementOverflowController {
         }
     }
 
+    /**
+     * @param {Element} entry
+     */
     addElements(entry) {
         if (this._dictionaries.size === 0) { return; }
 
         const elements = entry.querySelectorAll('.definition-item-inner');
         for (const element of elements) {
-            const {dictionary} = element.parentNode.dataset;
+            const {parentNode} = element;
+            if (parentNode === null) { continue; }
+            const {dictionary} = /** @type {HTMLElement} */ (parentNode).dataset;
+            if (typeof dictionary === 'undefined') { continue; }
             const dictionaryInfo = this._dictionaries.get(dictionary);
             if (typeof dictionaryInfo === 'undefined') { continue; }
 
@@ -88,6 +105,7 @@ class ElementOverflowController {
         }
     }
 
+    /** */
     clearElements() {
         this._elements.length = 0;
         this._windowEventListeners.removeAllEventListeners();
@@ -95,6 +113,7 @@ class ElementOverflowController {
 
     // Private
 
+    /** */
     _onWindowResize() {
         if (this._checkTimer !== null) {
             this._cancelIdleCallback(this._checkTimer);
@@ -102,18 +121,26 @@ class ElementOverflowController {
         this._checkTimer = this._requestIdleCallback(this._updateBind, 100);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onToggleButtonClick(e) {
-        const container = e.currentTarget.closest('.definition-item-inner');
+        const element = /** @type {Element} */ (e.currentTarget);
+        const container = element.closest('.definition-item-inner');
         if (container === null) { return; }
         container.classList.toggle('collapsed');
     }
 
+    /** */
     _update() {
         for (const element of this._elements) {
             this._updateElement(element);
         }
     }
 
+    /**
+     * @param {Element} element
+     */
     _updateElement(element) {
         const {classList} = element;
         classList.add('collapse-test');
@@ -122,6 +149,11 @@ class ElementOverflowController {
         classList.remove('collapse-test');
     }
 
+    /**
+     * @param {() => void} callback
+     * @param {number} timeout
+     * @returns {number}
+     */
     _requestIdleCallback(callback, timeout) {
         if (typeof requestIdleCallback === 'function') {
             return requestIdleCallback(callback, {timeout});
@@ -130,6 +162,9 @@ class ElementOverflowController {
         }
     }
 
+    /**
+     * @param {number} handle
+     */
     _cancelIdleCallback(handle) {
         if (typeof cancelIdleCallback === 'function') {
             cancelIdleCallback(handle);
diff --git a/ext/js/display/option-toggle-hotkey-handler.js b/ext/js/display/option-toggle-hotkey-handler.js
index 251e03fa40..58b185d5ae 100644
--- a/ext/js/display/option-toggle-hotkey-handler.js
+++ b/ext/js/display/option-toggle-hotkey-handler.js
@@ -17,13 +17,23 @@
  */
 
 class OptionToggleHotkeyHandler {
+    /**
+     * @param {Display} display
+     */
     constructor(display) {
+        /** @type {Display} */
         this._display = display;
+        /** @type {?DisplayNotification} */
         this._notification = null;
+        /** @type {?number} */
         this._notificationHideTimer = null;
+        /** @type {number} */
         this._notificationHideTimeout = 5000;
+        /** @type {string} */
+        this._source = `option-toggle-hotkey-handler-${generateId(16)}`;
     }
 
+    /** @type {number} */
     get notificationHideTimeout() {
         return this._notificationHideTimeout;
     }
@@ -32,6 +42,7 @@ class OptionToggleHotkeyHandler {
         this._notificationHideTimeout = value;
     }
 
+    /** */
     prepare() {
         this._display.hotkeyHandler.registerActions([
             ['toggleOption', this._onHotkeyActionToggleOption.bind(this)]
@@ -40,10 +51,17 @@ class OptionToggleHotkeyHandler {
 
     // Private
 
+    /**
+     * @param {unknown} argument
+     */
     _onHotkeyActionToggleOption(argument) {
+        if (typeof argument !== 'string') { return; }
         this._toggleOption(argument);
     }
 
+    /**
+     * @param {string} path
+     */
     async _toggleOption(path) {
         let value;
         try {
@@ -56,7 +74,7 @@ class OptionToggleHotkeyHandler {
             }]))[0];
             const {error} = result;
             if (typeof error !== 'undefined') {
-                throw deserializeError(error);
+                throw ExtensionError.deserialize(error);
             }
 
             value = result.result;
@@ -66,16 +84,18 @@ class OptionToggleHotkeyHandler {
 
             value = !value;
 
-            const result2 = (await yomichan.api.modifySettings([{
+            /** @type {import('settings-modifications').ScopedModificationSet} */
+            const modification = {
                 scope: 'profile',
                 action: 'set',
                 path,
                 value,
                 optionsContext
-            }]))[0];
+            };
+            const result2 = (await yomichan.api.modifySettings([modification], this._source))[0];
             const {error: error2} = result2;
             if (typeof error2 !== 'undefined') {
-                throw deserializeError(error2);
+                throw ExtensionError.deserialize(error2);
             }
 
             this._showNotification(this._createSuccessMessage(path, value), true);
@@ -84,12 +104,17 @@ class OptionToggleHotkeyHandler {
         }
     }
 
+    /**
+     * @param {string} path
+     * @param {unknown} value
+     * @returns {DocumentFragment}
+     */
     _createSuccessMessage(path, value) {
         const fragment = document.createDocumentFragment();
         const n1 = document.createElement('em');
         n1.textContent = path;
         const n2 = document.createElement('strong');
-        n2.textContent = value;
+        n2.textContent = `${value}`;
         fragment.appendChild(document.createTextNode('Option '));
         fragment.appendChild(n1);
         fragment.appendChild(document.createTextNode(' changed to '));
@@ -97,17 +122,13 @@ class OptionToggleHotkeyHandler {
         return fragment;
     }
 
+    /**
+     * @param {string} path
+     * @param {unknown} error
+     * @returns {DocumentFragment}
+     */
     _createErrorMessage(path, error) {
-        let message;
-        try {
-            ({message} = error);
-        } catch (e) {
-            // NOP
-        }
-        if (typeof message !== 'string') {
-            message = `${error}`;
-        }
-
+        const message = error instanceof Error ? error.message : `${error}`;
         const fragment = document.createDocumentFragment();
         const n1 = document.createElement('em');
         n1.textContent = path;
@@ -121,6 +142,10 @@ class OptionToggleHotkeyHandler {
         return fragment;
     }
 
+    /**
+     * @param {DocumentFragment} message
+     * @param {boolean} autoClose
+     */
     _showNotification(message, autoClose) {
         if (this._notification === null) {
             this._notification = this._display.createNotification(false);
@@ -136,12 +161,16 @@ class OptionToggleHotkeyHandler {
         }
     }
 
+    /**
+     * @param {boolean} animate
+     */
     _hideNotification(animate) {
         if (this._notification === null) { return; }
         this._notification.close(animate);
         this._stopHideNotificationTimer();
     }
 
+    /** */
     _stopHideNotificationTimer() {
         if (this._notificationHideTimer !== null) {
             clearTimeout(this._notificationHideTimer);
@@ -149,11 +178,13 @@ class OptionToggleHotkeyHandler {
         }
     }
 
+    /** */
     _onNotificationHideTimeout() {
         this._notificationHideTimer = null;
         this._hideNotification(true);
     }
 
+    /** */
     _onNotificationClick() {
         this._stopHideNotificationTimer();
     }
diff --git a/ext/js/display/query-parser.js b/ext/js/display/query-parser.js
index 205be579b8..4ef0fda525 100644
--- a/ext/js/display/query-parser.js
+++ b/ext/js/display/query-parser.js
@@ -20,22 +20,42 @@
  * TextScanner
  */
 
+/**
+ * @augments EventDispatcher<import('display').QueryParserEventType>
+ */
 class QueryParser extends EventDispatcher {
+    /**
+     * @param {import('display').QueryParserConstructorDetails} details
+     */
     constructor({getSearchContext, japaneseUtil}) {
         super();
+        /** @type {import('display').GetSearchContextCallback} */
         this._getSearchContext = getSearchContext;
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
+        /** @type {string} */
         this._text = '';
+        /** @type {?import('core').TokenObject} */
         this._setTextToken = null;
+        /** @type {?string} */
         this._selectedParser = null;
+        /** @type {import('settings').ParsingReadingMode} */
         this._readingMode = 'none';
+        /** @type {number} */
         this._scanLength = 1;
+        /** @type {boolean} */
         this._useInternalParser = true;
+        /** @type {boolean} */
         this._useMecabParser = false;
+        /** @type {import('api').ParseTextResult} */
         this._parseResults = [];
-        this._queryParser = document.querySelector('#query-parser-content');
-        this._queryParserModeContainer = document.querySelector('#query-parser-mode-container');
-        this._queryParserModeSelect = document.querySelector('#query-parser-mode-select');
+        /** @type {HTMLElement} */
+        this._queryParser = /** @type {HTMLElement} */ (document.querySelector('#query-parser-content'));
+        /** @type {HTMLElement} */
+        this._queryParserModeContainer = /** @type {HTMLElement} */ (document.querySelector('#query-parser-mode-container'));
+        /** @type {HTMLSelectElement} */
+        this._queryParserModeSelect = /** @type {HTMLSelectElement} */ (document.querySelector('#query-parser-mode-select'));
+        /** @type {TextScanner} */
         this._textScanner = new TextScanner({
             node: this._queryParser,
             getSearchContext,
@@ -45,10 +65,12 @@ class QueryParser extends EventDispatcher {
         });
     }
 
+    /** @type {string} */
     get text() {
         return this._text;
     }
 
+    /** */
     prepare() {
         this._textScanner.prepare();
         this._textScanner.on('clear', this._onTextScannerClear.bind(this));
@@ -56,6 +78,9 @@ class QueryParser extends EventDispatcher {
         this._queryParserModeSelect.addEventListener('change', this._onParserChange.bind(this), false);
     }
 
+    /**
+     * @param {import('display').QueryParserOptions} display
+     */
     setOptions({selectedParser, termSpacing, readingMode, useInternalParser, useMecabParser, scanning}) {
         let selectedParserChanged = false;
         if (selectedParser === null || typeof selectedParser === 'string') {
@@ -87,10 +112,14 @@ class QueryParser extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} text
+     */
     async setText(text) {
         this._text = text;
         this._setPreview(text);
 
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._setTextToken = token;
         this._parseResults = await yomichan.api.parseText(text, this._getOptionsContext(), this._scanLength, this._useInternalParser, this._useMecabParser);
@@ -104,32 +133,63 @@ class QueryParser extends EventDispatcher {
 
     // Private
 
+    /** */
     _onTextScannerClear() {
         this._textScanner.clearSelection();
     }
 
+    /**
+     * @param {import('text-scanner').SearchedEventDetails} e
+     */
     _onSearched(e) {
         const {error} = e;
         if (error !== null) {
             log.error(error);
             return;
         }
-        if (e.type === null) { return; }
-
-        e.sentenceOffset = this._getSentenceOffset(e.textSource);
 
-        this.trigger('searched', e);
+        const {
+            textScanner,
+            type,
+            dictionaryEntries,
+            sentence,
+            inputInfo,
+            textSource,
+            optionsContext
+        } = e;
+        if (type === null || dictionaryEntries === null || sentence === null || optionsContext === null) { return; }
+
+        /** @type {import('display').QueryParserSearchedEvent} */
+        const event2 = {
+            textScanner,
+            type,
+            dictionaryEntries,
+            sentence,
+            inputInfo,
+            textSource,
+            optionsContext,
+            sentenceOffset: this._getSentenceOffset(e.textSource)
+        };
+        this.trigger('searched', event2);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onParserChange(e) {
-        const value = e.currentTarget.value;
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        const value = element.value;
         this._setSelectedParser(value);
     }
 
+    /**
+     * @returns {import('settings').OptionsContext}
+     */
     _getOptionsContext() {
         return this._getSearchContext().optionsContext;
     }
 
+    /** */
     _refreshSelectedParser() {
         if (this._parseResults.length > 0 && !this._getParseResult()) {
             const value = this._parseResults[0].id;
@@ -137,22 +197,33 @@ class QueryParser extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} value
+     */
     _setSelectedParser(value) {
         const optionsContext = this._getOptionsContext();
-        yomichan.api.modifySettings([{
+        /** @type {import('settings-modifications').ScopedModificationSet} */
+        const modification = {
             action: 'set',
             path: 'parsing.selectedParser',
             value,
             scope: 'profile',
             optionsContext
-        }], 'search');
+        };
+        yomichan.api.modifySettings([modification], 'search');
     }
 
+    /**
+     * @returns {import('api').ParseTextResultItem|undefined}
+     */
     _getParseResult() {
         const selectedParser = this._selectedParser;
         return this._parseResults.find((r) => r.id === selectedParser);
     }
 
+    /**
+     * @param {string} text
+     */
     _setPreview(text) {
         const terms = [[{text, reading: ''}]];
         this._queryParser.textContent = '';
@@ -160,6 +231,7 @@ class QueryParser extends EventDispatcher {
         this._queryParser.appendChild(this._createParseResult(terms));
     }
 
+    /** */
     _renderParserSelect() {
         const visible = (this._parseResults.length > 1);
         if (visible) {
@@ -168,6 +240,7 @@ class QueryParser extends EventDispatcher {
         this._queryParserModeContainer.hidden = !visible;
     }
 
+    /** */
     _renderParseResult() {
         const parseResult = this._getParseResult();
         this._queryParser.textContent = '';
@@ -176,6 +249,11 @@ class QueryParser extends EventDispatcher {
         this._queryParser.appendChild(this._createParseResult(parseResult.content));
     }
 
+    /**
+     * @param {HTMLSelectElement} select
+     * @param {import('api').ParseTextResult} parseResults
+     * @param {?string} selectedParser
+     */
     _updateParserModeSelect(select, parseResults, selectedParser) {
         const fragment = document.createDocumentFragment();
 
@@ -208,6 +286,10 @@ class QueryParser extends EventDispatcher {
         select.selectedIndex = selectedIndex;
     }
 
+    /**
+     * @param {import('api').ParseTextLine[]} data
+     * @returns {DocumentFragment}
+     */
     _createParseResult(data) {
         let offset = 0;
         const fragment = document.createDocumentFragment();
@@ -229,6 +311,12 @@ class QueryParser extends EventDispatcher {
         return fragment;
     }
 
+    /**
+     * @param {string} text
+     * @param {string} reading
+     * @param {number} offset
+     * @returns {HTMLElement}
+     */
     _createSegment(text, reading, offset) {
         const segmentNode = document.createElement('ruby');
         segmentNode.className = 'query-parser-segment';
@@ -249,6 +337,11 @@ class QueryParser extends EventDispatcher {
         return segmentNode;
     }
 
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @returns {string}
+     */
     _convertReading(term, reading) {
         switch (this._readingMode) {
             case 'hiragana':
@@ -271,11 +364,15 @@ class QueryParser extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @returns {?number}
+     */
     _getSentenceOffset(textSource) {
         if (textSource.type === 'range') {
             const {range} = textSource;
             const node = this._getParentElement(range.startContainer);
-            if (node !== null) {
+            if (node !== null && node instanceof HTMLElement) {
                 const {offset} = node.dataset;
                 if (typeof offset === 'string') {
                     const value = Number.parseInt(offset, 10);
@@ -288,12 +385,16 @@ class QueryParser extends EventDispatcher {
         return null;
     }
 
+    /**
+     * @param {?Node} node
+     * @returns {?Element}
+     */
     _getParentElement(node) {
         const {ELEMENT_NODE} = Node;
         while (true) {
-            node = node.parentNode;
             if (node === null) { return null; }
-            if (node.nodeType === ELEMENT_NODE) { return node; }
+            if (node.nodeType === ELEMENT_NODE) { return /** @type {Element} */ (node); }
+            node = node.parentNode;
         }
     }
 }
diff --git a/ext/js/display/sandbox/pronunciation-generator.js b/ext/js/display/sandbox/pronunciation-generator.js
index 027771f601..e16daac610 100644
--- a/ext/js/display/sandbox/pronunciation-generator.js
+++ b/ext/js/display/sandbox/pronunciation-generator.js
@@ -17,10 +17,21 @@
  */
 
 class PronunciationGenerator {
+    /**
+     * @param {JapaneseUtil} japaneseUtil
+     */
     constructor(japaneseUtil) {
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
     }
 
+    /**
+     * @param {string[]} morae
+     * @param {number} downstepPosition
+     * @param {number[]} nasalPositions
+     * @param {number[]} devoicePositions
+     * @returns {HTMLSpanElement}
+     */
     createPronunciationText(morae, downstepPosition, nasalPositions, devoicePositions) {
         const jp = this._japaneseUtil;
         const nasalPositionsSet = nasalPositions.length > 0 ? new Set(nasalPositions) : null;
@@ -63,7 +74,7 @@ class PronunciationGenerator {
                 group.className = 'pronunciation-character-group';
 
                 const n2 = characterNodes[0];
-                const character = n2.textContent;
+                const character = /** @type {string} */ (n2.textContent);
 
                 const characterInfo = jp.getKanaDiacriticInfo(character);
                 if (characterInfo !== null) {
@@ -81,7 +92,7 @@ class PronunciationGenerator {
                 n3.className = 'pronunciation-nasal-indicator';
                 group.appendChild(n3);
 
-                n2.parentNode.replaceChild(group, n2);
+                /** @type {ParentNode} */ (n2.parentNode).replaceChild(group, n2);
                 group.insertBefore(n2, group.firstChild);
             }
 
@@ -94,6 +105,11 @@ class PronunciationGenerator {
         return container;
     }
 
+    /**
+     * @param {string[]} morae
+     * @param {number} downstepPosition
+     * @returns {SVGSVGElement}
+     */
     createPronunciationGraph(morae, downstepPosition) {
         const jp = this._japaneseUtil;
         const ii = morae.length;
@@ -145,12 +161,16 @@ class PronunciationGenerator {
         return svg;
     }
 
+    /**
+     * @param {number} downstepPosition
+     * @returns {HTMLSpanElement}
+     */
     createPronunciationDownstepPosition(downstepPosition) {
-        downstepPosition = `${downstepPosition}`;
+        const downstepPositionString = `${downstepPosition}`;
 
         const n1 = document.createElement('span');
         n1.className = 'pronunciation-downstep-notation';
-        n1.dataset.downstepPosition = downstepPosition;
+        n1.dataset.downstepPosition = downstepPositionString;
 
         let n2 = document.createElement('span');
         n2.className = 'pronunciation-downstep-notation-prefix';
@@ -159,7 +179,7 @@ class PronunciationGenerator {
 
         n2 = document.createElement('span');
         n2.className = 'pronunciation-downstep-notation-number';
-        n2.textContent = downstepPosition;
+        n2.textContent = downstepPositionString;
         n1.appendChild(n2);
 
         n2 = document.createElement('span');
@@ -172,15 +192,33 @@ class PronunciationGenerator {
 
     // Private
 
+    /**
+     * @param {Element} container
+     * @param {string} svgns
+     * @param {number} x
+     * @param {number} y
+     */
     _addGraphDot(container, svgns, x, y) {
         container.appendChild(this._createGraphCircle(svgns, 'pronunciation-graph-dot', x, y, '15'));
     }
 
+    /**
+     * @param {Element} container
+     * @param {string} svgns
+     * @param {number} x
+     * @param {number} y
+     */
     _addGraphDotDownstep(container, svgns, x, y) {
         container.appendChild(this._createGraphCircle(svgns, 'pronunciation-graph-dot-downstep1', x, y, '15'));
         container.appendChild(this._createGraphCircle(svgns, 'pronunciation-graph-dot-downstep2', x, y, '5'));
     }
 
+    /**
+     * @param {Element} container
+     * @param {string} svgns
+     * @param {number} x
+     * @param {number} y
+     */
     _addGraphTriangle(container, svgns, x, y) {
         const node = document.createElementNS(svgns, 'path');
         node.setAttribute('class', 'pronunciation-graph-triangle');
@@ -189,6 +227,14 @@ class PronunciationGenerator {
         container.appendChild(node);
     }
 
+    /**
+     * @param {string} svgns
+     * @param {string} className
+     * @param {number} x
+     * @param {number} y
+     * @param {string} radius
+     * @returns {Element}
+     */
     _createGraphCircle(svgns, className, x, y, radius) {
         const node = document.createElementNS(svgns, 'circle');
         node.setAttribute('class', className);
diff --git a/ext/js/display/sandbox/structured-content-generator.js b/ext/js/display/sandbox/structured-content-generator.js
index 2d3a620dbf..4f3788a28d 100644
--- a/ext/js/display/sandbox/structured-content-generator.js
+++ b/ext/js/display/sandbox/structured-content-generator.js
@@ -17,28 +17,51 @@
  */
 
 class StructuredContentGenerator {
+    /**
+     * @param {DisplayContentManager|AnkiTemplateRendererContentManager} contentManager
+     * @param {JapaneseUtil} japaneseUtil
+     * @param {Document} document
+     */
     constructor(contentManager, japaneseUtil, document) {
+        /** @type {DisplayContentManager|AnkiTemplateRendererContentManager} */
         this._contentManager = contentManager;
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
+        /** @type {Document} */
         this._document = document;
     }
 
+    /**
+     * @param {HTMLElement} node
+     * @param {import('structured-content').Content} content
+     * @param {string} dictionary
+     */
     appendStructuredContent(node, content, dictionary) {
         node.classList.add('structured-content');
         this._appendStructuredContent(node, content, dictionary, null);
     }
 
+    /**
+     * @param {import('structured-content').Content} content
+     * @param {string} dictionary
+     * @returns {HTMLElement}
+     */
     createStructuredContent(content, dictionary) {
         const node = this._createElement('span', 'structured-content');
         this._appendStructuredContent(node, content, dictionary, null);
         return node;
     }
 
+    /**
+     * @param {import('structured-content').ImageElementBase} data
+     * @param {string} dictionary
+     * @returns {HTMLAnchorElement}
+     */
     createDefinitionImage(data, dictionary) {
         const {
             path,
-            width,
-            height,
+            width = 100,
+            height = 100,
             preferredWidth,
             preferredHeight,
             title,
@@ -65,7 +88,7 @@ class StructuredContentGenerator {
             (hasPreferredHeight ? preferredHeight / invAspectRatio : width)
         );
 
-        const node = this._createElement('a', 'gloss-image-link');
+        const node = /** @type {HTMLAnchorElement} */ (this._createElement('a', 'gloss-image-link'));
         node.target = '_blank';
         node.rel = 'noreferrer noopener';
 
@@ -78,7 +101,7 @@ class StructuredContentGenerator {
         const imageBackground = this._createElement('span', 'gloss-image-background');
         imageContainer.appendChild(imageBackground);
 
-        const image = this._createElement('img', 'gloss-image');
+        const image = /** @type {HTMLImageElement} */ (this._createElement('img', 'gloss-image'));
         image.alt = '';
         imageContainer.appendChild(image);
 
@@ -126,6 +149,12 @@ class StructuredContentGenerator {
 
     // Private
 
+    /**
+     * @param {HTMLElement} container
+     * @param {import('structured-content').Content|undefined} content
+     * @param {string} dictionary
+     * @param {?string} language
+     */
     _appendStructuredContent(container, content, dictionary, language) {
         if (typeof content === 'string') {
             if (content.length > 0) {
@@ -151,16 +180,29 @@ class StructuredContentGenerator {
         }
     }
 
+    /**
+     * @param {string} tagName
+     * @param {string} className
+     * @returns {HTMLElement}
+     */
     _createElement(tagName, className) {
         const node = this._document.createElement(tagName);
         node.className = className;
         return node;
     }
 
+    /**
+     * @param {string} data
+     * @returns {Text}
+     */
     _createTextNode(data) {
         return this._document.createTextNode(data);
     }
 
+    /**
+     * @param {HTMLElement} element
+     * @param {import('structured-content').Data} data
+     */
     _setElementDataset(element, data) {
         for (let [key, value] of Object.entries(data)) {
             if (key.length > 0) {
@@ -175,6 +217,13 @@ class StructuredContentGenerator {
         }
     }
 
+    /**
+     * @param {HTMLAnchorElement} node
+     * @param {HTMLImageElement} image
+     * @param {HTMLElement} imageBackground
+     * @param {?string} url
+     * @param {boolean} unloaded
+     */
     _setImageData(node, image, imageBackground, url, unloaded) {
         if (url !== null) {
             image.src = url;
@@ -189,6 +238,12 @@ class StructuredContentGenerator {
         }
     }
 
+    /**
+     * @param {import('structured-content').Element} content
+     * @param {string} dictionary
+     * @param {?string} language
+     * @returns {?HTMLElement}
+     */
     _createStructuredContentGenericElement(content, dictionary, language) {
         const {tag} = content;
         switch (tag) {
@@ -222,6 +277,13 @@ class StructuredContentGenerator {
         return null;
     }
 
+    /**
+     * @param {string} tag
+     * @param {import('structured-content').UnstyledElement} content
+     * @param {string} dictionary
+     * @param {?string} language
+     * @returns {HTMLElement}
+     */
     _createStructuredContentTableElement(tag, content, dictionary, language) {
         const container = this._createElement('div', 'gloss-sc-table-container');
         const table = this._createStructuredContentElement(tag, content, dictionary, language, 'table', true, false);
@@ -229,6 +291,16 @@ class StructuredContentGenerator {
         return container;
     }
 
+    /**
+     * @param {string} tag
+     * @param {import('structured-content').StyledElement|import('structured-content').UnstyledElement|import('structured-content').TableElement|import('structured-content').LineBreak} content
+     * @param {string} dictionary
+     * @param {?string} language
+     * @param {'simple'|'table'|'table-cell'} type
+     * @param {boolean} hasChildren
+     * @param {boolean} hasStyle
+     * @returns {HTMLElement}
+     */
     _createStructuredContentElement(tag, content, dictionary, language, type, hasChildren, hasStyle) {
         const node = this._createElement(tag, `gloss-sc-${tag}`);
         const {data, lang} = content;
@@ -240,14 +312,15 @@ class StructuredContentGenerator {
         switch (type) {
             case 'table-cell':
                 {
-                    const {colSpan, rowSpan} = content;
-                    if (typeof colSpan === 'number') { node.colSpan = colSpan; }
-                    if (typeof rowSpan === 'number') { node.rowSpan = rowSpan; }
+                    const cell = /** @type {HTMLTableCellElement} */ (node);
+                    const {colSpan, rowSpan} = /** @type {import('structured-content').TableElement} */ (content);
+                    if (typeof colSpan === 'number') { cell.colSpan = colSpan; }
+                    if (typeof rowSpan === 'number') { cell.rowSpan = rowSpan; }
                 }
                 break;
         }
         if (hasStyle) {
-            const {style} = content;
+            const {style} = /** @type {import('structured-content').StyledElement} */ (content);
             if (typeof style === 'object' && style !== null) {
                 this._setStructuredContentElementStyle(node, style);
             }
@@ -258,6 +331,10 @@ class StructuredContentGenerator {
         return node;
     }
 
+    /**
+     * @param {HTMLElement} node
+     * @param {import('structured-content').StructuredContentStyle} contentStyle
+     */
     _setStructuredContentElementStyle(node, contentStyle) {
         const {style} = node;
         const {
@@ -290,6 +367,12 @@ class StructuredContentGenerator {
         if (typeof listStyleType === 'string') { style.listStyleType = listStyleType; }
     }
 
+    /**
+     * @param {import('structured-content').LinkElement} content
+     * @param {string} dictionary
+     * @param {?string} language
+     * @returns {HTMLAnchorElement}
+     */
     _createLinkElement(content, dictionary, language) {
         let {href} = content;
         const internal = href.startsWith('?');
@@ -297,7 +380,7 @@ class StructuredContentGenerator {
             href = `${location.protocol}//${location.host}/search.html${href.length > 1 ? href : ''}`;
         }
 
-        const node = this._createElement('a', 'gloss-link');
+        const node = /** @type {HTMLAnchorElement} */ (this._createElement('a', 'gloss-link'));
         node.dataset.external = `${!internal}`;
 
         const text = this._createElement('span', 'gloss-link-text');
diff --git a/ext/js/display/search-action-popup-controller.js b/ext/js/display/search-action-popup-controller.js
index e29ac0f405..aab85dd06f 100644
--- a/ext/js/display/search-action-popup-controller.js
+++ b/ext/js/display/search-action-popup-controller.js
@@ -17,10 +17,15 @@
  */
 
 class SearchActionPopupController {
+    /**
+     * @param {SearchPersistentStateController} searchPersistentStateController
+     */
     constructor(searchPersistentStateController) {
+        /** @type {SearchPersistentStateController} */
         this._searchPersistentStateController = searchPersistentStateController;
     }
 
+    /** */
     prepare() {
         const searchParams = new URLSearchParams(location.search);
         if (searchParams.get('action-popup') !== 'true') { return; }
diff --git a/ext/js/display/search-display-controller.js b/ext/js/display/search-display-controller.js
index 25d9d6c206..96b75cc9af 100644
--- a/ext/js/display/search-display-controller.js
+++ b/ext/js/display/search-display-controller.js
@@ -22,34 +22,63 @@
  */
 
 class SearchDisplayController {
+    /**
+     * @param {number|undefined} tabId
+     * @param {number|undefined} frameId
+     * @param {Display} display
+     * @param {DisplayAudio} displayAudio
+     * @param {JapaneseUtil} japaneseUtil
+     * @param {SearchPersistentStateController} searchPersistentStateController
+     */
     constructor(tabId, frameId, display, displayAudio, japaneseUtil, searchPersistentStateController) {
+        /** @type {number|undefined} */
         this._tabId = tabId;
+        /** @type {number|undefined} */
         this._frameId = frameId;
+        /** @type {Display} */
         this._display = display;
+        /** @type {DisplayAudio} */
         this._displayAudio = displayAudio;
+        /** @type {SearchPersistentStateController} */
         this._searchPersistentStateController = searchPersistentStateController;
-        this._searchButton = document.querySelector('#search-button');
-        this._searchBackButton = document.querySelector('#search-back-button');
-        this._queryInput = document.querySelector('#search-textbox');
-        this._introElement = document.querySelector('#intro');
-        this._clipboardMonitorEnableCheckbox = document.querySelector('#clipboard-monitor-enable');
-        this._wanakanaEnableCheckbox = document.querySelector('#wanakana-enable');
+        /** @type {HTMLButtonElement} */
+        this._searchButton = /** @type {HTMLButtonElement} */ (document.querySelector('#search-button'));
+        /** @type {HTMLButtonElement} */
+        this._searchBackButton = /** @type {HTMLButtonElement} */ (document.querySelector('#search-back-button'));
+        /** @type {HTMLTextAreaElement} */
+        this._queryInput = /** @type {HTMLTextAreaElement} */ (document.querySelector('#search-textbox'));
+        /** @type {HTMLElement} */
+        this._introElement = /** @type {HTMLElement} */ (document.querySelector('#intro'));
+        /** @type {HTMLInputElement} */
+        this._clipboardMonitorEnableCheckbox = /** @type {HTMLInputElement} */ (document.querySelector('#clipboard-monitor-enable'));
+        /** @type {HTMLInputElement} */
+        this._wanakanaEnableCheckbox = /** @type {HTMLInputElement} */ (document.querySelector('#wanakana-enable'));
+        /** @type {EventListenerCollection} */
         this._queryInputEvents = new EventListenerCollection();
+        /** @type {boolean} */
         this._queryInputEventsSetup = false;
+        /** @type {boolean} */
         this._wanakanaEnabled = false;
+        /** @type {boolean} */
         this._wanakanaBound = false;
+        /** @type {boolean} */
         this._introVisible = true;
+        /** @type {?number} */
         this._introAnimationTimer = null;
+        /** @type {boolean} */
         this._clipboardMonitorEnabled = false;
+        /** @type {ClipboardMonitor} */
         this._clipboardMonitor = new ClipboardMonitor({
             japaneseUtil,
             clipboardReader: {
                 getText: async () => (await yomichan.api.clipboardGet())
             }
         });
+        /** @type {import('core').MessageHandlerMap} */
         this._messageHandlers = new Map();
     }
 
+    /** */
     async prepare() {
         await this._display.updateOptions();
 
@@ -84,15 +113,22 @@ class SearchDisplayController {
         this._clipboardMonitorEnableCheckbox.addEventListener('change', this._onClipboardMonitorEnableChange.bind(this));
         this._display.hotkeyHandler.on('keydownNonHotkey', this._onKeyDown.bind(this));
 
-        this._onDisplayOptionsUpdated({options: this._display.getOptions()});
+        const displayOptions = this._display.getOptions();
+        if (displayOptions !== null) {
+            this._onDisplayOptionsUpdated({options: displayOptions});
+        }
     }
 
+    /**
+     * @param {import('display').SearchMode} mode
+     */
     setMode(mode) {
-        this._setMode(mode, true);
+        this._searchPersistentStateController.mode = mode;
     }
 
     // Actions
 
+    /** */
     _onActionFocusSearchBox() {
         if (this._queryInput === null) { return; }
         this._queryInput.focus();
@@ -101,22 +137,37 @@ class SearchDisplayController {
 
     // Messages
 
+    /**
+     * @param {{mode: import('display').SearchMode}} details
+     */
     _onMessageSetMode({mode}) {
-        this._searchPersistentStateController.mode = mode;
+        this.setMode(mode);
     }
 
+    /**
+     * @returns {import('display').SearchMode}
+     */
     _onMessageGetMode() {
         return this._searchPersistentStateController.mode;
     }
 
     // Private
 
+    /**
+     * @param {{action: string, params?: import('core').SerializableObject}} message
+     * @param {chrome.runtime.MessageSender} sender
+     * @param {(response?: unknown) => void} callback
+     * @returns {boolean}
+     */
     _onMessage({action, params}, sender, callback) {
         const messageHandler = this._messageHandlers.get(action);
         if (typeof messageHandler === 'undefined') { return false; }
         return invokeMessageHandler(messageHandler, params, callback, sender);
     }
 
+    /**
+     * @param {KeyboardEvent} e
+     */
     _onKeyDown(e) {
         const {activeElement} = document;
         if (
@@ -132,6 +183,7 @@ class SearchDisplayController {
         }
     }
 
+    /** */
     async _onOptionsUpdated() {
         await this._display.updateOptions();
         const query = this._queryInput.value;
@@ -140,15 +192,21 @@ class SearchDisplayController {
         }
     }
 
+    /**
+     * @param {import('display').OptionsUpdatedEvent} details
+     */
     _onDisplayOptionsUpdated({options}) {
         this._clipboardMonitorEnabled = options.clipboard.enableSearchPageMonitor;
         this._updateClipboardMonitorEnabled();
 
-        const enableWanakana = !!this._display.getOptions().general.enableWanakana;
+        const enableWanakana = !!options.general.enableWanakana;
         this._wanakanaEnableCheckbox.checked = enableWanakana;
         this._setWanakanaEnabled(enableWanakana);
     }
 
+    /**
+     * @param {import('display').ContentUpdateStartEvent} details
+     */
     _onContentUpdateStart({type, query}) {
         let animate = false;
         let valid = false;
@@ -182,38 +240,54 @@ class SearchDisplayController {
         this._setIntroVisible(!valid, animate);
     }
 
+    /** */
     _onSearchInput() {
         this._updateSearchHeight(false);
     }
 
+    /**
+     * @param {KeyboardEvent} e
+     */
     _onSearchKeydown(e) {
         if (e.isComposing) { return; }
         const {code} = e;
         if (!((code === 'Enter' || code === 'NumpadEnter') && !e.shiftKey)) { return; }
 
         // Search
+        const element = /** @type {HTMLElement} */ (e.currentTarget);
         e.preventDefault();
         e.stopImmediatePropagation();
-        this._display.blurElement(e.currentTarget);
+        this._display.blurElement(element);
         this._search(true, 'new', true, null);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onSearch(e) {
         e.preventDefault();
         this._search(true, 'new', true, null);
     }
 
+    /** */
     _onSearchBackButtonClick() {
         this._display.history.back();
     }
 
+    /** */
     _onCopy() {
         // ignore copy from search page
-        this._clipboardMonitor.setPreviousText(window.getSelection().toString().trim());
+        const selection = window.getSelection();
+        this._clipboardMonitor.setPreviousText(selection !== null ? selection.toString().trim() : '');
     }
 
+    /**
+     * @param {{text: string, animate?: boolean}} details
+     */
     _onExternalSearchUpdate({text, animate=true}) {
-        const {clipboard: {autoSearchContent, maximumSearchLength}} = this._display.getOptions();
+        const options = this._display.getOptions();
+        if (options === null) { return; }
+        const {clipboard: {autoSearchContent, maximumSearchLength}} = options;
         if (text.length > maximumSearchLength) {
             text = text.substring(0, maximumSearchLength);
         }
@@ -222,27 +296,41 @@ class SearchDisplayController {
         this._search(animate, 'clear', autoSearchContent, ['clipboard']);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onWanakanaEnableChange(e) {
-        const value = e.target.checked;
+        const element = /** @type {HTMLInputElement} */ (e.target);
+        const value = element.checked;
         this._setWanakanaEnabled(value);
-        yomichan.api.modifySettings([{
+        /** @type {import('settings-modifications').ScopedModificationSet} */
+        const modification = {
             action: 'set',
             path: 'general.enableWanakana',
             value,
             scope: 'profile',
             optionsContext: this._display.getOptionsContext()
-        }], 'search');
+        };
+        yomichan.api.modifySettings([modification], 'search');
     }
 
+    /**
+     * @param {Event} e
+     */
     _onClipboardMonitorEnableChange(e) {
-        const enabled = e.target.checked;
+        const element = /** @type {HTMLInputElement} */ (e.target);
+        const enabled = element.checked;
         this._setClipboardMonitorEnabled(enabled);
     }
 
+    /** */
     _onModeChange() {
         this._updateClipboardMonitorEnabled();
     }
 
+    /**
+     * @param {boolean} enabled
+     */
     _setWanakanaEnabled(enabled) {
         if (this._queryInputEventsSetup && this._wanakanaEnabled === enabled) { return; }
 
@@ -267,6 +355,10 @@ class SearchDisplayController {
         this._queryInputEventsSetup = true;
     }
 
+    /**
+     * @param {boolean} visible
+     * @param {boolean} animate
+     */
     _setIntroVisible(visible, animate) {
         if (this._introVisible === visible) {
             return;
@@ -290,6 +382,9 @@ class SearchDisplayController {
         }
     }
 
+    /**
+     * @param {boolean} animate
+     */
     _showIntro(animate) {
         if (animate) {
             const duration = 0.4;
@@ -310,6 +405,9 @@ class SearchDisplayController {
         }
     }
 
+    /**
+     * @param {boolean} animate
+     */
     _hideIntro(animate) {
         if (animate) {
             const duration = 0.4;
@@ -323,6 +421,9 @@ class SearchDisplayController {
         this._introElement.style.height = '0';
     }
 
+    /**
+     * @param {boolean} value
+     */
     async _setClipboardMonitorEnabled(value) {
         let modify = true;
         if (value) {
@@ -335,15 +436,18 @@ class SearchDisplayController {
 
         if (!modify) { return; }
 
-        await yomichan.api.modifySettings([{
+        /** @type {import('settings-modifications').ScopedModificationSet} */
+        const modification = {
             action: 'set',
             path: 'clipboard.enableSearchPageMonitor',
             value,
             scope: 'profile',
             optionsContext: this._display.getOptionsContext()
-        }], 'search');
+        };
+        await yomichan.api.modifySettings([modification], 'search');
     }
 
+    /** */
     _updateClipboardMonitorEnabled() {
         const enabled = this._clipboardMonitorEnabled;
         this._clipboardMonitorEnableCheckbox.checked = enabled;
@@ -354,6 +458,9 @@ class SearchDisplayController {
         }
     }
 
+    /**
+     * @returns {boolean}
+     */
     _canEnableClipboardMonitor() {
         switch (this._searchPersistentStateController.mode) {
             case 'popup':
@@ -364,6 +471,10 @@ class SearchDisplayController {
         }
     }
 
+    /**
+     * @param {string[]} permissions
+     * @returns {Promise<boolean>}
+     */
     _requestPermissions(permissions) {
         return new Promise((resolve) => {
             chrome.permissions.request(
@@ -376,15 +487,23 @@ class SearchDisplayController {
         });
     }
 
+    /**
+     * @param {boolean} animate
+     * @param {import('display').HistoryMode} historyMode
+     * @param {boolean} lookup
+     * @param {?import('settings').OptionsContextFlag[]} flags
+     */
     _search(animate, historyMode, lookup, flags) {
         const query = this._queryInput.value;
         const depth = this._display.depth;
         const url = window.location.href;
         const documentTitle = document.title;
+        /** @type {import('settings').OptionsContext} */
         const optionsContext = {depth, url};
         if (flags !== null) {
             optionsContext.flags = flags;
         }
+        /** @type {import('display').ContentDetails} */
         const details = {
             focus: false,
             historyMode,
@@ -399,7 +518,7 @@ class SearchDisplayController {
                 documentTitle
             },
             content: {
-                dictionaryEntries: null,
+                dictionaryEntries: void 0,
                 animate,
                 contentOrigin: {
                     tabId: this._tabId,
@@ -411,6 +530,9 @@ class SearchDisplayController {
         this._display.setContent(details);
     }
 
+    /**
+     * @param {boolean} shrink
+     */
     _updateSearchHeight(shrink) {
         const node = this._queryInput;
         if (shrink) {
@@ -423,12 +545,19 @@ class SearchDisplayController {
         }
     }
 
+    /**
+     * @param {import('core').MessageHandlerArray} handlers
+     */
     _registerMessageHandlers(handlers) {
         for (const [name, handlerInfo] of handlers) {
             this._messageHandlers.set(name, handlerInfo);
         }
     }
 
+    /**
+     * @param {?Element} element
+     * @returns {boolean}
+     */
     _isElementInput(element) {
         if (element === null) { return false; }
         switch (element.tagName.toLowerCase()) {
@@ -438,7 +567,7 @@ class SearchDisplayController {
             case 'select':
                 return true;
         }
-        if (element.isContentEditable) { return true; }
+        if (element instanceof HTMLElement && element.isContentEditable) { return true; }
         return false;
     }
 }
diff --git a/ext/js/display/search-main.js b/ext/js/display/search-main.js
index 77b9680418..d66037eee7 100644
--- a/ext/js/display/search-main.js
+++ b/ext/js/display/search-main.js
@@ -44,7 +44,9 @@
 
         const {tabId, frameId} = await yomichan.api.frameInformationGet();
 
-        const japaneseUtil = new JapaneseUtil(wanakana);
+        /** @type {import('wanakana')} */
+        const wanakanaLib = wanakana;
+        const japaneseUtil = new JapaneseUtil(wanakanaLib);
 
         const hotkeyHandler = new HotkeyHandler();
         hotkeyHandler.prepare();
diff --git a/ext/js/display/search-persistent-state-controller.js b/ext/js/display/search-persistent-state-controller.js
index 2b651ffa8f..615c8c2284 100644
--- a/ext/js/display/search-persistent-state-controller.js
+++ b/ext/js/display/search-persistent-state-controller.js
@@ -16,12 +16,17 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/**
+ * @augments EventDispatcher<import('display').SearchPersistentStateControllerEventType>
+ */
 class SearchPersistentStateController extends EventDispatcher {
     constructor() {
         super();
+        /** @type {import('display').SearchMode} */
         this._mode = null;
     }
 
+    /** @type {import('display').SearchMode} */
     get mode() {
         return this._mode;
     }
@@ -30,12 +35,14 @@ class SearchPersistentStateController extends EventDispatcher {
         this._setMode(value, true);
     }
 
+    /** */
     prepare() {
         this._updateMode();
     }
 
     // Private
 
+    /** */
     _updateMode() {
         let mode = null;
         try {
@@ -43,9 +50,13 @@ class SearchPersistentStateController extends EventDispatcher {
         } catch (e) {
             // Browsers can throw a SecurityError when cookie blocking is enabled.
         }
-        this._setMode(mode, false);
+        this._setMode(this._normalizeMode(mode), false);
     }
 
+    /**
+     * @param {import('display').SearchMode} mode
+     * @param {boolean} save
+     */
     _setMode(mode, save) {
         if (mode === this._mode) { return; }
         if (save) {
@@ -63,4 +74,18 @@ class SearchPersistentStateController extends EventDispatcher {
         document.documentElement.dataset.searchMode = (mode !== null ? mode : '');
         this.trigger('modeChange', {mode});
     }
+
+    /**
+     * @param {?string} mode
+     * @returns {import('display').SearchMode}
+     */
+    _normalizeMode(mode) {
+        switch (mode) {
+            case 'popup':
+            case 'action-popup':
+                return mode;
+            default:
+                return null;
+        }
+    }
 }
diff --git a/ext/js/dom/document-focus-controller.js b/ext/js/dom/document-focus-controller.js
index 937a7c1333..a66cefad88 100644
--- a/ext/js/dom/document-focus-controller.js
+++ b/ext/js/dom/document-focus-controller.js
@@ -29,7 +29,9 @@ class DocumentFocusController {
      *   should be automatically focused on prepare.
      */
     constructor(autofocusElementSelector=null) {
+        /** @type {?HTMLElement} */
         this._autofocusElement = (autofocusElementSelector !== null ? document.querySelector(autofocusElementSelector) : null);
+        /** @type {?HTMLElement} */
         this._contentScrollFocusElement = document.querySelector('#content-scroll-focus');
     }
 
@@ -46,7 +48,7 @@ class DocumentFocusController {
 
     /**
      * Removes focus from a given element.
-     * @param {Element} element The element to remove focus from.
+     * @param {HTMLElement} element The element to remove focus from.
      */
     blurElement(element) {
         if (document.activeElement !== element) { return; }
@@ -56,10 +58,14 @@ class DocumentFocusController {
 
     // Private
 
+    /** */
     _onWindowFocus() {
         this._updateFocusedElement(false);
     }
 
+    /**
+     * @param {boolean} force
+     */
     _updateFocusedElement(force) {
         const target = this._contentScrollFocusElement;
         if (target === null) { return; }
@@ -73,6 +79,7 @@ class DocumentFocusController {
         ) {
             // Get selection
             const selection = window.getSelection();
+            if (selection === null) { return; }
             const selectionRanges1 = this._getSelectionRanges(selection);
 
             // Note: This function will cause any selected text to be deselected on Firefox.
@@ -86,6 +93,10 @@ class DocumentFocusController {
         }
     }
 
+    /**
+     * @param {Selection} selection
+     * @returns {Range[]}
+     */
     _getSelectionRanges(selection) {
         const ranges = [];
         for (let i = 0, ii = selection.rangeCount; i < ii; ++i) {
@@ -94,6 +105,10 @@ class DocumentFocusController {
         return ranges;
     }
 
+    /**
+     * @param {Selection} selection
+     * @param {Range[]} ranges
+     */
     _setSelectionRanges(selection, ranges) {
         selection.removeAllRanges();
         for (const range of ranges) {
@@ -101,6 +116,11 @@ class DocumentFocusController {
         }
     }
 
+    /**
+     * @param {Range[]} ranges1
+     * @param {Range[]} ranges2
+     * @returns {boolean}
+     */
     _areRangesSame(ranges1, ranges2) {
         const ii = ranges1.length;
         if (ii !== ranges2.length) {
diff --git a/ext/js/dom/document-util.js b/ext/js/dom/document-util.js
index 9bca951b7f..6bf99a3780 100644
--- a/ext/js/dom/document-util.js
+++ b/ext/js/dom/document-util.js
@@ -26,30 +26,12 @@
  * This class contains utility functions related to the HTML document.
  */
 class DocumentUtil {
-    /**
-     * Options to configure how element detection is performed.
-     * @typedef {object} GetRangeFromPointOptions
-     * @property {boolean} deepContentScan Whether or deep content scanning should be performed. When deep content scanning is enabled,
-     *   some transparent overlay elements will be ignored when looking for the element at the input position.
-     * @property {boolean} normalizeCssZoom Whether or not zoom coordinates should be normalized.
-     */
-
-    /**
-     * Scans the document for text or elements with text information at the given coordinate.
-     * Coordinates are provided in [client space](https://developer.mozilla.org/en-US/docs/Web/CSS/CSSOM_View/Coordinate_systems).
-     * @callback GetRangeFromPointHandler
-     * @param {number} x The x coordinate to search at.
-     * @param {number} y The y coordinate to search at.
-     * @param {GetRangeFromPointOptions} options Options to configure how element detection is performed.
-     * @returns {?TextSourceRange|TextSourceElement} A range for the hovered text or element, or `null` if no applicable content was found.
-     */
-
     /**
      * Scans the document for text or elements with text information at the given coordinate.
      * Coordinates are provided in [client space](https://developer.mozilla.org/en-US/docs/Web/CSS/CSSOM_View/Coordinate_systems).
      * @param {number} x The x coordinate to search at.
      * @param {number} y The y coordinate to search at.
-     * @param {GetRangeFromPointOptions} options Options to configure how element detection is performed.
+     * @param {import('document-util').GetRangeFromPointOptions} options Options to configure how element detection is performed.
      * @returns {?TextSourceRange|TextSourceElement} A range for the hovered text or element, or `null` if no applicable content was found.
      */
     static getRangeFromPoint(x, y, options) {
@@ -61,8 +43,11 @@ class DocumentUtil {
         const {deepContentScan, normalizeCssZoom} = options;
 
         const elements = this._getElementsFromPoint(x, y, deepContentScan);
+        /** @type {?HTMLDivElement} */
         let imposter = null;
+        /** @type {?HTMLDivElement} */
         let imposterContainer = null;
+        /** @type {?Element} */
         let imposterSourceElement = null;
         if (elements.length > 0) {
             const element = elements[0];
@@ -72,14 +57,14 @@ class DocumentUtil {
                 case 'SELECT':
                     return TextSourceElement.create(element);
                 case 'INPUT':
-                    if (element.type === 'text') {
+                    if (/** @type {HTMLInputElement} */ (element).type === 'text') {
                         imposterSourceElement = element;
-                        [imposter, imposterContainer] = this._createImposter(element, false);
+                        [imposter, imposterContainer] = this._createImposter(/** @type {HTMLInputElement} */ (element), false);
                     }
                     break;
                 case 'TEXTAREA':
                     imposterSourceElement = element;
-                    [imposter, imposterContainer] = this._createImposter(element, true);
+                    [imposter, imposterContainer] = this._createImposter(/** @type {HTMLTextAreaElement} */ (element), true);
                     break;
             }
         }
@@ -87,14 +72,17 @@ class DocumentUtil {
         const range = this._caretRangeFromPointExt(x, y, deepContentScan ? elements : [], normalizeCssZoom);
         if (range !== null) {
             if (imposter !== null) {
-                this._setImposterStyle(imposterContainer.style, 'z-index', '-2147483646');
+                this._setImposterStyle(/** @type {HTMLDivElement} */ (imposterContainer).style, 'z-index', '-2147483646');
                 this._setImposterStyle(imposter.style, 'pointer-events', 'none');
-                return TextSourceRange.createFromImposter(range, imposterContainer, imposterSourceElement);
+                return TextSourceRange.createFromImposter(range, /** @type {HTMLDivElement} */ (imposterContainer), /** @type {HTMLElement} */ (imposterSourceElement));
             }
             return TextSourceRange.create(range);
         } else {
             if (imposterContainer !== null) {
-                imposterContainer.parentNode.removeChild(imposterContainer);
+                const {parentNode} = imposterContainer;
+                if (parentNode !== null) {
+                    parentNode.removeChild(imposterContainer);
+                }
             }
             return null;
         }
@@ -102,7 +90,7 @@ class DocumentUtil {
 
     /**
      * Registers a custom handler for scanning for text or elements at the input position.
-     * @param {GetRangeFromPointHandler} handler The handler callback which will be invoked when calling `getRangeFromPoint`.
+     * @param {import('document-util').GetRangeFromPointHandler} handler The handler callback which will be invoked when calling `getRangeFromPoint`.
      */
     static registerGetRangeFromPointHandler(handler) {
         this._getRangeFromPointHandlers.push(handler);
@@ -130,7 +118,7 @@ class DocumentUtil {
      *   ```js
      *   new Map([ [character: string, [otherCharacter: string, includeCharacterAtEnd: boolean]], ... ])
      *   ```
-     * @returns {{sentence: string, offset: number}} The sentence and the offset to the original source.
+     * @returns {{text: string, offset: number}} The sentence and the offset to the original source.
      */
     static extractSentence(source, layoutAwareScan, extent, terminateAtNewlines, terminatorMap, forwardQuoteMap, backwardQuoteMap) {
         // Scan text
@@ -219,11 +207,12 @@ class DocumentUtil {
     /**
      * Computes the scaling adjustment that is necessary for client space coordinates based on the
      * CSS zoom level.
-     * @param {Node} node A node in the document.
+     * @param {?Node} node A node in the document.
      * @returns {number} The scaling factor.
      */
     static computeZoomScale(node) {
         if (this._cssZoomSupported === null) {
+            // @ts-ignore - zoom is a non-standard property that exists in Chromium-based browsers
             this._cssZoomSupported = (typeof document.createElement('div').style.zoom === 'string');
         }
         if (!this._cssZoomSupported) { return 1; }
@@ -238,7 +227,7 @@ class DocumentUtil {
         for (; node !== null && node !== documentElement; node = node.parentNode) {
             const {nodeType} = node;
             if (nodeType === DOCUMENT_FRAGMENT_NODE) {
-                const {host} = node;
+                const {host} = /** @type {ShadowRoot} */ (node);
                 if (typeof host !== 'undefined') {
                     node = host;
                 }
@@ -246,9 +235,9 @@ class DocumentUtil {
             } else if (nodeType !== ELEMENT_NODE) {
                 continue;
             }
-            let {zoom} = getComputedStyle(node);
-            if (typeof zoom !== 'string') { continue; }
-            zoom = Number.parseFloat(zoom);
+            const zoomString = getComputedStyle(/** @type {HTMLElement} */ (node)).getPropertyValue('zoom');
+            if (typeof zoomString !== 'string' || zoomString.length === 0) { continue; }
+            const zoom = Number.parseFloat(zoomString);
             if (!Number.isFinite(zoom) || zoom === 0) { continue; }
             scale *= zoom;
         }
@@ -268,13 +257,13 @@ class DocumentUtil {
 
     /**
      * Converts multiple rects based on the CSS zoom scaling for a given node.
-     * @param {DOMRect[]} rects The rects to convert.
+     * @param {DOMRect[]|DOMRectList} rects The rects to convert.
      * @param {Node} node The node to compute the zoom from.
      * @returns {DOMRect[]} The updated rects, or the same rects array if no change is needed.
      */
     static convertMultipleRectZoomCoordinates(rects, node) {
         const scale = this.computeZoomScale(node);
-        if (scale === 1) { return rects; }
+        if (scale === 1) { return [...rects]; }
         const results = [];
         for (const rect of rects) {
             results.push(new DOMRect(rect.left * scale, rect.top * scale, rect.width * scale, rect.height * scale));
@@ -300,7 +289,7 @@ class DocumentUtil {
      * Checks whether a given point is contained within any rect in a list.
      * @param {number} x The horizontal coordinate.
      * @param {number} y The vertical coordinate.
-     * @param {DOMRect[]} rects The rect to check.
+     * @param {DOMRect[]|DOMRectList} rects The rect to check.
      * @returns {boolean} `true` if the point is inside any of the rects, `false` otherwise.
      */
     static isPointInAnyRect(x, y, rects) {
@@ -332,9 +321,10 @@ class DocumentUtil {
     /**
      * Gets an array of the active modifier keys.
      * @param {KeyboardEvent|MouseEvent|TouchEvent} event The event to check.
-     * @returns {string[]} An array of modifiers.
+     * @returns {import('input').ModifierKey[]} An array of modifiers.
      */
     static getActiveModifiers(event) {
+        /** @type {import('input').ModifierKey[]} */
         const modifiers = [];
         if (event.altKey) { modifiers.push('alt'); }
         if (event.ctrlKey) { modifiers.push('ctrl'); }
@@ -346,20 +336,24 @@ class DocumentUtil {
     /**
      * Gets an array of the active modifier keys and buttons.
      * @param {KeyboardEvent|MouseEvent|TouchEvent} event The event to check.
-     * @returns {string[]} An array of modifiers and buttons.
+     * @returns {import('input').Modifier[]} An array of modifiers and buttons.
      */
     static getActiveModifiersAndButtons(event) {
+        /** @type {import('input').Modifier[]} */
         const modifiers = this.getActiveModifiers(event);
-        this._getActiveButtons(event, modifiers);
+        if (event instanceof MouseEvent) {
+            this._getActiveButtons(event, modifiers);
+        }
         return modifiers;
     }
 
     /**
      * Gets an array of the active buttons.
-     * @param {KeyboardEvent|MouseEvent|TouchEvent} event The event to check.
-     * @returns {string[]} An array of modifiers and buttons.
+     * @param {MouseEvent} event The event to check.
+     * @returns {import('input').ModifierMouseButton[]} An array of modifiers and buttons.
      */
     static getActiveButtons(event) {
+        /** @type {import('input').ModifierMouseButton[]} */
         const buttons = [];
         this._getActiveButtons(event, buttons);
         return buttons;
@@ -367,7 +361,7 @@ class DocumentUtil {
 
     /**
      * Adds a fullscreen change event listener. This function handles all of the browser-specific variants.
-     * @param {Function} onFullscreenChanged The event callback.
+     * @param {EventListener} onFullscreenChanged The event callback.
      * @param {?EventListenerCollection} eventListenerCollection An optional `EventListenerCollection` to add the registration to.
      */
     static addFullscreenChangeEventListener(onFullscreenChanged, eventListenerCollection=null) {
@@ -395,8 +389,11 @@ class DocumentUtil {
     static getFullscreenElement() {
         return (
             document.fullscreenElement ||
+            // @ts-ignore - vendor prefix
             document.msFullscreenElement ||
+            // @ts-ignore - vendor prefix
             document.mozFullScreenElement ||
+            // @ts-ignore - vendor prefix
             document.webkitFullscreenElement ||
             null
         );
@@ -410,7 +407,7 @@ class DocumentUtil {
     static getNodesInRange(range) {
         const end = range.endContainer;
         const nodes = [];
-        for (let node = range.startContainer; node !== null; node = this.getNextNode(node)) {
+        for (let node = /** @type {?Node} */ (range.startContainer); node !== null; node = this.getNextNode(node)) {
             nodes.push(node);
             if (node === end) { break; }
         }
@@ -423,7 +420,7 @@ class DocumentUtil {
      * @returns {?Node} The next node, or `null` if there is no next node.
      */
     static getNextNode(node) {
-        let next = node.firstChild;
+        let next = /** @type {?Node} */ (node.firstChild);
         if (next === null) {
             while (true) {
                 next = node.nextSibling;
@@ -446,10 +443,14 @@ class DocumentUtil {
      */
     static anyNodeMatchesSelector(nodes, selector) {
         const ELEMENT_NODE = Node.ELEMENT_NODE;
-        for (let node of nodes) {
-            for (; node !== null; node = node.parentNode) {
-                if (node.nodeType !== ELEMENT_NODE) { continue; }
-                if (node.matches(selector)) { return true; }
+        // This is a rather ugly way of getting the "node" variable to be a nullable
+        for (let node of /** @type {(?Node)[]} */ (nodes)) {
+            while (node !== null) {
+                if (node.nodeType !== ELEMENT_NODE) {
+                    node = node.parentNode;
+                    continue;
+                }
+                if (/** @type {HTMLElement} */ (node).matches(selector)) { return true; }
                 break;
             }
         }
@@ -464,10 +465,11 @@ class DocumentUtil {
      */
     static everyNodeMatchesSelector(nodes, selector) {
         const ELEMENT_NODE = Node.ELEMENT_NODE;
-        for (let node of nodes) {
+        // This is a rather ugly way of getting the "node" variable to be a nullable
+        for (let node of /** @type {(?Node)[]} */ (nodes)) {
             while (true) {
                 if (node === null) { return false; }
-                if (node.nodeType === ELEMENT_NODE && node.matches(selector)) { break; }
+                if (node.nodeType === ELEMENT_NODE && /** @type {HTMLElement} */ (node).matches(selector)) { break; }
                 node = node.parentNode;
             }
         }
@@ -498,7 +500,7 @@ class DocumentUtil {
             case 'SELECT':
                 return true;
             default:
-                return element.isContentEditable;
+                return element instanceof HTMLElement && element.isContentEditable;
         }
     }
 
@@ -507,7 +509,7 @@ class DocumentUtil {
      * @param {DOMRect[]} rects The DOMRects to offset.
      * @param {number} x The horizontal offset amount.
      * @param {number} y The vertical offset amount.
-     * @returns {DOMRect} The DOMRects with the offset applied.
+     * @returns {DOMRect[]} The DOMRects with the offset applied.
      */
     static offsetDOMRects(rects, x, y) {
         const results = [];
@@ -520,8 +522,8 @@ class DocumentUtil {
     /**
      * Gets the parent writing mode of an element.
      * See: https://developer.mozilla.org/en-US/docs/Web/CSS/writing-mode.
-     * @param {Element} element The HTML element to check.
-     * @returns {string} The writing mode.
+     * @param {?Element} element The HTML element to check.
+     * @returns {import('document-util').NormalizedWritingMode} The writing mode.
      */
     static getElementWritingMode(element) {
         if (element !== null) {
@@ -537,52 +539,95 @@ class DocumentUtil {
      * Normalizes a CSS writing mode value by converting non-standard and deprecated values
      * into their corresponding standard vaules.
      * @param {string} writingMode The writing mode to normalize.
-     * @returns {string} The normalized writing mode.
+     * @returns {import('document-util').NormalizedWritingMode} The normalized writing mode.
      */
     static normalizeWritingMode(writingMode) {
         switch (writingMode) {
-            case 'lr':
-            case 'lr-tb':
-            case 'rl':
-                return 'horizontal-tb';
             case 'tb':
                 return 'vertical-lr';
             case 'tb-rl':
                 return 'vertical-rl';
-            default:
+            case 'horizontal-tb':
+            case 'vertical-rl':
+            case 'vertical-lr':
+            case 'sideways-rl':
+            case 'sideways-lr':
                 return writingMode;
+            default: // 'lr', 'lr-tb', 'rl'
+                return 'horizontal-tb';
         }
     }
 
     /**
      * Converts a value from an element to a number.
-     * @param {string} value A string representation of a number.
-     * @param {object} constraints An object which might contain `min`, `max`, and `step` fields which are used to constrain the value.
+     * @param {string} valueString A string representation of a number.
+     * @param {import('document-util').ToNumberConstraints} constraints An object which might contain `min`, `max`, and `step` fields which are used to constrain the value.
      * @returns {number} The parsed and constrained number.
      */
-    static convertElementValueToNumber(value, constraints) {
-        value = parseFloat(value);
+    static convertElementValueToNumber(valueString, constraints) {
+        let value = Number.parseFloat(valueString);
         if (!Number.isFinite(value)) { value = 0; }
 
-        let {min, max, step} = constraints;
-        min = this._convertToNumberOrNull(min);
-        max = this._convertToNumberOrNull(max);
-        step = this._convertToNumberOrNull(step);
+        const min = this._convertToNumberOrNull(constraints.min);
+        const max = this._convertToNumberOrNull(constraints.max);
+        const step = this._convertToNumberOrNull(constraints.step);
         if (typeof min === 'number') { value = Math.max(value, min); }
         if (typeof max === 'number') { value = Math.min(value, max); }
         if (typeof step === 'number' && step !== 0) { value = Math.round(value / step) * step; }
         return value;
     }
 
+    /**
+     * @param {string} value
+     * @returns {?import('input').Modifier}
+     */
+    static normalizeModifier(value) {
+        switch (value) {
+            case 'alt':
+            case 'ctrl':
+            case 'meta':
+            case 'shift':
+            case 'mouse0':
+            case 'mouse1':
+            case 'mouse2':
+            case 'mouse3':
+            case 'mouse4':
+            case 'mouse5':
+                return value;
+            default:
+                return null;
+        }
+    }
+
+    /**
+     * @param {string} value
+     * @returns {?import('input').ModifierKey}
+     */
+    static normalizeModifierKey(value) {
+        switch (value) {
+            case 'alt':
+            case 'ctrl':
+            case 'meta':
+            case 'shift':
+                return value;
+            default:
+                return null;
+        }
+    }
+
     // Private
 
+    /**
+     * @param {MouseEvent} event The event to check.
+     * @param {import('input').ModifierMouseButton[]|import('input').Modifier[]} array
+     */
     static _getActiveButtons(event, array) {
         let {buttons} = event;
         if (typeof buttons === 'number' && buttons > 0) {
             for (let i = 0; i < 6; ++i) {
                 const buttonFlag = (1 << i);
                 if ((buttons & buttonFlag) !== 0) {
-                    array.push(`mouse${i}`);
+                    array.push(/** @type {import('input').ModifierMouseButton} */ (`mouse${i}`));
                     buttons &= ~buttonFlag;
                     if (buttons === 0) { break; }
                 }
@@ -590,10 +635,20 @@ class DocumentUtil {
         }
     }
 
+    /**
+     * @param {CSSStyleDeclaration} style
+     * @param {string} propertyName
+     * @param {string} value
+     */
     static _setImposterStyle(style, propertyName, value) {
         style.setProperty(propertyName, value, 'important');
     }
 
+    /**
+     * @param {HTMLInputElement|HTMLTextAreaElement} element
+     * @param {boolean} isTextarea
+     * @returns {[imposter: ?HTMLDivElement, container: ?HTMLDivElement]}
+     */
     static _createImposter(element, isTextarea) {
         const body = document.body;
         if (body === null) { return [null, null]; }
@@ -670,6 +725,12 @@ class DocumentUtil {
         return [imposter, container];
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {boolean} all
+     * @returns {Element[]}
+     */
     static _getElementsFromPoint(x, y, all) {
         if (all) {
             // document.elementsFromPoint can return duplicates which must be removed.
@@ -681,6 +742,13 @@ class DocumentUtil {
         return e !== null ? [e] : [];
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {Range} range
+     * @param {boolean} normalizeCssZoom
+     * @returns {boolean}
+     */
     static _isPointInRange(x, y, range, normalizeCssZoom) {
         // Require a text node to start
         const {startContainer} = range;
@@ -723,16 +791,26 @@ class DocumentUtil {
         return false;
     }
 
+    /**
+     * @param {string} string
+     * @returns {boolean}
+     */
     static _isWhitespace(string) {
         return string.trim().length === 0;
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @returns {?Range}
+     */
     static _caretRangeFromPoint(x, y) {
         if (typeof document.caretRangeFromPoint === 'function') {
             // Chrome, Edge
             return document.caretRangeFromPoint(x, y);
         }
 
+        // @ts-ignore - caretPositionFromPoint is non-standard
         if (typeof document.caretPositionFromPoint === 'function') {
             // Firefox
             return this._caretPositionFromPoint(x, y);
@@ -742,8 +820,14 @@ class DocumentUtil {
         return null;
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @returns {?Range}
+     */
     static _caretPositionFromPoint(x, y) {
-        const position = document.caretPositionFromPoint(x, y);
+        // @ts-ignore - caretPositionFromPoint is non-standard
+        const position = /** @type {(x: number, y: number) => ?{offsetNode: Node, offset: number}} */ (document.caretPositionFromPoint)(x, y);
         if (position === null) {
             return null;
         }
@@ -761,8 +845,8 @@ class DocumentUtil {
             case Node.ELEMENT_NODE:
                 // Elements with user-select: all will return the element
                 // instead of a text point inside the element.
-                if (this._isElementUserSelectAll(node)) {
-                    return this._caretPositionFromPointNormalizeStyles(x, y, node);
+                if (this._isElementUserSelectAll(/** @type {Element} */ (node))) {
+                    return this._caretPositionFromPointNormalizeStyles(x, y, /** @type {Element} */ (node));
                 }
                 break;
         }
@@ -779,14 +863,23 @@ class DocumentUtil {
         }
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {Element} nextElement
+     * @returns {?Range}
+     */
     static _caretPositionFromPointNormalizeStyles(x, y, nextElement) {
         const previousStyles = new Map();
         try {
             while (true) {
-                this._recordPreviousStyle(previousStyles, nextElement);
-                nextElement.style.setProperty('user-select', 'text', 'important');
+                if (nextElement instanceof HTMLElement) {
+                    this._recordPreviousStyle(previousStyles, nextElement);
+                    nextElement.style.setProperty('user-select', 'text', 'important');
+                }
 
-                const position = document.caretPositionFromPoint(x, y);
+                // @ts-ignore - caretPositionFromPoint is non-standard
+                const position = /** @type {(x: number, y: number) => ?{offsetNode: Node, offset: number}} */ (document.caretPositionFromPoint)(x, y);
                 if (position === null) {
                     return null;
                 }
@@ -804,12 +897,12 @@ class DocumentUtil {
                     case Node.ELEMENT_NODE:
                         // Elements with user-select: all will return the element
                         // instead of a text point inside the element.
-                        if (this._isElementUserSelectAll(node)) {
+                        if (this._isElementUserSelectAll(/** @type {Element} */ (node))) {
                             if (previousStyles.has(node)) {
                                 // Recursive
                                 return null;
                             }
-                            nextElement = node;
+                            nextElement = /** @type {Element} */ (node);
                             continue;
                         }
                         break;
@@ -831,6 +924,13 @@ class DocumentUtil {
         }
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {Element[]} elements
+     * @param {boolean} normalizeCssZoom
+     * @returns {?Range}
+     */
     static _caretRangeFromPointExt(x, y, elements, normalizeCssZoom) {
         let previousStyles = null;
         try {
@@ -863,6 +963,12 @@ class DocumentUtil {
         }
     }
 
+    /**
+     * @param {Element[]} elements
+     * @param {number} i
+     * @param {Map<Element, ?string>} previousStyles
+     * @returns {number}
+     */
     static _disableTransparentElement(elements, i, previousStyles) {
         while (true) {
             if (i >= elements.length) {
@@ -871,19 +977,28 @@ class DocumentUtil {
 
             const element = elements[i++];
             if (this._isElementTransparent(element)) {
-                this._recordPreviousStyle(previousStyles, element);
-                element.style.setProperty('pointer-events', 'none', 'important');
+                if (element instanceof HTMLElement) {
+                    this._recordPreviousStyle(previousStyles, element);
+                    element.style.setProperty('pointer-events', 'none', 'important');
+                }
                 return i;
             }
         }
     }
 
+    /**
+     * @param {Map<Element, ?string>} previousStyles
+     * @param {Element} element
+     */
     static _recordPreviousStyle(previousStyles, element) {
         if (previousStyles.has(element)) { return; }
         const style = element.hasAttribute('style') ? element.getAttribute('style') : null;
         previousStyles.set(element, style);
     }
 
+    /**
+     * @param {Map<Element, ?string>} previousStyles
+     */
     static _revertStyles(previousStyles) {
         for (const [element, style] of previousStyles.entries()) {
             if (style === null) {
@@ -894,6 +1009,10 @@ class DocumentUtil {
         }
     }
 
+    /**
+     * @param {Element} element
+     * @returns {boolean}
+     */
     static _isElementTransparent(element) {
         if (
             element === document.body ||
@@ -909,14 +1028,26 @@ class DocumentUtil {
         );
     }
 
+    /**
+     * @param {string} cssColor
+     * @returns {boolean}
+     */
     static _isColorTransparent(cssColor) {
         return this._transparentColorPattern.test(cssColor);
     }
 
+    /**
+     * @param {Element} element
+     * @returns {boolean}
+     */
     static _isElementUserSelectAll(element) {
         return getComputedStyle(element).userSelect === 'all';
     }
 
+    /**
+     * @param {string|number|undefined} value
+     * @returns {?number}
+     */
     static _convertToNumberOrNull(value) {
         if (typeof value !== 'number') {
             if (typeof value !== 'string' || value.length === 0) {
@@ -927,9 +1058,12 @@ class DocumentUtil {
         return !Number.isNaN(value) ? value : null;
     }
 }
+/** @type {RegExp} */
 // eslint-disable-next-line no-underscore-dangle
 DocumentUtil._transparentColorPattern = /rgba\s*\([^)]*,\s*0(?:\.0+)?\s*\)/;
+/** @type {?boolean} */
 // eslint-disable-next-line no-underscore-dangle
 DocumentUtil._cssZoomSupported = null;
+/** @type {import('document-util').GetRangeFromPointHandler[]} */
 // eslint-disable-next-line no-underscore-dangle
 DocumentUtil._getRangeFromPointHandlers = [];
diff --git a/ext/js/dom/dom-data-binder.js b/ext/js/dom/dom-data-binder.js
index fca5cd9f4e..555955e0a5 100644
--- a/ext/js/dom/dom-data-binder.js
+++ b/ext/js/dom/dom-data-binder.js
@@ -22,42 +22,66 @@
  * TaskAccumulator
  */
 
+/**
+ * @template [T=unknown]
+ */
 class DOMDataBinder {
+    /**
+     * @param {import('dom-data-binder').ConstructorDetails<T>} details
+     */
     constructor({selector, createElementMetadata, compareElementMetadata, getValues, setValues, onError=null}) {
+        /** @type {string} */
         this._selector = selector;
+        /** @type {import('dom-data-binder').CreateElementMetadataCallback<T>} */
         this._createElementMetadata = createElementMetadata;
+        /** @type {import('dom-data-binder').CompareElementMetadataCallback<T>} */
         this._compareElementMetadata = compareElementMetadata;
+        /** @type {import('dom-data-binder').GetValuesCallback<T>} */
         this._getValues = getValues;
+        /** @type {import('dom-data-binder').SetValuesCallback<T>} */
         this._setValues = setValues;
+        /** @type {?import('dom-data-binder').OnErrorCallback<T>} */
         this._onError = onError;
+        /** @type {TaskAccumulator<import('dom-data-binder').ElementObserver<T>, import('dom-data-binder').UpdateTaskValue>} */
         this._updateTasks = new TaskAccumulator(this._onBulkUpdate.bind(this));
+        /** @type {TaskAccumulator<import('dom-data-binder').ElementObserver<T>, import('dom-data-binder').AssignTaskValue>} */
         this._assignTasks = new TaskAccumulator(this._onBulkAssign.bind(this));
-        this._selectorObserver = new SelectorObserver({
+        /** @type {SelectorObserver<import('dom-data-binder').ElementObserver<T>>} */
+        this._selectorObserver = /** @type {SelectorObserver<import('dom-data-binder').ElementObserver<T>>} */ (new SelectorObserver({
             selector,
             ignoreSelector: null,
             onAdded: this._createObserver.bind(this),
             onRemoved: this._removeObserver.bind(this),
             onChildrenUpdated: this._onObserverChildrenUpdated.bind(this),
             isStale: this._isObserverStale.bind(this)
-        });
+        }));
     }
 
+    /**
+     * @param {Element} element
+     */
     observe(element) {
         this._selectorObserver.observe(element, true);
     }
 
+    /** */
     disconnect() {
         this._selectorObserver.disconnect();
     }
 
+    /** */
     async refresh() {
         await this._updateTasks.enqueue(null, {all: true});
     }
 
     // Private
 
+    /**
+     * @param {import('dom-data-binder').UpdateTask<T>[]} tasks
+     */
     async _onBulkUpdate(tasks) {
         let all = false;
+        /** @type {import('dom-data-binder').ApplyTarget<T>[]} */
         const targets = [];
         for (const [observer, task] of tasks) {
             if (observer === null) {
@@ -84,17 +108,29 @@ class DOMDataBinder {
         this._applyValues(targets, responses, true);
     }
 
+    /**
+     * @param {import('dom-data-binder').AssignTask<T>[]} tasks
+     */
     async _onBulkAssign(tasks) {
-        const targets = tasks;
-        const args = targets.map(([observer, task]) => ({
-            element: observer.element,
-            metadata: observer.metadata,
-            value: task.data.value
-        }));
+        /** @type {import('dom-data-binder').ApplyTarget<T>[]} */
+        const targets = [];
+        const args = [];
+        for (const [observer, task] of tasks) {
+            if (observer === null) { continue; }
+            args.push({
+                element: observer.element,
+                metadata: observer.metadata,
+                value: task.data.value
+            });
+            targets.push([observer, task]);
+        }
         const responses = await this._setValues(args);
         this._applyValues(targets, responses, false);
     }
 
+    /**
+     * @param {import('dom-data-binder').ElementObserver<T>} observer
+     */
     _onElementChange(observer) {
         const value = this._getElementValue(observer.element);
         observer.value = value;
@@ -102,9 +138,12 @@ class DOMDataBinder {
         this._assignTasks.enqueue(observer, {value});
     }
 
+    /**
+     * @param {import('dom-data-binder').ApplyTarget<T>[]} targets
+     * @param {import('dom-data-binder').TaskResult[]} response
+     * @param {boolean} ignoreStale
+     */
     _applyValues(targets, response, ignoreStale) {
-        if (!Array.isArray(response)) { return; }
-
         for (let i = 0, ii = targets.length; i < ii; ++i) {
             const [observer, task] = targets[i];
             const {error, result} = response[i];
@@ -125,8 +164,14 @@ class DOMDataBinder {
         }
     }
 
+    /**
+     * @param {Element} element
+     * @returns {import('dom-data-binder').ElementObserver<T>|undefined}
+     */
     _createObserver(element) {
         const metadata = this._createElementMetadata(element);
+        if (typeof metadata === 'undefined') { return void 0; }
+        /** @type {import('dom-data-binder').ElementObserver<T>} */
         const observer = {
             element,
             type: this._getNormalizedElementType(element),
@@ -139,76 +184,121 @@ class DOMDataBinder {
 
         element.addEventListener('change', observer.onChange, false);
 
-        this._updateTasks.enqueue(observer);
+        this._updateTasks.enqueue(observer, {all: false});
 
         return observer;
     }
 
+    /**
+     * @param {Element} element
+     * @param {import('dom-data-binder').ElementObserver<T>} observer
+     */
     _removeObserver(element, observer) {
+        if (observer.onChange === null) { return; }
         element.removeEventListener('change', observer.onChange, false);
         observer.onChange = null;
     }
 
+    /**
+     * @param {Element} element
+     * @param {import('dom-data-binder').ElementObserver<T>} observer
+     */
     _onObserverChildrenUpdated(element, observer) {
         if (observer.hasValue) {
             this._setElementValue(element, observer.value);
         }
     }
 
+    /**
+     * @param {Element} element
+     * @param {import('dom-data-binder').ElementObserver<T>} observer
+     * @returns {boolean}
+     */
     _isObserverStale(element, observer) {
         const {type, metadata} = observer;
-        return !(
-            type === this._getNormalizedElementType(element) &&
-            this._compareElementMetadata(metadata, this._createElementMetadata(element))
-        );
+        if (type !== this._getNormalizedElementType(element)) { return false; }
+        const newMetadata = this._createElementMetadata(element);
+        return typeof newMetadata === 'undefined' || !this._compareElementMetadata(metadata, newMetadata);
     }
 
+    /**
+     * @param {Element} element
+     * @param {unknown} value
+     */
     _setElementValue(element, value) {
         switch (this._getNormalizedElementType(element)) {
             case 'checkbox':
-                element.checked = value;
+                /** @type {HTMLInputElement} */ (element).checked = typeof value === 'boolean' && value;
                 break;
             case 'text':
             case 'number':
             case 'textarea':
             case 'select':
-                element.value = value;
+                /** @type {HTMLInputElement|HTMLTextAreaElement|HTMLSelectElement} */ (element).value = typeof value === 'string' ? value : `${value}`;
                 break;
         }
 
-        const event = new CustomEvent('settingChanged', {detail: {value}});
+        /** @type {number|string|boolean} */
+        let safeValue;
+        switch (typeof value) {
+            case 'number':
+            case 'string':
+            case 'boolean':
+                safeValue = value;
+                break;
+            default:
+                safeValue = `${value}`;
+                break;
+        }
+        /** @type {import('dom-data-binder').SettingChangedEvent} */
+        const event = new CustomEvent('settingChanged', {detail: {value: safeValue}});
         element.dispatchEvent(event);
     }
 
+    /**
+     * @param {Element} element
+     * @returns {boolean|string|number|null}
+     */
     _getElementValue(element) {
         switch (this._getNormalizedElementType(element)) {
             case 'checkbox':
-                return !!element.checked;
+                return !!(/** @type {HTMLInputElement} */ (element).checked);
             case 'text':
-                return `${element.value}`;
+                return `${/** @type {HTMLInputElement} */ (element).value}`;
             case 'number':
-                return DocumentUtil.convertElementValueToNumber(element.value, element);
+                return DocumentUtil.convertElementValueToNumber(/** @type {HTMLInputElement} */ (element).value, /** @type {HTMLInputElement} */ (element));
             case 'textarea':
+                return /** @type {HTMLTextAreaElement} */ (element).value;
             case 'select':
-                return element.value;
+                return /** @type {HTMLSelectElement} */ (element).value;
         }
         return null;
     }
 
+    /**
+     * @param {Element} element
+     * @returns {import('dom-data-binder').NormalizedElementType}
+     */
     _getNormalizedElementType(element) {
         switch (element.nodeName.toUpperCase()) {
             case 'INPUT':
             {
-                let {type} = element;
-                if (type === 'password') { type = 'text'; }
-                return type;
+                const {type} = /** @type {HTMLInputElement} */ (element);
+                switch (type) {
+                    case 'text':
+                    case 'password':
+                        return 'text';
+                    case 'number':
+                    case 'checkbox':
+                        return type;
+                }
+                break;
             }
             case 'TEXTAREA':
                 return 'textarea';
             case 'SELECT':
                 return 'select';
-            default:
-                return null;
         }
+        return null;
     }
 }
diff --git a/ext/js/dom/dom-text-scanner.js b/ext/js/dom/dom-text-scanner.js
index dc5bd96aa3..b0e41d55ee 100644
--- a/ext/js/dom/dom-text-scanner.js
+++ b/ext/js/dom/dom-text-scanner.js
@@ -38,15 +38,25 @@ class DOMTextScanner {
         const resetOffset = (ruby !== null);
         if (resetOffset) { node = ruby; }
 
+        /** @type {Node} */
         this._node = node;
+        /** @type {number} */
         this._offset = offset;
+        /** @type {string} */
         this._content = '';
+        /** @type {number} */
         this._remainder = 0;
+        /** @type {boolean} */
         this._resetOffset = resetOffset;
+        /** @type {number} */
         this._newlines = 0;
+        /** @type {boolean} */
         this._lineHasWhitespace = false;
+        /** @type {boolean} */
         this._lineHasContent = false;
+        /** @type {boolean} */
         this._forcePreserveWhitespace = forcePreserveWhitespace;
+        /** @type {boolean} */
         this._generateLayoutContent = generateLayoutContent;
     }
 
@@ -101,8 +111,8 @@ class DOMTextScanner {
         const ELEMENT_NODE = Node.ELEMENT_NODE;
 
         const generateLayoutContent = this._generateLayoutContent;
-        let node = this._node;
-        let lastNode = node;
+        let node = /** @type {?Node} */ (this._node);
+        let lastNode = /** @type {Node} */ (node);
         let resetOffset = this._resetOffset;
         let newlines = 0;
         while (node !== null) {
@@ -113,8 +123,8 @@ class DOMTextScanner {
                 lastNode = node;
                 if (!(
                     forward ?
-                    this._seekTextNodeForward(node, resetOffset) :
-                    this._seekTextNodeBackward(node, resetOffset)
+                    this._seekTextNodeForward(/** @type {Text} */ (node), resetOffset) :
+                    this._seekTextNodeBackward(/** @type {Text} */ (node), resetOffset)
                 )) {
                     // Length reached
                     break;
@@ -122,18 +132,19 @@ class DOMTextScanner {
             } else if (nodeType === ELEMENT_NODE) {
                 lastNode = node;
                 this._offset = 0;
-                ({enterable, newlines} = DOMTextScanner.getElementSeekInfo(node));
+                ({enterable, newlines} = DOMTextScanner.getElementSeekInfo(/** @type {Element} */ (node)));
                 if (newlines > this._newlines && generateLayoutContent) {
                     this._newlines = newlines;
                 }
             }
 
+            /** @type {Node[]} */
             const exitedNodes = [];
             node = DOMTextScanner.getNextNode(node, forward, enterable, exitedNodes);
 
             for (const exitedNode of exitedNodes) {
                 if (exitedNode.nodeType !== ELEMENT_NODE) { continue; }
-                ({newlines} = DOMTextScanner.getElementSeekInfo(exitedNode));
+                ({newlines} = DOMTextScanner.getElementSeekInfo(/** @type {Element} */ (exitedNode)));
                 if (newlines > this._newlines && generateLayoutContent) {
                     this._newlines = newlines;
                 }
@@ -157,7 +168,7 @@ class DOMTextScanner {
      * @returns {boolean} `true` if scanning should continue, or `false` if the scan length has been reached.
      */
     _seekTextNodeForward(textNode, resetOffset) {
-        const nodeValue = textNode.nodeValue;
+        const nodeValue = /** @type {string} */ (textNode.nodeValue);
         const nodeValueLength = nodeValue.length;
         const {preserveNewlines, preserveWhitespace} = this._getWhitespaceSettings(textNode);
 
@@ -243,7 +254,7 @@ class DOMTextScanner {
      * @returns {boolean} `true` if scanning should continue, or `false` if the scan length has been reached.
      */
     _seekTextNodeBackward(textNode, resetOffset) {
-        const nodeValue = textNode.nodeValue;
+        const nodeValue = /** @type {string} */ (textNode.nodeValue);
         const nodeValueLength = nodeValue.length;
         const {preserveNewlines, preserveWhitespace} = this._getWhitespaceSettings(textNode);
 
@@ -352,6 +363,7 @@ class DOMTextScanner {
      * @returns {?Node} The next node in the document, or `null` if there is no next node.
      */
     static getNextNode(node, forward, visitChildren, exitedNodes) {
+        /** @type {?Node} */
         let next = visitChildren ? (forward ? node.firstChild : node.lastChild) : null;
         if (next === null) {
             while (true) {
@@ -371,14 +383,17 @@ class DOMTextScanner {
 
     /**
      * Gets the parent element of a given Node.
-     * @param {Node} node The node to check.
-     * @returns {?Node} The parent element if one exists, otherwise `null`.
+     * @param {?Node} node The node to check.
+     * @returns {?Element} The parent element if one exists, otherwise `null`.
      */
     static getParentElement(node) {
-        while (node !== null && node.nodeType !== Node.ELEMENT_NODE) {
+        while (node !== null) {
+            if (node.nodeType === Node.ELEMENT_NODE) {
+                return /** @type {Element} */ (node);
+            }
             node = node.parentNode;
         }
-        return node;
+        return null;
     }
 
     /**
@@ -389,11 +404,12 @@ class DOMTextScanner {
      * @returns {?HTMLElement} A <ruby> node if the input node is contained in one, otherwise `null`.
      */
     static getParentRubyElement(node) {
-        node = DOMTextScanner.getParentElement(node);
-        if (node !== null && node.nodeName.toUpperCase() === 'RT') {
-            node = node.parentNode;
-            if (node !== null && node.nodeName.toUpperCase() === 'RUBY') {
-                return node;
+        /** @type {?Node} */
+        let node2 = DOMTextScanner.getParentElement(node);
+        if (node2 !== null && node2.nodeName.toUpperCase() === 'RT') {
+            node2 = node2.parentNode;
+            if (node2 !== null && node2.nodeName.toUpperCase() === 'RUBY') {
+                return /** @type {HTMLElement} */ (node2);
             }
         }
         return null;
@@ -405,8 +421,8 @@ class DOMTextScanner {
      * @returns {{enterable: boolean, newlines: number}} The seek information.
      *   The `enterable` value indicates whether the content of this node should be entered.
      *   The `newlines` value corresponds to the number of newline characters that should be added.
-     *     1 newline corresponds to a simple new line in the layout.
-     *     2 newlines corresponds to a significant visual distinction since the previous content.
+     *   - 1 newline corresponds to a simple new line in the layout.
+     *   - 2 newlines corresponds to a significant visual distinction since the previous content.
      */
     static getElementSeekInfo(element) {
         let enterable = true;
@@ -506,8 +522,11 @@ class DOMTextScanner {
     static isStyleSelectable(style) {
         return !(
             style.userSelect === 'none' ||
+            // @ts-ignore - vendor prefix
             style.webkitUserSelect === 'none' ||
+            // @ts-ignore - vendor prefix
             style.MozUserSelect === 'none' ||
+            // @ts-ignore - vendor prefix
             style.msUserSelect === 'none'
         );
     }
@@ -515,7 +534,7 @@ class DOMTextScanner {
     /**
      * Checks whether a CSS color is transparent or not.
      * @param {string} cssColor A CSS color string, expected to be encoded in rgb(a) form.
-     * @returns {false} `true` if the color is transparent, otherwise `false`.
+     * @returns {boolean} `true` if the color is transparent, otherwise `false`.
      */
     static isCSSColorTransparent(cssColor) {
         return (
diff --git a/ext/js/dom/html-template-collection.js b/ext/js/dom/html-template-collection.js
index 4cdcf938a6..9919e3a71d 100644
--- a/ext/js/dom/html-template-collection.js
+++ b/ext/js/dom/html-template-collection.js
@@ -17,9 +17,15 @@
  */
 
 class HtmlTemplateCollection {
-    constructor(source) {
+    constructor() {
+        /** @type {Map<string, HTMLTemplateElement>} */
         this._templates = new Map();
+    }
 
+    /**
+     * @param {string|Document} source
+     */
+    load(source) {
         const sourceNode = (
             typeof source === 'string' ?
             new DOMParser().parseFromString(source, 'text/html') :
@@ -35,28 +41,53 @@ class HtmlTemplateCollection {
         }
     }
 
+    /**
+     * @template {Element} T
+     * @param {string} name
+     * @returns {T}
+     * @throws {Error}
+     */
     instantiate(name) {
         const template = this._templates.get(name);
-        return document.importNode(template.content.firstChild, true);
+        if (typeof template === 'undefined') { throw new Error(`Failed to find template: ${name}`); }
+        const {firstElementChild} = template.content;
+        if (firstElementChild === null) { throw new Error(`Failed to find template content element: ${name}`); }
+        return /** @type {T} */ (document.importNode(firstElementChild, true));
     }
 
+    /**
+     * @param {string} name
+     * @returns {DocumentFragment}
+     * @throws {Error}
+     */
     instantiateFragment(name) {
         const template = this._templates.get(name);
-        return document.importNode(template.content, true);
+        if (typeof template === 'undefined') { throw new Error(`Failed to find template: ${name}`); }
+        const {content} = template;
+        return document.importNode(content, true);
     }
 
+    /**
+     * @returns {IterableIterator<HTMLTemplateElement>}
+     */
     getAllTemplates() {
         return this._templates.values();
     }
 
     // Private
 
+    /**
+     * @param {HTMLTemplateElement} template
+     */
     _prepareTemplate(template) {
         if (template.dataset.removeWhitespaceText === 'true') {
             this._removeWhitespaceText(template);
         }
     }
 
+    /**
+     * @param {HTMLTemplateElement} template
+     */
     _removeWhitespaceText(template) {
         const {content} = template;
         const {TEXT_NODE} = Node;
@@ -65,7 +96,7 @@ class HtmlTemplateCollection {
         while (true) {
             const node = iterator.nextNode();
             if (node === null) { break; }
-            if (node.nodeType === TEXT_NODE && node.nodeValue.trim().length === 0) {
+            if (node.nodeType === TEXT_NODE && /** @type {string} */ (node.nodeValue).trim().length === 0) {
                 removeNodes.push(node);
             }
         }
diff --git a/ext/js/dom/native-simple-dom-parser.js b/ext/js/dom/native-simple-dom-parser.js
index 245386bd51..5d5b5c8874 100644
--- a/ext/js/dom/native-simple-dom-parser.js
+++ b/ext/js/dom/native-simple-dom-parser.js
@@ -17,35 +17,89 @@
  */
 
 class NativeSimpleDOMParser {
+    /**
+     * @param {string} content
+     */
     constructor(content) {
+        /** @type {Document} */
         this._document = new DOMParser().parseFromString(content, 'text/html');
     }
 
-    getElementById(id, root=null) {
-        return (root || this._document).querySelector(`[id='${id}']`);
+    /**
+     * @param {string} id
+     * @param {import('simple-dom-parser').Element} [root]
+     * @returns {?import('simple-dom-parser').Element}
+     */
+    getElementById(id, root) {
+        return this._convertElementOrDocument(root).querySelector(`[id='${id}']`);
     }
 
-    getElementByTagName(tagName, root=null) {
-        return (root || this._document).querySelector(tagName);
+    /**
+     * @param {string} tagName
+     * @param {import('simple-dom-parser').Element} [root]
+     * @returns {?import('simple-dom-parser').Element}
+     */
+    getElementByTagName(tagName, root) {
+        return this._convertElementOrDocument(root).querySelector(tagName);
     }
 
-    getElementsByTagName(tagName, root=null) {
-        return [...(root || this._document).querySelectorAll(tagName)];
+    /**
+     * @param {string} tagName
+     * @param {import('simple-dom-parser').Element} [root]
+     * @returns {import('simple-dom-parser').Element[]}
+     */
+    getElementsByTagName(tagName, root) {
+        return [...this._convertElementOrDocument(root).querySelectorAll(tagName)];
     }
 
-    getElementsByClassName(className, root=null) {
-        return [...(root || this._document).querySelectorAll(`.${className}`)];
+    /**
+     * @param {string} className
+     * @param {import('simple-dom-parser').Element} [root]
+     * @returns {import('simple-dom-parser').Element[]}
+     */
+    getElementsByClassName(className, root) {
+        return [...this._convertElementOrDocument(root).querySelectorAll(`.${className}`)];
     }
 
+    /**
+     * @param {import('simple-dom-parser').Element} element
+     * @param {string} attribute
+     * @returns {?string}
+     */
     getAttribute(element, attribute) {
-        return element.hasAttribute(attribute) ? element.getAttribute(attribute) : null;
+        const element2 = this._convertElement(element);
+        return element2.hasAttribute(attribute) ? element2.getAttribute(attribute) : null;
     }
 
+    /**
+     * @param {import('simple-dom-parser').Element} element
+     * @returns {string}
+     */
     getTextContent(element) {
-        return element.textContent;
+        const {textContent} = this._convertElement(element);
+        return typeof textContent === 'string' ? textContent : '';
     }
 
+    /**
+     * @returns {boolean}
+     */
     static isSupported() {
         return typeof DOMParser !== 'undefined';
     }
+
+    /**
+     * @param {import('simple-dom-parser').Element} element
+     * @returns {Element}
+     */
+    _convertElement(element) {
+        return /** @type {Element} */ (element);
+    }
+
+    /**
+     * @param {import('simple-dom-parser').Element|undefined} element
+     * @returns {Element|Document}
+     */
+    _convertElementOrDocument(element) {
+        return typeof element !== 'undefined' ? /** @type {Element} */ (element) : this._document;
+    }
 }
diff --git a/ext/js/dom/panel-element.js b/ext/js/dom/panel-element.js
index ac283d0279..34967a9bee 100644
--- a/ext/js/dom/panel-element.js
+++ b/ext/js/dom/panel-element.js
@@ -16,25 +16,45 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/**
+ * @augments EventDispatcher<import('panel-element').EventType>
+ */
 class PanelElement extends EventDispatcher {
+    /**
+     * @param {import('panel-element').ConstructorDetails} details
+     */
     constructor({node, closingAnimationDuration}) {
         super();
+        /** @type {HTMLElement} */
         this._node = node;
+        /** @type {number} */
         this._closingAnimationDuration = closingAnimationDuration;
+        /** @type {string} */
         this._hiddenAnimatingClass = 'hidden-animating';
+        /** @type {?MutationObserver} */
         this._mutationObserver = null;
+        /** @type {boolean} */
         this._visible = false;
+        /** @type {?number} */
         this._closeTimer = null;
     }
 
+    /** @type {HTMLElement} */
     get node() {
         return this._node;
     }
 
+    /**
+     * @returns {boolean}
+     */
     isVisible() {
         return !this._node.hidden;
     }
 
+    /**
+     * @param {boolean} value
+     * @param {boolean} [animate]
+     */
     setVisible(value, animate=true) {
         value = !!value;
         if (this.isVisible() === value) { return; }
@@ -61,6 +81,11 @@ class PanelElement extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('panel-element').EventType} eventName
+     * @param {(details: import('core').SafeAny) => void} callback
+     * @returns {void}
+     */
     on(eventName, callback) {
         if (eventName === 'visibilityChanged') {
             if (this._mutationObserver === null) {
@@ -76,6 +101,11 @@ class PanelElement extends EventDispatcher {
         return super.on(eventName, callback);
     }
 
+    /**
+     * @param {import('panel-element').EventType} eventName
+     * @param {(details: import('core').SafeAny) => void} callback
+     * @returns {boolean}
+     */
     off(eventName, callback) {
         const result = super.off(eventName, callback);
         if (eventName === 'visibilityChanged' && !this.hasListeners(eventName)) {
@@ -89,6 +119,7 @@ class PanelElement extends EventDispatcher {
 
     // Private
 
+    /** */
     _onMutation() {
         const visible = this.isVisible();
         if (this._visible === visible) { return; }
@@ -96,6 +127,9 @@ class PanelElement extends EventDispatcher {
         this.trigger('visibilityChanged', {visible});
     }
 
+    /**
+     * @param {boolean} reopening
+     */
     _completeClose(reopening) {
         this._closeTimer = null;
         this._node.classList.remove(this._hiddenAnimatingClass);
diff --git a/ext/js/dom/popup-menu.js b/ext/js/dom/popup-menu.js
index 4ab1e049ed..55adfb2d62 100644
--- a/ext/js/dom/popup-menu.js
+++ b/ext/js/dom/popup-menu.js
@@ -16,38 +16,58 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/**
+ * @augments EventDispatcher<import('popup-menu').EventType>
+ */
 class PopupMenu extends EventDispatcher {
+    /**
+     * @param {HTMLElement} sourceElement
+     * @param {HTMLElement} containerNode
+     */
     constructor(sourceElement, containerNode) {
         super();
+        /** @type {HTMLElement} */
         this._sourceElement = sourceElement;
+        /** @type {HTMLElement} */
         this._containerNode = containerNode;
-        this._node = containerNode.querySelector('.popup-menu');
-        this._bodyNode = containerNode.querySelector('.popup-menu-body');
+        /** @type {HTMLElement} */
+        this._node = /** @type {HTMLElement} */ (containerNode.querySelector('.popup-menu'));
+        /** @type {HTMLElement} */
+        this._bodyNode = /** @type {HTMLElement} */ (containerNode.querySelector('.popup-menu-body'));
+        /** @type {boolean} */
         this._isClosed = false;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {EventListenerCollection} */
         this._itemEventListeners = new EventListenerCollection();
     }
 
+    /** @type {HTMLElement} */
     get sourceElement() {
         return this._sourceElement;
     }
 
+    /** @type {HTMLElement} */
     get containerNode() {
         return this._containerNode;
     }
 
+    /** @type {HTMLElement} */
     get node() {
         return this._node;
     }
 
+    /** @type {HTMLElement} */
     get bodyNode() {
         return this._bodyNode;
     }
 
+    /** @type {boolean} */
     get isClosed() {
         return this._isClosed;
     }
 
+    /** */
     prepare() {
         this._setPosition();
         this._containerNode.focus();
@@ -59,17 +79,25 @@ class PopupMenu extends EventDispatcher {
 
         PopupMenu.openMenus.add(this);
 
+        /** @type {import('popup-menu').MenuOpenEventDetails} */
+        const detail = {menu: this};
+
         this._sourceElement.dispatchEvent(new CustomEvent('menuOpen', {
             bubbles: false,
             cancelable: false,
-            detail: {menu: this}
+            detail
         }));
     }
 
+    /**
+     * @param {boolean} [cancelable]
+     * @returns {boolean}
+     */
     close(cancelable=true) {
-        return this._close(null, 'close', cancelable, {});
+        return this._close(null, 'close', cancelable, null);
     }
 
+    /** */
     updateMenuItems() {
         this._itemEventListeners.removeAllEventListeners();
         const items = this._bodyNode.querySelectorAll('.popup-menu-item');
@@ -79,12 +107,16 @@ class PopupMenu extends EventDispatcher {
         }
     }
 
+    /** */
     updatePosition() {
         this._setPosition();
     }
 
     // Private
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMenuContainerClick(e) {
         if (e.currentTarget !== e.target) { return; }
         if (this._close(null, 'outside', true, e)) {
@@ -93,8 +125,11 @@ class PopupMenu extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMenuItemClick(e) {
-        const item = e.currentTarget;
+        const item = /** @type {HTMLButtonElement} */ (e.currentTarget);
         if (item.disabled) { return; }
         if (this._close(item, 'item', true, e)) {
             e.stopPropagation();
@@ -102,10 +137,12 @@ class PopupMenu extends EventDispatcher {
         }
     }
 
+    /** */
     _onWindowResize() {
-        this._close(null, 'resize', true, {});
+        this._close(null, 'resize', true, null);
     }
 
+    /** */
     _setPosition() {
         // Get flags
         let horizontal = 1;
@@ -185,11 +222,29 @@ class PopupMenu extends EventDispatcher {
         menu.style.top = `${y}px`;
     }
 
+    /**
+     * @param {?HTMLElement} item
+     * @param {import('popup-menu').CloseReason} cause
+     * @param {boolean} cancelable
+     * @param {?MouseEvent} originalEvent
+     * @returns {boolean}
+     */
     _close(item, cause, cancelable, originalEvent) {
         if (this._isClosed) { return true; }
-        const action = (item !== null ? item.dataset.menuAction : null);
+        /** @type {?string} */
+        let action = null;
+        if (item !== null) {
+            const {menuAction} = item.dataset;
+            if (typeof menuAction === 'string') { action = menuAction; }
+        }
+
+        const {altKey, ctrlKey, metaKey, shiftKey} = (
+            originalEvent !== null ?
+            originalEvent :
+            {altKey: false, ctrlKey: false, metaKey: false, shiftKey: false}
+        );
 
-        const {altKey=false, ctrlKey=false, metaKey=false, shiftKey=false} = originalEvent;
+        /** @type {import('popup-menu').MenuCloseEventDetails} */
         const detail = {
             menu: this,
             item,
diff --git a/ext/js/dom/sandbox/css-style-applier.js b/ext/js/dom/sandbox/css-style-applier.js
index 01936d26b8..81f1b98423 100644
--- a/ext/js/dom/sandbox/css-style-applier.js
+++ b/ext/js/dom/sandbox/css-style-applier.js
@@ -21,40 +21,21 @@
  * that is the same across different browsers.
  */
 class CssStyleApplier {
-    /**
-     * A CSS rule.
-     * @typedef {object} CssRule
-     * @property {string} selectors A CSS selector string representing one or more selectors.
-     * @property {CssDeclaration[]} styles A list of CSS property and value pairs.
-     */
-
-    /**
-     * A single CSS property declaration.
-     * @typedef {object} CssDeclaration
-     * @property {string} property A CSS property's name, using kebab-case.
-     * @property {string} value The property's value.
-     */
-
     /**
      * Creates a new instance of the class.
      * @param {string} styleDataUrl The local URL to the JSON file continaing the style rules.
-     *   The style rules should be of the format:
-     *   ```
-     *   [
-     *     {
-     *       selectors: [(selector:string)...],
-     *       styles: [
-     *         [(property:string), (value:string)]...
-     *       ]
-     *     }...
-     *   ]
-     *   ```
+     *   The style rules should follow the format of {@link CssStyleApplierRawStyleData}.
      */
     constructor(styleDataUrl) {
+        /** @type {string} */
         this._styleDataUrl = styleDataUrl;
+        /** @type {import('css-style-applier').CssRule[]} */
         this._styleData = [];
+        /** @type {Map<string, import('css-style-applier').CssRule[]>} */
         this._cachedRules = new Map();
+        /** @type {RegExp} */
         this._patternHtmlWhitespace = /[\t\r\n\f ]+/g;
+        /** @type {RegExp} */
         this._patternClassNameCharacter = /[0-9a-zA-Z-_]/;
     }
 
@@ -62,7 +43,8 @@ class CssStyleApplier {
      * Loads the data file for use.
      */
     async prepare() {
-        let rawData;
+        /** @type {import('css-style-applier').RawStyleData} */
+        let rawData = [];
         try {
             rawData = await this._fetchJsonAsset(this._styleDataUrl);
         } catch (e) {
@@ -92,7 +74,7 @@ class CssStyleApplier {
         const elementStyles = [];
         for (const element of elements) {
             const className = element.getAttribute('class');
-            if (className.length === 0) { continue; }
+            if (className === null || className.length === 0) { continue; }
             let cssTextNew = '';
             for (const {selectors, styles} of this._getCandidateCssRulesForClass(className)) {
                 if (!element.matches(selectors)) { continue; }
@@ -137,7 +119,7 @@ class CssStyleApplier {
     /**
      * Gets an array of candidate CSS rules which might match a specific class.
      * @param {string} className A whitespace-separated list of classes.
-     * @returns {CssRule[]} An array of candidate CSS rules.
+     * @returns {import('css-style-applier').CssRule[]} An array of candidate CSS rules.
      */
     _getCandidateCssRulesForClass(className) {
         let rules = this._cachedRules.get(className);
@@ -157,7 +139,7 @@ class CssStyleApplier {
 
     /**
      * Converts an array of CSS rules to a CSS string.
-     * @param {CssRule[]} styles An array of CSS rules.
+     * @param {import('css-style-applier').CssDeclaration[]} styles An array of CSS rules.
      * @returns {string} The CSS string.
      */
     _getCssText(styles) {
diff --git a/ext/js/dom/scroll-element.js b/ext/js/dom/scroll-element.js
index e7526db08a..ef73fffdbc 100644
--- a/ext/js/dom/scroll-element.js
+++ b/ext/js/dom/scroll-element.js
@@ -17,39 +17,68 @@
  */
 
 class ScrollElement {
+    /**
+     * @param {Element} node
+     */
     constructor(node) {
+        /** @type {Element} */
         this._node = node;
+        /** @type {?number} */
         this._animationRequestId = null;
+        /** @type {number} */
         this._animationStartTime = 0;
+        /** @type {number} */
         this._animationStartX = 0;
+        /** @type {number} */
         this._animationStartY = 0;
+        /** @type {number} */
         this._animationEndTime = 0;
+        /** @type {number} */
         this._animationEndX = 0;
+        /** @type {number} */
         this._animationEndY = 0;
+        /** @type {(time: number) => void} */
         this._requestAnimationFrameCallback = this._onAnimationFrame.bind(this);
     }
 
+    /** @type {number} */
     get x() {
         return this._node !== null ? this._node.scrollLeft : window.scrollX || window.pageXOffset;
     }
 
+    /** @type {number} */
     get y() {
         return this._node !== null ? this._node.scrollTop : window.scrollY || window.pageYOffset;
     }
 
+    /**
+     * @param {number} y
+     */
     toY(y) {
         this.to(this.x, y);
     }
 
+    /**
+     * @param {number} x
+     */
     toX(x) {
         this.to(x, this.y);
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     */
     to(x, y) {
         this.stop();
         this._scroll(x, y);
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {number} time
+     */
     animate(x, y, time) {
         this._animationStartX = this.x;
         this._animationStartY = this.y;
@@ -60,6 +89,7 @@ class ScrollElement {
         this._animationRequestId = window.requestAnimationFrame(this._requestAnimationFrameCallback);
     }
 
+    /** */
     stop() {
         if (this._animationRequestId === null) {
             return;
@@ -69,12 +99,18 @@ class ScrollElement {
         this._animationRequestId = null;
     }
 
+    /**
+     * @returns {DOMRect}
+     */
     getRect() {
         return this._node.getBoundingClientRect();
     }
 
     // Private
 
+    /**
+     * @param {number} time
+     */
     _onAnimationFrame(time) {
         if (time >= this._animationEndTime) {
             this._scroll(this._animationEndX, this._animationEndY);
@@ -91,6 +127,10 @@ class ScrollElement {
         this._animationRequestId = window.requestAnimationFrame(this._requestAnimationFrameCallback);
     }
 
+    /**
+     * @param {number} t
+     * @returns {number}
+     */
     _easeInOutCubic(t) {
         if (t < 0.5) {
             return (4.0 * t * t * t);
@@ -100,10 +140,20 @@ class ScrollElement {
         }
     }
 
+    /**
+     * @param {number} start
+     * @param {number} end
+     * @param {number} percent
+     * @returns {number}
+     */
     _lerp(start, end, percent) {
         return (end - start) * percent + start;
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     */
     _scroll(x, y) {
         if (this._node !== null) {
             this._node.scrollLeft = x;
diff --git a/ext/js/dom/selector-observer.js b/ext/js/dom/selector-observer.js
index 56f97202f7..bea0adfb24 100644
--- a/ext/js/dom/selector-observer.js
+++ b/ext/js/dom/selector-observer.js
@@ -18,55 +18,35 @@
 
 /**
  * Class which is used to observe elements matching a selector in specific element.
+ * @template T
  */
 class SelectorObserver {
-    /**
-     * @function OnAddedCallback
-     * @param {Element} element The element which was added.
-     * @returns {*} Custom data which is assigned to element and passed to callbacks.
-     */
-
-    /**
-     * @function OnRemovedCallback
-     * @param {Element} element The element which was removed.
-     * @param {*} data The custom data corresponding to the element.
-     */
-
-    /**
-     * @function OnChildrenUpdatedCallback
-     * @param {Element} element The element which had its children updated.
-     * @param {*} data The custom data corresponding to the element.
-     */
-
-    /**
-     * @function IsStaleCallback
-     * @param {Element} element The element which had its children updated.
-     * @param {*} data The custom data corresponding to the element.
-     * @returns {boolean} Whether or not the data is stale for the element.
-     */
-
     /**
      * Creates a new instance.
-     * @param {object} details The configuration for the object.
-     * @param {string} details.selector A string CSS selector used to find elements.
-     * @param {?string} details.ignoreSelector A string CSS selector used to filter elements, or `null` for no filtering.
-     * @param {OnAddedCallback} details.onAdded A function which is invoked for each element that is added that matches the selector.
-     * @param {?OnRemovedCallback} details.onRemoved A function which is invoked for each element that is removed, or `null`.
-     * @param {?OnChildrenUpdatedCallback} details.onChildrenUpdated A function which is invoked for each element which has its children updated, or `null`.
-     * @param {?IsStaleCallback} details.isStale A function which checks if the data is stale for a given element, or `null`.
-     *   If the element is stale, it will be removed and potentially re-added.
+     * @param {import('selector-observer').ConstructorDetails<T>} details The configuration for the object.
      */
     constructor({selector, ignoreSelector=null, onAdded=null, onRemoved=null, onChildrenUpdated=null, isStale=null}) {
+        /** @type {string} */
         this._selector = selector;
+        /** @type {?string} */
         this._ignoreSelector = ignoreSelector;
+        /** @type {?import('selector-observer').OnAddedCallback<T>} */
         this._onAdded = onAdded;
+        /** @type {?import('selector-observer').OnRemovedCallback<T>} */
         this._onRemoved = onRemoved;
+        /** @type {?import('selector-observer').OnChildrenUpdatedCallback<T>} */
         this._onChildrenUpdated = onChildrenUpdated;
+        /** @type {?import('selector-observer').IsStaleCallback<T>} */
         this._isStale = isStale;
+        /** @type {?Element} */
         this._observingElement = null;
+        /** @type {MutationObserver} */
         this._mutationObserver = new MutationObserver(this._onMutation.bind(this));
+        /** @type {Map<Node, import('selector-observer').Observer<T>>} */
         this._elementMap = new Map(); // Map([element => observer]...)
+        /** @type {Map<Node, Set<import('selector-observer').Observer<T>>>} */
         this._elementAncestorMap = new Map(); // Map([element => Set([observer]...)]...)
+        /** @type {boolean} */
         this._isObserving = false;
     }
 
@@ -100,9 +80,10 @@ class SelectorObserver {
             subtree: true
         });
 
+        const {parentNode} = element;
         this._onMutation([{
             type: 'childList',
-            target: element.parentNode,
+            target: parentNode !== null ? parentNode : element,
             addedNodes: [element],
             removedNodes: []
         }]);
@@ -124,17 +105,19 @@ class SelectorObserver {
 
     /**
      * Returns an iterable list of [element, data] pairs.
-     * @yields A sequence of [element, data] pairs.
+     * @yields {[element: Element, data: T]} A sequence of [element, data] pairs.
+     * @returns {Generator<[element: Element, data: T], void, unknown>}
      */
     *entries() {
-        for (const [element, {data}] of this._elementMap) {
+        for (const {element, data} of this._elementMap.values()) {
             yield [element, data];
         }
     }
 
     /**
      * Returns an iterable list of data for every element.
-     * @yields A sequence of data values.
+     * @yields {T} A sequence of data values.
+     * @returns {Generator<T, void, unknown>}
      */
     *datas() {
         for (const {data} of this._elementMap.values()) {
@@ -144,6 +127,9 @@ class SelectorObserver {
 
     // Private
 
+    /**
+     * @param {(MutationRecord|import('selector-observer').MutationRecordLike)[]} mutationList
+     */
     _onMutation(mutationList) {
         for (const mutation of mutationList) {
             switch (mutation.type) {
@@ -157,6 +143,9 @@ class SelectorObserver {
         }
     }
 
+    /**
+     * @param {MutationRecord|import('selector-observer').MutationRecordLike} record
+     */
     _onChildListMutation({addedNodes, removedNodes, target}) {
         const selector = this._selector;
         const ELEMENT_NODE = Node.ELEMENT_NODE;
@@ -171,10 +160,10 @@ class SelectorObserver {
 
         for (const node of addedNodes) {
             if (node.nodeType !== ELEMENT_NODE) { continue; }
-            if (node.matches(selector)) {
-                this._createObserver(node);
+            if (/** @type {Element} */ (node).matches(selector)) {
+                this._createObserver(/** @type {Element} */ (node));
             }
-            for (const childNode of node.querySelectorAll(selector)) {
+            for (const childNode of /** @type {Element} */ (node).querySelectorAll(selector)) {
                 this._createObserver(childNode);
             }
         }
@@ -183,7 +172,7 @@ class SelectorObserver {
             this._onChildrenUpdated !== null &&
             (addedNodes.length !== 0 || addedNodes.length !== 0)
         ) {
-            for (let node = target; node !== null; node = node.parentNode) {
+            for (let node = /** @type {?Node} */ (target); node !== null; node = node.parentNode) {
                 const observer = this._elementMap.get(node);
                 if (typeof observer !== 'undefined') {
                     this._onObserverChildrenUpdated(observer);
@@ -192,9 +181,12 @@ class SelectorObserver {
         }
     }
 
+    /**
+     * @param {MutationRecord|import('selector-observer').MutationRecordLike} record
+     */
     _onAttributeMutation({target}) {
         const selector = this._selector;
-        const observers = this._elementAncestorMap.get(target);
+        const observers = this._elementAncestorMap.get(/** @type {Element} */ (target));
         if (typeof observers !== 'undefined') {
             for (const observer of observers) {
                 const element = observer.element;
@@ -208,15 +200,19 @@ class SelectorObserver {
             }
         }
 
-        if (target.matches(selector)) {
-            this._createObserver(target);
+        if (/** @type {Element} */ (target).matches(selector)) {
+            this._createObserver(/** @type {Element} */ (target));
         }
     }
 
+    /**
+     * @param {Element} element
+     */
     _createObserver(element) {
         if (this._elementMap.has(element) || this._shouldIgnoreElement(element) || this._onAdded === null) { return; }
 
         const data = this._onAdded(element);
+        if (typeof data === 'undefined') { return; }
         const ancestors = this._getAncestors(element);
         const observer = {element, ancestors, data};
 
@@ -232,6 +228,9 @@ class SelectorObserver {
         }
     }
 
+    /**
+     * @param {import('selector-observer').Observer<T>} observer
+     */
     _removeObserver(observer) {
         const {element, ancestors, data} = observer;
 
@@ -252,26 +251,42 @@ class SelectorObserver {
         }
     }
 
+    /**
+     * @param {import('selector-observer').Observer<T>} observer
+     */
     _onObserverChildrenUpdated(observer) {
+        if (this._onChildrenUpdated === null) { return; }
         this._onChildrenUpdated(observer.element, observer.data);
     }
 
+    /**
+     * @param {import('selector-observer').Observer<T>} observer
+     * @returns {boolean}
+     */
     _isObserverStale(observer) {
         return (this._isStale !== null && this._isStale(observer.element, observer.data));
     }
 
+    /**
+     * @param {Element} element
+     * @returns {boolean}
+     */
     _shouldIgnoreElement(element) {
         return (this._ignoreSelector !== null && element.matches(this._ignoreSelector));
     }
 
+    /**
+     * @param {Node} node
+     * @returns {Node[]}
+     */
     _getAncestors(node) {
         const root = this._observingElement;
         const results = [];
-        while (true) {
-            results.push(node);
-            if (node === root) { break; }
-            node = node.parentNode;
-            if (node === null) { break; }
+        let n = /** @type {?Node} */ (node);
+        while (n !== null) {
+            results.push(n);
+            if (n === root) { break; }
+            n = n.parentNode;
         }
         return results;
     }
diff --git a/ext/js/dom/simple-dom-parser.js b/ext/js/dom/simple-dom-parser.js
index 266a465c8d..84972f438d 100644
--- a/ext/js/dom/simple-dom-parser.js
+++ b/ext/js/dom/simple-dom-parser.js
@@ -20,55 +20,91 @@
  * parse5
  */
 
+/**
+ * @augments import('simple-dom-parser').ISimpleDomParser
+ */
 class SimpleDOMParser {
+    /**
+     * @param {string} content
+     */
     constructor(content) {
-        this._document = parse5.parse(content);
+        /** @type {import('parse5')} */
+        // @ts-ignore - parse5 global is not defined in typescript declaration
+        this._parse5Lib = /** @type {import('parse5')} */ (parse5);
+        /** @type {import('parse5').TreeAdapter<import('parse5').DefaultTreeAdapterMap>} */
+        this._treeAdapter = this._parse5Lib.defaultTreeAdapter;
+        /** @type {import('simple-dom-parser').Parse5Document} */
+        this._document = this._parse5Lib.parse(content, {
+            treeAdapter: this._treeAdapter
+        });
+        /** @type {RegExp} */
         this._patternHtmlWhitespace = /[\t\r\n\f ]+/g;
     }
 
-    getElementById(id, root=null) {
+    /**
+     * @param {string} id
+     * @param {import('simple-dom-parser').Element} [root]
+     * @returns {?import('simple-dom-parser').Element}
+     */
+    getElementById(id, root) {
         for (const node of this._allNodes(root)) {
-            if (typeof node.tagName === 'string' && this.getAttribute(node, 'id') === id) {
-                return node;
-            }
+            if (!this._treeAdapter.isElementNode(node) || this.getAttribute(node, 'id') !== id) { continue; }
+            return node;
         }
         return null;
     }
 
-    getElementByTagName(tagName, root=null) {
+    /**
+     * @param {string} tagName
+     * @param {import('simple-dom-parser').Element} [root]
+     * @returns {?import('simple-dom-parser').Element}
+     */
+    getElementByTagName(tagName, root) {
         for (const node of this._allNodes(root)) {
-            if (node.tagName === tagName) {
-                return node;
-            }
+            if (!this._treeAdapter.isElementNode(node) || node.tagName !== tagName) { continue; }
+            return node;
         }
         return null;
     }
 
-    getElementsByTagName(tagName, root=null) {
+    /**
+     * @param {string} tagName
+     * @param {import('simple-dom-parser').Element} [root]
+     * @returns {import('simple-dom-parser').Element[]}
+     */
+    getElementsByTagName(tagName, root) {
         const results = [];
         for (const node of this._allNodes(root)) {
-            if (node.tagName === tagName) {
-                results.push(node);
-            }
+            if (!this._treeAdapter.isElementNode(node) || node.tagName !== tagName) { continue; }
+            results.push(node);
         }
         return results;
     }
 
-    getElementsByClassName(className, root=null) {
+    /**
+     * @param {string} className
+     * @param {import('simple-dom-parser').Element} [root]
+     * @returns {import('simple-dom-parser').Element[]}
+     */
+    getElementsByClassName(className, root) {
         const results = [];
         for (const node of this._allNodes(root)) {
-            if (typeof node.tagName === 'string') {
-                const nodeClassName = this.getAttribute(node, 'class');
-                if (nodeClassName !== null && this._hasToken(nodeClassName, className)) {
-                    results.push(node);
-                }
+            if (!this._treeAdapter.isElementNode(node)) { continue; }
+            const nodeClassName = this.getAttribute(node, 'class');
+            if (nodeClassName !== null && this._hasToken(nodeClassName, className)) {
+                results.push(node);
             }
         }
         return results;
     }
 
+    /**
+     * @param {import('simple-dom-parser').Element} element
+     * @param {string} attribute
+     * @returns {?string}
+     */
     getAttribute(element, attribute) {
-        for (const attr of element.attrs) {
+        for (const attr of /** @type {import('simple-dom-parser').Parse5Element} */ (element).attrs) {
             if (
                 attr.name === attribute &&
                 typeof attr.namespace === 'undefined'
@@ -79,43 +115,63 @@ class SimpleDOMParser {
         return null;
     }
 
+    /**
+     * @param {import('simple-dom-parser').Element} element
+     * @returns {string}
+     */
     getTextContent(element) {
         let source = '';
         for (const node of this._allNodes(element)) {
-            if (node.nodeName === '#text') {
+            if (this._treeAdapter.isTextNode(node)) {
                 source += node.value;
             }
         }
         return source;
     }
 
+    /**
+     * @returns {boolean}
+     */
     static isSupported() {
+        // @ts-ignore - parse5 global is not defined in typescript declaration
         return typeof parse5 !== 'undefined';
     }
 
     // Private
 
+    /**
+     * @param {import('simple-dom-parser').Element|undefined} root
+     * @returns {Generator<import('simple-dom-parser').Parse5ChildNode, void, unknown>}
+     * @yields {import('simple-dom-parser').Parse5ChildNode}
+     */
     *_allNodes(root) {
-        if (root === null) {
-            root = this._document;
-        }
-
         // Depth-first pre-order traversal
-        const nodeQueue = [root];
+        /** @type {import('simple-dom-parser').Parse5ChildNode[]} */
+        const nodeQueue = [];
+        if (typeof root !== 'undefined') {
+            nodeQueue.push(/** @type {import('simple-dom-parser').Parse5Element} */ (root));
+        } else {
+            nodeQueue.push(...this._document.childNodes);
+        }
         while (nodeQueue.length > 0) {
-            const node = nodeQueue.pop();
-
+            const node = /** @type {import('simple-dom-parser').Parse5ChildNode} */ (nodeQueue.pop());
             yield node;
-
-            const childNodes = node.childNodes;
-            if (typeof childNodes !== 'undefined') {
-                for (let i = childNodes.length - 1; i >= 0; --i) {
-                    nodeQueue.push(childNodes[i]);
+            if (this._treeAdapter.isElementNode(node)) {
+                const {childNodes} = node;
+                if (typeof childNodes !== 'undefined') {
+                    for (let i = childNodes.length - 1; i >= 0; --i) {
+                        nodeQueue.push(childNodes[i]);
+                    }
                 }
             }
         }
     }
 
+    /**
+     * @param {string} tokenListString
+     * @param {string} token
+     * @returns {boolean}
+     */
     _hasToken(tokenListString, token) {
         let start = 0;
         const pattern = this._patternHtmlWhitespace;
diff --git a/ext/js/dom/text-source-element.js b/ext/js/dom/text-source-element.js
index e37a3582a7..98f65900c7 100644
--- a/ext/js/dom/text-source-element.js
+++ b/ext/js/dom/text-source-element.js
@@ -34,16 +34,21 @@ class TextSourceElement {
      * @param {number} endOffset The text end offset position within the full content.
      */
     constructor(element, fullContent, startOffset, endOffset) {
+        /** @type {Element} */
         this._element = element;
+        /** @type {string} */
         this._fullContent = fullContent;
+        /** @type {number} */
         this._startOffset = startOffset;
+        /** @type {number} */
         this._endOffset = endOffset;
+        /** @type {string} */
         this._content = this._fullContent.substring(this._startOffset, this._endOffset);
     }
 
     /**
      * Gets the type name of this instance.
-     * @type {string}
+     * @type {'element'}
      */
     get type() {
         return 'element';
@@ -148,7 +153,7 @@ class TextSourceElement {
     /**
      * Gets writing mode that is used for this element.
      * See: https://developer.mozilla.org/en-US/docs/Web/CSS/writing-mode.
-     * @returns {string} The rects.
+     * @returns {import('document-util').NormalizedWritingMode} The writing mode.
      */
     getWritingMode() {
         return 'horizontal-tb';
@@ -207,23 +212,39 @@ class TextSourceElement {
      * @returns {string} The content string.
      */
     static _getElementContent(element) {
-        let content;
+        let content = '';
         switch (element.nodeName.toUpperCase()) {
             case 'BUTTON':
-                content = element.textContent;
+                {
+                    const {textContent} = /** @type {HTMLButtonElement} */ (element);
+                    if (textContent !== null) {
+                        content = textContent;
+                    }
+                }
                 break;
             case 'IMG':
-                content = element.getAttribute('alt') || '';
+                {
+                    const alt = /** @type {HTMLImageElement} */ (element).getAttribute('alt');
+                    if (typeof alt === 'string') {
+                        content = alt;
+                    }
+                }
                 break;
             case 'SELECT':
                 {
-                    const {selectedIndex, options} = element;
-                    const option = (selectedIndex >= 0 && selectedIndex < options.length ? options[selectedIndex] : null);
-                    content = (option !== null ? option.textContent : '');
+                    const {selectedIndex, options} = /** @type {HTMLSelectElement} */ (element);
+                    if (selectedIndex >= 0 && selectedIndex < options.length) {
+                        const {textContent} = options[selectedIndex];
+                        if (textContent !== null) {
+                            content = textContent;
+                        }
+                    }
                 }
                 break;
-            default:
-                content = `${element.value}`;
+            case 'INPUT':
+                {
+                    content = /** @type {HTMLInputElement} */ (element).value;
+                }
                 break;
         }
 
diff --git a/ext/js/dom/text-source-range.js b/ext/js/dom/text-source-range.js
index 8d6856b22b..3102b92a11 100644
--- a/ext/js/dom/text-source-range.js
+++ b/ext/js/dom/text-source-range.js
@@ -37,26 +37,33 @@ class TextSourceRange {
      * @param {?Element} imposterElement The temporary imposter element.
      * @param {?Element} imposterSourceElement The source element which the imposter is imitating.
      *   Must not be `null` if imposterElement is specified.
-     * @param {?Rect[]} cachedRects A set of cached `DOMRect`s representing the rects of the text source,
+     * @param {?DOMRect[]} cachedRects A set of cached `DOMRect`s representing the rects of the text source,
      *   which can be used after the imposter element is removed from the page.
      *   Must not be `null` if imposterElement is specified.
-     * @param {?Rect} cachedSourceRect A cached `DOMRect` representing the rect of the `imposterSourceElement`,
+     * @param {?DOMRect} cachedSourceRect A cached `DOMRect` representing the rect of the `imposterSourceElement`,
      *   which can be used after the imposter element is removed from the page.
      *   Must not be `null` if imposterElement is specified.
      */
     constructor(range, rangeStartOffset, content, imposterElement, imposterSourceElement, cachedRects, cachedSourceRect) {
+        /** @type {Range} */
         this._range = range;
+        /** @type {number} */
         this._rangeStartOffset = rangeStartOffset;
+        /** @type {string} */
         this._content = content;
+        /** @type {?Element} */
         this._imposterElement = imposterElement;
+        /** @type {?Element} */
         this._imposterSourceElement = imposterSourceElement;
+        /** @type {?DOMRect[]} */
         this._cachedRects = cachedRects;
+        /** @type {?DOMRect} */
         this._cachedSourceRect = cachedSourceRect;
     }
 
     /**
      * Gets the type name of this instance.
-     * @type {string}
+     * @type {'range'}
      */
     get type() {
         return 'range';
@@ -72,7 +79,7 @@ class TextSourceRange {
 
     /**
      * The starting offset for the range.
-     * @type {Range}
+     * @type {number}
      */
     get rangeStartOffset() {
         return this._rangeStartOffset;
@@ -170,12 +177,12 @@ class TextSourceRange {
     /**
      * Gets writing mode that is used for this element.
      * See: https://developer.mozilla.org/en-US/docs/Web/CSS/writing-mode.
-     * @returns {string} The rects.
+     * @returns {import('document-util').NormalizedWritingMode} The writing mode.
      */
     getWritingMode() {
         let node = this._isImposterDisconnected() ? this._imposterSourceElement : this._range.startContainer;
         if (node !== null && node.nodeType !== Node.ELEMENT_NODE) { node = node.parentElement; }
-        return DocumentUtil.getElementWritingMode(node);
+        return DocumentUtil.getElementWritingMode(/** @type {?Element} */ (node));
     }
 
     /**
@@ -184,6 +191,7 @@ class TextSourceRange {
     select() {
         if (this._imposterElement !== null) { return; }
         const selection = window.getSelection();
+        if (selection === null) { return; }
         selection.removeAllRanges();
         selection.addRange(this._range);
     }
@@ -194,6 +202,7 @@ class TextSourceRange {
     deselect() {
         if (this._imposterElement !== null) { return; }
         const selection = window.getSelection();
+        if (selection === null) { return; }
         selection.removeAllRanges();
     }
 
@@ -221,7 +230,7 @@ class TextSourceRange {
             try {
                 return this._range.compareBoundaryPoints(Range.START_TO_START, other.range) === 0;
             } catch (e) {
-                if (e.name === 'WrongDocumentError') {
+                if (e instanceof Error && e.name === 'WrongDocumentError') {
                     // This can happen with shadow DOMs if the ranges are in different documents.
                     return false;
                 }
@@ -270,9 +279,17 @@ class TextSourceRange {
 
     /**
      * Gets the cached rects for a disconnected imposter element.
-     * @returns {Rect[]} The rects for the element.
+     * @returns {DOMRect[]} The rects for the element.
+     * @throws {Error}
      */
     _getCachedRects() {
+        if (
+            this._cachedRects === null ||
+            this._cachedSourceRect === null ||
+            this._imposterSourceElement === null
+        ) {
+            throw new Error('Cached rects not valid for this instance');
+        }
         const sourceRect = DocumentUtil.convertRectZoomCoordinates(this._imposterSourceElement.getBoundingClientRect(), this._imposterSourceElement);
         return DocumentUtil.offsetDOMRects(
             this._cachedRects,
diff --git a/ext/js/extension/environment.js b/ext/js/extension/environment.js
index ec1e861253..59752d41a1 100644
--- a/ext/js/extension/environment.js
+++ b/ext/js/extension/environment.js
@@ -18,18 +18,29 @@
 
 class Environment {
     constructor() {
+        /** @type {?import('environment').Info} */
         this._cachedEnvironmentInfo = null;
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async prepare() {
         this._cachedEnvironmentInfo = await this._loadEnvironmentInfo();
     }
 
+    /**
+     * @returns {import('environment').Info}
+     * @throws {Error}
+     */
     getInfo() {
         if (this._cachedEnvironmentInfo === null) { throw new Error('Not prepared'); }
         return this._cachedEnvironmentInfo;
     }
 
+    /**
+     * @returns {Promise<import('environment').Info>}
+     */
     async _loadEnvironmentInfo() {
         const browser = await this._getBrowser();
         const os = await this._getOperatingSystem();
@@ -39,6 +50,9 @@ class Environment {
         };
     }
 
+    /**
+     * @returns {Promise<import('environment').OperatingSystem>}
+     */
     async _getOperatingSystem() {
         try {
             const {os} = await this._getPlatformInfo();
@@ -51,6 +65,9 @@ class Environment {
         return 'unknown';
     }
 
+    /**
+     * @returns {Promise<chrome.runtime.PlatformInfo>}
+     */
     _getPlatformInfo() {
         return new Promise((resolve, reject) => {
             chrome.runtime.getPlatformInfo((result) => {
@@ -64,6 +81,9 @@ class Environment {
         });
     }
 
+    /**
+     * @returns {Promise<import('environment').Browser>}
+     */
     async _getBrowser() {
         try {
             if (chrome.runtime.getURL('/').startsWith('ms-browser-extension://')) {
@@ -93,6 +113,9 @@ class Environment {
         }
     }
 
+    /**
+     * @returns {boolean};
+     */
     _isSafari() {
         const {vendor, userAgent} = navigator;
         return (
diff --git a/ext/js/general/cache-map.js b/ext/js/general/cache-map.js
index 817626abae..c0af37c645 100644
--- a/ext/js/general/cache-map.js
+++ b/ext/js/general/cache-map.js
@@ -17,6 +17,7 @@
  */
 
 /**
+ * @template K,V
  * Class which caches a map of values, keeping the most recently accessed values.
  */
 class CacheMap {
@@ -34,9 +35,13 @@ class CacheMap {
             throw new Error('Invalid maxCount');
         }
 
+        /** @type {number} */
         this._maxSize = maxSize;
+        /** @type {Map<K, import('cache-map').Node<K, V>>} */
         this._map = new Map();
+        /** @type {import('cache-map').Node<K, V>} */
         this._listFirst = this._createNode(null, null);
+        /** @type {import('cache-map').Node<K, V>} */
         this._listLast = this._createNode(null, null);
         this._resetEndNodes();
     }
@@ -59,7 +64,7 @@ class CacheMap {
 
     /**
      * Returns whether or not an element exists at the given key.
-     * @param {*} key The key of the element.
+     * @param {K} key The key of the element.
      * @returns {boolean} `true` if an element with the specified key exists, `false` otherwise.
      */
     has(key) {
@@ -68,20 +73,20 @@ class CacheMap {
 
     /**
      * Gets an element at the given key, if it exists. Otherwise, returns undefined.
-     * @param {*} key The key of the element.
-     * @returns {*} The existing value at the key, if any; `undefined` otherwise.
+     * @param {K} key The key of the element.
+     * @returns {V|undefined} The existing value at the key, if any; `undefined` otherwise.
      */
     get(key) {
         const node = this._map.get(key);
         if (typeof node === 'undefined') { return void 0; }
         this._updateRecency(node);
-        return node.value;
+        return /** @type {V} */ (node.value);
     }
 
     /**
      * Sets a value at a given key.
-     * @param {*} key The key of the element.
-     * @param {*} value The value to store in the cache.
+     * @param {K} key The key of the element.
+     * @param {V} value The value to store in the cache.
      */
     set(key, value) {
         let node = this._map.get(key);
@@ -97,9 +102,9 @@ class CacheMap {
 
             // Remove
             for (let removeCount = this._map.size - this._maxSize; removeCount > 0; --removeCount) {
-                node = this._listLast.previous;
+                node = /** @type {import('cache-map').Node<K, V>} */ (this._listLast.previous);
                 this._removeNode(node);
-                this._map.delete(node.key);
+                this._map.delete(/** @type {K} */ (node.key));
             }
         }
     }
@@ -114,28 +119,46 @@ class CacheMap {
 
     // Private
 
+    /**
+     * @param {import('cache-map').Node<K, V>} node
+     */
     _updateRecency(node) {
         this._removeNode(node);
         this._addNode(node, this._listFirst);
     }
 
+    /**
+     * @param {?K} key
+     * @param {?V} value
+     * @returns {import('cache-map').Node<K, V>}
+     */
     _createNode(key, value) {
         return {key, value, previous: null, next: null};
     }
 
+    /**
+     * @param {import('cache-map').Node<K, V>} node
+     * @param {import('cache-map').Node<K, V>} previous
+     */
     _addNode(node, previous) {
         const next = previous.next;
         node.next = next;
         node.previous = previous;
         previous.next = node;
-        next.previous = node;
+        /** @type {import('cache-map').Node<K, V>} */ (next).previous = node;
     }
 
+    /**
+     * @param {import('cache-map').Node<K, V>} node
+     */
     _removeNode(node) {
-        node.next.previous = node.previous;
-        node.previous.next = node.next;
+        /** @type {import('cache-map').Node<K, V>} */ (node.next).previous = node.previous;
+        /** @type {import('cache-map').Node<K, V>} */ (node.previous).next = node.next;
     }
 
+    /**
+     * @returns {void}
+     */
     _resetEndNodes() {
         this._listFirst.next = this._listLast;
         this._listLast.previous = this._listFirst;
diff --git a/ext/js/general/object-property-accessor.js b/ext/js/general/object-property-accessor.js
index 12b919357d..fbc9d6d63f 100644
--- a/ext/js/general/object-property-accessor.js
+++ b/ext/js/general/object-property-accessor.js
@@ -22,9 +22,10 @@
 class ObjectPropertyAccessor {
     /**
      * Create a new accessor for a specific object.
-     * @param {object} target The object which the getter and mutation methods are applied to.
+     * @param {unknown} target The object which the getter and mutation methods are applied to.
      */
     constructor(target) {
+        /** @type {unknown} */
         this._target = target;
     }
 
@@ -33,7 +34,7 @@ class ObjectPropertyAccessor {
      * @param {(string|number)[]} pathArray The path to the property on the target object.
      * @param {number} [pathLength] How many parts of the pathArray to use.
      *   This parameter is optional and defaults to the length of pathArray.
-     * @returns {*} The value found at the path.
+     * @returns {unknown} The value found at the path.
      * @throws {Error} An error is thrown if pathArray is not valid for the target object.
      */
     get(pathArray, pathLength) {
@@ -44,7 +45,7 @@ class ObjectPropertyAccessor {
             if (!ObjectPropertyAccessor.hasProperty(target, key)) {
                 throw new Error(`Invalid path: ${ObjectPropertyAccessor.getPathString(pathArray.slice(0, i + 1))}`);
             }
-            target = target[key];
+            target = /** @type {import('core').SerializableObject} */ (target)[key];
         }
         return target;
     }
@@ -52,7 +53,7 @@ class ObjectPropertyAccessor {
     /**
      * Sets the value at the specified path.
      * @param {(string|number)[]} pathArray The path to the property on the target object.
-     * @param {*} value The value to assign to the property.
+     * @param {unknown} value The value to assign to the property.
      * @throws {Error} An error is thrown if pathArray is not valid for the target object.
      */
     set(pathArray, value) {
@@ -65,7 +66,7 @@ class ObjectPropertyAccessor {
             throw new Error(`Invalid path: ${ObjectPropertyAccessor.getPathString(pathArray)}`);
         }
 
-        target[key] = value;
+        /** @type {import('core').SerializableObject} */ (target)[key] = value;
     }
 
     /**
@@ -87,7 +88,7 @@ class ObjectPropertyAccessor {
             throw new Error('Invalid type');
         }
 
-        delete target[key];
+        delete /** @type {import('core').SerializableObject} */ (target)[key];
     }
 
     /**
@@ -110,16 +111,16 @@ class ObjectPropertyAccessor {
         const key2 = pathArray2[ii2];
         if (!ObjectPropertyAccessor.isValidPropertyType(target2, key2)) { throw new Error(`Invalid path 2: ${ObjectPropertyAccessor.getPathString(pathArray2)}`); }
 
-        const value1 = target1[key1];
-        const value2 = target2[key2];
+        const value1 = /** @type {import('core').SerializableObject} */ (target1)[key1];
+        const value2 = /** @type {import('core').SerializableObject} */ (target2)[key2];
 
-        target1[key1] = value2;
+        /** @type {import('core').SerializableObject} */ (target1)[key1] = value2;
         try {
-            target2[key2] = value1;
+            /** @type {import('core').SerializableObject} */ (target2)[key2] = value1;
         } catch (e) {
             // Revert
             try {
-                target1[key1] = value1;
+                /** @type {import('core').SerializableObject} */ (target1)[key1] = value1;
             } catch (e2) {
                 // NOP
             }
@@ -178,7 +179,7 @@ class ObjectPropertyAccessor {
         let value = '';
         let escaped = false;
         for (const c of pathString) {
-            const v = c.codePointAt(0);
+            const v = /** @type {number} */ (c.codePointAt(0));
             switch (state) {
                 case 'empty': // Empty
                 case 'id-start': // Expecting identifier start
@@ -288,7 +289,7 @@ class ObjectPropertyAccessor {
 
     /**
      * Checks whether an object or array has the specified property.
-     * @param {*} object The object to test.
+     * @param {unknown} object The object to test.
      * @param {string|number} property The property to check for existence.
      *   This value should be a string if the object is a non-array object.
      *   For arrays, it should be an integer.
@@ -317,7 +318,7 @@ class ObjectPropertyAccessor {
 
     /**
      * Checks whether a property is valid for the given object
-     * @param {object} object The object to test.
+     * @param {unknown} object The object to test.
      * @param {string|number} property The property to check for existence.
      * @returns {boolean} `true` if the property is correct for the given object type, otherwise `false`.
      *   For arrays, this means that the property should be a positive integer.
diff --git a/ext/js/general/regex-util.js b/ext/js/general/regex-util.js
index 6e4668649b..54078d4012 100644
--- a/ext/js/general/regex-util.js
+++ b/ext/js/general/regex-util.js
@@ -60,7 +60,7 @@ class RegexUtil {
      * Applies the replacement string for a given regular expression match.
      * @param {string} replacement The replacement string that follows the format of the standard
      *   JavaScript regular expression replacement string.
-     * @param {object} match A match object returned from RegExp.match.
+     * @param {RegExpMatchArray} match A match object returned from RegExp.match.
      * @returns {string} A new string with the pattern replacement applied.
      */
     static applyMatchReplacement(replacement, match) {
@@ -78,11 +78,13 @@ class RegexUtil {
                     return groups[g2];
                 }
             } else {
+                let {index} = match;
+                if (typeof index !== 'number') { index = 0; }
                 switch (g0) {
                     case '$': return '$';
                     case '&': return match[0];
-                    case '`': return replacement.substring(0, match.index);
-                    case '\'': return replacement.substring(match.index + g0.length);
+                    case '`': return replacement.substring(0, index);
+                    case '\'': return replacement.substring(index + g0.length);
                 }
             }
             return g0;
diff --git a/ext/js/general/task-accumulator.js b/ext/js/general/task-accumulator.js
index b1185316a4..71474f8d74 100644
--- a/ext/js/general/task-accumulator.js
+++ b/ext/js/general/task-accumulator.js
@@ -16,25 +16,46 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/**
+ * @template K,V
+ */
 class TaskAccumulator {
+    /**
+     * @param {(tasks: [key: ?K, task: import('task-accumulator').Task<V>][]) => Promise<void>} runTasks
+     */
     constructor(runTasks) {
+        /** @type {?Promise<void>} */
         this._deferPromise = null;
+        /** @type {?Promise<void>} */
         this._activePromise = null;
+        /** @type {import('task-accumulator').Task<V>[]} */
         this._tasks = [];
+        /** @type {import('task-accumulator').Task<V>[]} */
         this._tasksActive = [];
+        /** @type {Map<K, import('task-accumulator').Task<V>>} */
         this._uniqueTasks = new Map();
+        /** @type {Map<K, import('task-accumulator').Task<V>>} */
         this._uniqueTasksActive = new Map();
+        /** @type {() => Promise<void>} */
         this._runTasksBind = this._runTasks.bind(this);
+        /** @type {() => void} */
         this._tasksCompleteBind = this._tasksComplete.bind(this);
-        this._runTasks = runTasks;
+        /** @type {(tasks: [key: ?K, task: import('task-accumulator').Task<V>][]) => Promise<void>} */
+        this._runTasksCallback = runTasks;
     }
 
+    /**
+     * @param {?K} key
+     * @param {V} data
+     * @returns {Promise<void>}
+     */
     enqueue(key, data) {
         if (this._deferPromise === null) {
             const promise = this._activePromise !== null ? this._activePromise : Promise.resolve();
             this._deferPromise = promise.then(this._runTasksBind);
         }
 
+        /** @type {import('task-accumulator').Task<V>} */
         const task = {data, stale: false};
         if (key !== null) {
             const activeTaskInfo = this._uniqueTasksActive.get(key);
@@ -50,6 +71,9 @@ class TaskAccumulator {
         return this._deferPromise;
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     _runTasks() {
         this._deferPromise = null;
 
@@ -62,18 +86,28 @@ class TaskAccumulator {
         return this._activePromise;
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _runTasksAsync() {
         try {
-            const allTasks = [
-                ...this._tasksActive.map((taskInfo) => [null, taskInfo]),
-                ...this._uniqueTasksActive.entries()
-            ];
-            await this._runTasks(allTasks);
+            /** @type {[key: ?K, task: import('task-accumulator').Task<V>][]} */
+            const allTasks = [];
+            for (const taskInfo of this._tasksActive) {
+                allTasks.push([null, taskInfo]);
+            }
+            for (const [key, taskInfo] of this._uniqueTasksActive) {
+                allTasks.push([key, taskInfo]);
+            }
+            await this._runTasksCallback(allTasks);
         } catch (e) {
             log.error(e);
         }
     }
 
+    /**
+     * @returns {void}
+     */
     _tasksComplete() {
         this._tasksActive.length = 0;
         this._uniqueTasksActive.clear();
diff --git a/ext/js/general/text-source-map.js b/ext/js/general/text-source-map.js
index 473fd0d093..aed7de78a7 100644
--- a/ext/js/general/text-source-map.js
+++ b/ext/js/general/text-source-map.js
@@ -17,15 +17,26 @@
  */
 
 class TextSourceMap {
+    /**
+     * @param {string} source
+     * @param {number[]|null} [mapping=null]
+     */
     constructor(source, mapping=null) {
+        /** @type {string} */
         this._source = source;
+        /** @type {?number[]} */
         this._mapping = (mapping !== null ? TextSourceMap.normalizeMapping(mapping) : null);
     }
 
+    /** @type {string} */
     get source() {
         return this._source;
     }
 
+    /**
+     * @param {unknown} other
+     * @returns {boolean}
+     */
     equals(other) {
         if (this === other) {
             return true;
@@ -61,6 +72,10 @@ class TextSourceMap {
         return true;
     }
 
+    /**
+     * @param {number} finalLength
+     * @returns {number}
+     */
     getSourceLength(finalLength) {
         const mapping = this._mapping;
         if (mapping === null) {
@@ -74,6 +89,10 @@ class TextSourceMap {
         return sourceLength;
     }
 
+    /**
+     * @param {number} index
+     * @param {number} count
+     */
     combine(index, count) {
         if (count <= 0) { return; }
 
@@ -89,6 +108,10 @@ class TextSourceMap {
         this._mapping[index] = sum;
     }
 
+    /**
+     * @param {number} index
+     * @param {number[]} items
+     */
     insert(index, ...items) {
         if (this._mapping === null) {
             this._mapping = TextSourceMap.createMapping(this._source);
@@ -97,14 +120,25 @@ class TextSourceMap {
         this._mapping.splice(index, 0, ...items);
     }
 
+    /**
+     * @returns {?number[]}
+     */
     getMappingCopy() {
         return this._mapping !== null ? [...this._mapping] : null;
     }
 
+    /**
+     * @param {string} text
+     * @returns {number[]}
+     */
     static createMapping(text) {
         return new Array(text.length).fill(1);
     }
 
+    /**
+     * @param {number[]} mapping
+     * @returns {number[]}
+     */
     static normalizeMapping(mapping) {
         const result = [];
         for (const value of mapping) {
diff --git a/ext/js/input/hotkey-handler.js b/ext/js/input/hotkey-handler.js
index 26a80b779a..3b206a45a7 100644
--- a/ext/js/input/hotkey-handler.js
+++ b/ext/js/input/hotkey-handler.js
@@ -22,28 +22,25 @@
 
 /**
  * Class which handles hotkey events and actions.
+ * @augments EventDispatcher<import('hotkey-handler').EventType>
  */
 class HotkeyHandler extends EventDispatcher {
-    /**
-     * Information describing a hotkey.
-     * @typedef {object} HotkeyDefinition
-     * @property {string} action A string indicating which action to perform.
-     * @property {string} key A keyboard key code indicating which key needs to be pressed.
-     * @property {string[]} modifiers An array of keyboard modifiers which also need to be pressed. Supports: `'alt', 'ctrl', 'shift', 'meta'`.
-     * @property {string[]} scopes An array of scopes for which the hotkey is valid. If this array does not contain `this.scope`, the hotkey will not be registered.
-     * @property {boolean} enabled A boolean indicating whether the hotkey is currently enabled.
-     */
-
     /**
      * Creates a new instance of the class.
      */
     constructor() {
         super();
+        /** @type {Map<string, (argument: unknown) => (boolean|void)>} */
         this._actions = new Map();
+        /** @type {Map<string, import('hotkey-handler').HotkeyHandlers>} */
         this._hotkeys = new Map();
+        /** @type {Map<import('settings').InputsHotkeyScope, import('settings').InputsHotkeyOptions[]>} */
         this._hotkeyRegistrations = new Map();
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {boolean} */
         this._isPrepared = false;
+        /** @type {boolean} */
         this._hasEventListeners = false;
     }
 
@@ -60,7 +57,7 @@ class HotkeyHandler extends EventDispatcher {
 
     /**
      * Registers a set of actions that this hotkey handler supports.
-     * @param {*[][]} actions An array of `[name, handler]` entries, where `name` is a string and `handler` is a function.
+     * @param {[name: string, handler: (argument: unknown) => (boolean|void)][]} actions An array of `[name, handler]` entries, where `name` is a string and `handler` is a function.
      */
     registerActions(actions) {
         for (const [name, handler] of actions) {
@@ -70,8 +67,8 @@ class HotkeyHandler extends EventDispatcher {
 
     /**
      * Registers a set of hotkeys for a given scope.
-     * @param {string} scope The scope that the hotkey definitions must be for in order to be activated.
-     * @param {HotkeyDefinition[]} hotkeys An array of hotkey definitions.
+     * @param {import('settings').InputsHotkeyScope} scope The scope that the hotkey definitions must be for in order to be activated.
+     * @param {import('settings').InputsHotkeyOptions[]} hotkeys An array of hotkey definitions.
      */
     registerHotkeys(scope, hotkeys) {
         let registrations = this._hotkeyRegistrations.get(scope);
@@ -85,7 +82,7 @@ class HotkeyHandler extends EventDispatcher {
 
     /**
      * Removes all registered hotkeys for a given scope.
-     * @param {string} scope The scope that the hotkey definitions were registered in.
+     * @param {import('settings').InputsHotkeyScope} scope The scope that the hotkey definitions were registered in.
      */
     clearHotkeys(scope) {
         const registrations = this._hotkeyRegistrations.get(scope);
@@ -98,8 +95,8 @@ class HotkeyHandler extends EventDispatcher {
     /**
      * Assigns a set of hotkeys for a given scope. This is an optimized shorthand for calling
      * `clearHotkeys`, then calling `registerHotkeys`.
-     * @param {string} scope The scope that the hotkey definitions must be for in order to be activated.
-     * @param {HotkeyDefinition[]} hotkeys An array of hotkey definitions.
+     * @param {import('settings').InputsHotkeyScope} scope The scope that the hotkey definitions must be for in order to be activated.
+     * @param {import('settings').InputsHotkeyOptions[]} hotkeys An array of hotkey definitions.
      */
     setHotkeys(scope, hotkeys) {
         let registrations = this._hotkeyRegistrations.get(scope);
@@ -109,14 +106,24 @@ class HotkeyHandler extends EventDispatcher {
         } else {
             registrations.length = 0;
         }
-        registrations.push(...hotkeys);
+        for (const {action, argument, key, modifiers, scopes, enabled} of hotkeys) {
+            registrations.push({
+                action,
+                argument,
+                key,
+                modifiers: [...modifiers],
+                scopes: [...scopes],
+                enabled
+            });
+        }
         this._updateHotkeyRegistrations();
     }
 
     /**
      * Adds a single event listener to a specific event.
-     * @param {string} eventName The string representing the event's name.
-     * @param {Function} callback The event listener callback to add.
+     * @template [TEventDetails=unknown]
+     * @param {import('hotkey-handler').EventType} eventName The string representing the event's name.
+     * @param {(details: TEventDetails) => void} callback The event listener callback to add.
      * @returns {void}
      */
     on(eventName, callback) {
@@ -128,8 +135,9 @@ class HotkeyHandler extends EventDispatcher {
 
     /**
      * Removes a single event listener from a specific event.
-     * @param {string} eventName The string representing the event's name.
-     * @param {Function} callback The event listener callback to add.
+     * @template [TEventDetails=unknown]
+     * @param {import('hotkey-handler').EventType} eventName The string representing the event's name.
+     * @param {(details: TEventDetails) => void} callback The event listener callback to add.
      * @returns {boolean} `true` if the callback was removed, `false` otherwise.
      */
     off(eventName, callback) {
@@ -142,37 +150,50 @@ class HotkeyHandler extends EventDispatcher {
     /**
      * Attempts to simulate an action for a given combination of key and modifiers.
      * @param {string} key A keyboard key code indicating which key needs to be pressed.
-     * @param {string[]} modifiers An array of keyboard modifiers which also need to be pressed. Supports: `'alt', 'ctrl', 'shift', 'meta'`.
+     * @param {import('input').ModifierKey[]} modifiers An array of keyboard modifiers which also need to be pressed. Supports: `'alt', 'ctrl', 'shift', 'meta'`.
      * @returns {boolean} `true` if an action was performed, `false` otherwise.
      */
     simulate(key, modifiers) {
         const hotkeyInfo = this._hotkeys.get(key);
         return (
             typeof hotkeyInfo !== 'undefined' &&
-            this._invokeHandlers(modifiers, hotkeyInfo)
+            this._invokeHandlers(modifiers, hotkeyInfo, key)
         );
     }
 
     // Message handlers
 
+    /**
+     * @param {{key: string, modifiers: import('input').ModifierKey[]}} details
+     * @returns {boolean}
+     */
     _onMessageForwardHotkey({key, modifiers}) {
         return this.simulate(key, modifiers);
     }
 
     // Private
 
-    _onKeyDown(e) {
-        const hotkeyInfo = this._hotkeys.get(e.code);
+    /**
+     * @param {KeyboardEvent} event
+     */
+    _onKeyDown(event) {
+        const hotkeyInfo = this._hotkeys.get(event.code);
         if (typeof hotkeyInfo !== 'undefined') {
-            const eventModifiers = DocumentUtil.getActiveModifiers(e);
-            if (this._invokeHandlers(eventModifiers, hotkeyInfo, e.key)) {
-                e.preventDefault();
+            const eventModifiers = DocumentUtil.getActiveModifiers(event);
+            if (this._invokeHandlers(eventModifiers, hotkeyInfo, event.key)) {
+                event.preventDefault();
                 return;
             }
         }
-        this.trigger('keydownNonHotkey', e);
+        this.trigger('keydownNonHotkey', event);
     }
 
+    /**
+     * @param {import('input').ModifierKey[]} modifiers
+     * @param {import('hotkey-handler').HotkeyHandlers} hotkeyInfo
+     * @param {string} key
+     * @returns {boolean}
+     */
     _invokeHandlers(modifiers, hotkeyInfo, key) {
         for (const {modifiers: handlerModifiers, action, argument} of hotkeyInfo.handlers) {
             if (!this._areSame(handlerModifiers, modifiers) || !this._isHotkeyPermitted(modifiers, key)) { continue; }
@@ -189,6 +210,11 @@ class HotkeyHandler extends EventDispatcher {
         return false;
     }
 
+    /**
+     * @param {Set<unknown>} set
+     * @param {unknown[]} array
+     * @returns {boolean}
+     */
     _areSame(set, array) {
         if (set.size !== array.length) { return false; }
         for (const value of array) {
@@ -199,6 +225,9 @@ class HotkeyHandler extends EventDispatcher {
         return true;
     }
 
+    /**
+     * @returns {void}
+     */
     _updateHotkeyRegistrations() {
         if (this._hotkeys.size === 0 && this._hotkeyRegistrations.size === 0) { return; }
 
@@ -219,10 +248,16 @@ class HotkeyHandler extends EventDispatcher {
         this._updateEventHandlers();
     }
 
+    /**
+     * @returns {void}
+     */
     _updateHasEventListeners() {
         this._hasEventListeners = this.hasListeners('keydownNonHotkey');
     }
 
+    /**
+     * @returns {void}
+     */
     _updateEventHandlers() {
         if (this._isPrepared && (this._hotkeys.size > 0 || this._hasEventListeners)) {
             if (this._eventListeners.size !== 0) { return; }
@@ -232,6 +267,11 @@ class HotkeyHandler extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('input').ModifierKey[]} modifiers
+     * @param {string} key
+     * @returns {boolean}
+     */
     _isHotkeyPermitted(modifiers, key) {
         return !(
             (modifiers.length === 0 || (modifiers.length === 1 && modifiers[0] === 'shift')) &&
@@ -240,6 +280,10 @@ class HotkeyHandler extends EventDispatcher {
         );
     }
 
+    /**
+     * @param {string} key
+     * @returns {boolean}
+     */
     _isKeyCharacterInput(key) {
         return key.length === 1;
     }
diff --git a/ext/js/input/hotkey-help-controller.js b/ext/js/input/hotkey-help-controller.js
index e5ea75dffb..9e4b2c1b50 100644
--- a/ext/js/input/hotkey-help-controller.js
+++ b/ext/js/input/hotkey-help-controller.js
@@ -22,21 +22,31 @@
 
 class HotkeyHelpController {
     constructor() {
+        /** @type {HotkeyUtil} */
         this._hotkeyUtil = new HotkeyUtil();
-        this._localActionHotseys = new Map();
+        /** @type {Map<string, string>} */
+        this._localActionHotkeys = new Map();
+        /** @type {Map<string, string>} */
         this._globalActionHotkeys = new Map();
+        /** @type {RegExp} */
         this._replacementPattern = /\{0\}/g;
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async prepare() {
         const {platform: {os}} = await yomichan.api.getEnvironmentInfo();
         this._hotkeyUtil.os = os;
         await this._setupGlobalCommands(this._globalActionHotkeys);
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     setOptions(options) {
         const hotkeys = options.inputs.hotkeys;
-        const hotkeyMap = this._localActionHotseys;
+        const hotkeyMap = this._localActionHotkeys;
         hotkeyMap.clear();
         for (const {enabled, action, key, modifiers} of hotkeys) {
             if (!enabled || key === null || action === '' || hotkeyMap.has(action)) { continue; }
@@ -44,28 +54,25 @@ class HotkeyHelpController {
         }
     }
 
+    /**
+     * @param {ParentNode} node
+     */
     setupNode(node) {
-        const globalPrexix = 'global:';
         const replacementPattern = this._replacementPattern;
-        for (const node2 of node.querySelectorAll('[data-hotkey]')) {
-            const data = JSON.parse(node2.dataset.hotkey);
-            let [action, attributes, values] = data;
-            if (!Array.isArray(attributes)) { attributes = [attributes]; }
+        for (const node2 of /** @type {NodeListOf<HTMLElement>} */ (node.querySelectorAll('[data-hotkey]'))) {
+            const info = this._getNodeInfo(node2);
+            if (info === null) { continue; }
+            const {action, global, attributes, values, defaultAttributeValues} = info;
             const multipleValues = Array.isArray(values);
-
-            const actionIsGlobal = action.startsWith(globalPrexix);
-            if (actionIsGlobal) { action = action.substring(globalPrexix.length); }
-
-            const defaultAttributeValues = this._getDefaultAttributeValues(node2, data, attributes);
-
-            const hotkey = (actionIsGlobal ? this._globalActionHotkeys : this._localActionHotseys).get(action);
-
+            const hotkey = (global ? this._globalActionHotkeys : this._localActionHotkeys).get(action);
             for (let i = 0, ii = attributes.length; i < ii; ++i) {
                 const attribute = attributes[i];
-                let value = null;
+                let value;
                 if (typeof hotkey !== 'undefined') {
-                    value = (multipleValues ? values[i] : values);
-                    value = value.replace(replacementPattern, hotkey);
+                    value = /** @type {unknown} */ (multipleValues ? values[i] : values);
+                    if (typeof value === 'string') {
+                        value = value.replace(replacementPattern, hotkey);
+                    }
                 } else {
                     value = defaultAttributeValues[i];
                 }
@@ -81,6 +88,9 @@ class HotkeyHelpController {
 
     // Private
 
+    /**
+     * @param {Map<string, string>} commandMap
+     */
     async _setupGlobalCommands(commandMap) {
         const commands = await new Promise((resolve, reject) => {
             if (!(isObject(chrome.commands) && typeof chrome.commands.getAll === 'function')) {
@@ -104,14 +114,23 @@ class HotkeyHelpController {
             const {key, modifiers} = this._hotkeyUtil.convertCommandToInput(shortcut);
             commandMap.set(name, this._hotkeyUtil.getInputDisplayValue(key, modifiers));
         }
-        return commandMap;
     }
 
+    /**
+     * @param {HTMLElement} node
+     * @param {unknown[]} data
+     * @param {string[]} attributes
+     * @returns {unknown[]}
+     */
     _getDefaultAttributeValues(node, data, attributes) {
         if (data.length > 3) {
-            return data[3];
+            const result = data[3];
+            if (Array.isArray(result)) {
+                return result;
+            }
         }
 
+        /** @type {(?string)[]} */
         const defaultAttributeValues = [];
         for (let i = 0, ii = attributes.length; i < ii; ++i) {
             const attribute = attributes[i];
@@ -122,4 +141,37 @@ class HotkeyHelpController {
         node.dataset.hotkey = JSON.stringify(data);
         return defaultAttributeValues;
     }
+
+    /**
+     * @param {HTMLElement} node
+     * @returns {?{action: string, global: boolean, attributes: string[], values: unknown, defaultAttributeValues: unknown[]}}
+     */
+    _getNodeInfo(node) {
+        const {hotkey} = node.dataset;
+        if (typeof hotkey !== 'string') { return null; }
+        const data = /** @type {unknown} */ (JSON.parse(hotkey));
+        if (!Array.isArray(data)) { return null; }
+        const [action, attributes, values] = data;
+        if (typeof action !== 'string') { return null; }
+        /** @type {string[]} */
+        const attributesArray = [];
+        if (Array.isArray(attributes)) {
+            for (const item of attributes) {
+                if (typeof item !== 'string') { continue; }
+                attributesArray.push(item);
+            }
+        } else if (typeof attributes === 'string') {
+            attributesArray.push(attributes);
+        }
+        const defaultAttributeValues = this._getDefaultAttributeValues(node, data, attributesArray);
+        const globalPrexix = 'global:';
+        const global = action.startsWith(globalPrexix);
+        return {
+            action: global ? action.substring(globalPrexix.length) : action,
+            global,
+            attributes,
+            values,
+            defaultAttributeValues
+        };
+    }
 }
diff --git a/ext/js/input/hotkey-util.js b/ext/js/input/hotkey-util.js
index eacbc5534e..18adf9cd91 100644
--- a/ext/js/input/hotkey-util.js
+++ b/ext/js/input/hotkey-util.js
@@ -22,19 +22,25 @@
 class HotkeyUtil {
     /**
      * Creates a new instance.
-     * @param {?string} os The operating system for this instance.
+     * @param {?import('environment').OperatingSystem} os The operating system for this instance.
      */
     constructor(os=null) {
+        /** @type {?import('environment').OperatingSystem} */
         this._os = os;
+        /** @type {string} */
         this._inputSeparator = ' + ';
+        /** @type {Map<import('input').Modifier, string>} */
         this._modifierKeyNames = new Map();
+        /** @type {RegExp} */
         this._mouseInputNamePattern = /^mouse(\d+)$/;
+        /** @type {Map<import('input').Modifier, number>} */
         this._modifierPriorities = new Map([
             ['meta', -4],
             ['ctrl', -3],
             ['alt', -2],
             ['shift', -1]
         ]);
+        /** @type {Intl.Collator} */
         this._stringComparer = new Intl.Collator('en-US'); // Invariant locale
 
         this._updateModifierKeyNames();
@@ -43,7 +49,7 @@ class HotkeyUtil {
     /**
      * Gets the operating system for this instance.
      * The operating system is used to display system-localized modifier key names.
-     * @type {?string}
+     * @type {?import('environment').OperatingSystem}
      */
     get os() {
         return this._os;
@@ -51,7 +57,7 @@ class HotkeyUtil {
 
     /**
      * Sets the operating system for this instance.
-     * @param {?string} value The value to assign.
+     * @param {?import('environment').OperatingSystem} value The value to assign.
      *   Valid values are: win, mac, linux, openbsd, cros, android.
      */
     set os(value) {
@@ -63,7 +69,7 @@ class HotkeyUtil {
     /**
      * Gets a display string for a key and a set of modifiers.
      * @param {?string} key The key code string, or `null` for no key.
-     * @param {string[]} modifiers An array of modifiers.
+     * @param {import('input').Modifier[]} modifiers An array of modifiers.
      *   Valid values are: ctrl, alt, shift, meta, or mouseN, where N is an integer.
      * @returns {string} A user-friendly string for the combination of key and modifiers.
      */
@@ -88,7 +94,7 @@ class HotkeyUtil {
 
     /**
      * Gets a display string for a single modifier.
-     * @param {string} modifier A string representing a modifier.
+     * @param {import('input').Modifier} modifier A string representing a modifier.
      *   Valid values are: ctrl, alt, shift, meta, or mouseN, where N is an integer.
      * @returns {string} A user-friendly string for the modifier.
      */
@@ -116,9 +122,9 @@ class HotkeyUtil {
 
     /**
      * Gets a display string for a single modifier.
-     * @param {string} modifier A string representing a modifier.
+     * @param {import('input').Modifier} modifier A string representing a modifier.
      *   Valid values are: ctrl, alt, shift, meta, or mouseN, where N is an integer.
-     * @returns {'mouse'|'key'} `'mouse'` if the modifier represents a mouse button, `'key'` otherwise.
+     * @returns {import('input').ModifierType} `'mouse'` if the modifier represents a mouse button, `'key'` otherwise.
      */
     getModifierType(modifier) {
         return (this._mouseInputNamePattern.test(modifier) ? 'mouse' : 'key');
@@ -126,18 +132,22 @@ class HotkeyUtil {
 
     /**
      * Converts an extension command string into a standard input.
-     * @param {string} command An extension command string.
-     * @returns {{key: ?string, modifiers: string[]}} An object `{key, modifiers}`, where key is a string (or `null`) representing the key, and modifiers is an array of modifier keys.
+     * @param {string|undefined} command An extension command string.
+     * @returns {{key: ?string, modifiers: import('input').ModifierKey[]}} An object `{key, modifiers}`, where key is a string (or `null`) representing the key, and modifiers is an array of modifier keys.
      */
     convertCommandToInput(command) {
         let key = null;
+        /** @type {Set<import('input').ModifierKey>} */
         const modifiers = new Set();
         if (typeof command === 'string' && command.length > 0) {
             const parts = command.split('+');
             const ii = parts.length - 1;
             key = this._convertCommandKeyToInputKey(parts[ii]);
             for (let i = 0; i < ii; ++i) {
-                modifiers.add(this._convertCommandModifierToInputModifier(parts[i]));
+                const modifier = this._convertCommandModifierToInputModifier(parts[i]);
+                if (modifier !== null) {
+                    modifiers.add(modifier);
+                }
             }
         }
         return {key, modifiers: this.sortModifiers([...modifiers])};
@@ -146,7 +156,7 @@ class HotkeyUtil {
     /**
      * Gets a command string for a specified input.
      * @param {?string} key The key code string, or `null` for no key.
-     * @param {string[]} modifiers An array of modifier keys.
+     * @param {import('input').Modifier[]} modifiers An array of modifier keys.
      *   Valid values are: ctrl, alt, shift, meta.
      * @returns {string} An extension command string representing the input.
      */
@@ -170,10 +180,11 @@ class HotkeyUtil {
     }
 
     /**
+     * @template {import('input').Modifier} TModifier
      * Sorts an array of modifiers.
-     * @param {string[]} modifiers An array of modifiers.
+     * @param {TModifier[]} modifiers An array of modifiers.
      *   Valid values are: ctrl, alt, shift, meta.
-     * @returns {string[]} A sorted array of modifiers. The array instance is the same as the input array.
+     * @returns {TModifier[]} A sorted array of modifiers. The array instance is the same as the input array.
      */
     sortModifiers(modifiers) {
         const pattern = this._mouseInputNamePattern;
@@ -181,10 +192,12 @@ class HotkeyUtil {
         const stringComparer = this._stringComparer;
 
         const count = modifiers.length;
+        /** @type {[modifier: TModifier, isMouse: 0|1, priority: number, index: number][]} */
         const modifierInfos = [];
         for (let i = 0; i < count; ++i) {
             const modifier = modifiers[i];
             const match = pattern.exec(modifier);
+            /** @type {[modifier: TModifier, isMouse: 0|1, priority: number, index: number]} */
             let info;
             if (match !== null) {
                 info = [modifier, 1, Number.parseInt(match[1], 10), i];
@@ -219,6 +232,10 @@ class HotkeyUtil {
 
     // Private
 
+    /**
+     * @param {?import('environment').OperatingSystem} os
+     * @returns {[modifier: import('input').ModifierKey, label: string][]}
+     */
     _getModifierKeyNames(os) {
         switch (os) {
             case 'win':
@@ -255,6 +272,9 @@ class HotkeyUtil {
         }
     }
 
+    /**
+     * @returns {void}
+     */
     _updateModifierKeyNames() {
         const map = this._modifierKeyNames;
         map.clear();
@@ -263,6 +283,10 @@ class HotkeyUtil {
         }
     }
 
+    /**
+     * @param {string} key
+     * @returns {string}
+     */
     _convertCommandKeyToInputKey(key) {
         if (key.length === 1) {
             key = `Key${key}`;
@@ -270,6 +294,10 @@ class HotkeyUtil {
         return key;
     }
 
+    /**
+     * @param {string} modifier
+     * @returns {?import('input').ModifierKey}
+     */
     _convertCommandModifierToInputModifier(modifier) {
         switch (modifier) {
             case 'Ctrl': return (this._os === 'mac' ? 'meta' : 'ctrl');
@@ -277,10 +305,14 @@ class HotkeyUtil {
             case 'Shift': return 'shift';
             case 'MacCtrl': return 'ctrl';
             case 'Command': return 'meta';
-            default: return modifier;
+            default: return null;
         }
     }
 
+    /**
+     * @param {string} key
+     * @returns {string}
+     */
     _convertInputKeyToCommandKey(key) {
         if (key.length === 4 && key.startsWith('Key')) {
             key = key.substring(3);
@@ -288,6 +320,10 @@ class HotkeyUtil {
         return key;
     }
 
+    /**
+     * @param {import('input').Modifier} modifier
+     * @returns {string}
+     */
     _convertInputModifierToCommandModifier(modifier) {
         switch (modifier) {
             case 'ctrl': return (this._os === 'mac' ? 'MacCtrl' : 'Ctrl');
diff --git a/ext/js/language/deinflector.js b/ext/js/language/deinflector.js
index b11aa918f0..ec3a6243eb 100644
--- a/ext/js/language/deinflector.js
+++ b/ext/js/language/deinflector.js
@@ -17,10 +17,18 @@
  */
 
 class Deinflector {
+    /**
+     * @param {import('deinflector').ReasonsRaw} reasons
+     */
     constructor(reasons) {
+        /** @type {import('deinflector').Reason[]} */
         this.reasons = Deinflector.normalizeReasons(reasons);
     }
 
+    /**
+     * @param {string} source
+     * @returns {import('translation-internal').Deinflection[]}
+     */
     deinflect(source) {
         const results = [this._createDeinflection(source, 0, [])];
         for (let i = 0; i < results.length; ++i) {
@@ -46,13 +54,25 @@ class Deinflector {
         return results;
     }
 
+    /**
+     * @param {string} term
+     * @param {import('translation-internal').DeinflectionRuleFlags} rules
+     * @param {string[]} reasons
+     * @returns {import('translation-internal').Deinflection}
+     */
     _createDeinflection(term, rules, reasons) {
         return {term, rules, reasons};
     }
 
+    /**
+     * @param {import('deinflector').ReasonsRaw} reasons
+     * @returns {import('deinflector').Reason[]}
+     */
     static normalizeReasons(reasons) {
+        /** @type {import('deinflector').Reason[]} */
         const normalizedReasons = [];
         for (const [reason, reasonInfo] of Object.entries(reasons)) {
+            /** @type {import('deinflector').ReasonVariant[]} */
             const variants = [];
             for (const {kanaIn, kanaOut, rulesIn, rulesOut} of reasonInfo) {
                 variants.push([
@@ -67,6 +87,10 @@ class Deinflector {
         return normalizedReasons;
     }
 
+    /**
+     * @param {string[]} rules
+     * @returns {import('translation-internal').DeinflectionRuleFlags}
+     */
     static rulesToRuleFlags(rules) {
         const ruleTypes = this._ruleTypes;
         let value = 0;
@@ -79,13 +103,14 @@ class Deinflector {
     }
 }
 
+/** @type {Map<string, import('translation-internal').DeinflectionRuleFlags>} */
 // eslint-disable-next-line no-underscore-dangle
 Deinflector._ruleTypes = new Map([
-    ['v1',    0b00000001], // Verb ichidan
-    ['v5',    0b00000010], // Verb godan
-    ['vs',    0b00000100], // Verb suru
-    ['vk',    0b00001000], // Verb kuru
-    ['vz',    0b00010000], // Verb zuru
-    ['adj-i', 0b00100000], // Adjective i
-    ['iru',   0b01000000] // Intermediate -iru endings for progressive or perfect tense
+    ['v1',    /** @type {import('translation-internal').DeinflectionRuleFlags} */ (0b00000001)], // Verb ichidan
+    ['v5',    /** @type {import('translation-internal').DeinflectionRuleFlags} */ (0b00000010)], // Verb godan
+    ['vs',    /** @type {import('translation-internal').DeinflectionRuleFlags} */ (0b00000100)], // Verb suru
+    ['vk',    /** @type {import('translation-internal').DeinflectionRuleFlags} */ (0b00001000)], // Verb kuru
+    ['vz',    /** @type {import('translation-internal').DeinflectionRuleFlags} */ (0b00010000)], // Verb zuru
+    ['adj-i', /** @type {import('translation-internal').DeinflectionRuleFlags} */ (0b00100000)], // Adjective i
+    ['iru',   /** @type {import('translation-internal').DeinflectionRuleFlags} */ (0b01000000)] // Intermediate -iru endings for progressive or perfect tense
 ]);
diff --git a/ext/js/language/dictionary-database.js b/ext/js/language/dictionary-database.js
index 9f2b9e45cf..ea7a360daa 100644
--- a/ext/js/language/dictionary-database.js
+++ b/ext/js/language/dictionary-database.js
@@ -22,29 +22,45 @@
 
 class DictionaryDatabase {
     constructor() {
+        /** @type {Database<import('dictionary-database').ObjectStoreName>} */
         this._db = new Database();
+        /** @type {string} */
         this._dbName = 'dict';
-        this._schemas = new Map();
+        /** @type {import('dictionary-database').CreateQuery<string>} */
         this._createOnlyQuery1 = (item) => IDBKeyRange.only(item);
+        /** @type {import('dictionary-database').CreateQuery<import('dictionary-database').DictionaryAndQueryRequest>} */
         this._createOnlyQuery2 = (item) => IDBKeyRange.only(item.query);
+        /** @type {import('dictionary-database').CreateQuery<import('dictionary-database').TermExactRequest>} */
         this._createOnlyQuery3 = (item) => IDBKeyRange.only(item.term);
+        /** @type {import('dictionary-database').CreateQuery<import('dictionary-database').MediaRequest>} */
         this._createOnlyQuery4 = (item) => IDBKeyRange.only(item.path);
+        /** @type {import('dictionary-database').CreateQuery<string>} */
         this._createBoundQuery1 = (item) => IDBKeyRange.bound(item, `${item}\uffff`, false, false);
+        /** @type {import('dictionary-database').CreateQuery<string>} */
         this._createBoundQuery2 = (item) => { item = stringReverse(item); return IDBKeyRange.bound(item, `${item}\uffff`, false, false); };
-        this._createTermBind1 = this._createTerm.bind(this, 'term', 'exact');
-        this._createTermBind2 = this._createTerm.bind(this, 'sequence', 'exact');
+        /** @type {import('dictionary-database').CreateResult<import('dictionary-database').TermExactRequest, import('dictionary-database').DatabaseTermEntryWithId, import('dictionary-database').TermEntry>} */
+        this._createTermBind1 = this._createTermExact.bind(this);
+        /** @type {import('dictionary-database').CreateResult<import('dictionary-database').DictionaryAndQueryRequest, import('dictionary-database').DatabaseTermEntryWithId, import('dictionary-database').TermEntry>} */
+        this._createTermBind2 = this._createTermSequenceExact.bind(this);
+        /** @type {import('dictionary-database').CreateResult<string, import('dictionary-database').DatabaseTermMeta, import('dictionary-database').TermMeta>} */
         this._createTermMetaBind = this._createTermMeta.bind(this);
+        /** @type {import('dictionary-database').CreateResult<string, import('dictionary-database').DatabaseKanjiEntry, import('dictionary-database').KanjiEntry>} */
         this._createKanjiBind = this._createKanji.bind(this);
+        /** @type {import('dictionary-database').CreateResult<string, import('dictionary-database').DatabaseKanjiMeta, import('dictionary-database').KanjiMeta>} */
         this._createKanjiMetaBind = this._createKanjiMeta.bind(this);
+        /** @type {import('dictionary-database').CreateResult<import('dictionary-database').MediaRequest, import('dictionary-database').MediaDataArrayBufferContent, import('dictionary-database').Media>} */
         this._createMediaBind = this._createMedia.bind(this);
     }
 
+    /** */
     async prepare() {
         await this._db.open(
             this._dbName,
             60,
-            [
-                {
+            /** @type {import('database').StructureDefinition<import('dictionary-database').ObjectStoreName>[]} */
+            ([
+                /** @type {import('database').StructureDefinition<import('dictionary-database').ObjectStoreName>} */
+                ({
                     version: 20,
                     stores: {
                         terms: {
@@ -64,7 +80,7 @@ class DictionaryDatabase {
                             indices: ['title', 'version']
                         }
                     }
-                },
+                }),
                 {
                     version: 30,
                     stores: {
@@ -109,18 +125,25 @@ class DictionaryDatabase {
                         }
                     }
                 }
-            ]
+            ])
         );
     }
 
+    /** */
     async close() {
         this._db.close();
     }
 
+    /**
+     * @returns {boolean}
+     */
     isPrepared() {
         return this._db.isOpen();
     }
 
+    /**
+     * @returns {Promise<boolean>}
+     */
     async purge() {
         if (this._db.isOpening()) {
             throw new Error('Cannot purge database while opening');
@@ -139,14 +162,13 @@ class DictionaryDatabase {
         return result;
     }
 
+    /**
+     * @param {string} dictionaryName
+     * @param {number} progressRate
+     * @param {import('dictionary-database').DeleteDictionaryProgressCallback} onProgress
+     */
     async deleteDictionary(dictionaryName, progressRate, onProgress) {
-        if (typeof progressRate !== 'number') {
-            progressRate = 1;
-        }
-        if (typeof onProgress !== 'function') {
-            onProgress = () => {};
-        }
-
+        /** @type {[objectStoreName: import('dictionary-database').ObjectStoreName, key: string][][]} */
         const targetGroups = [
             [
                 ['kanji', 'dictionary'],
@@ -166,6 +188,7 @@ class DictionaryDatabase {
             storeCount += targets.length;
         }
 
+        /** @type {import('dictionary-database').DeleteDictionaryProgressData} */
         const progressData = {
             count: 0,
             processed: 0,
@@ -173,6 +196,10 @@ class DictionaryDatabase {
             storesProcesed: 0
         };
 
+        /**
+         * @param {IDBValidKey[]} keys
+         * @returns {IDBValidKey[]}
+         */
         const filterKeys = (keys) => {
             ++progressData.storesProcesed;
             progressData.count += keys.length;
@@ -198,8 +225,15 @@ class DictionaryDatabase {
         }
     }
 
+    /**
+     * @param {string[]} termList
+     * @param {import('dictionary-database').DictionarySet} dictionaries
+     * @param {import('dictionary-database').MatchType} matchType
+     * @returns {Promise<import('dictionary-database').TermEntry[]>}
+     */
     findTermsBulk(termList, dictionaries, matchType) {
         const visited = new Set();
+        /** @type {import('dictionary-database').FindPredicate<string, import('dictionary-database').DatabaseTermEntryWithId>} */
         const predicate = (row) => {
             if (!dictionaries.has(row.dictionary)) { return false; }
             const {id} = row;
@@ -225,54 +259,106 @@ class DictionaryDatabase {
         return this._findMultiBulk('terms', indexNames, termList, createQuery, predicate, createResult);
     }
 
+    /**
+     * @param {import('dictionary-database').TermExactRequest[]} termList
+     * @param {import('dictionary-database').DictionarySet} dictionaries
+     * @returns {Promise<import('dictionary-database').TermEntry[]>}
+     */
     findTermsExactBulk(termList, dictionaries) {
+        /** @type {import('dictionary-database').FindPredicate<import('dictionary-database').TermExactRequest, import('dictionary-database').DatabaseTermEntry>} */
         const predicate = (row, item) => (row.reading === item.reading && dictionaries.has(row.dictionary));
         return this._findMultiBulk('terms', ['expression'], termList, this._createOnlyQuery3, predicate, this._createTermBind1);
     }
 
+    /**
+     * @param {import('dictionary-database').DictionaryAndQueryRequest[]} items
+     * @returns {Promise<import('dictionary-database').TermEntry[]>}
+     */
     findTermsBySequenceBulk(items) {
+        /** @type {import('dictionary-database').FindPredicate<import('dictionary-database').DictionaryAndQueryRequest, import('dictionary-database').DatabaseTermEntry>} */
         const predicate = (row, item) => (row.dictionary === item.dictionary);
         return this._findMultiBulk('terms', ['sequence'], items, this._createOnlyQuery2, predicate, this._createTermBind2);
     }
 
+    /**
+     * @param {string[]} termList
+     * @param {import('dictionary-database').DictionarySet} dictionaries
+     * @returns {Promise<import('dictionary-database').TermMeta[]>}
+     */
     findTermMetaBulk(termList, dictionaries) {
+        /** @type {import('dictionary-database').FindPredicate<string, import('dictionary-database').DatabaseTermMeta>} */
         const predicate = (row) => dictionaries.has(row.dictionary);
         return this._findMultiBulk('termMeta', ['expression'], termList, this._createOnlyQuery1, predicate, this._createTermMetaBind);
     }
 
+    /**
+     * @param {string[]} kanjiList
+     * @param {import('dictionary-database').DictionarySet} dictionaries
+     * @returns {Promise<import('dictionary-database').KanjiEntry[]>}
+     */
     findKanjiBulk(kanjiList, dictionaries) {
+        /** @type {import('dictionary-database').FindPredicate<string, import('dictionary-database').DatabaseKanjiEntry>} */
         const predicate = (row) => dictionaries.has(row.dictionary);
         return this._findMultiBulk('kanji', ['character'], kanjiList, this._createOnlyQuery1, predicate, this._createKanjiBind);
     }
 
+    /**
+     * @param {string[]} kanjiList
+     * @param {import('dictionary-database').DictionarySet} dictionaries
+     * @returns {Promise<import('dictionary-database').KanjiMeta[]>}
+     */
     findKanjiMetaBulk(kanjiList, dictionaries) {
+        /** @type {import('dictionary-database').FindPredicate<string, import('dictionary-database').DatabaseKanjiMeta>} */
         const predicate = (row) => dictionaries.has(row.dictionary);
         return this._findMultiBulk('kanjiMeta', ['character'], kanjiList, this._createOnlyQuery1, predicate, this._createKanjiMetaBind);
     }
 
+    /**
+     * @param {import('dictionary-database').DictionaryAndQueryRequest[]} items
+     * @returns {Promise<(import('dictionary-database').Tag|undefined)[]>}
+     */
     findTagMetaBulk(items) {
+        /** @type {import('dictionary-database').FindPredicate<import('dictionary-database').DictionaryAndQueryRequest, import('dictionary-database').Tag>} */
         const predicate = (row, item) => (row.dictionary === item.dictionary);
         return this._findFirstBulk('tagMeta', 'name', items, this._createOnlyQuery2, predicate);
     }
 
-    findTagForTitle(name, title) {
+    /**
+     * @param {string} name
+     * @param {string} dictionary
+     * @returns {Promise<?import('dictionary-database').Tag>}
+     */
+    findTagForTitle(name, dictionary) {
         const query = IDBKeyRange.only(name);
-        return this._db.find('tagMeta', 'name', query, (row) => (row.dictionary === title), null, null);
+        return this._db.find('tagMeta', 'name', query, (row) => (/** @type {import('dictionary-database').Tag} */ (row).dictionary === dictionary), null, null);
     }
 
+    /**
+     * @param {import('dictionary-database').MediaRequest[]} items
+     * @returns {Promise<import('dictionary-database').Media[]>}
+     */
     getMedia(items) {
+        /** @type {import('dictionary-database').FindPredicate<import('dictionary-database').MediaRequest, import('dictionary-database').MediaDataArrayBufferContent>} */
         const predicate = (row, item) => (row.dictionary === item.dictionary);
         return this._findMultiBulk('media', ['path'], items, this._createOnlyQuery4, predicate, this._createMediaBind);
     }
 
+    /**
+     * @returns {Promise<import('dictionary-importer').Summary[]>}
+     */
     getDictionaryInfo() {
         return new Promise((resolve, reject) => {
             const transaction = this._db.transaction(['dictionaries'], 'readonly');
             const objectStore = transaction.objectStore('dictionaries');
-            this._db.getAll(objectStore, null, resolve, reject);
+            this._db.getAll(objectStore, null, resolve, reject, null);
         });
     }
 
+    /**
+     * @param {string[]} dictionaryNames
+     * @param {boolean} getTotal
+     * @returns {Promise<import('dictionary-database').DictionaryCounts>}
+     */
     getDictionaryCounts(dictionaryNames, getTotal) {
         return new Promise((resolve, reject) => {
             const targets = [
@@ -291,10 +377,11 @@ class DictionaryDatabase {
                 return {objectStore, index};
             });
 
+            /** @type {import('database').CountTarget[]} */
             const countTargets = [];
             if (getTotal) {
                 for (const {objectStore} of databaseTargets) {
-                    countTargets.push([objectStore, null]);
+                    countTargets.push([objectStore, void 0]);
                 }
             }
             for (const dictionaryName of dictionaryNames) {
@@ -304,18 +391,23 @@ class DictionaryDatabase {
                 }
             }
 
+            /**
+             * @param {number[]} results
+             */
             const onCountComplete = (results) => {
                 const resultCount = results.length;
                 const targetCount = targets.length;
+                /** @type {import('dictionary-database').DictionaryCountGroup[]} */
                 const counts = [];
                 for (let i = 0; i < resultCount; i += targetCount) {
+                    /** @type {import('dictionary-database').DictionaryCountGroup} */
                     const countGroup = {};
                     for (let j = 0; j < targetCount; ++j) {
                         countGroup[targets[j][0]] = results[i + j];
                     }
                     counts.push(countGroup);
                 }
-                const total = getTotal ? counts.shift() : null;
+                const total = getTotal ? /** @type {import('dictionary-database').DictionaryCountGroup} */ (counts.shift()) : null;
                 resolve({total, counts});
             };
 
@@ -323,22 +415,47 @@ class DictionaryDatabase {
         });
     }
 
+    /**
+     * @param {string} title
+     * @returns {Promise<boolean>}
+     */
     async dictionaryExists(title) {
         const query = IDBKeyRange.only(title);
         const result = await this._db.find('dictionaries', 'title', query, null, null, void 0);
         return typeof result !== 'undefined';
     }
 
+    /**
+     * @template {import('dictionary-database').ObjectStoreName} T
+     * @param {T} objectStoreName
+     * @param {import('dictionary-database').ObjectStoreData<T>[]} items
+     * @param {number} start
+     * @param {number} count
+     * @returns {Promise<void>}
+     */
     bulkAdd(objectStoreName, items, start, count) {
         return this._db.bulkAdd(objectStoreName, items, start, count);
     }
 
     // Private
 
+    /**
+     * @template [TRow=unknown]
+     * @template [TItem=unknown]
+     * @template [TResult=unknown]
+     * @param {import('dictionary-database').ObjectStoreName} objectStoreName
+     * @param {string[]} indexNames
+     * @param {TItem[]} items
+     * @param {import('dictionary-database').CreateQuery<TItem>} createQuery
+     * @param {import('dictionary-database').FindPredicate<TItem, TRow>} predicate
+     * @param {import('dictionary-database').CreateResult<TItem, TRow, TResult>} createResult
+     * @returns {Promise<TResult[]>}
+     */
     _findMultiBulk(objectStoreName, indexNames, items, createQuery, predicate, createResult) {
         return new Promise((resolve, reject) => {
             const itemCount = items.length;
             const indexCount = indexNames.length;
+            /** @type {TResult[]} */
             const results = [];
             if (itemCount === 0 || indexCount === 0) {
                 resolve(results);
@@ -353,6 +470,10 @@ class DictionaryDatabase {
             }
             let completeCount = 0;
             const requiredCompleteCount = itemCount * indexCount;
+            /**
+             * @param {TRow[]} rows
+             * @param {import('dictionary-database').FindMultiBulkData<TItem>} data
+             */
             const onGetAll = (rows, data) => {
                 for (const row of rows) {
                     if (predicate(row, data.item)) {
@@ -367,15 +488,28 @@ class DictionaryDatabase {
                 const item = items[i];
                 const query = createQuery(item);
                 for (let j = 0; j < indexCount; ++j) {
-                    this._db.getAll(indexList[j], query, onGetAll, reject, {item, itemIndex: i, indexIndex: j});
+                    /** @type {import('dictionary-database').FindMultiBulkData<TItem>} */
+                    const data = {item, itemIndex: i, indexIndex: j};
+                    this._db.getAll(indexList[j], query, onGetAll, reject, data);
                 }
             }
         });
     }
 
+    /**
+     * @template [TRow=unknown]
+     * @template [TItem=unknown]
+     * @param {import('dictionary-database').ObjectStoreName} objectStoreName
+     * @param {string} indexName
+     * @param {TItem[]} items
+     * @param {import('dictionary-database').CreateQuery<TItem>} createQuery
+     * @param {import('dictionary-database').FindPredicate<TItem, TRow>} predicate
+     * @returns {Promise<(TRow|undefined)[]>}
+     */
     _findFirstBulk(objectStoreName, indexName, items, createQuery, predicate) {
         return new Promise((resolve, reject) => {
             const itemCount = items.length;
+            /** @type {(TRow|undefined)[]} */
             const results = new Array(itemCount);
             if (itemCount === 0) {
                 resolve(results);
@@ -386,6 +520,10 @@ class DictionaryDatabase {
             const objectStore = transaction.objectStore(objectStoreName);
             const index = objectStore.index(indexName);
             let completeCount = 0;
+            /**
+             * @param {TRow|undefined} row
+             * @param {number} itemIndex
+             */
             const onFind = (row, itemIndex) => {
                 results[itemIndex] = row;
                 if (++completeCount >= itemCount) {
@@ -400,16 +538,47 @@ class DictionaryDatabase {
         });
     }
 
+    /**
+     * @param {import('dictionary-database').MatchType} matchType
+     * @param {import('dictionary-database').DatabaseTermEntryWithId} row
+     * @param {import('dictionary-database').FindMultiBulkData<string>} data
+     * @returns {import('dictionary-database').TermEntry}
+     */
     _createTermGeneric(matchType, row, data) {
         const matchSourceIsTerm = (data.indexIndex === 0);
         const matchSource = (matchSourceIsTerm ? 'term' : 'reading');
         if ((matchSourceIsTerm ? row.expression : row.reading) === data.item) {
             matchType = 'exact';
         }
-        return this._createTerm(matchSource, matchType, row, data);
+        return this._createTerm(matchSource, matchType, row, data.itemIndex);
+    }
+
+    /**
+     * @param {import('dictionary-database').DatabaseTermEntryWithId} row
+     * @param {import('dictionary-database').FindMultiBulkData<import('dictionary-database').TermExactRequest>} data
+     * @returns {import('dictionary-database').TermEntry}
+     */
+    _createTermExact(row, data) {
+        return this._createTerm('term', 'exact', row, data.itemIndex);
     }
 
-    _createTerm(matchSource, matchType, row, {itemIndex: index}) {
+    /**
+     * @param {import('dictionary-database').DatabaseTermEntryWithId} row
+     * @param {import('dictionary-database').FindMultiBulkData<import('dictionary-database').DictionaryAndQueryRequest>} data
+     * @returns {import('dictionary-database').TermEntry}
+     */
+    _createTermSequenceExact(row, data) {
+        return this._createTerm('sequence', 'exact', row, data.itemIndex);
+    }
+
+    /**
+     * @param {import('dictionary-database').MatchSource} matchSource
+     * @param {import('dictionary-database').MatchType} matchType
+     * @param {import('dictionary-database').DatabaseTermEntryWithId} row
+     * @param {number} index
+     * @returns {import('dictionary-database').TermEntry}
+     */
+    _createTerm(matchSource, matchType, row, index) {
         const {sequence} = row;
         return {
             index,
@@ -428,7 +597,13 @@ class DictionaryDatabase {
         };
     }
 
+    /**
+     * @param {import('dictionary-database').DatabaseKanjiEntry} row
+     * @param {import('dictionary-database').FindMultiBulkData<string>} data
+     * @returns {import('dictionary-database').KanjiEntry}
+     */
     _createKanji(row, {itemIndex: index}) {
+        const {stats} = row;
         return {
             index,
             character: row.character,
@@ -436,23 +611,51 @@ class DictionaryDatabase {
             kunyomi: this._splitField(row.kunyomi),
             tags: this._splitField(row.tags),
             definitions: row.meanings,
-            stats: row.stats,
+            stats: typeof stats === 'object' && stats !== null ? stats : {},
             dictionary: row.dictionary
         };
     }
 
+    /**
+     * @param {import('dictionary-database').DatabaseTermMeta} row
+     * @param {import('dictionary-database').FindMultiBulkData<string>} data
+     * @returns {import('dictionary-database').TermMeta}
+     * @throws {Error}
+     */
     _createTermMeta({expression: term, mode, data, dictionary}, {itemIndex: index}) {
-        return {term, mode, data, dictionary, index};
+        switch (mode) {
+            case 'freq':
+                return {index, term, mode, data, dictionary};
+            case 'pitch':
+                return {index, term, mode, data, dictionary};
+            default:
+                throw new Error(`Unknown mode: ${mode}`);
+        }
     }
 
+    /**
+     * @param {import('dictionary-database').DatabaseKanjiMeta} row
+     * @param {import('dictionary-database').FindMultiBulkData<string>} data
+     * @returns {import('dictionary-database').KanjiMeta}
+     */
     _createKanjiMeta({character, mode, data, dictionary}, {itemIndex: index}) {
-        return {character, mode, data, dictionary, index};
+        return {index, character, mode, data, dictionary};
     }
 
+    /**
+     * @param {import('dictionary-database').MediaDataArrayBufferContent} row
+     * @param {import('dictionary-database').FindMultiBulkData<import('dictionary-database').MediaRequest>} data
+     * @returns {import('dictionary-database').Media}
+     */
     _createMedia(row, {itemIndex: index}) {
-        return Object.assign({}, row, {index});
+        const {dictionary, path, mediaType, width, height, content} = row;
+        return {index, dictionary, path, mediaType, width, height, content};
     }
 
+    /**
+     * @param {unknown} field
+     * @returns {string[]}
+     */
     _splitField(field) {
         return typeof field === 'string' && field.length > 0 ? field.split(' ') : [];
     }
diff --git a/ext/js/language/dictionary-importer-media-loader.js b/ext/js/language/dictionary-importer-media-loader.js
index 4024d0b3e3..a0b1089b6f 100644
--- a/ext/js/language/dictionary-importer-media-loader.js
+++ b/ext/js/language/dictionary-importer-media-loader.js
@@ -20,15 +20,7 @@
  * Class used for loading and validating media during the dictionary import process.
  */
 class DictionaryImporterMediaLoader {
-    /**
-     * Attempts to load an image using an ArrayBuffer and a media type to return details about it.
-     * @param {ArrayBuffer} content The binary content for the image, encoded as an ArrayBuffer.
-     * @param {string} mediaType The media type for the image content.
-     * @param {Transferable[]} [transfer] An optional array of data that should be transferred in `postMessage` calls.
-     *   When the resulting promise resolves, this array will contain the `content` object.
-     * @returns {Promise<{content: ArrayBuffer, width: number, height: number}>} Details about the requested image content.
-     * @throws {Error} An error can be thrown if the image fails to load.
-     */
+    /** @type {import('dictionary-importer-media-loader').GetImageDetailsFunction} */
     getImageDetails(content, mediaType, transfer) {
         return new Promise((resolve, reject) => {
             const image = new Image();
diff --git a/ext/js/language/dictionary-importer.js b/ext/js/language/dictionary-importer.js
index 718d9f1cf3..d97c42e65a 100644
--- a/ext/js/language/dictionary-importer.js
+++ b/ext/js/language/dictionary-importer.js
@@ -19,16 +19,30 @@
 /* global
  * JSZip
  * JsonSchema
+ * JsonSchemaError
  * MediaUtil
  */
 
 class DictionaryImporter {
+    /**
+     * @param {import('dictionary-importer-media-loader').GenericMediaLoader} mediaLoader
+     * @param {import('dictionary-importer').OnProgressCallback} [onProgress]
+     */
     constructor(mediaLoader, onProgress) {
+        /** @type {import('dictionary-importer-media-loader').GenericMediaLoader} */
         this._mediaLoader = mediaLoader;
+        /** @type {import('dictionary-importer').OnProgressCallback} */
         this._onProgress = typeof onProgress === 'function' ? onProgress : () => {};
-        this._progressData = null;
+        /** @type {import('dictionary-importer').ProgressData} */
+        this._progressData = this._createProgressData();
     }
 
+    /**
+     * @param {DictionaryDatabase} dictionaryDatabase
+     * @param {ArrayBuffer} archiveContent
+     * @param {import('dictionary-importer').ImportDetails} details
+     * @returns {Promise<import('dictionary-importer').ImportResult>}
+     */
     async importDictionary(dictionaryDatabase, archiveContent, details) {
         if (!dictionaryDatabase) {
             throw new Error('Invalid database');
@@ -40,7 +54,9 @@ class DictionaryImporter {
         this._progressReset();
 
         // Read archive
-        const archive = await JSZip.loadAsync(archiveContent);
+        // @ts-ignore - JSZip global not defined in type definitions
+        const jszip = /** @type {import('jszip')} */ (JSZip);
+        const archive = await jszip.loadAsync(archiveContent);
 
         // Read and validate index
         const indexFileName = 'index.json';
@@ -49,15 +65,15 @@ class DictionaryImporter {
             throw new Error('No dictionary index found in archive');
         }
 
-        const index = JSON.parse(await indexFile.async('string'));
+        const index = /** @type {import('dictionary-data').Index} */ (JSON.parse(await indexFile.async('string')));
 
         const indexSchema = await this._getSchema('/data/schemas/dictionary-index-schema.json');
         this._validateJsonSchema(index, indexSchema, indexFileName);
 
         const dictionaryTitle = index.title;
-        const version = index.format || index.version;
+        const version = typeof index.format === 'number' ? index.format : index.version;
 
-        if (!dictionaryTitle || !index.revision) {
+        if (typeof version !== 'number' || !dictionaryTitle || !index.revision) {
             throw new Error('Unrecognized dictionary format');
         }
 
@@ -66,13 +82,6 @@ class DictionaryImporter {
             throw new Error('Dictionary is already imported');
         }
 
-        // Data format converters
-        const convertTermBankEntry = (version === 1 ? this._convertTermBankEntryV1.bind(this) : this._convertTermBankEntryV3.bind(this));
-        const convertTermMetaBankEntry = this._convertTermMetaBankEntry.bind(this);
-        const convertKanjiBankEntry = (version === 1 ? this._convertKanjiBankEntryV1.bind(this) : this._convertKanjiBankEntryV3.bind(this));
-        const convertKanjiMetaBankEntry = this._convertKanjiMetaBankEntry.bind(this);
-        const convertTagBankEntry = this._convertTagBankEntry.bind(this);
-
         // Load schemas
         this._progressNextStep(0);
         const dataBankSchemaPaths = this._getDataBankSchemaPaths(version);
@@ -87,11 +96,19 @@ class DictionaryImporter {
 
         // Load data
         this._progressNextStep(termFiles.length + termMetaFiles.length + kanjiFiles.length + kanjiMetaFiles.length + tagFiles.length);
-        const termList      = await this._readFileSequence(termFiles,      convertTermBankEntry,      dataBankSchemas[0], dictionaryTitle);
-        const termMetaList  = await this._readFileSequence(termMetaFiles,  convertTermMetaBankEntry,  dataBankSchemas[1], dictionaryTitle);
-        const kanjiList     = await this._readFileSequence(kanjiFiles,     convertKanjiBankEntry,     dataBankSchemas[2], dictionaryTitle);
-        const kanjiMetaList = await this._readFileSequence(kanjiMetaFiles, convertKanjiMetaBankEntry, dataBankSchemas[3], dictionaryTitle);
-        const tagList       = await this._readFileSequence(tagFiles,       convertTagBankEntry,       dataBankSchemas[4], dictionaryTitle);
+        const termList = await (
+            version === 1 ?
+            this._readFileSequence(termFiles, this._convertTermBankEntryV1.bind(this), dataBankSchemas[0], dictionaryTitle) :
+            this._readFileSequence(termFiles, this._convertTermBankEntryV3.bind(this), dataBankSchemas[0], dictionaryTitle)
+        );
+        const termMetaList = await this._readFileSequence(termMetaFiles, this._convertTermMetaBankEntry.bind(this), dataBankSchemas[1], dictionaryTitle);
+        const kanjiList = await (
+            version === 1 ?
+            this._readFileSequence(kanjiFiles, this._convertKanjiBankEntryV1.bind(this), dataBankSchemas[2], dictionaryTitle) :
+            this._readFileSequence(kanjiFiles, this._convertKanjiBankEntryV3.bind(this), dataBankSchemas[2], dictionaryTitle)
+        );
+        const kanjiMetaList = await this._readFileSequence(kanjiMetaFiles, this._convertKanjiMetaBankEntry.bind(this), dataBankSchemas[3], dictionaryTitle);
+        const tagList = await this._readFileSequence(tagFiles, this._convertTagBankEntry.bind(this), dataBankSchemas[4], dictionaryTitle);
         this._addOldIndexTags(index, tagList, dictionaryTitle);
 
         // Prefix wildcard support
@@ -106,6 +123,7 @@ class DictionaryImporter {
         // Extended data support
         this._progressNextStep(termList.length);
         const formatProgressInterval = 1000;
+        /** @type {import('dictionary-importer').ImportRequirement[]} */
         const requirements = [];
         for (let i = 0, ii = termList.length; i < ii; ++i) {
             const entry = termList[i];
@@ -129,6 +147,7 @@ class DictionaryImporter {
         // Add dictionary descriptor
         this._progressNextStep(termList.length + termMetaList.length + kanjiList.length + kanjiMetaList.length + tagList.length + media.length);
 
+        /** @type {import('dictionary-importer').SummaryCounts} */
         const counts = {
             terms: {total: termList.length},
             termMeta: this._getMetaCounts(termMetaList),
@@ -141,9 +160,15 @@ class DictionaryImporter {
         dictionaryDatabase.bulkAdd('dictionaries', [summary], 0, 1);
 
         // Add data
+        /** @type {Error[]} */
         const errors = [];
         const maxTransactionLength = 1000;
 
+        /**
+         * @template {import('dictionary-database').ObjectStoreName} T
+         * @param {T} objectStoreName
+         * @param {import('dictionary-database').ObjectStoreData<T>[]} entries
+         */
         const bulkAdd = async (objectStoreName, entries) => {
             const ii = entries.length;
             for (let i = 0; i < ii; i += maxTransactionLength) {
@@ -152,7 +177,7 @@ class DictionaryImporter {
                 try {
                     await dictionaryDatabase.bulkAdd(objectStoreName, entries, i, count);
                 } catch (e) {
-                    errors.push(e);
+                    errors.push(e instanceof Error ? e : new Error(`${e}`));
                 }
 
                 this._progressData.index += count;
@@ -172,16 +197,27 @@ class DictionaryImporter {
         return {result: summary, errors};
     }
 
-    _progressReset() {
-        this._progressData = {
+    /**
+     * @returns {import('dictionary-importer').ProgressData}
+     */
+    _createProgressData() {
+        return {
             stepIndex: 0,
             stepCount: 6,
             index: 0,
             count: 0
         };
+    }
+
+    /** */
+    _progressReset() {
+        this._progressData = this._createProgressData();
         this._progress();
     }
 
+    /**
+     * @param {number} count
+     */
     _progressNextStep(count) {
         ++this._progressData.stepIndex;
         this._progressData.index = 0;
@@ -189,17 +225,31 @@ class DictionaryImporter {
         this._progress();
     }
 
+    /** */
     _progress() {
         this._onProgress(this._progressData);
     }
 
+    /**
+     * @param {string} dictionaryTitle
+     * @param {number} version
+     * @param {import('dictionary-data').Index} index
+     * @param {{prefixWildcardsSupported: boolean, counts: import('dictionary-importer').SummaryCounts}} details
+     * @returns {import('dictionary-importer').Summary}
+     */
     _createSummary(dictionaryTitle, version, index, details) {
+        const indexSequenced = index.sequenced;
+        const {prefixWildcardsSupported, counts} = details;
+
+        /** @type {import('dictionary-importer').Summary} */
         const summary = {
             title: dictionaryTitle,
             revision: index.revision,
-            sequenced: index.sequenced,
+            sequenced: typeof indexSequenced === 'boolean' && indexSequenced,
             version,
-            importDate: Date.now()
+            importDate: Date.now(),
+            prefixWildcardsSupported,
+            counts
         };
 
         const {author, url, description, attribution, frequencyMode} = index;
@@ -209,16 +259,24 @@ class DictionaryImporter {
         if (typeof attribution === 'string') { summary.attribution = attribution; }
         if (typeof frequencyMode === 'string') { summary.frequencyMode = frequencyMode; }
 
-        Object.assign(summary, details);
-
         return summary;
     }
 
+    /**
+     * @param {string} fileName
+     * @returns {Promise<JsonSchema>}
+     */
     async _getSchema(fileName) {
-        const schema = await this._fetchJsonAsset(fileName);
+        const schema = /** @type {import('json-schema').Schema} */ (await this._fetchJsonAsset(fileName));
         return new JsonSchema(schema);
     }
 
+    /**
+     * @param {unknown} value
+     * @param {JsonSchema} schema
+     * @param {string} fileName
+     * @throws {Error}
+     */
     _validateJsonSchema(value, schema, fileName) {
         try {
             schema.validate(value);
@@ -227,16 +285,26 @@ class DictionaryImporter {
         }
     }
 
-    _formatSchemaError(e, fileName) {
-        const valuePathString = this._getSchemaErrorPathString(e.valueStack, 'dictionary');
-        const schemaPathString = this._getSchemaErrorPathString(e.schemaStack, 'schema');
+    /**
+     * @param {unknown} error
+     * @param {string} fileName
+     * @returns {ExtensionError}
+     */
+    _formatSchemaError(error, fileName) {
+        const valuePathString = error instanceof JsonSchemaError ? this._getSchemaErrorPathString(error.valueStack, 'dictionary') : '<unknown>';
+        const schemaPathString = error instanceof JsonSchemaError ? this._getSchemaErrorPathString(error.schemaStack, 'schema') : '<unknown>';
 
-        const e2 = new Error(`Dictionary has invalid data in '${fileName}' for value '${valuePathString}', validated against '${schemaPathString}': ${e.message}`);
-        e2.data = e;
+        const e2 = new ExtensionError(`Dictionary has invalid data in '${fileName}' for value '${valuePathString}', validated against '${schemaPathString}': ${error instanceof Error ? error.message : `${error}`}`);
+        e2.data = error;
 
         return e2;
     }
 
+    /**
+     * @param {(import('json-schema').ValueStackItem|import('json-schema').SchemaStackItem)[]} infoList
+     * @param {string} base
+     * @returns {string}
+     */
     _getSchemaErrorPathString(infoList, base='') {
         let result = base;
         for (const {path} of infoList) {
@@ -262,6 +330,10 @@ class DictionaryImporter {
         return result;
     }
 
+    /**
+     * @param {number} version
+     * @returns {[termBank: string, termMetaBank: string, kanjiBank: string, kanjiMetaBank: string, tagBank: string]}
+     */
     _getDataBankSchemaPaths(version) {
         const termBank = (
             version === 1 ?
@@ -280,6 +352,13 @@ class DictionaryImporter {
         return [termBank, termMetaBank, kanjiBank, kanjiMetaBank, tagBank];
     }
 
+    /**
+     * @param {import('dictionary-data').TermGlossaryText|import('dictionary-data').TermGlossaryImage|import('dictionary-data').TermGlossaryStructuredContent} data
+     * @param {import('dictionary-database').DatabaseTermEntry} entry
+     * @param {import('dictionary-importer').ImportRequirement[]} requirements
+     * @returns {import('dictionary-data').TermGlossary}
+     * @throws {Error}
+     */
     _formatDictionaryTermGlossaryObject(data, entry, requirements) {
         switch (data.type) {
             case 'text':
@@ -289,16 +368,32 @@ class DictionaryImporter {
             case 'structured-content':
                 return this._formatStructuredContent(data, entry, requirements);
             default:
-                throw new Error(`Unhandled data type: ${data.type}`);
+                throw new Error(`Unhandled data type: ${/** @type {import('core').SerializableObject} */ (data).type}`);
         }
     }
 
+    /**
+     * @param {import('dictionary-data').TermGlossaryImage} data
+     * @param {import('dictionary-database').DatabaseTermEntry} entry
+     * @param {import('dictionary-importer').ImportRequirement[]} requirements
+     * @returns {import('dictionary-data').TermGlossaryImage}
+     */
     _formatDictionaryTermGlossaryImage(data, entry, requirements) {
-        const target = {};
-        requirements.push({type: 'image', target, args: [data, entry]});
+        /** @type {import('dictionary-data').TermGlossaryImage} */
+        const target = {
+            type: 'image',
+            path: '' // Will be populated during requirement resolution
+        };
+        requirements.push({type: 'image', target, source: data, entry});
         return target;
     }
 
+    /**
+     * @param {import('dictionary-data').TermGlossaryStructuredContent} data
+     * @param {import('dictionary-database').DatabaseTermEntry} entry
+     * @param {import('dictionary-importer').ImportRequirement[]} requirements
+     * @returns {import('dictionary-data').TermGlossaryStructuredContent}
+     */
     _formatStructuredContent(data, entry, requirements) {
         const content = this._prepareStructuredContent(data.content, entry, requirements);
         return {
@@ -307,6 +402,12 @@ class DictionaryImporter {
         };
     }
 
+    /**
+     * @param {import('structured-content').Content} content
+     * @param {import('dictionary-database').DatabaseTermEntry} entry
+     * @param {import('dictionary-importer').ImportRequirement[]} requirements
+     * @returns {import('structured-content').Content}
+     */
     _prepareStructuredContent(content, entry, requirements) {
         if (typeof content === 'string' || !(typeof content === 'object' && content !== null)) {
             return content;
@@ -329,14 +430,31 @@ class DictionaryImporter {
         return content;
     }
 
+    /**
+     * @param {import('structured-content').ImageElement} content
+     * @param {import('dictionary-database').DatabaseTermEntry} entry
+     * @param {import('dictionary-importer').ImportRequirement[]} requirements
+     * @returns {import('structured-content').ImageElement}
+     */
     _prepareStructuredContentImage(content, entry, requirements) {
-        const target = {};
-        requirements.push({type: 'structured-content-image', target, args: [content, entry]});
+        /** @type {import('structured-content').ImageElement} */
+        const target = {
+            tag: 'img',
+            path: '' // Will be populated during requirement resolution
+        };
+        requirements.push({type: 'structured-content-image', target, source: content, entry});
         return target;
     }
 
+    /**
+     * @param {import('dictionary-importer').ImportRequirement[]} requirements
+     * @param {import('jszip')} archive
+     * @returns {Promise<{media: import('dictionary-database').MediaDataArrayBufferContent[]}>}
+     */
     async _resolveAsyncRequirements(requirements, archive) {
+        /** @type {Map<string, import('dictionary-database').MediaDataArrayBufferContent>} */
         const media = new Map();
+        /** @type {import('dictionary-importer').ImportRequirementContext} */
         const context = {archive, media};
 
         for (const requirement of requirements) {
@@ -348,37 +466,65 @@ class DictionaryImporter {
         };
     }
 
+    /**
+     * @param {import('dictionary-importer').ImportRequirementContext} context
+     * @param {import('dictionary-importer').ImportRequirement} requirement
+     */
     async _resolveAsyncRequirement(context, requirement) {
-        const {type, target, args} = requirement;
-        let result;
-        switch (type) {
+        switch (requirement.type) {
             case 'image':
-                result = await this._resolveDictionaryTermGlossaryImage(context, ...args);
+                await this._resolveDictionaryTermGlossaryImage(
+                    context,
+                    requirement.target,
+                    requirement.source,
+                    requirement.entry
+                );
                 break;
             case 'structured-content-image':
-                result = await this._resolveStructuredContentImage(context, ...args);
+                await this._resolveStructuredContentImage(
+                    context,
+                    requirement.target,
+                    requirement.source,
+                    requirement.entry
+                );
                 break;
             default:
                 return;
         }
-        Object.assign(target, result);
         ++this._progressData.index;
         this._progress();
     }
 
-    async _resolveDictionaryTermGlossaryImage(context, data, entry) {
-        return await this._createImageData(context, data, entry, {type: 'image'});
-    }
-
-    async _resolveStructuredContentImage(context, content, entry) {
-        const {verticalAlign, sizeUnits} = content;
-        const result = await this._createImageData(context, content, entry, {tag: 'img'});
-        if (typeof verticalAlign === 'string') { result.verticalAlign = verticalAlign; }
-        if (typeof sizeUnits === 'string') { result.sizeUnits = sizeUnits; }
-        return result;
-    }
-
-    async _createImageData(context, data, entry, attributes) {
+    /**
+     * @param {import('dictionary-importer').ImportRequirementContext} context
+     * @param {import('dictionary-data').TermGlossaryImage} target
+     * @param {import('dictionary-data').TermGlossaryImage} source
+     * @param {import('dictionary-database').DatabaseTermEntry} entry
+     */
+    async _resolveDictionaryTermGlossaryImage(context, target, source, entry) {
+        await this._createImageData(context, target, source, entry);
+    }
+
+    /**
+     * @param {import('dictionary-importer').ImportRequirementContext} context
+     * @param {import('structured-content').ImageElement} target
+     * @param {import('structured-content').ImageElement} source
+     * @param {import('dictionary-database').DatabaseTermEntry} entry
+     */
+    async _resolveStructuredContentImage(context, target, source, entry) {
+        const {verticalAlign, sizeUnits} = source;
+        await this._createImageData(context, target, source, entry);
+        if (typeof verticalAlign === 'string') { target.verticalAlign = verticalAlign; }
+        if (typeof sizeUnits === 'string') { target.sizeUnits = sizeUnits; }
+    }
+
+    /**
+     * @param {import('dictionary-importer').ImportRequirementContext} context
+     * @param {import('structured-content').ImageElementBase} target
+     * @param {import('structured-content').ImageElementBase} source
+     * @param {import('dictionary-database').DatabaseTermEntry} entry
+     */
+    async _createImageData(context, target, source, entry) {
         const {
             path,
             width: preferredWidth,
@@ -391,26 +537,37 @@ class DictionaryImporter {
             background,
             collapsed,
             collapsible
-        } = data;
+        } = source;
         const {width, height} = await this._getImageMedia(context, path, entry);
-        const newData = Object.assign({}, attributes, {path, width, height});
-        if (typeof preferredWidth === 'number') { newData.preferredWidth = preferredWidth; }
-        if (typeof preferredHeight === 'number') { newData.preferredHeight = preferredHeight; }
-        if (typeof title === 'string') { newData.title = title; }
-        if (typeof description === 'string') { newData.description = description; }
-        if (typeof pixelated === 'boolean') { newData.pixelated = pixelated; }
-        if (typeof imageRendering === 'string') { newData.imageRendering = imageRendering; }
-        if (typeof appearance === 'string') { newData.appearance = appearance; }
-        if (typeof background === 'boolean') { newData.background = background; }
-        if (typeof collapsed === 'boolean') { newData.collapsed = collapsed; }
-        if (typeof collapsible === 'boolean') { newData.collapsible = collapsible; }
-        return newData;
-    }
-
+        target.path = path;
+        target.width = width;
+        target.height = height;
+        if (typeof preferredWidth === 'number') { target.preferredWidth = preferredWidth; }
+        if (typeof preferredHeight === 'number') { target.preferredHeight = preferredHeight; }
+        if (typeof title === 'string') { target.title = title; }
+        if (typeof description === 'string') { target.description = description; }
+        if (typeof pixelated === 'boolean') { target.pixelated = pixelated; }
+        if (typeof imageRendering === 'string') { target.imageRendering = imageRendering; }
+        if (typeof appearance === 'string') { target.appearance = appearance; }
+        if (typeof background === 'boolean') { target.background = background; }
+        if (typeof collapsed === 'boolean') { target.collapsed = collapsed; }
+        if (typeof collapsible === 'boolean') { target.collapsible = collapsible; }
+    }
+
+    /**
+     * @param {import('dictionary-importer').ImportRequirementContext} context
+     * @param {string} path
+     * @param {import('dictionary-database').DatabaseTermEntry} entry
+     * @returns {Promise<import('dictionary-database').MediaDataArrayBufferContent>}
+     */
     async _getImageMedia(context, path, entry) {
         const {media} = context;
         const {dictionary} = entry;
 
+        /**
+         * @param {string} message
+         * @returns {Error}
+         */
         const createError = (message) => {
             const {expression, reading} = entry;
             const readingSource = reading.length > 0 ? ` (${reading})`: '';
@@ -462,6 +619,10 @@ class DictionaryImporter {
         return mediaData;
     }
 
+    /**
+     * @param {string} url
+     * @returns {Promise<unknown>}
+     */
     async _fetchJsonAsset(url) {
         const response = await fetch(url, {
             method: 'GET',
@@ -477,6 +638,11 @@ class DictionaryImporter {
         return await response.json();
     }
 
+    /**
+     * @param {import('dictionary-data').TermV1} entry
+     * @param {string} dictionary
+     * @returns {import('dictionary-database').DatabaseTermEntry}
+     */
     _convertTermBankEntryV1(entry, dictionary) {
         let [expression, reading, definitionTags, rules, score, ...glossary] = entry;
         expression = this._normalizeTermOrReading(expression);
@@ -484,6 +650,11 @@ class DictionaryImporter {
         return {expression, reading, definitionTags, rules, score, glossary, dictionary};
     }
 
+    /**
+     * @param {import('dictionary-data').TermV3} entry
+     * @param {string} dictionary
+     * @returns {import('dictionary-database').DatabaseTermEntry}
+     */
     _convertTermBankEntryV3(entry, dictionary) {
         let [expression, reading, definitionTags, rules, score, glossary, sequence, termTags] = entry;
         expression = this._normalizeTermOrReading(expression);
@@ -491,40 +662,75 @@ class DictionaryImporter {
         return {expression, reading, definitionTags, rules, score, glossary, sequence, termTags, dictionary};
     }
 
+    /**
+     * @param {import('dictionary-data').TermMeta} entry
+     * @param {string} dictionary
+     * @returns {import('dictionary-database').DatabaseTermMeta}
+     */
     _convertTermMetaBankEntry(entry, dictionary) {
         const [expression, mode, data] = entry;
-        return {expression, mode, data, dictionary};
+        return /** @type {import('dictionary-database').DatabaseTermMeta} */ ({expression, mode, data, dictionary});
     }
 
+    /**
+     * @param {import('dictionary-data').KanjiV1} entry
+     * @param {string} dictionary
+     * @returns {import('dictionary-database').DatabaseKanjiEntry}
+     */
     _convertKanjiBankEntryV1(entry, dictionary) {
         const [character, onyomi, kunyomi, tags, ...meanings] = entry;
         return {character, onyomi, kunyomi, tags, meanings, dictionary};
     }
 
+    /**
+     * @param {import('dictionary-data').KanjiV3} entry
+     * @param {string} dictionary
+     * @returns {import('dictionary-database').DatabaseKanjiEntry}
+     */
     _convertKanjiBankEntryV3(entry, dictionary) {
         const [character, onyomi, kunyomi, tags, meanings, stats] = entry;
         return {character, onyomi, kunyomi, tags, meanings, stats, dictionary};
     }
 
+    /**
+     * @param {import('dictionary-data').KanjiMeta} entry
+     * @param {string} dictionary
+     * @returns {import('dictionary-database').DatabaseKanjiMeta}
+     */
     _convertKanjiMetaBankEntry(entry, dictionary) {
         const [character, mode, data] = entry;
         return {character, mode, data, dictionary};
     }
 
+    /**
+     * @param {import('dictionary-data').Tag} entry
+     * @param {string} dictionary
+     * @returns {import('dictionary-database').Tag}
+     */
     _convertTagBankEntry(entry, dictionary) {
         const [name, category, order, notes, score] = entry;
         return {name, category, order, notes, score, dictionary};
     }
 
+    /**
+     * @param {import('dictionary-data').Index} index
+     * @param {import('dictionary-database').Tag[]} results
+     * @param {string} dictionary
+     */
     _addOldIndexTags(index, results, dictionary) {
         const {tagMeta} = index;
         if (typeof tagMeta !== 'object' || tagMeta === null) { return; }
-        for (const name of Object.keys(tagMeta)) {
-            const {category, order, notes, score} = tagMeta[name];
+        for (const [name, value] of Object.entries(tagMeta)) {
+            const {category, order, notes, score} = value;
             results.push({name, category, order, notes, score, dictionary});
         }
     }
 
+    /**
+     * @param {import('jszip')} archive
+     * @param {string} fileNameFormat
+     * @returns {import('jszip').JSZipObject[]}
+     */
     _getArchiveFiles(archive, fileNameFormat) {
         const indexPosition = fileNameFormat.indexOf('?');
         const prefix = fileNameFormat.substring(0, indexPosition);
@@ -539,6 +745,15 @@ class DictionaryImporter {
         return results;
     }
 
+    /**
+     * @template [TEntry=unknown]
+     * @template [TResult=unknown]
+     * @param {import('jszip').JSZipObject[]} files
+     * @param {(entry: TEntry, dictionaryTitle: string) => TResult} convertEntry
+     * @param {JsonSchema} schema
+     * @param {string} dictionaryTitle
+     * @returns {Promise<TResult[]>}
+     */
     async _readFileSequence(files, convertEntry, schema, dictionaryTitle) {
         const progressData = this._progressData;
         let count = 0;
@@ -547,14 +762,14 @@ class DictionaryImporter {
             schema.progressInterval = 1000;
             schema.progress = (s) => {
                 const index = s.getValueStackLength() > 1 ? s.getValueStackItem(1).path : 0;
-                progressData.index = startIndex + (index / count);
+                progressData.index = startIndex + ((typeof index === 'number' ? index : 0) / count);
                 this._progress();
             };
         }
 
         const results = [];
         for (const file of files) {
-            const entries = JSON.parse(await file.async('string'));
+            const entries = /** @type {unknown} */ (JSON.parse(await file.async('string')));
 
             count = Array.isArray(entries) ? Math.max(entries.length, 1) : 1;
             startIndex = progressData.index;
@@ -565,20 +780,28 @@ class DictionaryImporter {
             progressData.index = startIndex + 1;
             this._progress();
 
-            for (const entry of entries) {
-                results.push(convertEntry(entry, dictionaryTitle));
+            if (Array.isArray(entries)) {
+                for (const entry of entries) {
+                    results.push(convertEntry(/** @type {TEntry} */ (entry), dictionaryTitle));
+                }
             }
         }
         return results;
     }
 
+    /**
+     * @param {import('dictionary-database').DatabaseTermMeta[]|import('dictionary-database').DatabaseKanjiMeta[]} metaList
+     * @returns {import('dictionary-importer').SummaryMetaCount}
+     */
     _getMetaCounts(metaList) {
+        /** @type {Map<string, number>} */
         const countsMap = new Map();
         for (const {mode} of metaList) {
             let count = countsMap.get(mode);
             count = typeof count !== 'undefined' ? count + 1 : 1;
             countsMap.set(mode, count);
         }
+        /** @type {import('dictionary-importer').SummaryMetaCount} */
         const counts = {total: metaList.length};
         for (const [key, value] of countsMap.entries()) {
             if (Object.prototype.hasOwnProperty.call(counts, key)) { continue; }
@@ -587,6 +810,10 @@ class DictionaryImporter {
         return counts;
     }
 
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
     _normalizeTermOrReading(text) {
         // Note: this function should not perform String.normalize on the text,
         // as it will characters in an undesirable way.
diff --git a/ext/js/language/dictionary-worker-handler.js b/ext/js/language/dictionary-worker-handler.js
index 0e3e849501..47e33dd902 100644
--- a/ext/js/language/dictionary-worker-handler.js
+++ b/ext/js/language/dictionary-worker-handler.js
@@ -24,17 +24,22 @@
 
 class DictionaryWorkerHandler {
     constructor() {
+        /** @type {DictionaryWorkerMediaLoader} */
         this._mediaLoader = new DictionaryWorkerMediaLoader();
     }
 
+    /** */
     prepare() {
         self.addEventListener('message', this._onMessage.bind(this), false);
     }
 
     // Private
 
-    _onMessage(e) {
-        const {action, params} = e.data;
+    /**
+     * @param {MessageEvent<import('dictionary-worker-handler').Message>} event
+     */
+    _onMessage(event) {
+        const {action, params} = event.data;
         switch (action) {
             case 'importDictionary':
                 this._onMessageWithProgress(params, this._importDictionary.bind(this));
@@ -51,7 +56,15 @@ class DictionaryWorkerHandler {
         }
     }
 
+    /**
+     * @template [T=unknown]
+     * @param {T} params
+     * @param {(details: T, onProgress: import('dictionary-worker-handler').OnProgressCallback) => Promise<unknown>} handler
+     */
     async _onMessageWithProgress(params, handler) {
+        /**
+         * @param {...unknown} args
+         */
         const onProgress = (...args) => {
             self.postMessage({
                 action: 'progress',
@@ -63,11 +76,16 @@ class DictionaryWorkerHandler {
             const result = await handler(params, onProgress);
             response = {result};
         } catch (e) {
-            response = {error: serializeError(e)};
+            response = {error: ExtensionError.serialize(e)};
         }
         self.postMessage({action: 'complete', params: response});
     }
 
+    /**
+     * @param {import('dictionary-worker-handler').ImportDictionaryMessageParams} details
+     * @param {import('dictionary-worker-handler').OnProgressCallback} onProgress
+     * @returns {Promise<import('dictionary-worker').MessageCompleteResultSerialized>}
+     */
     async _importDictionary({details, archiveContent}, onProgress) {
         const dictionaryDatabase = await this._getPreparedDictionaryDatabase();
         try {
@@ -75,13 +93,18 @@ class DictionaryWorkerHandler {
             const {result, errors} = await dictionaryImporter.importDictionary(dictionaryDatabase, archiveContent, details);
             return {
                 result,
-                errors: errors.map((error) => serializeError(error))
+                errors: errors.map((error) => ExtensionError.serialize(error))
             };
         } finally {
             dictionaryDatabase.close();
         }
     }
 
+    /**
+     * @param {import('dictionary-worker-handler').DeleteDictionaryMessageParams} details
+     * @param {import('dictionary-database').DeleteDictionaryProgressCallback} onProgress
+     * @returns {Promise<void>}
+     */
     async _deleteDictionary({dictionaryTitle}, onProgress) {
         const dictionaryDatabase = await this._getPreparedDictionaryDatabase();
         try {
@@ -91,6 +114,10 @@ class DictionaryWorkerHandler {
         }
     }
 
+    /**
+     * @param {import('dictionary-worker-handler').GetDictionaryCountsMessageParams} details
+     * @returns {Promise<import('dictionary-database').DictionaryCounts>}
+     */
     async _getDictionaryCounts({dictionaryNames, getTotal}) {
         const dictionaryDatabase = await this._getPreparedDictionaryDatabase();
         try {
@@ -100,6 +127,9 @@ class DictionaryWorkerHandler {
         }
     }
 
+    /**
+     * @returns {Promise<DictionaryDatabase>}
+     */
     async _getPreparedDictionaryDatabase() {
         const dictionaryDatabase = new DictionaryDatabase();
         await dictionaryDatabase.prepare();
diff --git a/ext/js/language/dictionary-worker-main.js b/ext/js/language/dictionary-worker-main.js
index cbb3247ca6..5984e5ce66 100644
--- a/ext/js/language/dictionary-worker-main.js
+++ b/ext/js/language/dictionary-worker-main.js
@@ -23,6 +23,7 @@
 self.importScripts(
     '/lib/jszip.min.js',
     '/js/core.js',
+    '/js/core/extension-error.js',
     '/js/data/database.js',
     '/js/data/json-schema.js',
     '/js/general/cache-map.js',
diff --git a/ext/js/language/dictionary-worker-media-loader.js b/ext/js/language/dictionary-worker-media-loader.js
index d2ef4fae4f..8160dc5823 100644
--- a/ext/js/language/dictionary-worker-media-loader.js
+++ b/ext/js/language/dictionary-worker-media-loader.js
@@ -25,12 +25,13 @@ class DictionaryWorkerMediaLoader {
      * Creates a new instance of the media loader.
      */
     constructor() {
+        /** @type {Map<string, {resolve: (result: import('dictionary-worker-media-loader').ImageDetails) => void, reject: (reason?: import('core').RejectionReason) => void}>} */
         this._requests = new Map();
     }
 
     /**
      * Handles a response message posted to the worker thread.
-     * @param {{id: string, error: object|undefined, result: any|undefined}} params Details of the response.
+     * @param {import('dictionary-worker-media-loader').HandleMessageParams} params Details of the response.
      */
     handleMessage(params) {
         const {id} = params;
@@ -39,24 +40,19 @@ class DictionaryWorkerMediaLoader {
         this._requests.delete(id);
         const {error} = params;
         if (typeof error !== 'undefined') {
-            request.reject(deserializeError(error));
+            request.reject(ExtensionError.deserialize(error));
         } else {
             request.resolve(params.result);
         }
     }
 
-    /**
-     * Attempts to load an image using an ArrayBuffer and a media type to return details about it.
-     * @param {ArrayBuffer} content The binary content for the image, encoded as an ArrayBuffer.
-     * @param {string} mediaType The media type for the image content.
-     * @returns {Promise<{content: ArrayBuffer, width: number, height: number}>} Details about the requested image content.
-     * @throws {Error} An error can be thrown if the image fails to load.
-     */
+    /** @type {import('dictionary-importer-media-loader').GetImageDetailsFunction} */
     getImageDetails(content, mediaType) {
         return new Promise((resolve, reject) => {
             const id = generateId(16);
             this._requests.set(id, {resolve, reject});
-            self.postMessage({
+            // This is executed in a Worker context, so the self needs to be force cast
+            /** @type {Worker} */ (/** @type {unknown} */ (self)).postMessage({
                 action: 'getImageDetails',
                 params: {id, content, mediaType}
             }, [content]);
diff --git a/ext/js/language/dictionary-worker.js b/ext/js/language/dictionary-worker.js
index b415a34686..f2e81425a4 100644
--- a/ext/js/language/dictionary-worker.js
+++ b/ext/js/language/dictionary-worker.js
@@ -22,32 +22,60 @@
 
 class DictionaryWorker {
     constructor() {
+        /** @type {DictionaryImporterMediaLoader} */
         this._dictionaryImporterMediaLoader = new DictionaryImporterMediaLoader();
     }
 
+    /**
+     * @param {ArrayBuffer} archiveContent
+     * @param {import('dictionary-importer').ImportDetails} details
+     * @param {?import('dictionary-worker').ImportProgressCallback} onProgress
+     * @returns {Promise<import('dictionary-importer').ImportResult>}
+     */
     importDictionary(archiveContent, details, onProgress) {
         return this._invoke(
             'importDictionary',
             {details, archiveContent},
             [archiveContent],
             onProgress,
-            this._formatimportDictionaryResult.bind(this)
+            this._formatImportDictionaryResult.bind(this)
         );
     }
 
+    /**
+     * @param {string} dictionaryTitle
+     * @param {?import('dictionary-worker').DeleteProgressCallback} onProgress
+     * @returns {Promise<void>}
+     */
     deleteDictionary(dictionaryTitle, onProgress) {
-        return this._invoke('deleteDictionary', {dictionaryTitle}, [], onProgress);
+        return this._invoke('deleteDictionary', {dictionaryTitle}, [], onProgress, null);
     }
 
+    /**
+     * @param {string[]} dictionaryNames
+     * @param {boolean} getTotal
+     * @returns {Promise<import('dictionary-database').DictionaryCounts>}
+     */
     getDictionaryCounts(dictionaryNames, getTotal) {
-        return this._invoke('getDictionaryCounts', {dictionaryNames, getTotal}, [], null);
+        return this._invoke('getDictionaryCounts', {dictionaryNames, getTotal}, [], null, null);
     }
 
     // Private
 
+    /**
+     * @template [TParams=import('core').SerializableObject]
+     * @template [TResponseRaw=unknown]
+     * @template [TResponse=unknown]
+     * @param {string} action
+     * @param {TParams} params
+     * @param {Transferable[]} transfer
+     * @param {?(arg: import('core').SafeAny) => void} onProgress
+     * @param {?(result: TResponseRaw) => TResponse} formatResult
+     */
     _invoke(action, params, transfer, onProgress, formatResult) {
         return new Promise((resolve, reject) => {
             const worker = new Worker('/js/language/dictionary-worker-main.js', {});
+            /** @type {import('dictionary-worker').InvokeDetails<TResponseRaw, TResponse>} */
             const details = {
                 complete: false,
                 worker,
@@ -57,20 +85,29 @@ class DictionaryWorker {
                 onProgress,
                 formatResult
             };
-            const onMessage = this._onMessage.bind(this, details);
+            // Ugly typecast below due to not being able to explicitly state the template types
+            /** @type {(event: MessageEvent<import('dictionary-worker').MessageData<TResponseRaw>>) => void} */
+            const onMessage = /** @type {(details: import('dictionary-worker').InvokeDetails<TResponseRaw, TResponse>, event: MessageEvent<import('dictionary-worker').MessageData<TResponseRaw>>) => void} */ (this._onMessage).bind(this, details);
             details.onMessage = onMessage;
             worker.addEventListener('message', onMessage);
             worker.postMessage({action, params}, transfer);
         });
     }
 
-    _onMessage(details, e) {
+    /**
+     * @template [TResponseRaw=unknown]
+     * @template [TResponse=unknown]
+     * @param {import('dictionary-worker').InvokeDetails<TResponseRaw, TResponse>} details
+     * @param {MessageEvent<import('dictionary-worker').MessageData<TResponseRaw>>} event
+     */
+    _onMessage(details, event) {
         if (details.complete) { return; }
-        const {action, params} = e.data;
+        const {action, params} = event.data;
         switch (action) {
             case 'complete':
                 {
                     const {worker, resolve, reject, onMessage, formatResult} = details;
+                    if (worker === null || onMessage === null || resolve === null || reject === null) { return; }
                     details.complete = true;
                     details.worker = null;
                     details.resolve = null;
@@ -87,50 +124,82 @@ class DictionaryWorker {
                 this._onMessageProgress(params, details.onProgress);
                 break;
             case 'getImageDetails':
-                this._onMessageGetImageDetails(params, details.worker);
+                {
+                    const {worker} = details;
+                    if (worker === null) { return; }
+                    this._onMessageGetImageDetails(params, worker);
+                }
                 break;
         }
     }
 
+    /**
+     * @template [TResponseRaw=unknown]
+     * @template [TResponse=unknown]
+     * @param {import('dictionary-worker').MessageCompleteParams<TResponseRaw>} params
+     * @param {(result: TResponse) => void} resolve
+     * @param {(reason?: import('core').RejectionReason) => void} reject
+     * @param {?(result: TResponseRaw) => TResponse} formatResult
+     */
     _onMessageComplete(params, resolve, reject, formatResult) {
         const {error} = params;
         if (typeof error !== 'undefined') {
-            reject(deserializeError(error));
+            reject(ExtensionError.deserialize(error));
         } else {
-            let {result} = params;
-            try {
-                if (typeof formatResult === 'function') {
-                    result = formatResult(result);
+            const {result} = params;
+            if (typeof formatResult === 'function') {
+                let result2;
+                try {
+                    result2 = formatResult(result);
+                } catch (e) {
+                    reject(e);
+                    return;
                 }
-            } catch (e) {
-                reject(e);
-                return;
+                resolve(result2);
+            } else {
+                // If formatResult is not provided, the response is assumed to be the same type
+                resolve(/** @type {TResponse} */ (/** @type {unknown} */ (result)));
             }
-            resolve(result);
         }
     }
 
+    /**
+     * @param {import('dictionary-worker').MessageProgressParams} params
+     * @param {?(...args: unknown[]) => void} onProgress
+     */
     _onMessageProgress(params, onProgress) {
         if (typeof onProgress !== 'function') { return; }
         const {args} = params;
         onProgress(...args);
     }
 
+    /**
+     * @param {import('dictionary-worker').MessageGetImageDetailsParams} params
+     * @param {Worker} worker
+     */
     async _onMessageGetImageDetails(params, worker) {
         const {id, content, mediaType} = params;
+        /** @type {Transferable[]} */
         const transfer = [];
         let response;
         try {
             const result = await this._dictionaryImporterMediaLoader.getImageDetails(content, mediaType, transfer);
             response = {id, result};
         } catch (e) {
-            response = {id, error: serializeError(e)};
+            response = {id, error: ExtensionError.serialize(e)};
         }
         worker.postMessage({action: 'getImageDetails.response', params: response}, transfer);
     }
 
-    _formatimportDictionaryResult(result) {
-        result.errors = result.errors.map((error) => deserializeError(error));
-        return result;
+    /**
+     * @param {import('dictionary-worker').MessageCompleteResultSerialized} response
+     * @returns {import('dictionary-worker').MessageCompleteResult}
+     */
+    _formatImportDictionaryResult(response) {
+        const {result, errors} = response;
+        return {
+            result,
+            errors: errors.map((error) => ExtensionError.deserialize(error))
+        };
     }
 }
diff --git a/ext/js/language/sandbox/dictionary-data-util.js b/ext/js/language/sandbox/dictionary-data-util.js
index 323076e8b6..7fb73e2e50 100644
--- a/ext/js/language/sandbox/dictionary-data-util.js
+++ b/ext/js/language/sandbox/dictionary-data-util.js
@@ -17,6 +17,10 @@
  */
 
 class DictionaryDataUtil {
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {import('dictionary-data-util').TagGroup[]}
+     */
     static groupTermTags(dictionaryEntry) {
         const {headwords} = dictionaryEntry;
         const headwordCount = headwords.length;
@@ -27,8 +31,8 @@ class DictionaryDataUtil {
             const {tags} = headwords[i];
             for (const tag of tags) {
                 if (uniqueCheck) {
-                    const {name, category, notes, dictionary} = tag;
-                    const key = this._createMapKey([name, category, notes, dictionary]);
+                    const {name, category, content, dictionaries} = tag;
+                    const key = this._createMapKey([name, category, content, dictionaries]);
                     const index = resultsIndexMap.get(key);
                     if (typeof index !== 'undefined') {
                         const existingItem = results[index];
@@ -45,11 +49,16 @@ class DictionaryDataUtil {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {import('dictionary-data-util').DictionaryFrequency<import('dictionary-data-util').TermFrequency>[]}
+     */
     static groupTermFrequencies(dictionaryEntry) {
-        const {headwords, frequencies} = dictionaryEntry;
+        const {headwords, frequencies: sourceFrequencies} = dictionaryEntry;
 
+        /** @type {import('dictionary-data-util').TermFrequenciesMap1} */
         const map1 = new Map();
-        for (const {headwordIndex, dictionary, hasReading, frequency, displayValue} of frequencies) {
+        for (const {headwordIndex, dictionary, hasReading, frequency, displayValue} of sourceFrequencies) {
             const {term, reading} = headwords[headwordIndex];
 
             let map2 = map1.get(dictionary);
@@ -68,12 +77,30 @@ class DictionaryDataUtil {
 
             frequencyData.values.set(this._createMapKey([frequency, displayValue]), {frequency, displayValue});
         }
-        return this._createFrequencyGroupsFromMap(map1);
+
+        const results = [];
+        for (const [dictionary, map2] of map1.entries()) {
+            const frequencies = [];
+            for (const {term, reading, values} of map2.values()) {
+                frequencies.push({
+                    term,
+                    reading,
+                    values: [...values.values()]
+                });
+            }
+            results.push({dictionary, frequencies});
+        }
+        return results;
     }
 
-    static groupKanjiFrequencies(frequencies) {
+    /**
+     * @param {import('dictionary').KanjiFrequency[]} sourceFrequencies
+     * @returns {import('dictionary-data-util').DictionaryFrequency<import('dictionary-data-util').KanjiFrequency>[]}
+     */
+    static groupKanjiFrequencies(sourceFrequencies) {
+        /** @type {import('dictionary-data-util').KanjiFrequenciesMap1} */
         const map1 = new Map();
-        for (const {dictionary, character, frequency, displayValue} of frequencies) {
+        for (const {dictionary, character, frequency, displayValue} of sourceFrequencies) {
             let map2 = map1.get(dictionary);
             if (typeof map2 === 'undefined') {
                 map2 = new Map();
@@ -88,9 +115,25 @@ class DictionaryDataUtil {
 
             frequencyData.values.set(this._createMapKey([frequency, displayValue]), {frequency, displayValue});
         }
-        return this._createFrequencyGroupsFromMap(map1);
+
+        const results = [];
+        for (const [dictionary, map2] of map1.entries()) {
+            const frequencies = [];
+            for (const {character, values} of map2.values()) {
+                frequencies.push({
+                    character,
+                    values: [...values.values()]
+                });
+            }
+            results.push({dictionary, frequencies});
+        }
+        return results;
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     * @returns {import('dictionary-data-util').DictionaryGroupedPronunciations[]}
+     */
     static getGroupedPronunciations(dictionaryEntry) {
         const {headwords, pronunciations} = dictionaryEntry;
 
@@ -101,6 +144,7 @@ class DictionaryDataUtil {
             allReadings.add(reading);
         }
 
+        /** @type {Map<string, import('dictionary-data-util').GroupedPronunciationInternal[]>} */
         const groupedPronunciationsMap = new Map();
         for (const {headwordIndex, dictionary, pitches} of pronunciations) {
             const {term, reading} = headwords[headwordIndex];
@@ -118,9 +162,7 @@ class DictionaryDataUtil {
                         position,
                         nasalPositions,
                         devoicePositions,
-                        tags,
-                        exclusiveTerms: [],
-                        exclusiveReadings: []
+                        tags
                     };
                     dictionaryGroupedPronunciationList.push(groupedPronunciation);
                 }
@@ -128,27 +170,39 @@ class DictionaryDataUtil {
             }
         }
 
+        /** @type {import('dictionary-data-util').DictionaryGroupedPronunciations[]} */
+        const results2 = [];
         const multipleReadings = (allReadings.size > 1);
-        for (const dictionaryGroupedPronunciationList of groupedPronunciationsMap.values()) {
+        for (const [dictionary, dictionaryGroupedPronunciationList] of groupedPronunciationsMap.entries()) {
+            /** @type {import('dictionary-data-util').GroupedPronunciation[]} */
+            const pronunciations2 = [];
             for (const groupedPronunciation of dictionaryGroupedPronunciationList) {
-                const {terms, reading, exclusiveTerms, exclusiveReadings} = groupedPronunciation;
-                if (!this._areSetsEqual(terms, allTerms)) {
-                    exclusiveTerms.push(...this._getSetIntersection(terms, allTerms));
-                }
+                const {terms, reading, position, nasalPositions, devoicePositions, tags} = groupedPronunciation;
+                const exclusiveTerms = !this._areSetsEqual(terms, allTerms) ? this._getSetIntersection(terms, allTerms) : [];
+                const exclusiveReadings = [];
                 if (multipleReadings) {
                     exclusiveReadings.push(reading);
                 }
-                groupedPronunciation.terms = [...terms];
+                pronunciations2.push({
+                    terms: [...terms],
+                    reading,
+                    position,
+                    nasalPositions,
+                    devoicePositions,
+                    tags,
+                    exclusiveTerms,
+                    exclusiveReadings
+                });
             }
-        }
-
-        const results2 = [];
-        for (const [dictionary, pronunciations2] of groupedPronunciationsMap.entries()) {
             results2.push({dictionary, pronunciations: pronunciations2});
         }
         return results2;
     }
 
+    /**
+     * @param {import('dictionary').Tag[]|import('anki-templates').Tag[]} termTags
+     * @returns {import('dictionary-data-util').TermFrequencyType}
+     */
     static getTermFrequency(termTags) {
         let totalScore = 0;
         for (const {score} of termTags) {
@@ -163,10 +217,19 @@ class DictionaryDataUtil {
         }
     }
 
+    /**
+     * @param {import('dictionary').TermHeadword[]} headwords
+     * @param {number[]} headwordIndices
+     * @param {Set<string>} allTermsSet
+     * @param {Set<string>} allReadingsSet
+     * @returns {string[]}
+     */
     static getDisambiguations(headwords, headwordIndices, allTermsSet, allReadingsSet) {
         if (allTermsSet.size <= 1 && allReadingsSet.size <= 1) { return []; }
 
+        /** @type {Set<string>} */
         const terms = new Set();
+        /** @type {Set<string>} */
         const readings = new Set();
         for (const headwordIndex of headwordIndices) {
             const {term, reading} = headwords[headwordIndex];
@@ -174,6 +237,7 @@ class DictionaryDataUtil {
             readings.add(reading);
         }
 
+        /** @type {string[]} */
         const disambiguations = [];
         const addTerms = !this._areSetsEqual(terms, allTermsSet);
         const addReadings = !this._areSetsEqual(readings, allReadingsSet);
@@ -191,6 +255,10 @@ class DictionaryDataUtil {
         return disambiguations;
     }
 
+    /**
+     * @param {string[]} wordClasses
+     * @returns {boolean}
+     */
     static isNonNounVerbOrAdjective(wordClasses) {
         let isVerbOrAdjective = false;
         let isSuruVerb = false;
@@ -218,19 +286,15 @@ class DictionaryDataUtil {
 
     // Private
 
-    static _createFrequencyGroupsFromMap(map) {
-        const results = [];
-        for (const [dictionary, map2] of map.entries()) {
-            const frequencies = [];
-            for (const frequencyData of map2.values()) {
-                frequencyData.values = [...frequencyData.values.values()];
-                frequencies.push(frequencyData);
-            }
-            results.push({dictionary, frequencies});
-        }
-        return results;
-    }
-
+    /**
+     * @param {string} reading
+     * @param {number} position
+     * @param {number[]} nasalPositions
+     * @param {number[]} devoicePositions
+     * @param {import('dictionary').Tag[]} tags
+     * @param {import('dictionary-data-util').GroupedPronunciationInternal[]} groupedPronunciationList
+     * @returns {?import('dictionary-data-util').GroupedPronunciationInternal}
+     */
     static _findExistingGroupedPronunciation(reading, position, nasalPositions, devoicePositions, tags, groupedPronunciationList) {
         for (const pitchInfo of groupedPronunciationList) {
             if (
@@ -246,6 +310,12 @@ class DictionaryDataUtil {
         return null;
     }
 
+    /**
+     * @template [T=unknown]
+     * @param {T[]} array1
+     * @param {T[]} array2
+     * @returns {boolean}
+     */
     static _areArraysEqual(array1, array2) {
         const ii = array1.length;
         if (ii !== array2.length) { return false; }
@@ -255,6 +325,11 @@ class DictionaryDataUtil {
         return true;
     }
 
+    /**
+     * @param {import('dictionary').Tag[]} tagList1
+     * @param {import('dictionary').Tag[]} tagList2
+     * @returns {boolean}
+     */
     static _areTagListsEqual(tagList1, tagList2) {
         const ii = tagList1.length;
         if (tagList2.length !== ii) { return false; }
@@ -262,7 +337,7 @@ class DictionaryDataUtil {
         for (let i = 0; i < ii; ++i) {
             const tag1 = tagList1[i];
             const tag2 = tagList2[i];
-            if (tag1.name !== tag2.name || tag1.dictionary !== tag2.dictionary) {
+            if (tag1.name !== tag2.name || !this._areArraysEqual(tag1.dictionaries, tag2.dictionaries)) {
                 return false;
             }
         }
@@ -270,6 +345,12 @@ class DictionaryDataUtil {
         return true;
     }
 
+    /**
+     * @template [T=unknown]
+     * @param {Set<T>} set1
+     * @param {Set<T>} set2
+     * @returns {boolean}
+     */
     static _areSetsEqual(set1, set2) {
         if (set1.size !== set2.size) {
             return false;
@@ -284,6 +365,12 @@ class DictionaryDataUtil {
         return true;
     }
 
+    /**
+     * @template [T=unknown]
+     * @param {Set<T>} set1
+     * @param {Set<T>} set2
+     * @returns {T[]}
+     */
     static _getSetIntersection(set1, set2) {
         const result = [];
         for (const value of set1) {
@@ -294,6 +381,10 @@ class DictionaryDataUtil {
         return result;
     }
 
+    /**
+     * @param {unknown[]} array
+     * @returns {string}
+     */
     static _createMapKey(array) {
         return JSON.stringify(array);
     }
diff --git a/ext/js/language/sandbox/japanese-util.js b/ext/js/language/sandbox/japanese-util.js
index eee70f9cfb..e70a1a38bf 100644
--- a/ext/js/language/sandbox/japanese-util.js
+++ b/ext/js/language/sandbox/japanese-util.js
@@ -16,710 +16,878 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-const JapaneseUtil = (() => {
-    const HIRAGANA_SMALL_TSU_CODE_POINT = 0x3063;
-    const KATAKANA_SMALL_TSU_CODE_POINT = 0x30c3;
-    const KATAKANA_SMALL_KA_CODE_POINT = 0x30f5;
-    const KATAKANA_SMALL_KE_CODE_POINT = 0x30f6;
-    const KANA_PROLONGED_SOUND_MARK_CODE_POINT = 0x30fc;
-
-    const HIRAGANA_RANGE = [0x3040, 0x309f];
-    const KATAKANA_RANGE = [0x30a0, 0x30ff];
-
-    const HIRAGANA_CONVERSION_RANGE = [0x3041, 0x3096];
-    const KATAKANA_CONVERSION_RANGE = [0x30a1, 0x30f6];
-
-    const KANA_RANGES = [HIRAGANA_RANGE, KATAKANA_RANGE];
-
-    const CJK_UNIFIED_IDEOGRAPHS_RANGE = [0x4e00, 0x9fff];
-    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_A_RANGE = [0x3400, 0x4dbf];
-    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_B_RANGE = [0x20000, 0x2a6df];
-    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_C_RANGE = [0x2a700, 0x2b73f];
-    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_D_RANGE = [0x2b740, 0x2b81f];
-    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_E_RANGE = [0x2b820, 0x2ceaf];
-    const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_F_RANGE = [0x2ceb0, 0x2ebef];
-    const CJK_COMPATIBILITY_IDEOGRAPHS_RANGE = [0xf900, 0xfaff];
-    const CJK_COMPATIBILITY_IDEOGRAPHS_SUPPLEMENT_RANGE = [0x2f800, 0x2fa1f];
-    const CJK_IDEOGRAPH_RANGES = [
-        CJK_UNIFIED_IDEOGRAPHS_RANGE,
-        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_A_RANGE,
-        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_B_RANGE,
-        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_C_RANGE,
-        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_D_RANGE,
-        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_E_RANGE,
-        CJK_UNIFIED_IDEOGRAPHS_EXTENSION_F_RANGE,
-        CJK_COMPATIBILITY_IDEOGRAPHS_RANGE,
-        CJK_COMPATIBILITY_IDEOGRAPHS_SUPPLEMENT_RANGE
-    ];
-
-    // Japanese character ranges, roughly ordered in order of expected frequency
-    const JAPANESE_RANGES = [
-        HIRAGANA_RANGE,
-        KATAKANA_RANGE,
-
-        ...CJK_IDEOGRAPH_RANGES,
-
-        [0xff66, 0xff9f], // Halfwidth katakana
-
-        [0x30fb, 0x30fc], // Katakana punctuation
-        [0xff61, 0xff65], // Kana punctuation
-        [0x3000, 0x303f], // CJK punctuation
-
-        [0xff10, 0xff19], // Fullwidth numbers
-        [0xff21, 0xff3a], // Fullwidth upper case Latin letters
-        [0xff41, 0xff5a], // Fullwidth lower case Latin letters
-
-        [0xff01, 0xff0f], // Fullwidth punctuation 1
-        [0xff1a, 0xff1f], // Fullwidth punctuation 2
-        [0xff3b, 0xff3f], // Fullwidth punctuation 3
-        [0xff5b, 0xff60], // Fullwidth punctuation 4
-        [0xffe0, 0xffee]  // Currency markers
-    ];
-
-    const SMALL_KANA_SET = new Set(Array.from('ぁぃぅぇぉゃゅょゎァィゥェォャュョヮ'));
-
-    const HALFWIDTH_KATAKANA_MAPPING = new Map([
-        ['ｦ', 'ヲヺ-'],
-        ['ｧ', 'ァ--'],
-        ['ｨ', 'ィ--'],
-        ['ｩ', 'ゥ--'],
-        ['ｪ', 'ェ--'],
-        ['ｫ', 'ォ--'],
-        ['ｬ', 'ャ--'],
-        ['ｭ', 'ュ--'],
-        ['ｮ', 'ョ--'],
-        ['ｯ', 'ッ--'],
-        ['ｰ', 'ー--'],
-        ['ｱ', 'ア--'],
-        ['ｲ', 'イ--'],
-        ['ｳ', 'ウヴ-'],
-        ['ｴ', 'エ--'],
-        ['ｵ', 'オ--'],
-        ['ｶ', 'カガ-'],
-        ['ｷ', 'キギ-'],
-        ['ｸ', 'クグ-'],
-        ['ｹ', 'ケゲ-'],
-        ['ｺ', 'コゴ-'],
-        ['ｻ', 'サザ-'],
-        ['ｼ', 'シジ-'],
-        ['ｽ', 'スズ-'],
-        ['ｾ', 'セゼ-'],
-        ['ｿ', 'ソゾ-'],
-        ['ﾀ', 'タダ-'],
-        ['ﾁ', 'チヂ-'],
-        ['ﾂ', 'ツヅ-'],
-        ['ﾃ', 'テデ-'],
-        ['ﾄ', 'トド-'],
-        ['ﾅ', 'ナ--'],
-        ['ﾆ', 'ニ--'],
-        ['ﾇ', 'ヌ--'],
-        ['ﾈ', 'ネ--'],
-        ['ﾉ', 'ノ--'],
-        ['ﾊ', 'ハバパ'],
-        ['ﾋ', 'ヒビピ'],
-        ['ﾌ', 'フブプ'],
-        ['ﾍ', 'ヘベペ'],
-        ['ﾎ', 'ホボポ'],
-        ['ﾏ', 'マ--'],
-        ['ﾐ', 'ミ--'],
-        ['ﾑ', 'ム--'],
-        ['ﾒ', 'メ--'],
-        ['ﾓ', 'モ--'],
-        ['ﾔ', 'ヤ--'],
-        ['ﾕ', 'ユ--'],
-        ['ﾖ', 'ヨ--'],
-        ['ﾗ', 'ラ--'],
-        ['ﾘ', 'リ--'],
-        ['ﾙ', 'ル--'],
-        ['ﾚ', 'レ--'],
-        ['ﾛ', 'ロ--'],
-        ['ﾜ', 'ワ--'],
-        ['ﾝ', 'ン--']
-    ]);
-
-    const VOWEL_TO_KANA_MAPPING = new Map([
-        ['a', 'ぁあかがさざただなはばぱまゃやらゎわヵァアカガサザタダナハバパマャヤラヮワヵヷ'],
-        ['i', 'ぃいきぎしじちぢにひびぴみりゐィイキギシジチヂニヒビピミリヰヸ'],
-        ['u', 'ぅうくぐすずっつづぬふぶぷむゅゆるゥウクグスズッツヅヌフブプムュユルヴ'],
-        ['e', 'ぇえけげせぜてでねへべぺめれゑヶェエケゲセゼテデネヘベペメレヱヶヹ'],
-        ['o', 'ぉおこごそぞとどのほぼぽもょよろをォオコゴソゾトドノホボポモョヨロヲヺ'],
-        ['', 'のノ']
-    ]);
-
-    const KANA_TO_VOWEL_MAPPING = (() => {
-        const map = new Map();
-        for (const [vowel, characters] of VOWEL_TO_KANA_MAPPING) {
-            for (const character of characters) {
-                map.set(character, vowel);
-            }
-        }
-        return map;
-    })();
-
-    const DIACRITIC_MAPPING = (() => {
-        const kana = 'うゔ-かが-きぎ-くぐ-けげ-こご-さざ-しじ-すず-せぜ-そぞ-ただ-ちぢ-つづ-てで-とど-はばぱひびぴふぶぷへべぺほぼぽワヷ-ヰヸ-ウヴ-ヱヹ-ヲヺ-カガ-キギ-クグ-ケゲ-コゴ-サザ-シジ-スズ-セゼ-ソゾ-タダ-チヂ-ツヅ-テデ-トド-ハバパヒビピフブプヘベペホボポ';
-        const map = new Map();
-        for (let i = 0, ii = kana.length; i < ii; i += 3) {
-            const character = kana[i];
-            const dakuten = kana[i + 1];
-            const handakuten = kana[i + 2];
-            map.set(dakuten, {character, type: 'dakuten'});
-            if (handakuten !== '-') {
-                map.set(handakuten, {character, type: 'handakuten'});
-            }
+const HIRAGANA_SMALL_TSU_CODE_POINT = 0x3063;
+const KATAKANA_SMALL_TSU_CODE_POINT = 0x30c3;
+const KATAKANA_SMALL_KA_CODE_POINT = 0x30f5;
+const KATAKANA_SMALL_KE_CODE_POINT = 0x30f6;
+const KANA_PROLONGED_SOUND_MARK_CODE_POINT = 0x30fc;
+
+/** @type {import('japanese-util').CodepointRange} */
+const HIRAGANA_RANGE = [0x3040, 0x309f];
+/** @type {import('japanese-util').CodepointRange} */
+const KATAKANA_RANGE = [0x30a0, 0x30ff];
+
+/** @type {import('japanese-util').CodepointRange} */
+const HIRAGANA_CONVERSION_RANGE = [0x3041, 0x3096];
+/** @type {import('japanese-util').CodepointRange} */
+const KATAKANA_CONVERSION_RANGE = [0x30a1, 0x30f6];
+
+/** @type {import('japanese-util').CodepointRange[]} */
+const KANA_RANGES = [HIRAGANA_RANGE, KATAKANA_RANGE];
+
+/** @type {import('japanese-util').CodepointRange} */
+const CJK_UNIFIED_IDEOGRAPHS_RANGE = [0x4e00, 0x9fff];
+/** @type {import('japanese-util').CodepointRange} */
+const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_A_RANGE = [0x3400, 0x4dbf];
+/** @type {import('japanese-util').CodepointRange} */
+const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_B_RANGE = [0x20000, 0x2a6df];
+/** @type {import('japanese-util').CodepointRange} */
+const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_C_RANGE = [0x2a700, 0x2b73f];
+/** @type {import('japanese-util').CodepointRange} */
+const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_D_RANGE = [0x2b740, 0x2b81f];
+/** @type {import('japanese-util').CodepointRange} */
+const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_E_RANGE = [0x2b820, 0x2ceaf];
+/** @type {import('japanese-util').CodepointRange} */
+const CJK_UNIFIED_IDEOGRAPHS_EXTENSION_F_RANGE = [0x2ceb0, 0x2ebef];
+/** @type {import('japanese-util').CodepointRange} */
+const CJK_COMPATIBILITY_IDEOGRAPHS_RANGE = [0xf900, 0xfaff];
+/** @type {import('japanese-util').CodepointRange} */
+const CJK_COMPATIBILITY_IDEOGRAPHS_SUPPLEMENT_RANGE = [0x2f800, 0x2fa1f];
+/** @type {import('japanese-util').CodepointRange[]} */
+const CJK_IDEOGRAPH_RANGES = [
+    CJK_UNIFIED_IDEOGRAPHS_RANGE,
+    CJK_UNIFIED_IDEOGRAPHS_EXTENSION_A_RANGE,
+    CJK_UNIFIED_IDEOGRAPHS_EXTENSION_B_RANGE,
+    CJK_UNIFIED_IDEOGRAPHS_EXTENSION_C_RANGE,
+    CJK_UNIFIED_IDEOGRAPHS_EXTENSION_D_RANGE,
+    CJK_UNIFIED_IDEOGRAPHS_EXTENSION_E_RANGE,
+    CJK_UNIFIED_IDEOGRAPHS_EXTENSION_F_RANGE,
+    CJK_COMPATIBILITY_IDEOGRAPHS_RANGE,
+    CJK_COMPATIBILITY_IDEOGRAPHS_SUPPLEMENT_RANGE
+];
+
+// Japanese character ranges, roughly ordered in order of expected frequency
+/** @type {import('japanese-util').CodepointRange[]} */
+const JAPANESE_RANGES = [
+    HIRAGANA_RANGE,
+    KATAKANA_RANGE,
+
+    ...CJK_IDEOGRAPH_RANGES,
+
+    [0xff66, 0xff9f], // Halfwidth katakana
+
+    [0x30fb, 0x30fc], // Katakana punctuation
+    [0xff61, 0xff65], // Kana punctuation
+    [0x3000, 0x303f], // CJK punctuation
+
+    [0xff10, 0xff19], // Fullwidth numbers
+    [0xff21, 0xff3a], // Fullwidth upper case Latin letters
+    [0xff41, 0xff5a], // Fullwidth lower case Latin letters
+
+    [0xff01, 0xff0f], // Fullwidth punctuation 1
+    [0xff1a, 0xff1f], // Fullwidth punctuation 2
+    [0xff3b, 0xff3f], // Fullwidth punctuation 3
+    [0xff5b, 0xff60], // Fullwidth punctuation 4
+    [0xffe0, 0xffee]  // Currency markers
+];
+
+const SMALL_KANA_SET = new Set(Array.from('ぁぃぅぇぉゃゅょゎァィゥェォャュョヮ'));
+
+const HALFWIDTH_KATAKANA_MAPPING = new Map([
+    ['ｦ', 'ヲヺ-'],
+    ['ｧ', 'ァ--'],
+    ['ｨ', 'ィ--'],
+    ['ｩ', 'ゥ--'],
+    ['ｪ', 'ェ--'],
+    ['ｫ', 'ォ--'],
+    ['ｬ', 'ャ--'],
+    ['ｭ', 'ュ--'],
+    ['ｮ', 'ョ--'],
+    ['ｯ', 'ッ--'],
+    ['ｰ', 'ー--'],
+    ['ｱ', 'ア--'],
+    ['ｲ', 'イ--'],
+    ['ｳ', 'ウヴ-'],
+    ['ｴ', 'エ--'],
+    ['ｵ', 'オ--'],
+    ['ｶ', 'カガ-'],
+    ['ｷ', 'キギ-'],
+    ['ｸ', 'クグ-'],
+    ['ｹ', 'ケゲ-'],
+    ['ｺ', 'コゴ-'],
+    ['ｻ', 'サザ-'],
+    ['ｼ', 'シジ-'],
+    ['ｽ', 'スズ-'],
+    ['ｾ', 'セゼ-'],
+    ['ｿ', 'ソゾ-'],
+    ['ﾀ', 'タダ-'],
+    ['ﾁ', 'チヂ-'],
+    ['ﾂ', 'ツヅ-'],
+    ['ﾃ', 'テデ-'],
+    ['ﾄ', 'トド-'],
+    ['ﾅ', 'ナ--'],
+    ['ﾆ', 'ニ--'],
+    ['ﾇ', 'ヌ--'],
+    ['ﾈ', 'ネ--'],
+    ['ﾉ', 'ノ--'],
+    ['ﾊ', 'ハバパ'],
+    ['ﾋ', 'ヒビピ'],
+    ['ﾌ', 'フブプ'],
+    ['ﾍ', 'ヘベペ'],
+    ['ﾎ', 'ホボポ'],
+    ['ﾏ', 'マ--'],
+    ['ﾐ', 'ミ--'],
+    ['ﾑ', 'ム--'],
+    ['ﾒ', 'メ--'],
+    ['ﾓ', 'モ--'],
+    ['ﾔ', 'ヤ--'],
+    ['ﾕ', 'ユ--'],
+    ['ﾖ', 'ヨ--'],
+    ['ﾗ', 'ラ--'],
+    ['ﾘ', 'リ--'],
+    ['ﾙ', 'ル--'],
+    ['ﾚ', 'レ--'],
+    ['ﾛ', 'ロ--'],
+    ['ﾜ', 'ワ--'],
+    ['ﾝ', 'ン--']
+]);
+
+const VOWEL_TO_KANA_MAPPING = new Map([
+    ['a', 'ぁあかがさざただなはばぱまゃやらゎわヵァアカガサザタダナハバパマャヤラヮワヵヷ'],
+    ['i', 'ぃいきぎしじちぢにひびぴみりゐィイキギシジチヂニヒビピミリヰヸ'],
+    ['u', 'ぅうくぐすずっつづぬふぶぷむゅゆるゥウクグスズッツヅヌフブプムュユルヴ'],
+    ['e', 'ぇえけげせぜてでねへべぺめれゑヶェエケゲセゼテデネヘベペメレヱヶヹ'],
+    ['o', 'ぉおこごそぞとどのほぼぽもょよろをォオコゴソゾトドノホボポモョヨロヲヺ'],
+    ['', 'のノ']
+]);
+
+const KANA_TO_VOWEL_MAPPING = (() => {
+    /** @type {Map<string, string>} */
+    const map = new Map();
+    for (const [vowel, characters] of VOWEL_TO_KANA_MAPPING) {
+        for (const character of characters) {
+            map.set(character, vowel);
         }
-        return map;
-    })();
-
-
-    function isCodePointInRange(codePoint, [min, max]) {
-        return (codePoint >= min && codePoint <= max);
     }
+    return map;
+})();
 
-    function isCodePointInRanges(codePoint, ranges) {
-        for (const [min, max] of ranges) {
-            if (codePoint >= min && codePoint <= max) {
-                return true;
-            }
+const DIACRITIC_MAPPING = (() => {
+    const kana = 'うゔ-かが-きぎ-くぐ-けげ-こご-さざ-しじ-すず-せぜ-そぞ-ただ-ちぢ-つづ-てで-とど-はばぱひびぴふぶぷへべぺほぼぽワヷ-ヰヸ-ウヴ-ヱヹ-ヲヺ-カガ-キギ-クグ-ケゲ-コゴ-サザ-シジ-スズ-セゼ-ソゾ-タダ-チヂ-ツヅ-テデ-トド-ハバパヒビピフブプヘベペホボポ';
+    /** @type {Map<string, {character: string, type: import('japanese-util').DiacriticType}>} */
+    const map = new Map();
+    for (let i = 0, ii = kana.length; i < ii; i += 3) {
+        const character = kana[i];
+        const dakuten = kana[i + 1];
+        const handakuten = kana[i + 2];
+        map.set(dakuten, {character, type: 'dakuten'});
+        if (handakuten !== '-') {
+            map.set(handakuten, {character, type: 'handakuten'});
         }
-        return false;
     }
+    return map;
+})();
+
 
-    function getProlongedHiragana(previousCharacter) {
-        switch (KANA_TO_VOWEL_MAPPING.get(previousCharacter)) {
-            case 'a': return 'あ';
-            case 'i': return 'い';
-            case 'u': return 'う';
-            case 'e': return 'え';
-            case 'o': return 'う';
-            default: return null;
+/**
+ * @param {number} codePoint
+ * @param {import('japanese-util').CodepointRange} range
+ * @returns {boolean}
+ */
+// eslint-disable-next-line no-implicit-globals
+function isCodePointInRange(codePoint, [min, max]) {
+    return (codePoint >= min && codePoint <= max);
+}
+
+/**
+ * @param {number} codePoint
+ * @param {import('japanese-util').CodepointRange[]} ranges
+ * @returns {boolean}
+ */
+// eslint-disable-next-line no-implicit-globals
+function isCodePointInRanges(codePoint, ranges) {
+    for (const [min, max] of ranges) {
+        if (codePoint >= min && codePoint <= max) {
+            return true;
         }
     }
+    return false;
+}
 
+/**
+ * @param {string} previousCharacter
+ * @returns {?string}
+ */
+// eslint-disable-next-line no-implicit-globals
+function getProlongedHiragana(previousCharacter) {
+    switch (KANA_TO_VOWEL_MAPPING.get(previousCharacter)) {
+        case 'a': return 'あ';
+        case 'i': return 'い';
+        case 'u': return 'う';
+        case 'e': return 'え';
+        case 'o': return 'う';
+        default: return null;
+    }
+}
 
-    // eslint-disable-next-line no-shadow
-    class JapaneseUtil {
-        constructor(wanakana=null) {
-            this._wanakana = wanakana;
-        }
 
-        // Character code testing functions
+// eslint-disable-next-line no-shadow
+class JapaneseUtil {
+    /**
+     * @param {?import('wanakana')} wanakana
+     */
+    constructor(wanakana=null) {
+        /** @type {?import('wanakana')} */
+        this._wanakana = wanakana;
+    }
 
-        isCodePointKanji(codePoint) {
-            return isCodePointInRanges(codePoint, CJK_IDEOGRAPH_RANGES);
-        }
+    // Character code testing functions
 
-        isCodePointKana(codePoint) {
-            return isCodePointInRanges(codePoint, KANA_RANGES);
-        }
+    /**
+     * @param {number} codePoint
+     * @returns {boolean}
+     */
+    isCodePointKanji(codePoint) {
+        return isCodePointInRanges(codePoint, CJK_IDEOGRAPH_RANGES);
+    }
 
-        isCodePointJapanese(codePoint) {
-            return isCodePointInRanges(codePoint, JAPANESE_RANGES);
-        }
+    /**
+     * @param {number} codePoint
+     * @returns {boolean}
+     */
+    isCodePointKana(codePoint) {
+        return isCodePointInRanges(codePoint, KANA_RANGES);
+    }
 
-        // String testing functions
+    /**
+     * @param {number} codePoint
+     * @returns {boolean}
+     */
+    isCodePointJapanese(codePoint) {
+        return isCodePointInRanges(codePoint, JAPANESE_RANGES);
+    }
 
-        isStringEntirelyKana(str) {
-            if (str.length === 0) { return false; }
-            for (const c of str) {
-                if (!isCodePointInRanges(c.codePointAt(0), KANA_RANGES)) {
-                    return false;
-                }
+    // String testing functions
+
+    /**
+     * @param {string} str
+     * @returns {boolean}
+     */
+    isStringEntirelyKana(str) {
+        if (str.length === 0) { return false; }
+        for (const c of str) {
+            if (!isCodePointInRanges(/** @type {number} */ (c.codePointAt(0)), KANA_RANGES)) {
+                return false;
             }
-            return true;
         }
+        return true;
+    }
 
-        isStringPartiallyJapanese(str) {
-            if (str.length === 0) { return false; }
-            for (const c of str) {
-                if (isCodePointInRanges(c.codePointAt(0), JAPANESE_RANGES)) {
-                    return true;
-                }
+    /**
+     * @param {string} str
+     * @returns {boolean}
+     */
+    isStringPartiallyJapanese(str) {
+        if (str.length === 0) { return false; }
+        for (const c of str) {
+            if (isCodePointInRanges(/** @type {number} */ (c.codePointAt(0)), JAPANESE_RANGES)) {
+                return true;
             }
-            return false;
         }
+        return false;
+    }
 
-        // Mora functions
+    // Mora functions
 
-        isMoraPitchHigh(moraIndex, pitchAccentDownstepPosition) {
-            switch (pitchAccentDownstepPosition) {
-                case 0: return (moraIndex > 0);
-                case 1: return (moraIndex < 1);
-                default: return (moraIndex > 0 && moraIndex < pitchAccentDownstepPosition);
-            }
+    /**
+     * @param {number} moraIndex
+     * @param {number} pitchAccentDownstepPosition
+     * @returns {boolean}
+     */
+    isMoraPitchHigh(moraIndex, pitchAccentDownstepPosition) {
+        switch (pitchAccentDownstepPosition) {
+            case 0: return (moraIndex > 0);
+            case 1: return (moraIndex < 1);
+            default: return (moraIndex > 0 && moraIndex < pitchAccentDownstepPosition);
         }
+    }
 
-        getPitchCategory(text, pitchAccentDownstepPosition, isVerbOrAdjective) {
-            if (pitchAccentDownstepPosition === 0) {
-                return 'heiban';
-            }
-            if (isVerbOrAdjective) {
-                return pitchAccentDownstepPosition > 0 ? 'kifuku' : null;
-            }
-            if (pitchAccentDownstepPosition === 1) {
-                return 'atamadaka';
-            }
-            if (pitchAccentDownstepPosition > 1) {
-                return pitchAccentDownstepPosition >= this.getKanaMoraCount(text) ? 'odaka' : 'nakadaka';
-            }
-            return null;
+    /**
+     * @param {string} text
+     * @param {number} pitchAccentDownstepPosition
+     * @param {boolean} isVerbOrAdjective
+     * @returns {?import('japanese-util').PitchCategory}
+     */
+    getPitchCategory(text, pitchAccentDownstepPosition, isVerbOrAdjective) {
+        if (pitchAccentDownstepPosition === 0) {
+            return 'heiban';
+        }
+        if (isVerbOrAdjective) {
+            return pitchAccentDownstepPosition > 0 ? 'kifuku' : null;
+        }
+        if (pitchAccentDownstepPosition === 1) {
+            return 'atamadaka';
         }
+        if (pitchAccentDownstepPosition > 1) {
+            return pitchAccentDownstepPosition >= this.getKanaMoraCount(text) ? 'odaka' : 'nakadaka';
+        }
+        return null;
+    }
 
-        getKanaMorae(text) {
-            const morae = [];
-            let i;
-            for (const c of text) {
-                if (SMALL_KANA_SET.has(c) && (i = morae.length) > 0) {
-                    morae[i - 1] += c;
-                } else {
-                    morae.push(c);
-                }
+    /**
+     * @param {string} text
+     * @returns {string[]}
+     */
+    getKanaMorae(text) {
+        const morae = [];
+        let i;
+        for (const c of text) {
+            if (SMALL_KANA_SET.has(c) && (i = morae.length) > 0) {
+                morae[i - 1] += c;
+            } else {
+                morae.push(c);
             }
-            return morae;
         }
+        return morae;
+    }
 
-        getKanaMoraCount(text) {
-            let moraCount = 0;
-            for (const c of text) {
-                if (!(SMALL_KANA_SET.has(c) && moraCount > 0)) {
-                    ++moraCount;
-                }
+    /**
+     * @param {string} text
+     * @returns {number}
+     */
+    getKanaMoraCount(text) {
+        let moraCount = 0;
+        for (const c of text) {
+            if (!(SMALL_KANA_SET.has(c) && moraCount > 0)) {
+                ++moraCount;
             }
-            return moraCount;
         }
+        return moraCount;
+    }
 
-        // Conversion functions
+    // Conversion functions
 
-        convertToKana(text) {
-            return this._getWanakana().toKana(text);
-        }
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
+    convertToKana(text) {
+        return this._getWanakana().toKana(text);
+    }
 
-        convertToKanaSupported() {
-            return this._wanakana !== null;
-        }
+    /**
+     * @returns {boolean}
+     */
+    convertToKanaSupported() {
+        return this._wanakana !== null;
+    }
 
-        convertKatakanaToHiragana(text, keepProlongedSoundMarks=false) {
-            let result = '';
-            const offset = (HIRAGANA_CONVERSION_RANGE[0] - KATAKANA_CONVERSION_RANGE[0]);
-            for (let char of text) {
-                const codePoint = char.codePointAt(0);
-                switch (codePoint) {
-                    case KATAKANA_SMALL_KA_CODE_POINT:
-                    case KATAKANA_SMALL_KE_CODE_POINT:
-                        // No change
-                        break;
-                    case KANA_PROLONGED_SOUND_MARK_CODE_POINT:
-                        if (!keepProlongedSoundMarks && result.length > 0) {
-                            const char2 = getProlongedHiragana(result[result.length - 1]);
-                            if (char2 !== null) { char = char2; }
-                        }
-                        break;
-                    default:
-                        if (isCodePointInRange(codePoint, KATAKANA_CONVERSION_RANGE)) {
-                            char = String.fromCodePoint(codePoint + offset);
-                        }
-                        break;
-                }
-                result += char;
+    /**
+     * @param {string} text
+     * @param {boolean} [keepProlongedSoundMarks]
+     * @returns {string}
+     */
+    convertKatakanaToHiragana(text, keepProlongedSoundMarks=false) {
+        let result = '';
+        const offset = (HIRAGANA_CONVERSION_RANGE[0] - KATAKANA_CONVERSION_RANGE[0]);
+        for (let char of text) {
+            const codePoint = /** @type {number} */ (char.codePointAt(0));
+            switch (codePoint) {
+                case KATAKANA_SMALL_KA_CODE_POINT:
+                case KATAKANA_SMALL_KE_CODE_POINT:
+                    // No change
+                    break;
+                case KANA_PROLONGED_SOUND_MARK_CODE_POINT:
+                    if (!keepProlongedSoundMarks && result.length > 0) {
+                        const char2 = getProlongedHiragana(result[result.length - 1]);
+                        if (char2 !== null) { char = char2; }
+                    }
+                    break;
+                default:
+                    if (isCodePointInRange(codePoint, KATAKANA_CONVERSION_RANGE)) {
+                        char = String.fromCodePoint(codePoint + offset);
+                    }
+                    break;
             }
-            return result;
+            result += char;
         }
+        return result;
+    }
 
-        convertHiraganaToKatakana(text) {
-            let result = '';
-            const offset = (KATAKANA_CONVERSION_RANGE[0] - HIRAGANA_CONVERSION_RANGE[0]);
-            for (let char of text) {
-                const codePoint = char.codePointAt(0);
-                if (isCodePointInRange(codePoint, HIRAGANA_CONVERSION_RANGE)) {
-                    char = String.fromCodePoint(codePoint + offset);
-                }
-                result += char;
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
+    convertHiraganaToKatakana(text) {
+        let result = '';
+        const offset = (KATAKANA_CONVERSION_RANGE[0] - HIRAGANA_CONVERSION_RANGE[0]);
+        for (let char of text) {
+            const codePoint = /** @type {number} */ (char.codePointAt(0));
+            if (isCodePointInRange(codePoint, HIRAGANA_CONVERSION_RANGE)) {
+                char = String.fromCodePoint(codePoint + offset);
             }
-            return result;
+            result += char;
         }
+        return result;
+    }
 
-        convertToRomaji(text) {
-            const wanakana = this._getWanakana();
-            return wanakana.toRomaji(text);
-        }
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
+    convertToRomaji(text) {
+        const wanakana = this._getWanakana();
+        return wanakana.toRomaji(text);
+    }
 
-        convertToRomajiSupported() {
-            return this._wanakana !== null;
-        }
+    /**
+     * @returns {boolean}
+     */
+    convertToRomajiSupported() {
+        return this._wanakana !== null;
+    }
 
-        convertNumericToFullWidth(text) {
-            let result = '';
-            for (const char of text) {
-                let c = char.codePointAt(0);
-                if (c >= 0x30 && c <= 0x39) { // ['0', '9']
-                    c += 0xff10 - 0x30; // 0xff10 = '0' full width
-                    result += String.fromCodePoint(c);
-                } else {
-                    result += char;
-                }
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
+    convertNumericToFullWidth(text) {
+        let result = '';
+        for (const char of text) {
+            let c = /** @type {number} */ (char.codePointAt(0));
+            if (c >= 0x30 && c <= 0x39) { // ['0', '9']
+                c += 0xff10 - 0x30; // 0xff10 = '0' full width
+                result += String.fromCodePoint(c);
+            } else {
+                result += char;
             }
-            return result;
         }
+        return result;
+    }
 
-        convertHalfWidthKanaToFullWidth(text, sourceMap=null) {
-            let result = '';
-
-            // This function is safe to use charCodeAt instead of codePointAt, since all
-            // the relevant characters are represented with a single UTF-16 character code.
-            for (let i = 0, ii = text.length; i < ii; ++i) {
-                const c = text[i];
-                const mapping = HALFWIDTH_KATAKANA_MAPPING.get(c);
-                if (typeof mapping !== 'string') {
-                    result += c;
-                    continue;
-                }
-
-                let index = 0;
-                switch (text.charCodeAt(i + 1)) {
-                    case 0xff9e: // dakuten
-                        index = 1;
-                        break;
-                    case 0xff9f: // handakuten
-                        index = 2;
-                        break;
-                }
-
-                let c2 = mapping[index];
-                if (index > 0) {
-                    if (c2 === '-') { // invalid
-                        index = 0;
-                        c2 = mapping[0];
-                    } else {
-                        ++i;
-                    }
-                }
-
-                if (sourceMap !== null && index > 0) {
-                    sourceMap.combine(result.length, 1);
-                }
-                result += c2;
+    /**
+     * @param {string} text
+     * @param {?TextSourceMap} [sourceMap]
+     * @returns {string}
+     */
+    convertHalfWidthKanaToFullWidth(text, sourceMap=null) {
+        let result = '';
+
+        // This function is safe to use charCodeAt instead of codePointAt, since all
+        // the relevant characters are represented with a single UTF-16 character code.
+        for (let i = 0, ii = text.length; i < ii; ++i) {
+            const c = text[i];
+            const mapping = HALFWIDTH_KATAKANA_MAPPING.get(c);
+            if (typeof mapping !== 'string') {
+                result += c;
+                continue;
             }
 
-            return result;
-        }
+            let index = 0;
+            switch (text.charCodeAt(i + 1)) {
+                case 0xff9e: // dakuten
+                    index = 1;
+                    break;
+                case 0xff9f: // handakuten
+                    index = 2;
+                    break;
+            }
 
-        convertAlphabeticToKana(text, sourceMap=null) {
-            let part = '';
-            let result = '';
-
-            for (const char of text) {
-                // Note: 0x61 is the character code for 'a'
-                let c = char.codePointAt(0);
-                if (c >= 0x41 && c <= 0x5a) { // ['A', 'Z']
-                    c += (0x61 - 0x41);
-                } else if (c >= 0x61 && c <= 0x7a) { // ['a', 'z']
-                    // NOP; c += (0x61 - 0x61);
-                } else if (c >= 0xff21 && c <= 0xff3a) { // ['A', 'Z'] fullwidth
-                    c += (0x61 - 0xff21);
-                } else if (c >= 0xff41 && c <= 0xff5a) { // ['a', 'z'] fullwidth
-                    c += (0x61 - 0xff41);
-                } else if (c === 0x2d || c === 0xff0d) { // '-' or fullwidth dash
-                    c = 0x2d; // '-'
+            let c2 = mapping[index];
+            if (index > 0) {
+                if (c2 === '-') { // invalid
+                    index = 0;
+                    c2 = mapping[0];
                 } else {
-                    if (part.length > 0) {
-                        result += this._convertAlphabeticPartToKana(part, sourceMap, result.length);
-                        part = '';
-                    }
-                    result += char;
-                    continue;
+                    ++i;
                 }
-                part += String.fromCodePoint(c);
             }
 
-            if (part.length > 0) {
-                result += this._convertAlphabeticPartToKana(part, sourceMap, result.length);
+            if (sourceMap !== null && index > 0) {
+                sourceMap.combine(result.length, 1);
             }
-            return result;
+            result += c2;
         }
 
-        convertAlphabeticToKanaSupported() {
-            return this._wanakana !== null;
+        return result;
+    }
+
+    /**
+     * @param {string} text
+     * @param {?TextSourceMap} sourceMap
+     * @returns {string}
+     */
+    convertAlphabeticToKana(text, sourceMap=null) {
+        let part = '';
+        let result = '';
+
+        for (const char of text) {
+            // Note: 0x61 is the character code for 'a'
+            let c = /** @type {number} */ (char.codePointAt(0));
+            if (c >= 0x41 && c <= 0x5a) { // ['A', 'Z']
+                c += (0x61 - 0x41);
+            } else if (c >= 0x61 && c <= 0x7a) { // ['a', 'z']
+                // NOP; c += (0x61 - 0x61);
+            } else if (c >= 0xff21 && c <= 0xff3a) { // ['A', 'Z'] fullwidth
+                c += (0x61 - 0xff21);
+            } else if (c >= 0xff41 && c <= 0xff5a) { // ['a', 'z'] fullwidth
+                c += (0x61 - 0xff41);
+            } else if (c === 0x2d || c === 0xff0d) { // '-' or fullwidth dash
+                c = 0x2d; // '-'
+            } else {
+                if (part.length > 0) {
+                    result += this._convertAlphabeticPartToKana(part, sourceMap, result.length);
+                    part = '';
+                }
+                result += char;
+                continue;
+            }
+            part += String.fromCodePoint(c);
         }
 
-        getKanaDiacriticInfo(character) {
-            const info = DIACRITIC_MAPPING.get(character);
-            return typeof info !== 'undefined' ? {character: info.character, type: info.type} : null;
+        if (part.length > 0) {
+            result += this._convertAlphabeticPartToKana(part, sourceMap, result.length);
         }
+        return result;
+    }
 
-        // Furigana distribution
+    /**
+     * @returns {boolean}
+     */
+    convertAlphabeticToKanaSupported() {
+        return this._wanakana !== null;
+    }
 
-        distributeFurigana(term, reading) {
-            if (reading === term) {
-                // Same
-                return [this._createFuriganaSegment(term, '')];
-            }
+    /**
+     * @param {string} character
+     * @returns {?{character: string, type: import('japanese-util').DiacriticType}}
+     */
+    getKanaDiacriticInfo(character) {
+        const info = DIACRITIC_MAPPING.get(character);
+        return typeof info !== 'undefined' ? {character: info.character, type: info.type} : null;
+    }
 
-            const groups = [];
-            let groupPre = null;
-            let isKanaPre = null;
-            for (const c of term) {
-                const codePoint = c.codePointAt(0);
-                const isKana = this.isCodePointKana(codePoint);
-                if (isKana === isKanaPre) {
-                    groupPre.text += c;
-                } else {
-                    groupPre = {isKana, text: c, textNormalized: null};
-                    groups.push(groupPre);
-                    isKanaPre = isKana;
-                }
-            }
-            for (const group of groups) {
-                if (group.isKana) {
-                    group.textNormalized = this.convertKatakanaToHiragana(group.text);
-                }
+    // Furigana distribution
+
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @returns {import('japanese-util').FuriganaSegment[]}
+     */
+    distributeFurigana(term, reading) {
+        if (reading === term) {
+            // Same
+            return [this._createFuriganaSegment(term, '')];
+        }
+
+        /** @type {import('japanese-util').FuriganaGroup[]} */
+        const groups = [];
+        /** @type {?import('japanese-util').FuriganaGroup} */
+        let groupPre = null;
+        let isKanaPre = null;
+        for (const c of term) {
+            const codePoint = /** @type {number} */ (c.codePointAt(0));
+            const isKana = this.isCodePointKana(codePoint);
+            if (isKana === isKanaPre) {
+                /** @type {import('japanese-util').FuriganaGroup} */ (groupPre).text += c;
+            } else {
+                groupPre = {isKana, text: c, textNormalized: null};
+                groups.push(groupPre);
+                isKanaPre = isKana;
             }
-
-            const readingNormalized = this.convertKatakanaToHiragana(reading);
-            const segments = this._segmentizeFurigana(reading, readingNormalized, groups, 0);
-            if (segments !== null) {
-                return segments;
+        }
+        for (const group of groups) {
+            if (group.isKana) {
+                group.textNormalized = this.convertKatakanaToHiragana(group.text);
             }
-
-            // Fallback
-            return [this._createFuriganaSegment(term, reading)];
         }
 
-        distributeFuriganaInflected(term, reading, source) {
-            const termNormalized = this.convertKatakanaToHiragana(term);
-            const readingNormalized = this.convertKatakanaToHiragana(reading);
-            const sourceNormalized = this.convertKatakanaToHiragana(source);
-
-            let mainText = term;
-            let stemLength = this._getStemLength(termNormalized, sourceNormalized);
+        const readingNormalized = this.convertKatakanaToHiragana(reading);
+        const segments = this._segmentizeFurigana(reading, readingNormalized, groups, 0);
+        if (segments !== null) {
+            return segments;
+        }
 
-            // Check if source is derived from the reading instead of the term
-            const readingStemLength = this._getStemLength(readingNormalized, sourceNormalized);
-            if (readingStemLength > 0 && readingStemLength >= stemLength) {
-                mainText = reading;
-                stemLength = readingStemLength;
-                reading = `${source.substring(0, stemLength)}${reading.substring(stemLength)}`;
-            }
+        // Fallback
+        return [this._createFuriganaSegment(term, reading)];
+    }
 
-            const segments = [];
-            if (stemLength > 0) {
-                mainText = `${source.substring(0, stemLength)}${mainText.substring(stemLength)}`;
-                const segments2 = this.distributeFurigana(mainText, reading);
-                let consumed = 0;
-                for (const segment of segments2) {
-                    const {text} = segment;
-                    const start = consumed;
-                    consumed += text.length;
-                    if (consumed < stemLength) {
-                        segments.push(segment);
-                    } else if (consumed === stemLength) {
-                        segments.push(segment);
-                        break;
-                    } else {
-                        if (start < stemLength) {
-                            segments.push(this._createFuriganaSegment(mainText.substring(start, stemLength), ''));
-                        }
-                        break;
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @param {string} source
+     * @returns {import('japanese-util').FuriganaSegment[]}
+     */
+    distributeFuriganaInflected(term, reading, source) {
+        const termNormalized = this.convertKatakanaToHiragana(term);
+        const readingNormalized = this.convertKatakanaToHiragana(reading);
+        const sourceNormalized = this.convertKatakanaToHiragana(source);
+
+        let mainText = term;
+        let stemLength = this._getStemLength(termNormalized, sourceNormalized);
+
+        // Check if source is derived from the reading instead of the term
+        const readingStemLength = this._getStemLength(readingNormalized, sourceNormalized);
+        if (readingStemLength > 0 && readingStemLength >= stemLength) {
+            mainText = reading;
+            stemLength = readingStemLength;
+            reading = `${source.substring(0, stemLength)}${reading.substring(stemLength)}`;
+        }
+
+        const segments = [];
+        if (stemLength > 0) {
+            mainText = `${source.substring(0, stemLength)}${mainText.substring(stemLength)}`;
+            const segments2 = this.distributeFurigana(mainText, reading);
+            let consumed = 0;
+            for (const segment of segments2) {
+                const {text} = segment;
+                const start = consumed;
+                consumed += text.length;
+                if (consumed < stemLength) {
+                    segments.push(segment);
+                } else if (consumed === stemLength) {
+                    segments.push(segment);
+                    break;
+                } else {
+                    if (start < stemLength) {
+                        segments.push(this._createFuriganaSegment(mainText.substring(start, stemLength), ''));
                     }
+                    break;
                 }
             }
+        }
 
-            if (stemLength < source.length) {
-                const remainder = source.substring(stemLength);
-                const segmentCount = segments.length;
-                if (segmentCount > 0 && segments[segmentCount - 1].reading.length === 0) {
-                    // Append to the last segment if it has an empty reading
-                    segments[segmentCount - 1].text += remainder;
-                } else {
-                    // Otherwise, create a new segment
-                    segments.push(this._createFuriganaSegment(remainder, ''));
-                }
+        if (stemLength < source.length) {
+            const remainder = source.substring(stemLength);
+            const segmentCount = segments.length;
+            if (segmentCount > 0 && segments[segmentCount - 1].reading.length === 0) {
+                // Append to the last segment if it has an empty reading
+                segments[segmentCount - 1].text += remainder;
+            } else {
+                // Otherwise, create a new segment
+                segments.push(this._createFuriganaSegment(remainder, ''));
             }
-
-            return segments;
         }
 
-        // Miscellaneous
-
-        collapseEmphaticSequences(text, fullCollapse, sourceMap=null) {
-            let result = '';
-            let collapseCodePoint = -1;
-            const hasSourceMap = (sourceMap !== null);
-            for (const char of text) {
-                const c = char.codePointAt(0);
-                if (
-                    c === HIRAGANA_SMALL_TSU_CODE_POINT ||
-                    c === KATAKANA_SMALL_TSU_CODE_POINT ||
-                    c === KANA_PROLONGED_SOUND_MARK_CODE_POINT
-                ) {
-                    if (collapseCodePoint !== c) {
-                        collapseCodePoint = c;
-                        if (!fullCollapse) {
-                            result += char;
-                            continue;
-                        }
+        return segments;
+    }
+
+    // Miscellaneous
+
+    /**
+     * @param {string} text
+     * @param {boolean} fullCollapse
+     * @param {?TextSourceMap} [sourceMap]
+     * @returns {string}
+     */
+    collapseEmphaticSequences(text, fullCollapse, sourceMap=null) {
+        let result = '';
+        let collapseCodePoint = -1;
+        const hasSourceMap = (sourceMap !== null);
+        for (const char of text) {
+            const c = char.codePointAt(0);
+            if (
+                c === HIRAGANA_SMALL_TSU_CODE_POINT ||
+                c === KATAKANA_SMALL_TSU_CODE_POINT ||
+                c === KANA_PROLONGED_SOUND_MARK_CODE_POINT
+            ) {
+                if (collapseCodePoint !== c) {
+                    collapseCodePoint = c;
+                    if (!fullCollapse) {
+                        result += char;
+                        continue;
                     }
-                } else {
-                    collapseCodePoint = -1;
-                    result += char;
-                    continue;
                 }
+            } else {
+                collapseCodePoint = -1;
+                result += char;
+                continue;
+            }
 
-                if (hasSourceMap) {
-                    sourceMap.combine(Math.max(0, result.length - 1), 1);
-                }
+            if (hasSourceMap) {
+                sourceMap.combine(Math.max(0, result.length - 1), 1);
             }
-            return result;
         }
+        return result;
+    }
 
-        // Private
-
-        _createFuriganaSegment(text, reading) {
-            return {text, reading};
-        }
+    // Private
 
-        _segmentizeFurigana(reading, readingNormalized, groups, groupsStart) {
-            const groupCount = groups.length - groupsStart;
-            if (groupCount <= 0) {
-                return reading.length === 0 ? [] : null;
-            }
+    /**
+     * @param {string} text
+     * @param {string} reading
+     * @returns {import('japanese-util').FuriganaSegment}
+     */
+    _createFuriganaSegment(text, reading) {
+        return {text, reading};
+    }
 
-            const group = groups[groupsStart];
-            const {isKana, text} = group;
-            const textLength = text.length;
-            if (isKana) {
-                const {textNormalized} = group;
-                if (readingNormalized.startsWith(textNormalized)) {
-                    const segments = this._segmentizeFurigana(
-                        reading.substring(textLength),
-                        readingNormalized.substring(textLength),
-                        groups,
-                        groupsStart + 1
-                    );
-                    if (segments !== null) {
-                        if (reading.startsWith(text)) {
-                            segments.unshift(this._createFuriganaSegment(text, ''));
-                        } else {
-                            segments.unshift(...this._getFuriganaKanaSegments(text, reading));
-                        }
-                        return segments;
+    /**
+     * @param {string} reading
+     * @param {string} readingNormalized
+     * @param {import('japanese-util').FuriganaGroup[]} groups
+     * @param {number} groupsStart
+     * @returns {?(import('japanese-util').FuriganaSegment[])}
+     */
+    _segmentizeFurigana(reading, readingNormalized, groups, groupsStart) {
+        const groupCount = groups.length - groupsStart;
+        if (groupCount <= 0) {
+            return reading.length === 0 ? [] : null;
+        }
+
+        const group = groups[groupsStart];
+        const {isKana, text} = group;
+        const textLength = text.length;
+        if (isKana) {
+            const {textNormalized} = group;
+            if (textNormalized !== null && readingNormalized.startsWith(textNormalized)) {
+                const segments = this._segmentizeFurigana(
+                    reading.substring(textLength),
+                    readingNormalized.substring(textLength),
+                    groups,
+                    groupsStart + 1
+                );
+                if (segments !== null) {
+                    if (reading.startsWith(text)) {
+                        segments.unshift(this._createFuriganaSegment(text, ''));
+                    } else {
+                        segments.unshift(...this._getFuriganaKanaSegments(text, reading));
                     }
+                    return segments;
                 }
-                return null;
-            } else {
-                let result = null;
-                for (let i = reading.length; i >= textLength; --i) {
-                    const segments = this._segmentizeFurigana(
-                        reading.substring(i),
-                        readingNormalized.substring(i),
-                        groups,
-                        groupsStart + 1
-                    );
-                    if (segments !== null) {
-                        if (result !== null) {
-                            // More than one way to segmentize the tail; mark as ambiguous
-                            return null;
-                        }
-                        const segmentReading = reading.substring(0, i);
-                        segments.unshift(this._createFuriganaSegment(text, segmentReading));
-                        result = segments;
-                    }
-                    // There is only one way to segmentize the last non-kana group
-                    if (groupCount === 1) {
-                        break;
+            }
+            return null;
+        } else {
+            let result = null;
+            for (let i = reading.length; i >= textLength; --i) {
+                const segments = this._segmentizeFurigana(
+                    reading.substring(i),
+                    readingNormalized.substring(i),
+                    groups,
+                    groupsStart + 1
+                );
+                if (segments !== null) {
+                    if (result !== null) {
+                        // More than one way to segmentize the tail; mark as ambiguous
+                        return null;
                     }
+                    const segmentReading = reading.substring(0, i);
+                    segments.unshift(this._createFuriganaSegment(text, segmentReading));
+                    result = segments;
+                }
+                // There is only one way to segmentize the last non-kana group
+                if (groupCount === 1) {
+                    break;
                 }
-                return result;
-            }
-        }
-
-        _getFuriganaKanaSegments(text, reading) {
-            const textLength = text.length;
-            const newSegments = [];
-            let start = 0;
-            let state = (reading[0] === text[0]);
-            for (let i = 1; i < textLength; ++i) {
-                const newState = (reading[i] === text[i]);
-                if (state === newState) { continue; }
-                newSegments.push(this._createFuriganaSegment(text.substring(start, i), state ? '' : reading.substring(start, i)));
-                state = newState;
-                start = i;
             }
-            newSegments.push(this._createFuriganaSegment(text.substring(start, textLength), state ? '' : reading.substring(start, textLength)));
-            return newSegments;
+            return result;
         }
+    }
 
-        _getWanakana() {
-            const wanakana = this._wanakana;
-            if (wanakana === null) { throw new Error('Functions which use WanaKana are not supported in this context'); }
-            return wanakana;
-        }
+    /**
+     * @param {string} text
+     * @param {string} reading
+     * @returns {import('japanese-util').FuriganaSegment[]}
+     */
+    _getFuriganaKanaSegments(text, reading) {
+        const textLength = text.length;
+        const newSegments = [];
+        let start = 0;
+        let state = (reading[0] === text[0]);
+        for (let i = 1; i < textLength; ++i) {
+            const newState = (reading[i] === text[i]);
+            if (state === newState) { continue; }
+            newSegments.push(this._createFuriganaSegment(text.substring(start, i), state ? '' : reading.substring(start, i)));
+            state = newState;
+            start = i;
+        }
+        newSegments.push(this._createFuriganaSegment(text.substring(start, textLength), state ? '' : reading.substring(start, textLength)));
+        return newSegments;
+    }
 
-        _convertAlphabeticPartToKana(text, sourceMap, sourceMapStart) {
-            const wanakana = this._getWanakana();
-            const result = wanakana.toHiragana(text);
-
-            // Generate source mapping
-            if (sourceMap !== null) {
-                let i = 0;
-                let resultPos = 0;
-                const ii = text.length;
-                while (i < ii) {
-                    // Find smallest matching substring
-                    let iNext = i + 1;
-                    let resultPosNext = result.length;
-                    while (iNext < ii) {
-                        const t = wanakana.toHiragana(text.substring(0, iNext));
-                        if (t === result.substring(0, t.length)) {
-                            resultPosNext = t.length;
-                            break;
-                        }
-                        ++iNext;
-                    }
+    /**
+     * @returns {import('wanakana')}
+     * @throws {Error}
+     */
+    _getWanakana() {
+        const wanakana = this._wanakana;
+        if (wanakana === null) { throw new Error('Functions which use WanaKana are not supported in this context'); }
+        return wanakana;
+    }
 
-                    // Merge characters
-                    const removals = iNext - i - 1;
-                    if (removals > 0) {
-                        sourceMap.combine(sourceMapStart, removals);
+    /**
+     * @param {string} text
+     * @param {?TextSourceMap} sourceMap
+     * @param {number} sourceMapStart
+     * @returns {string}
+     */
+    _convertAlphabeticPartToKana(text, sourceMap, sourceMapStart) {
+        const wanakana = this._getWanakana();
+        const result = wanakana.toHiragana(text);
+
+        // Generate source mapping
+        if (sourceMap !== null) {
+            let i = 0;
+            let resultPos = 0;
+            const ii = text.length;
+            while (i < ii) {
+                // Find smallest matching substring
+                let iNext = i + 1;
+                let resultPosNext = result.length;
+                while (iNext < ii) {
+                    const t = wanakana.toHiragana(text.substring(0, iNext));
+                    if (t === result.substring(0, t.length)) {
+                        resultPosNext = t.length;
+                        break;
                     }
-                    ++sourceMapStart;
+                    ++iNext;
+                }
 
-                    // Empty elements
-                    const additions = resultPosNext - resultPos - 1;
-                    for (let j = 0; j < additions; ++j) {
-                        sourceMap.insert(sourceMapStart, 0);
-                        ++sourceMapStart;
-                    }
+                // Merge characters
+                const removals = iNext - i - 1;
+                if (removals > 0) {
+                    sourceMap.combine(sourceMapStart, removals);
+                }
+                ++sourceMapStart;
 
-                    i = iNext;
-                    resultPos = resultPosNext;
+                // Empty elements
+                const additions = resultPosNext - resultPos - 1;
+                for (let j = 0; j < additions; ++j) {
+                    sourceMap.insert(sourceMapStart, 0);
+                    ++sourceMapStart;
                 }
-            }
 
-            return result;
+                i = iNext;
+                resultPos = resultPosNext;
+            }
         }
 
-        _getStemLength(text1, text2) {
-            const minLength = Math.min(text1.length, text2.length);
-            if (minLength === 0) { return 0; }
+        return result;
+    }
 
-            let i = 0;
-            while (true) {
-                const char1 = text1.codePointAt(i);
-                const char2 = text2.codePointAt(i);
-                if (char1 !== char2) { break; }
-                const charLength = String.fromCodePoint(char1).length;
-                i += charLength;
-                if (i >= minLength) {
-                    if (i > minLength) {
-                        i -= charLength; // Don't consume partial UTF16 surrogate characters
-                    }
-                    break;
+    /**
+     * @param {string} text1
+     * @param {string} text2
+     * @returns {number}
+     */
+    _getStemLength(text1, text2) {
+        const minLength = Math.min(text1.length, text2.length);
+        if (minLength === 0) { return 0; }
+
+        let i = 0;
+        while (true) {
+            const char1 = /** @type {number} */ (text1.codePointAt(i));
+            const char2 = /** @type {number} */ (text2.codePointAt(i));
+            if (char1 !== char2) { break; }
+            const charLength = String.fromCodePoint(char1).length;
+            i += charLength;
+            if (i >= minLength) {
+                if (i > minLength) {
+                    i -= charLength; // Don't consume partial UTF16 surrogate characters
                 }
+                break;
             }
-            return i;
         }
+        return i;
     }
-
-
-    return JapaneseUtil;
-})();
+}
diff --git a/ext/js/language/text-scanner.js b/ext/js/language/text-scanner.js
index 6fa7a4548c..515af978b9 100644
--- a/ext/js/language/text-scanner.js
+++ b/ext/js/language/text-scanner.js
@@ -18,9 +18,16 @@
 
 /* global
  * DocumentUtil
+ * TextSourceElement
  */
 
+/**
+ * @augments EventDispatcher<import('text-scanner').EventType>
+ */
 class TextScanner extends EventDispatcher {
+    /**
+     * @param {import('text-scanner').ConstructorDetails} details
+     */
     constructor({
         node,
         getSearchContext,
@@ -32,67 +39,121 @@ class TextScanner extends EventDispatcher {
         searchOnClickOnly=false
     }) {
         super();
+        /** @type {HTMLElement|Window} */
         this._node = node;
+        /** @type {import('text-scanner').GetSearchContextCallback} */
         this._getSearchContext = getSearchContext;
+        /** @type {?(() => Element[])} */
         this._ignoreElements = ignoreElements;
+        /** @type {?((x: number, y: number) => Promise<boolean>)} */
         this._ignorePoint = ignorePoint;
+        /** @type {boolean} */
         this._searchTerms = searchTerms;
+        /** @type {boolean} */
         this._searchKanji = searchKanji;
+        /** @type {boolean} */
         this._searchOnClick = searchOnClick;
+        /** @type {boolean} */
         this._searchOnClickOnly = searchOnClickOnly;
 
+        /** @type {boolean} */
         this._isPrepared = false;
+        /** @type {?string} */
         this._includeSelector = null;
+        /** @type {?string} */
         this._excludeSelector = null;
 
+        /** @type {?import('text-scanner').InputInfo} */
         this._inputInfoCurrent = null;
+        /** @type {?Promise<boolean>} */
         this._scanTimerPromise = null;
+        /** @type {?(value: boolean) => void} */
+        this._scanTimerPromiseResolve = null;
+        /** @type {?import('text-source').TextSource} */
         this._textSourceCurrent = null;
+        /** @type {boolean} */
         this._textSourceCurrentSelected = false;
+        /** @type {boolean} */
         this._pendingLookup = false;
+        /** @type {?import('text-scanner').SelectionRestoreInfo} */
         this._selectionRestoreInfo = null;
 
+        /** @type {boolean} */
         this._deepContentScan = false;
+        /** @type {boolean} */
         this._normalizeCssZoom = true;
+        /** @type {boolean} */
         this._selectText = false;
+        /** @type {number} */
         this._delay = 0;
+        /** @type {boolean} */
         this._touchInputEnabled = false;
+        /** @type {boolean} */
         this._pointerEventsEnabled = false;
+        /** @type {number} */
         this._scanLength = 1;
+        /** @type {boolean} */
         this._layoutAwareScan = false;
+        /** @type {boolean} */
         this._preventMiddleMouse = false;
+        /** @type {boolean} */
         this._matchTypePrefix = false;
+        /** @type {number} */
         this._sentenceScanExtent = 0;
+        /** @type {boolean} */
         this._sentenceTerminateAtNewlines = true;
+        /** @type {Map<string, [includeCharacterAtStart: boolean, includeCharacterAtEnd: boolean]>} */
         this._sentenceTerminatorMap = new Map();
+        /** @type {Map<string, [character: string, includeCharacterAtStart: boolean]>} */
         this._sentenceForwardQuoteMap = new Map();
+        /** @type {Map<string, [character: string, includeCharacterAtEnd: boolean]>} */
         this._sentenceBackwardQuoteMap = new Map();
+        /** @type {import('text-scanner').InputConfig[]} */
         this._inputs = [];
 
+        /** @type {boolean} */
         this._enabled = false;
+        /** @type {boolean} */
         this._enabledValue = false;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
 
+        /** @type {boolean} */
         this._preventNextClickScan = false;
+        /** @type {?number} */
         this._preventNextClickScanTimer = null;
+        /** @type {number} */
         this._preventNextClickScanTimerDuration = 50;
+        /** @type {() => void} */
         this._preventNextClickScanTimerCallback = this._onPreventNextClickScanTimeout.bind(this);
 
+        /** @type {?number} */
         this._primaryTouchIdentifier = null;
+        /** @type {boolean} */
         this._preventNextContextMenu = false;
+        /** @type {boolean} */
         this._preventNextMouseDown = false;
+        /** @type {boolean} */
         this._preventNextClick = false;
+        /** @type {boolean} */
         this._preventScroll = false;
+        /** @type {0|1|2|3} */
         this._penPointerState = 0; // 0 = not active; 1 = hovering; 2 = touching; 3 = hovering after touching
+        /** @type {Map<number, string>} */
         this._pointerIdTypeMap = new Map();
 
+        /** @type {boolean} */
         this._canClearSelection = true;
 
+        /** @type {?number} */
         this._textSelectionTimer = null;
+        /** @type {boolean} */
         this._yomichanIsChangingTextSelectionNow = false;
+        /** @type {boolean} */
         this._userHasNotSelectedAnythingManually = true;
     }
 
+    /** @type {boolean} */
     get canClearSelection() {
         return this._canClearSelection;
     }
@@ -101,6 +162,7 @@ class TextScanner extends EventDispatcher {
         this._canClearSelection = value;
     }
 
+    /** @type {?string} */
     get includeSelector() {
         return this._includeSelector;
     }
@@ -109,6 +171,7 @@ class TextScanner extends EventDispatcher {
         this._includeSelector = value;
     }
 
+    /** @type {?string} */
     get excludeSelector() {
         return this._excludeSelector;
     }
@@ -117,15 +180,22 @@ class TextScanner extends EventDispatcher {
         this._excludeSelector = value;
     }
 
+    /** */
     prepare() {
         this._isPrepared = true;
         this.setEnabled(this._enabled);
     }
 
+    /**
+     * @returns {boolean}
+     */
     isEnabled() {
         return this._enabled;
     }
 
+    /**
+     * @param {boolean} enabled
+     */
     setEnabled(enabled) {
         this._enabled = enabled;
 
@@ -145,10 +215,13 @@ class TextScanner extends EventDispatcher {
 
         if (value) {
             this._hookEvents();
-            this._userHasNotSelectedAnythingManually = window.getSelection().isCollapsed;
+            this._userHasNotSelectedAnythingManually = this._computeUserHasNotSelectedAnythingManually();
         }
     }
 
+    /**
+     * @param {import('text-scanner').Options} options
+     */
     setOptions({
         inputs,
         deepContentScan,
@@ -199,7 +272,7 @@ class TextScanner extends EventDispatcher {
         if (typeof sentenceParsingOptions === 'object' && sentenceParsingOptions !== null) {
             const {scanExtent, terminationCharacterMode, terminationCharacters} = sentenceParsingOptions;
             if (typeof scanExtent === 'number') {
-                this._sentenceScanExtent = sentenceParsingOptions.scanExtent;
+                this._sentenceScanExtent = scanExtent;
             }
             if (typeof terminationCharacterMode === 'string') {
                 this._sentenceTerminateAtNewlines = (terminationCharacterMode === 'custom' || terminationCharacterMode === 'newlines');
@@ -228,6 +301,12 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {number} length
+     * @param {boolean} layoutAwareScan
+     * @returns {string}
+     */
     getTextSourceContent(textSource, length, layoutAwareScan) {
         const clonedTextSource = textSource.clone();
 
@@ -242,10 +321,14 @@ class TextScanner extends EventDispatcher {
         return clonedTextSource.text();
     }
 
+    /**
+     * @returns {boolean}
+     */
     hasSelection() {
         return (this._textSourceCurrent !== null);
     }
 
+    /** */
     clearSelection() {
         if (!this._canClearSelection) { return; }
         if (this._textSourceCurrent !== null) {
@@ -262,15 +345,21 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @returns {?import('text-source').TextSource}
+     */
     getCurrentTextSource() {
         return this._textSourceCurrent;
     }
 
+    /**
+     * @param {?import('text-source').TextSource} textSource
+     */
     setCurrentTextSource(textSource) {
         this._textSourceCurrent = textSource;
-        if (this._selectText && this._userHasNotSelectedAnythingManually) {
+        if (this._selectText && this._userHasNotSelectedAnythingManually && textSource !== null) {
             this._yomichanIsChangingTextSelectionNow = true;
-            this._textSourceCurrent.select();
+            textSource.select();
             if (this._textSelectionTimer !== null) { clearTimeout(this._textSelectionTimer); }
             // This timeout uses a 50ms delay to ensure that the selectionchange event has time to occur.
             // If the delay is 0ms, the timeout will sometimes complete before the event.
@@ -284,6 +373,9 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @returns {Promise<boolean>}
+     */
     async searchLast() {
         if (this._textSourceCurrent !== null && this._inputInfoCurrent !== null) {
             await this._search(this._textSourceCurrent, this._searchTerms, this._searchKanji, this._inputInfoCurrent);
@@ -292,6 +384,11 @@ class TextScanner extends EventDispatcher {
         return false;
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {import('text-scanner').InputInfoDetail} [inputDetail]
+     * @returns {Promise<?import('text-scanner').SearchedEventDetails>}
+     */
     async search(textSource, inputDetail) {
         const inputInfo = this._createInputInfo(null, 'script', 'script', true, [], [], inputDetail);
         return await this._search(textSource, this._searchTerms, this._searchKanji, inputInfo);
@@ -299,6 +396,11 @@ class TextScanner extends EventDispatcher {
 
     // Private
 
+    /**
+     * @param {import('settings').OptionsContext} baseOptionsContext
+     * @param {import('text-scanner').InputInfo} inputInfo
+     * @returns {import('settings').OptionsContext}
+     */
     _createOptionsContextForInput(baseOptionsContext, inputInfo) {
         const optionsContext = clone(baseOptionsContext);
         const {modifiers, modifierKeys} = inputInfo;
@@ -307,20 +409,33 @@ class TextScanner extends EventDispatcher {
         return optionsContext;
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {boolean} searchTerms
+     * @param {boolean} searchKanji
+     * @param {import('text-scanner').InputInfo} inputInfo
+     * @returns {Promise<?import('text-scanner').SearchedEventDetails>}
+     */
     async _search(textSource, searchTerms, searchKanji, inputInfo) {
+        /** @type {?import('dictionary').DictionaryEntry[]} */
         let dictionaryEntries = null;
+        /** @type {?import('display').HistoryStateSentence} */
         let sentence = null;
+        /** @type {?import('display').PageType} */
         let type = null;
+        /** @type {?Error} */
         let error = null;
         let searched = false;
+        /** @type {?import('settings').OptionsContext} */
         let optionsContext = null;
+        /** @type {?import('text-scanner').SearchResultDetail} */
         let detail = null;
 
         try {
             const inputInfoDetail = inputInfo.detail;
             const selectionRestoreInfo = (
-                (isObject(inputInfoDetail) && inputInfoDetail.restoreSelection) ?
-                (this._inputInfoCurrent === null ? this._createSelectionRestoreInfo() : void 0) :
+                (typeof inputInfoDetail === 'object' && inputInfoDetail !== null && inputInfoDetail.restoreSelection) ?
+                (this._inputInfoCurrent === null ? this._createSelectionRestoreInfo() : null) :
                 null
             );
 
@@ -328,8 +443,11 @@ class TextScanner extends EventDispatcher {
                 return null;
             }
 
-            ({optionsContext, detail} = await this._getSearchContext());
-            optionsContext = this._createOptionsContextForInput(optionsContext, inputInfo);
+            const getSearchContextPromise = this._getSearchContext();
+            const getSearchContextResult = getSearchContextPromise instanceof Promise ? await getSearchContextPromise : getSearchContextPromise;
+            const {detail: detail2} = getSearchContextResult;
+            if (typeof detail2 !== 'undefined') { detail = detail2; }
+            optionsContext = this._createOptionsContextForInput(getSearchContextResult.optionsContext, inputInfo);
 
             searched = true;
 
@@ -338,9 +456,9 @@ class TextScanner extends EventDispatcher {
             if (result !== null) {
                 ({dictionaryEntries, sentence, type} = result);
                 valid = true;
-            } else if (textSource !== null && textSource.type === 'element' && await this._hasJapanese(textSource.fullContent)) {
+            } else if (textSource !== null && textSource instanceof TextSourceElement && await this._hasJapanese(textSource.fullContent)) {
                 dictionaryEntries = [];
-                sentence = {sentence: '', offset: 0};
+                sentence = {text: '', offset: 0};
                 type = 'terms';
                 valid = true;
             }
@@ -353,11 +471,12 @@ class TextScanner extends EventDispatcher {
                 }
             }
         } catch (e) {
-            error = e;
+            error = e instanceof Error ? e : new Error(`A search error occurred: ${e}`);
         }
 
         if (!searched) { return null; }
 
+        /** @type {import('text-scanner').SearchedEventDetails} */
         const results = {
             textScanner: this,
             type,
@@ -373,41 +492,55 @@ class TextScanner extends EventDispatcher {
         return results;
     }
 
+    /** */
     _resetPreventNextClickScan() {
         this._preventNextClickScan = false;
         if (this._preventNextClickScanTimer !== null) { clearTimeout(this._preventNextClickScanTimer); }
         this._preventNextClickScanTimer = setTimeout(this._preventNextClickScanTimerCallback, this._preventNextClickScanTimerDuration);
     }
 
+    /** */
     _onPreventNextClickScanTimeout() {
         this._preventNextClickScanTimer = null;
     }
 
+    /** */
     _onSelectionChange() {
         if (this._preventNextClickScanTimer !== null) { return; } // Ignore deselection that occurs at the start of the click
         this._preventNextClickScan = true;
     }
 
+    /** */
     _onSelectionChangeCheckUserSelection() {
         if (this._yomichanIsChangingTextSelectionNow) { return; }
-        this._userHasNotSelectedAnythingManually = window.getSelection().isCollapsed;
+        this._userHasNotSelectedAnythingManually = this._computeUserHasNotSelectedAnythingManually();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onSearchClickMouseDown(e) {
         if (e.button !== 0) { return; }
         this._resetPreventNextClickScan();
     }
 
+    /** */
     _onSearchClickTouchStart() {
         this._resetPreventNextClickScan();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMouseOver(e) {
-        if (this._ignoreElements !== null && this._ignoreElements().includes(e.target)) {
+        if (this._ignoreElements !== null && this._ignoreElements().includes(/** @type {Element} */ (e.target))) {
             this._scanTimerClear();
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMouseMove(e) {
         this._scanTimerClear();
 
@@ -417,6 +550,10 @@ class TextScanner extends EventDispatcher {
         this._searchAtFromMouseMove(e.clientX, e.clientY, inputInfo);
     }
 
+    /**
+     * @param {MouseEvent} e
+     * @returns {boolean|void}
+     */
     _onMouseDown(e) {
         if (this._preventNextMouseDown) {
             this._preventNextMouseDown = false;
@@ -442,10 +579,15 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /** */
     _onMouseOut() {
         this._scanTimerClear();
     }
 
+    /**
+     * @param {MouseEvent} e
+     * @returns {boolean|void}
+     */
     _onClick(e) {
         if (this._preventNextClick) {
             this._preventNextClick = false;
@@ -459,6 +601,9 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onSearchClick(e) {
         const preventNextClickScan = this._preventNextClickScan;
         this._preventNextClickScan = false;
@@ -475,10 +620,15 @@ class TextScanner extends EventDispatcher {
         this._searchAt(e.clientX, e.clientY, inputInfo);
     }
 
+    /** */
     _onAuxClick() {
         this._preventNextContextMenu = false;
     }
 
+    /**
+     * @param {MouseEvent} e
+     * @returns {boolean|void}
+     */
     _onContextMenu(e) {
         if (this._preventNextContextMenu) {
             this._preventNextContextMenu = false;
@@ -488,6 +638,9 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {TouchEvent} e
+     */
     _onTouchStart(e) {
         if (this._primaryTouchIdentifier !== null || e.changedTouches.length === 0) {
             return;
@@ -497,13 +650,20 @@ class TextScanner extends EventDispatcher {
         this._onPrimaryTouchStart(e, clientX, clientY, identifier);
     }
 
+    /**
+     * @param {TouchEvent|PointerEvent} e
+     * @param {number} x
+     * @param {number} y
+     * @param {number} identifier
+     */
     _onPrimaryTouchStart(e, x, y, identifier) {
         this._preventScroll = false;
         this._preventNextContextMenu = false;
         this._preventNextMouseDown = false;
         this._preventNextClick = false;
 
-        if (DocumentUtil.isPointInSelection(x, y, window.getSelection())) {
+        const selection = window.getSelection();
+        if (selection !== null && DocumentUtil.isPointInSelection(x, y, selection)) {
             return;
         }
 
@@ -512,11 +672,14 @@ class TextScanner extends EventDispatcher {
         if (this._pendingLookup) { return; }
 
         const inputInfo = this._getMatchingInputGroupFromEvent('touch', 'touchStart', e);
-        if (inputInfo === null || !inputInfo.input.scanOnTouchPress) { return; }
+        if (inputInfo === null || !(inputInfo.input !== null && inputInfo.input.scanOnTouchPress)) { return; }
 
         this._searchAtFromTouchStart(x, y, inputInfo);
     }
 
+    /**
+     * @param {TouchEvent} e
+     */
     _onTouchEnd(e) {
         if (this._primaryTouchIdentifier === null) { return; }
 
@@ -527,6 +690,12 @@ class TextScanner extends EventDispatcher {
         this._onPrimaryTouchEnd(e, clientX, clientY, true);
     }
 
+    /**
+     * @param {TouchEvent|PointerEvent} e
+     * @param {number} x
+     * @param {number} y
+     * @param {boolean} allowSearch
+     */
     _onPrimaryTouchEnd(e, x, y, allowSearch) {
         this._primaryTouchIdentifier = null;
         this._preventScroll = false;
@@ -537,11 +706,14 @@ class TextScanner extends EventDispatcher {
         if (!allowSearch) { return; }
 
         const inputInfo = this._getMatchingInputGroupFromEvent('touch', 'touchEnd', e);
-        if (inputInfo === null || !inputInfo.input.scanOnTouchRelease) { return; }
+        if (inputInfo === null || !(inputInfo.input !== null && inputInfo.input.scanOnTouchRelease)) { return; }
 
         this._searchAtFromTouchEnd(x, y, inputInfo);
     }
 
+    /**
+     * @param {TouchEvent} e
+     */
     _onTouchCancel(e) {
         if (this._primaryTouchIdentifier === null) { return; }
 
@@ -551,6 +723,9 @@ class TextScanner extends EventDispatcher {
         this._onPrimaryTouchEnd(e, 0, 0, false);
     }
 
+    /**
+     * @param {TouchEvent} e
+     */
     _onTouchMove(e) {
         if (this._primaryTouchIdentifier === null) { return; }
 
@@ -567,13 +742,18 @@ class TextScanner extends EventDispatcher {
         const inputInfo = this._getMatchingInputGroupFromEvent('touch', 'touchMove', e);
         if (inputInfo === null) { return; }
 
-        if (inputInfo.input.scanOnTouchMove) {
+        const {input} = inputInfo;
+        if (input !== null && input.scanOnTouchMove) {
             this._searchAt(primaryTouch.clientX, primaryTouch.clientY, inputInfo);
         }
 
         e.preventDefault(); // Disable scroll
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onPointerOver(e) {
         const {pointerType, pointerId, isPrimary} = e;
         if (pointerType === 'pen') {
@@ -583,11 +763,15 @@ class TextScanner extends EventDispatcher {
         if (!isPrimary) { return; }
         switch (pointerType) {
             case 'mouse': return this._onMousePointerOver(e);
-            case 'touch': return this._onTouchPointerOver(e);
+            case 'touch': return this._onTouchPointerOver();
             case 'pen': return this._onPenPointerOver(e);
         }
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onPointerDown(e) {
         if (!e.isPrimary) { return; }
         switch (this._getPointerEventType(e)) {
@@ -597,6 +781,10 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onPointerMove(e) {
         if (!e.isPrimary) { return; }
         switch (this._getPointerEventType(e)) {
@@ -606,92 +794,144 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onPointerUp(e) {
         if (!e.isPrimary) { return; }
         switch (this._getPointerEventType(e)) {
-            case 'mouse': return this._onMousePointerUp(e);
+            case 'mouse': return this._onMousePointerUp();
             case 'touch': return this._onTouchPointerUp(e);
             case 'pen': return this._onPenPointerUp(e);
         }
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onPointerCancel(e) {
         this._pointerIdTypeMap.delete(e.pointerId);
         if (!e.isPrimary) { return; }
         switch (e.pointerType) {
-            case 'mouse': return this._onMousePointerCancel(e);
+            case 'mouse': return this._onMousePointerCancel();
             case 'touch': return this._onTouchPointerCancel(e);
-            case 'pen': return this._onPenPointerCancel(e);
+            case 'pen': return this._onPenPointerCancel();
         }
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onPointerOut(e) {
         this._pointerIdTypeMap.delete(e.pointerId);
         if (!e.isPrimary) { return; }
         switch (e.pointerType) {
-            case 'mouse': return this._onMousePointerOut(e);
-            case 'touch': return this._onTouchPointerOut(e);
-            case 'pen': return this._onPenPointerOut(e);
+            case 'mouse': return this._onMousePointerOut();
+            case 'touch': return this._onTouchPointerOut();
+            case 'pen': return this._onPenPointerOut();
         }
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onMousePointerOver(e) {
         return this._onMouseOver(e);
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onMousePointerDown(e) {
         return this._onMouseDown(e);
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onMousePointerMove(e) {
         return this._onMouseMove(e);
     }
 
+    /** */
     _onMousePointerUp() {
         // NOP
     }
 
-    _onMousePointerCancel(e) {
-        return this._onMouseOut(e);
+    /**
+     * @returns {boolean|void}
+     */
+    _onMousePointerCancel() {
+        return this._onMouseOut();
     }
 
-    _onMousePointerOut(e) {
-        return this._onMouseOut(e);
+    /**
+     * @returns {boolean|void}
+     */
+    _onMousePointerOut() {
+        return this._onMouseOut();
     }
 
+    /** */
     _onTouchPointerOver() {
         // NOP
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onTouchPointerDown(e) {
         const {clientX, clientY, pointerId} = e;
         this._onPrimaryTouchStart(e, clientX, clientY, pointerId);
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onTouchPointerMove(e) {
         if (!this._preventScroll || !e.cancelable) {
             return;
         }
 
         const inputInfo = this._getMatchingInputGroupFromEvent('touch', 'touchMove', e);
-        if (inputInfo === null || !inputInfo.input.scanOnTouchMove) { return; }
+        if (inputInfo === null || !(inputInfo.input !== null && inputInfo.input.scanOnTouchMove)) { return; }
 
         this._searchAt(e.clientX, e.clientY, inputInfo);
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onTouchPointerUp(e) {
         const {clientX, clientY} = e;
         return this._onPrimaryTouchEnd(e, clientX, clientY, true);
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {boolean|void}
+     */
     _onTouchPointerCancel(e) {
         return this._onPrimaryTouchEnd(e, 0, 0, false);
     }
 
+    /** */
     _onTouchPointerOut() {
         // NOP
     }
 
+    /**
+     * @param {PointerEvent} e
+     */
     _onTouchMovePreventScroll(e) {
         if (!this._preventScroll) { return; }
 
@@ -702,31 +942,45 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {PointerEvent} e
+     */
     _onPenPointerOver(e) {
         this._penPointerState = 1;
         this._searchAtFromPen(e, 'pointerOver', false);
     }
 
+    /**
+     * @param {PointerEvent} e
+     */
     _onPenPointerDown(e) {
         this._penPointerState = 2;
         this._searchAtFromPen(e, 'pointerDown', true);
     }
 
+    /**
+     * @param {PointerEvent} e
+     */
     _onPenPointerMove(e) {
         if (this._penPointerState === 2 && (!this._preventScroll || !e.cancelable)) { return; }
         this._searchAtFromPen(e, 'pointerMove', true);
     }
 
+    /**
+     * @param {PointerEvent} e
+     */
     _onPenPointerUp(e) {
         this._penPointerState = 3;
         this._preventScroll = false;
         this._searchAtFromPen(e, 'pointerUp', false);
     }
 
-    _onPenPointerCancel(e) {
-        this._onPenPointerOut(e);
+    /** */
+    _onPenPointerCancel() {
+        this._onPenPointerOut();
     }
 
+    /** */
     _onPenPointerOut() {
         this._penPointerState = 0;
         this._preventScroll = false;
@@ -735,32 +989,54 @@ class TextScanner extends EventDispatcher {
         this._preventNextClick = false;
     }
 
+    /**
+     * @returns {Promise<boolean>}
+     */
     async _scanTimerWait() {
         const delay = this._delay;
-        const promise = promiseTimeout(delay, true);
+        const promise = /** @type {Promise<boolean>} */ (new Promise((resolve) => {
+            /** @type {?number} */
+            let timeout = setTimeout(() => {
+                timeout = null;
+                resolve(true);
+            }, delay);
+            this._scanTimerPromiseResolve = (value) => {
+                if (timeout === null) { return; }
+                clearTimeout(timeout);
+                timeout = null;
+                resolve(value);
+            };
+        }));
         this._scanTimerPromise = promise;
         try {
             return await promise;
         } finally {
             if (this._scanTimerPromise === promise) {
                 this._scanTimerPromise = null;
+                this._scanTimerPromiseResolve = null;
             }
         }
     }
 
+    /** */
     _scanTimerClear() {
-        if (this._scanTimerPromise !== null) {
-            this._scanTimerPromise.resolve(false);
-            this._scanTimerPromise = null;
-        }
+        if (this._scanTimerPromiseResolve === null) { return; }
+        this._scanTimerPromiseResolve(false);
+        this._scanTimerPromiseResolve = null;
+        this._scanTimerPromise = null;
     }
 
+    /**
+     * @returns {boolean}
+     */
     _arePointerEventsSupported() {
         return (this._pointerEventsEnabled && typeof PointerEvent !== 'undefined');
     }
 
+    /** */
     _hookEvents() {
         const capture = true;
+        /** @type {import('event-listener-collection').AddEventListenerArgs[]} */
         let eventListenerInfos;
         if (this._searchOnClickOnly) {
             eventListenerInfos = this._getMouseClickOnlyEventListeners(capture);
@@ -778,11 +1054,15 @@ class TextScanner extends EventDispatcher {
 
         eventListenerInfos.push(this._getSelectionChangeCheckUserSelectionListener());
 
-        for (const args of eventListenerInfos) {
+        for (const [...args] of eventListenerInfos) {
             this._eventListeners.addEventListener(...args);
         }
     }
 
+    /**
+     * @param {boolean} capture
+     * @returns {import('event-listener-collection').AddEventListenerArgs[]}
+     */
     _getPointerEventListeners(capture) {
         return [
             [this._node, 'pointerover', this._onPointerOver.bind(this), capture],
@@ -798,6 +1078,10 @@ class TextScanner extends EventDispatcher {
         ];
     }
 
+    /**
+     * @param {boolean} capture
+     * @returns {import('event-listener-collection').AddEventListenerArgs[]}
+     */
     _getMouseEventListeners(capture) {
         return [
             [this._node, 'mousedown', this._onMouseDown.bind(this), capture],
@@ -808,6 +1092,10 @@ class TextScanner extends EventDispatcher {
         ];
     }
 
+    /**
+     * @param {boolean} capture
+     * @returns {import('event-listener-collection').AddEventListenerArgs[]}
+     */
     _getTouchEventListeners(capture) {
         return [
             [this._node, 'auxclick', this._onAuxClick.bind(this), capture],
@@ -819,14 +1107,23 @@ class TextScanner extends EventDispatcher {
         ];
     }
 
+    /**
+     * @param {boolean} capture
+     * @returns {import('event-listener-collection').AddEventListenerArgs[]}
+     */
     _getMouseClickOnlyEventListeners(capture) {
         return [
             [this._node, 'click', this._onClick.bind(this), capture]
         ];
     }
 
+    /**
+     * @param {boolean} capture
+     * @returns {import('event-listener-collection').AddEventListenerArgs[]}
+     */
     _getMouseClickOnlyEventListeners2(capture) {
         const {documentElement} = document;
+        /** @type {import('event-listener-collection').AddEventListenerArgs[]} */
         const entries = [
             [document, 'selectionchange', this._onSelectionChange.bind(this)]
         ];
@@ -839,10 +1136,18 @@ class TextScanner extends EventDispatcher {
         return entries;
     }
 
+    /**
+     * @returns {import('event-listener-collection').AddEventListenerArgs}
+     */
     _getSelectionChangeCheckUserSelectionListener() {
         return [document, 'selectionchange', this._onSelectionChangeCheckUserSelection.bind(this)];
     }
 
+    /**
+     * @param {TouchList} touchList
+     * @param {number} identifier
+     * @returns {?Touch}
+     */
     _getTouch(touchList, identifier) {
         for (const touch of touchList) {
             if (touch.identifier === identifier) {
@@ -852,6 +1157,13 @@ class TextScanner extends EventDispatcher {
         return null;
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {boolean} searchTerms
+     * @param {boolean} searchKanji
+     * @param {import('settings').OptionsContext} optionsContext
+     * @returns {Promise<?import('text-scanner').SearchResults>}
+     */
     async _findDictionaryEntries(textSource, searchTerms, searchKanji, optionsContext) {
         if (textSource === null) {
             return null;
@@ -867,6 +1179,11 @@ class TextScanner extends EventDispatcher {
         return null;
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {import('settings').OptionsContext} optionsContext
+     * @returns {Promise<?import('text-scanner').TermSearchResults>}
+     */
     async _findTermDictionaryEntries(textSource, optionsContext) {
         const scanLength = this._scanLength;
         const sentenceScanExtent = this._sentenceScanExtent;
@@ -878,6 +1195,7 @@ class TextScanner extends EventDispatcher {
         const searchText = this.getTextSourceContent(textSource, scanLength, layoutAwareScan);
         if (searchText.length === 0) { return null; }
 
+        /** @type {import('api').FindTermsDetails} */
         const details = {};
         if (this._matchTypePrefix) { details.matchType = 'prefix'; }
         const {dictionaryEntries, originalTextLength} = await yomichan.api.termsFind(searchText, details, optionsContext);
@@ -897,6 +1215,11 @@ class TextScanner extends EventDispatcher {
         return {dictionaryEntries, sentence, type: 'terms'};
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {import('settings').OptionsContext} optionsContext
+     * @returns {Promise<?import('text-scanner').KanjiSearchResults>}
+     */
     async _findKanjiDictionaryEntries(textSource, optionsContext) {
         const sentenceScanExtent = this._sentenceScanExtent;
         const sentenceTerminateAtNewlines = this._sentenceTerminateAtNewlines;
@@ -924,6 +1247,11 @@ class TextScanner extends EventDispatcher {
         return {dictionaryEntries, sentence, type: 'kanji'};
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {import('text-scanner').InputInfo} inputInfo
+     */
     async _searchAt(x, y, inputInfo) {
         if (this._pendingLookup) { return; }
 
@@ -947,11 +1275,13 @@ class TextScanner extends EventDispatcher {
                 deepContentScan: this._deepContentScan,
                 normalizeCssZoom: this._normalizeCssZoom
             });
-            try {
-                await this._search(textSource, searchTerms, searchKanji, inputInfo);
-            } finally {
-                if (textSource !== null) {
-                    textSource.cleanup();
+            if (textSource !== null) {
+                try {
+                    await this._search(textSource, searchTerms, searchKanji, inputInfo);
+                } finally {
+                    if (textSource !== null) {
+                        textSource.cleanup();
+                    }
                 }
             }
         } catch (e) {
@@ -961,6 +1291,11 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {import('text-scanner').InputInfo} inputInfo
+     */
     async _searchAtFromMouseMove(x, y, inputInfo) {
         if (this._pendingLookup) { return; }
 
@@ -974,15 +1309,21 @@ class TextScanner extends EventDispatcher {
         await this._searchAt(x, y, inputInfo);
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {import('text-scanner').InputInfo} inputInfo
+     */
     async _searchAtFromTouchStart(x, y, inputInfo) {
         const textSourceCurrentPrevious = this._textSourceCurrent !== null ? this._textSourceCurrent.clone() : null;
-        const preventScroll = inputInfo.input.preventTouchScrolling;
+        const {input} = inputInfo;
+        const preventScroll = input !== null && input.preventTouchScrolling;
 
         await this._searchAt(x, y, inputInfo);
 
         if (
             this._textSourceCurrent !== null &&
-            !this._textSourceCurrent.hasSameStart(textSourceCurrentPrevious)
+            !(textSourceCurrentPrevious !== null && this._textSourceCurrent.hasSameStart(textSourceCurrentPrevious))
         ) {
             this._preventScroll = preventScroll;
             this._preventNextContextMenu = true;
@@ -990,10 +1331,20 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {import('text-scanner').InputInfo} inputInfo
+     */
     async _searchAtFromTouchEnd(x, y, inputInfo) {
         await this._searchAt(x, y, inputInfo);
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @param {import('text-scanner').PointerEventType} eventType
+     * @param {boolean} prevent
+     */
     async _searchAtFromPen(e, eventType, prevent) {
         if (this._pendingLookup) { return; }
 
@@ -1001,9 +1352,9 @@ class TextScanner extends EventDispatcher {
         if (inputInfo === null) { return; }
 
         const {input} = inputInfo;
-        if (!this._isPenEventSupported(eventType, input)) { return; }
+        if (input === null || !this._isPenEventSupported(eventType, input)) { return; }
 
-        const preventScroll = input.preventPenScrolling;
+        const preventScroll = input !== null && input.preventPenScrolling;
 
         await this._searchAt(e.clientX, e.clientY, inputInfo);
 
@@ -1018,6 +1369,11 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('text-scanner').PointerEventType} eventType
+     * @param {import('text-scanner').InputConfig} input
+     * @returns {boolean}
+     */
     _isPenEventSupported(eventType, input) {
         switch (eventType) {
             case 'pointerDown':
@@ -1037,12 +1393,25 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {import('text-scanner').PointerType} pointerType
+     * @param {import('text-scanner').PointerEventType} eventType
+     * @param {MouseEvent|TouchEvent} event
+     * @returns {?import('text-scanner').InputInfo}
+     */
     _getMatchingInputGroupFromEvent(pointerType, eventType, event) {
         const modifiers = DocumentUtil.getActiveModifiersAndButtons(event);
         const modifierKeys = DocumentUtil.getActiveModifiers(event);
         return this._getMatchingInputGroup(pointerType, eventType, modifiers, modifierKeys);
     }
 
+    /**
+     * @param {import('text-scanner').PointerType} pointerType
+     * @param {import('text-scanner').PointerEventType} eventType
+     * @param {import('input').Modifier[]} modifiers
+     * @param {import('input').ModifierKey[]} modifierKeys
+     * @returns {?import('text-scanner').InputInfo}
+     */
     _getMatchingInputGroup(pointerType, eventType, modifiers, modifierKeys) {
         let fallbackIndex = -1;
         const modifiersSet = new Set(modifiers);
@@ -1066,10 +1435,25 @@ class TextScanner extends EventDispatcher {
         );
     }
 
+    /**
+     * @param {?import('text-scanner').InputConfig} input
+     * @param {import('text-scanner').PointerType} pointerType
+     * @param {import('text-scanner').PointerEventType} eventType
+     * @param {boolean} passive
+     * @param {import('input').Modifier[]} modifiers
+     * @param {import('input').ModifierKey[]} modifierKeys
+     * @param {import('text-scanner').InputInfoDetail} [detail]
+     * @returns {import('text-scanner').InputInfo}
+     */
     _createInputInfo(input, pointerType, eventType, passive, modifiers, modifierKeys, detail) {
         return {input, pointerType, eventType, passive, modifiers, modifierKeys, detail};
     }
 
+    /**
+     * @param {Set<string>} set
+     * @param {string[]} values
+     * @returns {boolean}
+     */
     _setHasAll(set, values) {
         for (const value of values) {
             if (!set.has(value)) {
@@ -1079,6 +1463,10 @@ class TextScanner extends EventDispatcher {
         return true;
     }
 
+    /**
+     * @param {import('text-scanner').InputOptionsOuter} input
+     * @returns {import('text-scanner').InputConfig}
+     */
     _convertInput(input) {
         const {options} = input;
         return {
@@ -1100,6 +1488,10 @@ class TextScanner extends EventDispatcher {
         };
     }
 
+    /**
+     * @param {string} value
+     * @returns {string[]}
+     */
     _getInputArray(value) {
         return (
             typeof value === 'string' ?
@@ -1108,6 +1500,10 @@ class TextScanner extends EventDispatcher {
         );
     }
 
+    /**
+     * @param {{mouse: boolean, touch: boolean, pen: boolean}} details
+     * @returns {Set<'mouse'|'touch'|'pen'>}
+     */
     _getInputTypeSet({mouse, touch, pen}) {
         const set = new Set();
         if (mouse) { set.add('mouse'); }
@@ -1116,16 +1512,30 @@ class TextScanner extends EventDispatcher {
         return set;
     }
 
+    /**
+     * @param {unknown} value
+     * @returns {boolean}
+     */
     _getInputBoolean(value) {
         return typeof value === 'boolean' && value;
     }
 
+    /**
+     * @param {PointerEvent} e
+     * @returns {string}
+     */
     _getPointerEventType(e) {
         // Workaround for Firefox bug not detecting certain 'touch' events as 'pen' events.
         const cachedPointerType = this._pointerIdTypeMap.get(e.pointerId);
         return (typeof cachedPointerType !== 'undefined' ? cachedPointerType : e.pointerType);
     }
 
+    /**
+     * @param {import('text-source').TextSource} textSource
+     * @param {?string} includeSelector
+     * @param {?string} excludeSelector
+     * @param {boolean} layoutAwareScan
+     */
     _constrainTextSource(textSource, includeSelector, excludeSelector, layoutAwareScan) {
         let length = textSource.text().length;
         while (length > 0) {
@@ -1142,6 +1552,10 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} text
+     * @returns {Promise<boolean>}
+     */
     async _hasJapanese(text) {
         try {
             return await yomichan.api.textHasJapaneseCharacters(text);
@@ -1150,19 +1564,28 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @returns {import('text-scanner').SelectionRestoreInfo}
+     */
     _createSelectionRestoreInfo() {
         const ranges = [];
         const selection = window.getSelection();
-        for (let i = 0, ii = selection.rangeCount; i < ii; ++i) {
-            const range = selection.getRangeAt(i);
-            ranges.push(range.cloneRange());
+        if (selection !== null) {
+            for (let i = 0, ii = selection.rangeCount; i < ii; ++i) {
+                const range = selection.getRangeAt(i);
+                ranges.push(range.cloneRange());
+            }
         }
         return {ranges};
     }
 
+    /**
+     * @param {import('text-scanner').SelectionRestoreInfo} selectionRestoreInfo
+     */
     _restoreSelection(selectionRestoreInfo) {
         const {ranges} = selectionRestoreInfo;
         const selection = window.getSelection();
+        if (selection === null) { return; }
         selection.removeAllRanges();
         for (const range of ranges) {
             try {
@@ -1173,7 +1596,18 @@ class TextScanner extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} reason
+     */
     _triggerClear(reason) {
         this.trigger('clear', {reason});
     }
+
+    /**
+     * @returns {boolean}
+     */
+    _computeUserHasNotSelectedAnythingManually() {
+        const selection = window.getSelection();
+        return selection === null || selection.isCollapsed;
+    }
 }
diff --git a/ext/js/language/translator.js b/ext/js/language/translator.js
index edb38bfb54..18bbecfb56 100644
--- a/ext/js/language/translator.js
+++ b/ext/js/language/translator.js
@@ -26,35 +26,29 @@
  * Class which finds term and kanji dictionary entries for text.
  */
 class Translator {
-    /**
-     * Information about how popup content should be shown, specifically related to the outer popup frame.
-     * @typedef {object} TermFrequency
-     * @property {string} term The term.
-     * @property {string} reading The reading of the term.
-     * @property {string} dictionary The name of the dictionary that the term frequency originates from.
-     * @property {boolean} hasReading Whether or not a reading was specified.
-     * @property {number|string} frequency The frequency value for the term.
-     */
-
     /**
      * Creates a new Translator instance.
-     * @param {object} details The details for the class.
-     * @param {JapaneseUtil} details.japaneseUtil An instance of JapaneseUtil.
-     * @param {DictionaryDatabase} details.database An instance of DictionaryDatabase.
+     * @param {import('translator').ConstructorDetails} details The details for the class.
      */
     constructor({japaneseUtil, database}) {
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
+        /** @type {DictionaryDatabase} */
         this._database = database;
+        /** @type {?Deinflector} */
         this._deinflector = null;
+        /** @type {import('translator').DictionaryTagCache} */
         this._tagCache = new Map();
+        /** @type {Intl.Collator} */
         this._stringComparer = new Intl.Collator('en-US'); // Invariant locale
+        /** @type {RegExp} */
         this._numberRegex = /[+-]?(\d+(\.\d*)?|\.\d+)([eE][+-]?\d+)?/;
     }
 
     /**
      * Initializes the instance for use. The public API should not be used until
      * this function has been called.
-     * @param {object} deinflectionReasons The raw deinflections reasons data that the Deinflector uses.
+     * @param {import('deinflector').ReasonsRaw} deinflectionReasons The raw deinflections reasons data that the Deinflector uses.
      */
     prepare(deinflectionReasons) {
         this._deinflector = new Deinflector(deinflectionReasons);
@@ -69,22 +63,23 @@ class Translator {
 
     /**
      * Finds term definitions for the given text.
-     * @param {string} mode The mode to use for finding terms, which determines the format of the resulting array.
+     * @param {import('translator').FindTermsMode} mode The mode to use for finding terms, which determines the format of the resulting array.
      *   One of: 'group', 'merge', 'split', 'simple'
      * @param {string} text The text to find terms for.
-     * @param {Translation.FindTermsOptions} options A object describing settings about the lookup.
-     * @returns {{dictionaryEntries: Translation.TermDictionaryEntry[], originalTextLength: number}} An object containing dictionary entries and the length of the original source text.
+     * @param {import('translation').FindTermsOptions} options A object describing settings about the lookup.
+     * @returns {Promise<{dictionaryEntries: import('dictionary').TermDictionaryEntry[], originalTextLength: number}>} An object containing dictionary entries and the length of the original source text.
      */
     async findTerms(mode, text, options) {
         const {enabledDictionaryMap, excludeDictionaryDefinitions, sortFrequencyDictionary, sortFrequencyDictionaryOrder} = options;
-        let {dictionaryEntries, originalTextLength} = await this._findTermsInternal(text, enabledDictionaryMap, options);
+        const tagAggregator = new TranslatorTagAggregator();
+        let {dictionaryEntries, originalTextLength} = await this._findTermsInternal(text, enabledDictionaryMap, options, tagAggregator);
 
         switch (mode) {
             case 'group':
-                dictionaryEntries = this._groupDictionaryEntriesByHeadword(dictionaryEntries);
+                dictionaryEntries = this._groupDictionaryEntriesByHeadword(dictionaryEntries, tagAggregator);
                 break;
             case 'merge':
-                dictionaryEntries = await this._getRelatedDictionaryEntries(dictionaryEntries, options.mainDictionary, enabledDictionaryMap);
+                dictionaryEntries = await this._getRelatedDictionaryEntries(dictionaryEntries, options.mainDictionary, enabledDictionaryMap, tagAggregator);
                 break;
         }
 
@@ -92,11 +87,9 @@ class Translator {
             this._removeExcludedDefinitions(dictionaryEntries, excludeDictionaryDefinitions);
         }
 
-        if (mode === 'simple') {
-            this._clearTermTags(dictionaryEntries);
-        } else {
-            await this._addTermMeta(dictionaryEntries, enabledDictionaryMap);
-            await this._expandTermTags(dictionaryEntries);
+        if (mode !== 'simple') {
+            await this._addTermMeta(dictionaryEntries, enabledDictionaryMap, tagAggregator);
+            await this._expandTagGroupsAndGroup(tagAggregator.getTagExpansionTargets());
         }
 
         if (sortFrequencyDictionary !== null) {
@@ -120,8 +113,8 @@ class Translator {
      * @param {string} text The text to find kanji definitions for. This string can be of any length,
      *   but is typically just one character, which is a single kanji. If the string is multiple
      *   characters long, each character will be searched in the database.
-     * @param {Translation.FindKanjiOptions} options A object describing settings about the lookup.
-     * @returns {Translation.KanjiDictionaryEntry[]} An array of definitions. See the _createKanjiDefinition() function for structure details.
+     * @param {import('translation').FindKanjiOptions} options A object describing settings about the lookup.
+     * @returns {Promise<import('dictionary').KanjiDictionaryEntry[]>} An array of definitions. See the _createKanjiDefinition() function for structure details.
      */
     async findKanji(text, options) {
         const {enabledDictionaryMap} = options;
@@ -135,19 +128,18 @@ class Translator {
 
         this._sortDatabaseEntriesByIndex(databaseEntries);
 
+        /** @type {import('dictionary').KanjiDictionaryEntry[]} */
         const dictionaryEntries = [];
+        const tagAggregator = new TranslatorTagAggregator();
         for (const {character, onyomi, kunyomi, tags, definitions, stats, dictionary} of databaseEntries) {
             const expandedStats = await this._expandKanjiStats(stats, dictionary);
-
-            const tagGroups = [];
-            if (tags.length > 0) { tagGroups.push(this._createTagGroup(dictionary, tags)); }
-
-            const dictionaryEntry = this._createKanjiDictionaryEntry(character, dictionary, onyomi, kunyomi, tagGroups, expandedStats, definitions);
+            const dictionaryEntry = this._createKanjiDictionaryEntry(character, dictionary, onyomi, kunyomi, expandedStats, definitions);
             dictionaryEntries.push(dictionaryEntry);
+            tagAggregator.addTags(dictionaryEntry.tags, dictionary, tags);
         }
 
         await this._addKanjiMeta(dictionaryEntries, enabledDictionaryMap);
-        await this._expandKanjiTags(dictionaryEntries);
+        await this._expandTagGroupsAndGroup(tagAggregator.getTagExpansionTargets());
 
         this._sortKanjiDictionaryEntryData(dictionaryEntries);
 
@@ -159,8 +151,8 @@ class Translator {
      * and a list of dictionaries.
      * @param {{term: string, reading: string|null}[]} termReadingList An array of `{term, reading}` pairs. If reading is null,
      *   the reading won't be compared.
-     * @param {Iterable<string>} dictionaries An array of dictionary names.
-     * @returns {TermFrequency[]} An array of term frequencies.
+     * @param {string[]} dictionaries An array of dictionary names.
+     * @returns {Promise<import('translator').TermFrequencySimple[]>} An array of term frequencies.
      */
     async getTermFrequencies(termReadingList, dictionaries) {
         const dictionarySet = new Set();
@@ -171,25 +163,26 @@ class Translator {
         const termList = termReadingList.map(({term}) => term);
         const metas = await this._database.findTermMetaBulk(termList, dictionarySet);
 
+        /** @type {import('translator').TermFrequencySimple[]} */
         const results = [];
         for (const {mode, data, dictionary, index} of metas) {
             if (mode !== 'freq') { continue; }
             let {term, reading} = termReadingList[index];
-            let frequency = data;
-            const hasReading = (data !== null && typeof data === 'object');
-            if (hasReading) {
-                if (data.reading !== reading) {
-                    if (reading !== null) { continue; }
-                    reading = data.reading;
-                }
-                frequency = data.frequency;
+            const hasReading = (data !== null && typeof data === 'object' && typeof data.reading === 'string');
+            if (hasReading && data.reading !== reading) {
+                if (reading !== null) { continue; }
+                reading = data.reading;
             }
+            const frequency = hasReading ? data.frequency : /** @type {import('dictionary-data').GenericFrequencyData} */ (data);
+            const {frequency: frequencyValue, displayValue, displayValueParsed} = this._getFrequencyInfo(frequency);
             results.push({
                 term,
                 reading,
                 dictionary,
                 hasReading,
-                frequency
+                frequency: frequencyValue,
+                displayValue,
+                displayValueParsed
             });
         }
         return results;
@@ -197,7 +190,14 @@ class Translator {
 
     // Find terms internal implementation
 
-    async _findTermsInternal(text, enabledDictionaryMap, options) {
+    /**
+     * @param {string} text
+     * @param {Map<string, import('translation').FindTermDictionary>} enabledDictionaryMap
+     * @param {import('translation').FindTermsOptions} options
+     * @param {TranslatorTagAggregator} tagAggregator
+     * @returns {Promise<{dictionaryEntries: import('dictionary').TermDictionaryEntry[], originalTextLength: number}>}
+     */
+    async _findTermsInternal(text, enabledDictionaryMap, options, tagAggregator) {
         if (options.removeNonJapaneseCharacters) {
             text = this._getJapaneseOnlyText(text);
         }
@@ -216,7 +216,7 @@ class Translator {
             for (const databaseEntry of databaseEntries) {
                 const {id} = databaseEntry;
                 if (ids.has(id)) { continue; }
-                const dictionaryEntry = this._createTermDictionaryEntryFromDatabaseEntry(databaseEntry, originalText, transformedText, deinflectedText, reasons, true, enabledDictionaryMap);
+                const dictionaryEntry = this._createTermDictionaryEntryFromDatabaseEntry(databaseEntry, originalText, transformedText, deinflectedText, reasons, true, enabledDictionaryMap, tagAggregator);
                 dictionaryEntries.push(dictionaryEntry);
                 ids.add(id);
             }
@@ -225,11 +225,17 @@ class Translator {
         return {dictionaryEntries, originalTextLength};
     }
 
+    /**
+     * @param {string} text
+     * @param {Map<string, import('translation').FindTermDictionary>} enabledDictionaryMap
+     * @param {import('translation').FindTermsOptions} options
+     * @returns {Promise<import('translation-internal').DatabaseDeinflection[]>}
+     */
     async _findTermsInternal2(text, enabledDictionaryMap, options) {
         const deinflections = (
             options.deinflect ?
             this._getAllDeinflections(text, options) :
-            [this._createDeinflection(text, text, text, 0, [], [])]
+            [this._createDeinflection(text, text, text, 0, [])]
         );
         if (deinflections.length === 0) { return []; }
 
@@ -266,7 +272,13 @@ class Translator {
 
     // Deinflections and text transformations
 
+    /**
+     * @param {string} text
+     * @param {import('translation').FindTermsOptions} options
+     * @returns {import('translation-internal').DatabaseDeinflection[]}
+     */
     _getAllDeinflections(text, options) {
+        /** @type {import('translation-internal').TextDeinflectionOptionsArrays} */
         const textOptionVariantArray = [
             this._getTextReplacementsVariants(options),
             this._getTextOptionEntryVariants(options.convertHalfWidthCharacters),
@@ -278,9 +290,10 @@ class Translator {
         ];
 
         const jp = this._japaneseUtil;
+        /** @type {import('translation-internal').DatabaseDeinflection[]} */
         const deinflections = [];
         const used = new Set();
-        for (const [textReplacements, halfWidth, numeric, alphabetic, katakana, hiragana, [collapseEmphatic, collapseEmphaticFull]] of this._getArrayVariants(textOptionVariantArray)) {
+        for (const [textReplacements, halfWidth, numeric, alphabetic, katakana, hiragana, [collapseEmphatic, collapseEmphaticFull]] of /** @type {Generator<import('translation-internal').TextDeinflectionOptions, void, unknown>} */ (this._getArrayVariants(textOptionVariantArray))) {
             let text2 = text;
             const sourceMap = new TextSourceMap(text2);
             if (textReplacements !== null) {
@@ -310,14 +323,20 @@ class Translator {
                 if (used.has(source)) { break; }
                 used.add(source);
                 const rawSource = sourceMap.source.substring(0, sourceMap.getSourceLength(i));
-                for (const {term, rules, reasons} of this._deinflector.deinflect(source)) {
-                    deinflections.push(this._createDeinflection(rawSource, source, term, rules, reasons, []));
+                for (const {term, rules, reasons} of /** @type {Deinflector} */ (this._deinflector).deinflect(source)) {
+                    deinflections.push(this._createDeinflection(rawSource, source, term, rules, reasons));
                 }
             }
         }
         return deinflections;
     }
 
+    /**
+     * @param {string} text
+     * @param {TextSourceMap} sourceMap
+     * @param {import('translation').FindTermsTextReplacement[]} replacements
+     * @returns {string}
+     */
     _applyTextReplacements(text, sourceMap, replacements) {
         for (const {pattern, replacement} of replacements) {
             text = RegexUtil.applyTextReplacement(text, sourceMap, pattern, replacement);
@@ -325,11 +344,15 @@ class Translator {
         return text;
     }
 
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
     _getJapaneseOnlyText(text) {
         const jp = this._japaneseUtil;
         let length = 0;
         for (const c of text) {
-            if (!jp.isCodePointJapanese(c.codePointAt(0))) {
+            if (!jp.isCodePointJapanese(/** @type {number} */ (c.codePointAt(0)))) {
                 return text.substring(0, length);
             }
             length += c.length;
@@ -337,6 +360,10 @@ class Translator {
         return text;
     }
 
+    /**
+     * @param {import('translation').FindTermsVariantMode} value
+     * @returns {boolean[]}
+     */
     _getTextOptionEntryVariants(value) {
         switch (value) {
             case 'true': return [true];
@@ -345,7 +372,12 @@ class Translator {
         }
     }
 
+    /**
+     * @param {import('translation').FindTermsOptions} options
+     * @returns {[collapseEmphatic: boolean, collapseEmphaticFull: boolean][]}
+     */
     _getCollapseEmphaticOptions(options) {
+        /** @type {[collapseEmphatic: boolean, collapseEmphaticFull: boolean][]} */
         const collapseEmphaticOptions = [[false, false]];
         switch (options.collapseEmphaticSequences) {
             case 'true':
@@ -358,20 +390,43 @@ class Translator {
         return collapseEmphaticOptions;
     }
 
+    /**
+     * @param {import('translation').FindTermsOptions} options
+     * @returns {(import('translation').FindTermsTextReplacement[] | null)[]}
+     */
     _getTextReplacementsVariants(options) {
         return options.textReplacements;
     }
 
-    _createDeinflection(originalText, transformedText, deinflectedText, rules, reasons, databaseEntries) {
-        return {originalText, transformedText, deinflectedText, rules, reasons, databaseEntries};
+    /**
+     * @param {string} originalText
+     * @param {string} transformedText
+     * @param {string} deinflectedText
+     * @param {import('translation-internal').DeinflectionRuleFlags} rules
+     * @param {string[]} reasons
+     * @returns {import('translation-internal').DatabaseDeinflection}
+     */
+    _createDeinflection(originalText, transformedText, deinflectedText, rules, reasons) {
+        return {originalText, transformedText, deinflectedText, rules, reasons, databaseEntries: []};
     }
 
     // Term dictionary entry grouping
 
-    async _getRelatedDictionaryEntries(dictionaryEntries, mainDictionary, enabledDictionaryMap) {
+    /**
+     * @param {import('dictionary').TermDictionaryEntry[]} dictionaryEntries
+     * @param {string} mainDictionary
+     * @param {import('translation').TermEnabledDictionaryMap} enabledDictionaryMap
+     * @param {TranslatorTagAggregator} tagAggregator
+     * @returns {Promise<import('dictionary').TermDictionaryEntry[]>}
+     */
+    async _getRelatedDictionaryEntries(dictionaryEntries, mainDictionary, enabledDictionaryMap, tagAggregator) {
+        /** @type {import('translator').SequenceQuery[]} */
         const sequenceList = [];
+        /** @type {import('translator').DictionaryEntryGroup[]} */
         const groupedDictionaryEntries = [];
+        /** @type {Map<number, import('translator').DictionaryEntryGroup>} */
         const groupedDictionaryEntriesMap = new Map();
+        /** @type {Map<number, import('dictionary').TermDictionaryEntry>} */
         const ungroupedDictionaryEntriesMap = new Map();
         for (const dictionaryEntry of dictionaryEntries) {
             const {definitions: [{id, dictionary, sequences: [sequence]}]} = dictionaryEntry;
@@ -395,24 +450,31 @@ class Translator {
 
         if (sequenceList.length > 0) {
             const secondarySearchDictionaryMap = this._getSecondarySearchDictionaryMap(enabledDictionaryMap);
-            await this._addRelatedDictionaryEntries(groupedDictionaryEntries, ungroupedDictionaryEntriesMap, sequenceList, enabledDictionaryMap);
+            await this._addRelatedDictionaryEntries(groupedDictionaryEntries, ungroupedDictionaryEntriesMap, sequenceList, enabledDictionaryMap, tagAggregator);
             for (const group of groupedDictionaryEntries) {
                 this._sortTermDictionaryEntriesById(group.dictionaryEntries);
             }
             if (ungroupedDictionaryEntriesMap.size !== 0 || secondarySearchDictionaryMap.size !== 0) {
-                await this._addSecondaryRelatedDictionaryEntries(groupedDictionaryEntries, ungroupedDictionaryEntriesMap, enabledDictionaryMap, secondarySearchDictionaryMap);
+                await this._addSecondaryRelatedDictionaryEntries(groupedDictionaryEntries, ungroupedDictionaryEntriesMap, enabledDictionaryMap, secondarySearchDictionaryMap, tagAggregator);
             }
         }
 
         const newDictionaryEntries = [];
         for (const group of groupedDictionaryEntries) {
-            newDictionaryEntries.push(this._createGroupedDictionaryEntry(group.dictionaryEntries, true));
+            newDictionaryEntries.push(this._createGroupedDictionaryEntry(group.dictionaryEntries, true, tagAggregator));
         }
-        newDictionaryEntries.push(...this._groupDictionaryEntriesByHeadword(ungroupedDictionaryEntriesMap.values()));
+        newDictionaryEntries.push(...this._groupDictionaryEntriesByHeadword(ungroupedDictionaryEntriesMap.values(), tagAggregator));
         return newDictionaryEntries;
     }
 
-    async _addRelatedDictionaryEntries(groupedDictionaryEntries, ungroupedDictionaryEntriesMap, sequenceList, enabledDictionaryMap) {
+    /**
+     * @param {import('translator').DictionaryEntryGroup[]} groupedDictionaryEntries
+     * @param {Map<number, import('dictionary').TermDictionaryEntry>} ungroupedDictionaryEntriesMap
+     * @param {import('translator').SequenceQuery[]} sequenceList
+     * @param {import('translation').TermEnabledDictionaryMap} enabledDictionaryMap
+     * @param {TranslatorTagAggregator} tagAggregator
+     */
+    async _addRelatedDictionaryEntries(groupedDictionaryEntries, ungroupedDictionaryEntriesMap, sequenceList, enabledDictionaryMap, tagAggregator) {
         const databaseEntries = await this._database.findTermsBySequenceBulk(sequenceList);
         for (const databaseEntry of databaseEntries) {
             const {dictionaryEntries, ids} = groupedDictionaryEntries[databaseEntry.index];
@@ -420,15 +482,23 @@ class Translator {
             if (ids.has(id)) { continue; }
 
             const {term} = databaseEntry;
-            const dictionaryEntry = this._createTermDictionaryEntryFromDatabaseEntry(databaseEntry, term, term, term, [], false, enabledDictionaryMap);
+            const dictionaryEntry = this._createTermDictionaryEntryFromDatabaseEntry(databaseEntry, term, term, term, [], false, enabledDictionaryMap, tagAggregator);
             dictionaryEntries.push(dictionaryEntry);
             ids.add(id);
             ungroupedDictionaryEntriesMap.delete(id);
         }
     }
 
-    async _addSecondaryRelatedDictionaryEntries(groupedDictionaryEntries, ungroupedDictionaryEntriesMap, enabledDictionaryMap, secondarySearchDictionaryMap) {
+    /**
+     * @param {import('translator').DictionaryEntryGroup[]} groupedDictionaryEntries
+     * @param {Map<number, import('dictionary').TermDictionaryEntry>} ungroupedDictionaryEntriesMap
+     * @param {import('translation').TermEnabledDictionaryMap} enabledDictionaryMap
+     * @param {import('translation').TermEnabledDictionaryMap} secondarySearchDictionaryMap
+     * @param {TranslatorTagAggregator} tagAggregator
+     */
+    async _addSecondaryRelatedDictionaryEntries(groupedDictionaryEntries, ungroupedDictionaryEntriesMap, enabledDictionaryMap, secondarySearchDictionaryMap, tagAggregator) {
         // Prepare grouping info
+        /** @type {import('dictionary-database').TermExactRequest[]} */
         const termList = [];
         const targetList = [];
         const targetMap = new Map();
@@ -479,7 +549,7 @@ class Translator {
             for (const {ids, dictionaryEntries} of target.groups) {
                 if (ids.has(id)) { continue; }
 
-                const dictionaryEntry = this._createTermDictionaryEntryFromDatabaseEntry(databaseEntry, sourceText, sourceText, sourceText, [], false, enabledDictionaryMap);
+                const dictionaryEntry = this._createTermDictionaryEntryFromDatabaseEntry(databaseEntry, sourceText, sourceText, sourceText, [], false, enabledDictionaryMap, tagAggregator);
                 dictionaryEntries.push(dictionaryEntry);
                 ids.add(id);
                 ungroupedDictionaryEntriesMap.delete(id);
@@ -487,7 +557,12 @@ class Translator {
         }
     }
 
-    _groupDictionaryEntriesByHeadword(dictionaryEntries) {
+    /**
+     * @param {Iterable<import('dictionary').TermDictionaryEntry>} dictionaryEntries
+     * @param {TranslatorTagAggregator} tagAggregator
+     * @returns {import('dictionary').TermDictionaryEntry[]}
+     */
+    _groupDictionaryEntriesByHeadword(dictionaryEntries, tagAggregator) {
         const groups = new Map();
         for (const dictionaryEntry of dictionaryEntries) {
             const {inflections, headwords: [{term, reading}]} = dictionaryEntry;
@@ -502,13 +577,17 @@ class Translator {
 
         const newDictionaryEntries = [];
         for (const groupDictionaryEntries of groups.values()) {
-            newDictionaryEntries.push(this._createGroupedDictionaryEntry(groupDictionaryEntries, false));
+            newDictionaryEntries.push(this._createGroupedDictionaryEntry(groupDictionaryEntries, false, tagAggregator));
         }
         return newDictionaryEntries;
     }
 
     // Removing data
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry[]} dictionaryEntries
+     * @param {Set<string>} excludeDictionaryDefinitions
+     */
     _removeExcludedDefinitions(dictionaryEntries, excludeDictionaryDefinitions) {
         for (let i = dictionaryEntries.length - 1; i >= 0; --i) {
             const dictionaryEntry = dictionaryEntries[i];
@@ -529,6 +608,9 @@ class Translator {
         }
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry} dictionaryEntry
+     */
     _removeUnusedHeadwords(dictionaryEntry) {
         const {definitions, pronunciations, frequencies, headwords} = dictionaryEntry;
         const removeHeadwordIndices = new Set();
@@ -543,6 +625,7 @@ class Translator {
 
         if (removeHeadwordIndices.size === 0) { return; }
 
+        /** @type {Map<number, number>} */
         const indexRemap = new Map();
         let oldIndex = 0;
         for (let i = 0, ii = headwords.length; i < ii; ++i) {
@@ -561,6 +644,10 @@ class Translator {
         this._updateArrayItemsHeadwordIndex(frequencies, indexRemap);
     }
 
+    /**
+     * @param {import('dictionary').TermDefinition[]} definitions
+     * @param {Map<number, number>} indexRemap
+     */
     _updateDefinitionHeadwordIndices(definitions, indexRemap) {
         for (const {headwordIndices} of definitions) {
             for (let i = headwordIndices.length - 1; i >= 0; --i) {
@@ -574,6 +661,10 @@ class Translator {
         }
     }
 
+    /**
+     * @param {import('dictionary').TermPronunciation[]|import('dictionary').TermFrequency[]} array
+     * @param {Map<number, number>} indexRemap
+     */
     _updateArrayItemsHeadwordIndex(array, indexRemap) {
         for (let i = array.length - 1; i >= 0; --i) {
             const item = array[i];
@@ -587,6 +678,11 @@ class Translator {
         }
     }
 
+    /**
+     * @param {import('dictionary').TermPronunciation[]|import('dictionary').TermFrequency[]|import('dictionary').TermDefinition[]} array
+     * @param {Set<string>} excludeDictionaryDefinitions
+     * @returns {boolean}
+     */
     _removeArrayItemsWithDictionary(array, excludeDictionaryDefinitions) {
         let changed = false;
         for (let j = array.length - 1; j >= 0; --j) {
@@ -598,45 +694,48 @@ class Translator {
         return changed;
     }
 
-    _removeTagGroupsWithDictionary(array, excludeDictionaryDefinitions) {
-        for (const {tags} of array) {
-            this._removeArrayItemsWithDictionary(tags, excludeDictionaryDefinitions);
+    /**
+     * @param {import('dictionary').Tag[]} array
+     * @param {Set<string>} excludeDictionaryDefinitions
+     * @returns {boolean}
+     */
+    _removeArrayItemsWithDictionary2(array, excludeDictionaryDefinitions) {
+        let changed = false;
+        for (let j = array.length - 1; j >= 0; --j) {
+            const {dictionaries} = array[j];
+            if (this._hasAny(excludeDictionaryDefinitions, dictionaries)) { continue; }
+            array.splice(j, 1);
+            changed = true;
         }
+        return changed;
     }
 
-    // Tags
-
-    _getTermTagTargets(dictionaryEntries) {
-        const tagTargets = [];
-        for (const {headwords, definitions, pronunciations} of dictionaryEntries) {
-            this._addTagExpansionTargets(tagTargets, headwords);
-            this._addTagExpansionTargets(tagTargets, definitions);
-            for (const {pitches} of pronunciations) {
-                this._addTagExpansionTargets(tagTargets, pitches);
-            }
+    /**
+     * @param {import('dictionary').TermDefinition[]|import('dictionary').TermHeadword[]} array
+     * @param {Set<string>} excludeDictionaryDefinitions
+     */
+    _removeTagGroupsWithDictionary(array, excludeDictionaryDefinitions) {
+        for (const {tags} of array) {
+            this._removeArrayItemsWithDictionary2(tags, excludeDictionaryDefinitions);
         }
-        return tagTargets;
     }
 
-    _clearTermTags(dictionaryEntries) {
-        this._getTermTagTargets(dictionaryEntries);
-    }
-
-    async _expandTermTags(dictionaryEntries) {
-        const tagTargets = this._getTermTagTargets(dictionaryEntries);
-        await this._expandTagGroups(tagTargets);
-        this._groupTags(tagTargets);
-    }
+    // Tags
 
-    async _expandKanjiTags(dictionaryEntries) {
-        const tagTargets = [];
-        this._addTagExpansionTargets(tagTargets, dictionaryEntries);
-        await this._expandTagGroups(tagTargets);
-        this._groupTags(tagTargets);
+    /**
+     * @param {import('translator').TagExpansionTarget[]} tagExpansionTargets
+     */
+    async _expandTagGroupsAndGroup(tagExpansionTargets) {
+        await this._expandTagGroups(tagExpansionTargets);
+        this._groupTags(tagExpansionTargets);
     }
 
+    /**
+     * @param {import('translator').TagExpansionTarget[]} tagTargets
+     */
     async _expandTagGroups(tagTargets) {
         const allItems = [];
+        /** @type {import('translator').TagTargetMap} */
         const targetMap = new Map();
         for (const {tagGroups, tags} of tagTargets) {
             for (const {dictionary, tagNames} of tagGroups) {
@@ -682,10 +781,12 @@ class Translator {
             const databaseTags = await this._database.findTagMetaBulk(nonCachedItems);
             for (let i = 0; i < nonCachedItemCount; ++i) {
                 const item = nonCachedItems[i];
-                let databaseTag = databaseTags[i];
-                if (typeof databaseTag === 'undefined') { databaseTag = null; }
-                item.databaseTag = databaseTag;
-                item.cache.set(item.query, databaseTag);
+                const databaseTag = databaseTags[i];
+                const databaseTag2 = typeof databaseTag !== 'undefined' ? databaseTag : null;
+                item.databaseTag = databaseTag2;
+                if (item.cache !== null) {
+                    item.cache.set(item.query, databaseTag2);
+                }
             }
         }
 
@@ -696,8 +797,16 @@ class Translator {
         }
     }
 
+    /**
+     * @param {import('translator').TagExpansionTarget[]} tagTargets
+     */
     _groupTags(tagTargets) {
         const stringComparer = this._stringComparer;
+        /**
+         * @param {import('dictionary').Tag} v1
+         * @param {import('dictionary').Tag} v2
+         * @returns {number}
+         */
         const compare = (v1, v2) => {
             const i = v1.order - v2.order;
             return i !== 0 ? i : stringComparer.compare(v1.name, v2.name);
@@ -710,16 +819,9 @@ class Translator {
         }
     }
 
-    _addTagExpansionTargets(tagTargets, objects) {
-        for (const value of objects) {
-            const tagGroups = value.tags;
-            if (tagGroups.length === 0) { continue; }
-            const tags = [];
-            value.tags = tags;
-            tagTargets.push({tagGroups, tags});
-        }
-    }
-
+    /**
+     * @param {import('dictionary').Tag[]} tags
+     */
     _mergeSimilarTags(tags) {
         let tagCount = tags.length;
         for (let i = 0; i < tagCount; ++i) {
@@ -740,6 +842,11 @@ class Translator {
         }
     }
 
+    /**
+     * @param {import('dictionary').Tag[]} tags
+     * @param {string} category
+     * @returns {string[]}
+     */
     _getTagNamesWithCategory(tags, category) {
         const results = [];
         for (const tag of tags) {
@@ -750,6 +857,9 @@ class Translator {
         return results;
     }
 
+    /**
+     * @param {import('dictionary').TermDefinition[]} definitions
+     */
     _flagRedundantDefinitionTags(definitions) {
         if (definitions.length === 0) { return; }
 
@@ -784,7 +894,12 @@ class Translator {
 
     // Metadata
 
-    async _addTermMeta(dictionaryEntries, enabledDictionaryMap) {
+    /**
+     * @param {import('dictionary').TermDictionaryEntry[]} dictionaryEntries
+     * @param {import('translation').TermEnabledDictionaryMap} enabledDictionaryMap
+     * @param {TranslatorTagAggregator} tagAggregator
+     */
+    async _addTermMeta(dictionaryEntries, enabledDictionaryMap, tagAggregator) {
         const headwordMap = new Map();
         const headwordMapKeys = [];
         const headwordReadingMaps = [];
@@ -816,16 +931,11 @@ class Translator {
                 switch (mode) {
                     case 'freq':
                         {
-                            let frequency = data;
                             const hasReading = (data !== null && typeof data === 'object' && typeof data.reading === 'string');
-                            if (hasReading) {
-                                if (data.reading !== reading) { continue; }
-                                frequency = data.frequency;
-                            }
+                            if (hasReading && data.reading !== reading) { continue; }
+                            const frequency = hasReading ? data.frequency : /** @type {import('dictionary-data').GenericFrequencyData} */ (data);
                             for (const {frequencies, headwordIndex} of targets) {
-                                let displayValue;
-                                let displayValueParsed;
-                                ({frequency, displayValue, displayValueParsed} = this._getFrequencyInfo(frequency));
+                                const {frequency: frequencyValue, displayValue, displayValueParsed} = this._getFrequencyInfo(frequency);
                                 frequencies.push(this._createTermFrequency(
                                     frequencies.length,
                                     headwordIndex,
@@ -833,7 +943,7 @@ class Translator {
                                     dictionaryIndex,
                                     dictionaryPriority,
                                     hasReading,
-                                    frequency,
+                                    frequencyValue,
                                     displayValue,
                                     displayValueParsed
                                 ));
@@ -843,11 +953,13 @@ class Translator {
                     case 'pitch':
                         {
                             if (data.reading !== reading) { continue; }
+                            /** @type {import('dictionary').TermPitch[]} */
                             const pitches = [];
                             for (const {position, tags, nasal, devoice} of data.pitches) {
+                                /** @type {import('dictionary').Tag[]} */
                                 const tags2 = [];
-                                if (Array.isArray(tags) && tags.length > 0) {
-                                    tags2.push(this._createTagGroup(dictionary, tags));
+                                if (Array.isArray(tags)) {
+                                    tagAggregator.addTags(tags2, dictionary, tags);
                                 }
                                 const nasalPositions = this._toNumberArray(nasal);
                                 const devoicePositions = this._toNumberArray(devoice);
@@ -870,6 +982,10 @@ class Translator {
         }
     }
 
+    /**
+     * @param {import('dictionary').KanjiDictionaryEntry[]} dictionaryEntries
+     * @param {import('translation').KanjiEnabledDictionaryMap} enabledDictionaryMap
+     */
     async _addKanjiMeta(dictionaryEntries, enabledDictionaryMap) {
         const kanjiList = [];
         for (const {character} of dictionaryEntries) {
@@ -900,6 +1016,11 @@ class Translator {
         }
     }
 
+    /**
+     * @param {{[key: string]: (string|number)}} stats
+     * @param {string} dictionary
+     * @returns {Promise<import('dictionary').KanjiStatGroups>}
+     */
     async _expandKanjiStats(stats, dictionary) {
         const statsEntries = Object.entries(stats);
         const items = [];
@@ -910,10 +1031,11 @@ class Translator {
 
         const databaseInfos = await this._database.findTagMetaBulk(items);
 
+        /** @type {Map<string, import('dictionary').KanjiStat[]>} */
         const statsGroups = new Map();
         for (let i = 0, ii = statsEntries.length; i < ii; ++i) {
             const databaseInfo = databaseInfos[i];
-            if (databaseInfo === null) { continue; }
+            if (typeof databaseInfo === 'undefined') { continue; }
 
             const [name, value] = statsEntries[i];
             const {category} = databaseInfo;
@@ -926,6 +1048,7 @@ class Translator {
             group.push(this._createKanjiStat(name, value, databaseInfo, dictionary));
         }
 
+        /** @type {import('dictionary').KanjiStatGroups} */
         const groupedStats = {};
         for (const [category, group] of statsGroups.entries()) {
             this._sortKanjiStats(group);
@@ -934,6 +1057,9 @@ class Translator {
         return groupedStats;
     }
 
+    /**
+     * @param {import('dictionary').KanjiStat[]} stats
+     */
     _sortKanjiStats(stats) {
         if (stats.length <= 1) { return; }
         const stringComparer = this._stringComparer;
@@ -943,45 +1069,59 @@ class Translator {
         });
     }
 
+    /**
+     * @param {string} value
+     * @returns {number}
+     */
     _convertStringToNumber(value) {
         const match = this._numberRegex.exec(value);
         if (match === null) { return 0; }
-        value = Number.parseFloat(match[0]);
-        return Number.isFinite(value) ? value : 0;
+        const result = Number.parseFloat(match[0]);
+        return Number.isFinite(result) ? result : 0;
     }
 
+    /**
+     * @param {import('dictionary-data').GenericFrequencyData} frequency
+     * @returns {{frequency: number, displayValue: ?string, displayValueParsed: boolean}}
+     */
     _getFrequencyInfo(frequency) {
+        let frequencyValue = 0;
         let displayValue = null;
         let displayValueParsed = false;
         if (typeof frequency === 'object' && frequency !== null) {
-            ({value: frequency, displayValue} = frequency);
-            if (typeof frequency !== 'number') { frequency = 0; }
-            if (typeof displayValue !== 'string') { displayValue = null; }
+            const {value: frequencyValue2, displayValue: displayValue2} = frequency;
+            if (typeof frequencyValue2 === 'number') { frequencyValue = frequencyValue2; }
+            if (typeof displayValue2 === 'string') { displayValue = displayValue2; }
         } else {
             switch (typeof frequency) {
                 case 'number':
-                    // No change
+                    frequencyValue = frequency;
                     break;
                 case 'string':
                     displayValue = frequency;
                     displayValueParsed = true;
-                    frequency = this._convertStringToNumber(frequency);
-                    break;
-                default:
-                    frequency = 0;
+                    frequencyValue = this._convertStringToNumber(frequency);
                     break;
             }
         }
-        return {frequency, displayValue, displayValueParsed};
+        return {frequency: frequencyValue, displayValue, displayValueParsed};
     }
 
     // Helpers
 
+    /**
+     * @param {string} name
+     * @returns {string}
+     */
     _getNameBase(name) {
         const pos = name.indexOf(':');
         return (pos >= 0 ? name.substring(0, pos) : name);
     }
 
+    /**
+     * @param {import('translation').TermEnabledDictionaryMap} enabledDictionaryMap
+     * @returns {import('translation').TermEnabledDictionaryMap}
+     */
     _getSecondarySearchDictionaryMap(enabledDictionaryMap) {
         const secondarySearchDictionaryMap = new Map();
         for (const [dictionary, details] of enabledDictionaryMap.entries()) {
@@ -991,12 +1131,22 @@ class Translator {
         return secondarySearchDictionaryMap;
     }
 
+    /**
+     * @param {string} dictionary
+     * @param {import('translation').TermEnabledDictionaryMap|import('translation').KanjiEnabledDictionaryMap} enabledDictionaryMap
+     * @returns {{index: number, priority: number}}
+     */
     _getDictionaryOrder(dictionary, enabledDictionaryMap) {
         const info = enabledDictionaryMap.get(dictionary);
         const {index, priority} = typeof info !== 'undefined' ? info : {index: enabledDictionaryMap.size, priority: 0};
         return {index, priority};
     }
 
+    /**
+     * @param {[...args: unknown[][]]} arrayVariants
+     * @yields {[...args: unknown[]]}
+     * @returns {Generator<unknown[], void, unknown>}
+     */
     *_getArrayVariants(arrayVariants) {
         const ii = arrayVariants.length;
 
@@ -1017,16 +1167,31 @@ class Translator {
         }
     }
 
+    /**
+     * @param {unknown[]} array
+     * @returns {string}
+     */
     _createMapKey(array) {
         return JSON.stringify(array);
     }
 
+    /**
+     * @param {number|number[]|undefined} value
+     * @returns {number[]}
+     */
     _toNumberArray(value) {
         return Array.isArray(value) ? value : (typeof value === 'number' ? [value] : []);
     }
 
     // Kanji data
 
+    /**
+     * @param {string} name
+     * @param {string|number} value
+     * @param {import('dictionary-database').Tag} databaseInfo
+     * @param {string} dictionary
+     * @returns {import('dictionary').KanjiStat}
+     */
     _createKanjiStat(name, value, databaseInfo, dictionary) {
         const {category, notes, order, score} = databaseInfo;
         return {
@@ -1035,23 +1200,43 @@ class Translator {
             content: (typeof notes === 'string' ? notes : ''),
             order: (typeof order === 'number' ? order : 0),
             score: (typeof score === 'number' ? score : 0),
-            dictionary: (typeof dictionary === 'string' ? dictionary : null),
+            dictionary,
             value
         };
     }
 
+    /**
+     * @param {number} index
+     * @param {string} dictionary
+     * @param {number} dictionaryIndex
+     * @param {number} dictionaryPriority
+     * @param {string} character
+     * @param {number} frequency
+     * @param {?string} displayValue
+     * @param {boolean} displayValueParsed
+     * @returns {import('dictionary').KanjiFrequency}
+     */
     _createKanjiFrequency(index, dictionary, dictionaryIndex, dictionaryPriority, character, frequency, displayValue, displayValueParsed) {
         return {index, dictionary, dictionaryIndex, dictionaryPriority, character, frequency, displayValue, displayValueParsed};
     }
 
-    _createKanjiDictionaryEntry(character, dictionary, onyomi, kunyomi, tags, stats, definitions) {
+    /**
+     * @param {string} character
+     * @param {string} dictionary
+     * @param {string[]} onyomi
+     * @param {string[]} kunyomi
+     * @param {import('dictionary').KanjiStatGroups} stats
+     * @param {string[]} definitions
+     * @returns {import('dictionary').KanjiDictionaryEntry}
+     */
+    _createKanjiDictionaryEntry(character, dictionary, onyomi, kunyomi, stats, definitions) {
         return {
             type: 'kanji',
             character,
             dictionary,
             onyomi,
             kunyomi,
-            tags,
+            tags: [],
             stats,
             definitions,
             frequencies: []
@@ -1060,8 +1245,17 @@ class Translator {
 
     // Term data
 
+    /**
+     * @param {?import('dictionary-database').Tag} databaseTag
+     * @param {string} name
+     * @param {string} dictionary
+     * @returns {import('dictionary').Tag}
+     */
     _createTag(databaseTag, name, dictionary) {
-        const {category, notes, order, score} = (databaseTag !== null ? databaseTag : {});
+        let category, notes, order, score;
+        if (typeof databaseTag === 'object' && databaseTag !== null) {
+            ({category, notes, order, score} = databaseTag);
+        }
         return {
             name,
             category: (typeof category === 'string' && category.length > 0 ? category : 'default'),
@@ -1073,18 +1267,46 @@ class Translator {
         };
     }
 
-    _createTagGroup(dictionary, tagNames) {
-        return {dictionary, tagNames};
-    }
-
+    /**
+     * @param {string} originalText
+     * @param {string} transformedText
+     * @param {string} deinflectedText
+     * @param {import('dictionary').TermSourceMatchType} matchType
+     * @param {import('dictionary').TermSourceMatchSource} matchSource
+     * @param {boolean} isPrimary
+     * @returns {import('dictionary').TermSource}
+     */
     _createSource(originalText, transformedText, deinflectedText, matchType, matchSource, isPrimary) {
         return {originalText, transformedText, deinflectedText, matchType, matchSource, isPrimary};
     }
 
+    /**
+     * @param {number} index
+     * @param {string} term
+     * @param {string} reading
+     * @param {import('dictionary').TermSource[]} sources
+     * @param {import('dictionary').Tag[]} tags
+     * @param {string[]} wordClasses
+     * @returns {import('dictionary').TermHeadword}
+     */
     _createTermHeadword(index, term, reading, sources, tags, wordClasses) {
         return {index, term, reading, sources, tags, wordClasses};
     }
 
+    /**
+     * @param {number} index
+     * @param {number[]} headwordIndices
+     * @param {string} dictionary
+     * @param {number} dictionaryIndex
+     * @param {number} dictionaryPriority
+     * @param {number} id
+     * @param {number} score
+     * @param {number[]} sequences
+     * @param {boolean} isPrimary
+     * @param {import('dictionary').Tag[]} tags
+     * @param {import('dictionary-data').TermGlossary[]} entries
+     * @returns {import('dictionary').TermDefinition}
+     */
     _createTermDefinition(index, headwordIndices, dictionary, dictionaryIndex, dictionaryPriority, id, score, sequences, isPrimary, tags, entries) {
         return {
             index,
@@ -1102,14 +1324,47 @@ class Translator {
         };
     }
 
+    /**
+     * @param {number} index
+     * @param {number} headwordIndex
+     * @param {string} dictionary
+     * @param {number} dictionaryIndex
+     * @param {number} dictionaryPriority
+     * @param {import('dictionary').TermPitch[]} pitches
+     * @returns {import('dictionary').TermPronunciation}
+     */
     _createTermPronunciation(index, headwordIndex, dictionary, dictionaryIndex, dictionaryPriority, pitches) {
         return {index, headwordIndex, dictionary, dictionaryIndex, dictionaryPriority, pitches};
     }
 
+    /**
+     * @param {number} index
+     * @param {number} headwordIndex
+     * @param {string} dictionary
+     * @param {number} dictionaryIndex
+     * @param {number} dictionaryPriority
+     * @param {boolean} hasReading
+     * @param {number} frequency
+     * @param {?string} displayValue
+     * @param {boolean} displayValueParsed
+     * @returns {import('dictionary').TermFrequency}
+     */
     _createTermFrequency(index, headwordIndex, dictionary, dictionaryIndex, dictionaryPriority, hasReading, frequency, displayValue, displayValueParsed) {
         return {index, headwordIndex, dictionary, dictionaryIndex, dictionaryPriority, hasReading, frequency, displayValue, displayValueParsed};
     }
 
+    /**
+     * @param {boolean} isPrimary
+     * @param {string[]} inflections
+     * @param {number} score
+     * @param {number} dictionaryIndex
+     * @param {number} dictionaryPriority
+     * @param {number} sourceTermExactMatchCount
+     * @param {number} maxTransformedTextLength
+     * @param {import('dictionary').TermHeadword[]} headwords
+     * @param {import('dictionary').TermDefinition[]} definitions
+     * @returns {import('dictionary').TermDictionaryEntry}
+     */
     _createTermDictionaryEntry(isPrimary, inflections, score, dictionaryIndex, dictionaryPriority, sourceTermExactMatchCount, maxTransformedTextLength, headwords, definitions) {
         return {
             type: 'term',
@@ -1128,7 +1383,18 @@ class Translator {
         };
     }
 
-    _createTermDictionaryEntryFromDatabaseEntry(databaseEntry, originalText, transformedText, deinflectedText, reasons, isPrimary, enabledDictionaryMap) {
+    /**
+     * @param {import('dictionary-database').TermEntry} databaseEntry
+     * @param {string} originalText
+     * @param {string} transformedText
+     * @param {string} deinflectedText
+     * @param {string[]} reasons
+     * @param {boolean} isPrimary
+     * @param {Map<string, import('translation').FindTermDictionary>} enabledDictionaryMap
+     * @param {TranslatorTagAggregator} tagAggregator
+     * @returns {import('dictionary').TermDictionaryEntry}
+     */
+    _createTermDictionaryEntryFromDatabaseEntry(databaseEntry, originalText, transformedText, deinflectedText, reasons, isPrimary, enabledDictionaryMap, tagAggregator) {
         const {matchType, matchSource, term, reading: rawReading, definitionTags, termTags, definitions, score, dictionary, id, sequence: rawSequence, rules} = databaseEntry;
         const reading = (rawReading.length > 0 ? rawReading : term);
         const {index: dictionaryIndex, priority: dictionaryPriority} = this._getDictionaryOrder(dictionary, enabledDictionaryMap);
@@ -1138,10 +1404,12 @@ class Translator {
         const hasSequence = (rawSequence >= 0);
         const sequence = hasSequence ? rawSequence : -1;
 
+        /** @type {import('dictionary').Tag[]} */
         const headwordTagGroups = [];
+        /** @type {import('dictionary').Tag[]} */
         const definitionTagGroups = [];
-        if (termTags.length > 0) { headwordTagGroups.push(this._createTagGroup(dictionary, termTags)); }
-        if (definitionTags.length > 0) { definitionTagGroups.push(this._createTagGroup(dictionary, definitionTags)); }
+        tagAggregator.addTags(headwordTagGroups, dictionary, termTags);
+        tagAggregator.addTags(definitionTagGroups, dictionary, definitionTags);
 
         return this._createTermDictionaryEntry(
             isPrimary,
@@ -1156,12 +1424,19 @@ class Translator {
         );
     }
 
-    _createGroupedDictionaryEntry(dictionaryEntries, checkDuplicateDefinitions) {
+    /**
+     * @param {import('dictionary').TermDictionaryEntry[]} dictionaryEntries
+     * @param {boolean} checkDuplicateDefinitions
+     * @param {TranslatorTagAggregator} tagAggregator
+     * @returns {import('dictionary').TermDictionaryEntry}
+     */
+    _createGroupedDictionaryEntry(dictionaryEntries, checkDuplicateDefinitions, tagAggregator) {
         // Headwords are generated before sorting, so that the order of dictionaryEntries can be maintained
         const definitionEntries = [];
+        /** @type {Map<string, import('dictionary').TermHeadword>} */
         const headwords = new Map();
         for (const dictionaryEntry of dictionaryEntries) {
-            const headwordIndexMap = this._addTermHeadwords(headwords, dictionaryEntry.headwords);
+            const headwordIndexMap = this._addTermHeadwords(headwords, dictionaryEntry.headwords, tagAggregator);
             definitionEntries.push({index: definitionEntries.length, dictionaryEntry, headwordIndexMap});
         }
 
@@ -1176,7 +1451,9 @@ class Translator {
         let dictionaryPriority = Number.MIN_SAFE_INTEGER;
         let maxTransformedTextLength = 0;
         let isPrimary = false;
+        /** @type {import('dictionary').TermDefinition[]} */
         const definitions = [];
+        /** @type {?Map<string, import('dictionary').TermDefinition>} */
         const definitionsMap = checkDuplicateDefinitions ? new Map() : null;
         let inflections = null;
 
@@ -1192,8 +1469,8 @@ class Translator {
                     inflections = dictionaryEntryInflections;
                 }
             }
-            if (checkDuplicateDefinitions) {
-                this._addTermDefinitions(definitions, definitionsMap, dictionaryEntry.definitions, headwordIndexMap);
+            if (definitionsMap !== null) {
+                this._addTermDefinitions(definitions, definitionsMap, dictionaryEntry.definitions, headwordIndexMap, tagAggregator);
             } else {
                 this._addTermDefinitionsFast(definitions, dictionaryEntry.definitions, headwordIndexMap);
             }
@@ -1226,6 +1503,11 @@ class Translator {
 
     // Data collection addition functions
 
+    /**
+     * @template [T=unknown]
+     * @param {T[]} list
+     * @param {T[]} newItems
+     */
     _addUniqueSimple(list, newItems) {
         for (const item of newItems) {
             if (!list.includes(item)) {
@@ -1234,6 +1516,10 @@ class Translator {
         }
     }
 
+    /**
+     * @param {import('dictionary').TermSource[]} sources
+     * @param {import('dictionary').TermSource[]} newSources
+     */
     _addUniqueSources(sources, newSources) {
         if (newSources.length === 0) { return; }
         if (sources.length === 0) {
@@ -1262,27 +1548,14 @@ class Translator {
         }
     }
 
-    _addUniqueTagGroups(tagGroups, newTagGroups) {
-        if (newTagGroups.length === 0) { return; }
-        for (const newTagGroup of newTagGroups) {
-            const {dictionary} = newTagGroup;
-            const ii = tagGroups.length;
-            if (ii > 0) {
-                let i = 0;
-                for (; i < ii; ++i) {
-                    const tagGroup = tagGroups[i];
-                    if (tagGroup.dictionary === dictionary) {
-                        this._addUniqueSimple(tagGroup.tagNames, newTagGroup.tagNames);
-                        break;
-                    }
-                }
-                if (i < ii) { continue; }
-            }
-            tagGroups.push(newTagGroup);
-        }
-    }
-
-    _addTermHeadwords(headwordsMap, headwords) {
+    /**
+     * @param {Map<string, import('dictionary').TermHeadword>} headwordsMap
+     * @param {import('dictionary').TermHeadword[]} headwords
+     * @param {TranslatorTagAggregator} tagAggregator
+     * @returns {number[]}
+     */
+    _addTermHeadwords(headwordsMap, headwords, tagAggregator) {
+        /** @type {number[]} */
         const headwordIndexMap = [];
         for (const {term, reading, sources, tags, wordClasses} of headwords) {
             const key = this._createMapKey([term, reading]);
@@ -1292,13 +1565,17 @@ class Translator {
                 headwordsMap.set(key, headword);
             }
             this._addUniqueSources(headword.sources, sources);
-            this._addUniqueTagGroups(headword.tags, tags);
             this._addUniqueSimple(headword.wordClasses, wordClasses);
+            tagAggregator.mergeTags(headword.tags, tags);
             headwordIndexMap.push(headword.index);
         }
         return headwordIndexMap;
     }
 
+    /**
+     * @param {number[]} headwordIndices
+     * @param {number} headwordIndex
+     */
     _addUniqueTermHeadwordIndex(headwordIndices, headwordIndex) {
         let end = headwordIndices.length;
         if (end === 0) {
@@ -1322,6 +1599,11 @@ class Translator {
         headwordIndices.splice(start, 0, headwordIndex);
     }
 
+    /**
+     * @param {import('dictionary').TermDefinition[]} definitions
+     * @param {import('dictionary').TermDefinition[]} newDefinitions
+     * @param {number[]} headwordIndexMap
+     */
     _addTermDefinitionsFast(definitions, newDefinitions, headwordIndexMap) {
         for (const {headwordIndices, dictionary, dictionaryIndex, dictionaryPriority, sequences, id, score, isPrimary, tags, entries} of newDefinitions) {
             const headwordIndicesNew = [];
@@ -1332,7 +1614,14 @@ class Translator {
         }
     }
 
-    _addTermDefinitions(definitions, definitionsMap, newDefinitions, headwordIndexMap) {
+    /**
+     * @param {import('dictionary').TermDefinition[]} definitions
+     * @param {Map<string, import('dictionary').TermDefinition>} definitionsMap
+     * @param {import('dictionary').TermDefinition[]} newDefinitions
+     * @param {number[]} headwordIndexMap
+     * @param {TranslatorTagAggregator} tagAggregator
+     */
+    _addTermDefinitions(definitions, definitionsMap, newDefinitions, headwordIndexMap, tagAggregator) {
         for (const {headwordIndices, dictionary, dictionaryIndex, dictionaryPriority, sequences, id, score, isPrimary, tags, entries} of newDefinitions) {
             const key = this._createMapKey([dictionary, ...entries]);
             let definition = definitionsMap.get(key);
@@ -1351,19 +1640,36 @@ class Translator {
             for (const headwordIndex of headwordIndices) {
                 this._addUniqueTermHeadwordIndex(newHeadwordIndices, headwordIndexMap[headwordIndex]);
             }
-            this._addUniqueTagGroups(definition.tags, tags);
+            tagAggregator.mergeTags(definition.tags, tags);
         }
     }
 
     // Sorting functions
 
+    /**
+     * @param {import('dictionary-database').TermEntry[]|import('dictionary-database').KanjiEntry[]} databaseEntries
+     */
     _sortDatabaseEntriesByIndex(databaseEntries) {
         if (databaseEntries.length <= 1) { return; }
-        databaseEntries.sort((a, b) => a.index - b.index);
+        /**
+         * @param {import('dictionary-database').TermEntry|import('dictionary-database').KanjiEntry} v1
+         * @param {import('dictionary-database').TermEntry|import('dictionary-database').KanjiEntry} v2
+         * @returns {number}
+         */
+        const compareFunction = (v1, v2) => v1.index - v2.index;
+        databaseEntries.sort(compareFunction);
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry[]} dictionaryEntries
+     */
     _sortTermDictionaryEntries(dictionaryEntries) {
         const stringComparer = this._stringComparer;
+        /**
+         * @param {import('dictionary').TermDictionaryEntry} v1
+         * @param {import('dictionary').TermDictionaryEntry} v2
+         * @returns {number}
+         */
         const compareFunction = (v1, v2) => {
             // Sort by length of source term
             let i = v2.maxTransformedTextLength - v1.maxTransformedTextLength;
@@ -1414,7 +1720,15 @@ class Translator {
         dictionaryEntries.sort(compareFunction);
     }
 
+    /**
+     * @param {import('dictionary').TermDefinition[]} definitions
+     */
     _sortTermDictionaryEntryDefinitions(definitions) {
+        /**
+         * @param {import('dictionary').TermDefinition} v1
+         * @param {import('dictionary').TermDefinition} v2
+         * @returns {number}
+         */
         const compareFunction = (v1, v2) => {
             // Sort by frequency order
             let i = v1.frequencyOrder - v2.frequencyOrder;
@@ -1450,12 +1764,23 @@ class Translator {
         definitions.sort(compareFunction);
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry[]} dictionaryEntries
+     */
     _sortTermDictionaryEntriesById(dictionaryEntries) {
         if (dictionaryEntries.length <= 1) { return; }
         dictionaryEntries.sort((a, b) => a.definitions[0].id - b.definitions[0].id);
     }
 
+    /**
+     * @param {import('dictionary').TermFrequency[]|import('dictionary').TermPronunciation[]} dataList
+     */
     _sortTermDictionaryEntrySimpleData(dataList) {
+        /**
+         * @param {import('dictionary').TermFrequency|import('dictionary').TermPronunciation} v1
+         * @param {import('dictionary').TermFrequency|import('dictionary').TermPronunciation} v2
+         * @returns {number}
+         */
         const compare = (v1, v2) => {
             // Sort by dictionary priority
             let i = v2.dictionaryPriority - v1.dictionaryPriority;
@@ -1476,7 +1801,15 @@ class Translator {
         dataList.sort(compare);
     }
 
+    /**
+     * @param {import('dictionary').KanjiDictionaryEntry[]} dictionaryEntries
+     */
     _sortKanjiDictionaryEntryData(dictionaryEntries) {
+        /**
+         * @param {import('dictionary').KanjiFrequency} v1
+         * @param {import('dictionary').KanjiFrequency} v2
+         * @returns {number}
+         */
         const compare = (v1, v2) => {
             // Sort by dictionary priority
             let i = v2.dictionaryPriority - v1.dictionaryPriority;
@@ -1496,6 +1829,11 @@ class Translator {
         }
     }
 
+    /**
+     * @param {import('dictionary').TermDictionaryEntry[]} dictionaryEntries
+     * @param {string} dictionary
+     * @param {boolean} ascending
+     */
     _updateSortFrequencies(dictionaryEntries, dictionary, ascending) {
         const frequencyMap = new Map();
         for (const dictionaryEntry of dictionaryEntries) {
@@ -1534,4 +1872,102 @@ class Translator {
             frequencyMap.clear();
         }
     }
+
+    // Miscellaneous
+
+    /**
+     * @template T
+     * @param {Set<T>} set
+     * @param {T[]} values
+     * @returns {boolean}
+     */
+    _hasAny(set, values) {
+        for (const value of values) {
+            if (set.has(value)) { return true; }
+        }
+        return false;
+    }
+}
+
+class TranslatorTagAggregator {
+    constructor() {
+        /** @type {Map<import('dictionary').Tag[], import('translator').TagGroup[]>} */
+        this._tagExpansionTargetMap = new Map();
+    }
+
+    /**
+     * @param {import('dictionary').Tag[]} tags
+     * @param {string} dictionary
+     * @param {string[]} tagNames
+     */
+    addTags(tags, dictionary, tagNames) {
+        if (tagNames.length === 0) { return; }
+        const tagGroups = this._getOrCreateTagGroups(tags);
+        const tagGroup = this._getOrCreateTagGroup(tagGroups, dictionary);
+        this._addUniqueTags(tagGroup, tagNames);
+    }
+
+    /**
+     * @returns {import('translator').TagExpansionTarget[]}
+     */
+    getTagExpansionTargets() {
+        const results = [];
+        for (const [tags, tagGroups] of this._tagExpansionTargetMap) {
+            results.push({tags, tagGroups});
+        }
+        return results;
+    }
+
+    /**
+     * @param {import('dictionary').Tag[]} tags
+     * @param {import('dictionary').Tag[]} newTags
+     */
+    mergeTags(tags, newTags) {
+        const newTagGroups = this._tagExpansionTargetMap.get(newTags);
+        if (typeof newTagGroups === 'undefined') { return; }
+        const tagGroups = this._getOrCreateTagGroups(tags);
+        for (const {dictionary, tagNames} of newTagGroups) {
+            const tagGroup = this._getOrCreateTagGroup(tagGroups, dictionary);
+            this._addUniqueTags(tagGroup, tagNames);
+        }
+    }
+
+    /**
+     * @param {import('dictionary').Tag[]} tags
+     * @returns {import('translator').TagGroup[]}
+     */
+    _getOrCreateTagGroups(tags) {
+        let tagGroups = this._tagExpansionTargetMap.get(tags);
+        if (typeof tagGroups === 'undefined') {
+            tagGroups = [];
+            this._tagExpansionTargetMap.set(tags, tagGroups);
+        }
+        return tagGroups;
+    }
+
+    /**
+     * @param {import('translator').TagGroup[]} tagGroups
+     * @param {string} dictionary
+     * @returns {import('translator').TagGroup}
+     */
+    _getOrCreateTagGroup(tagGroups, dictionary) {
+        for (const tagGroup of tagGroups) {
+            if (tagGroup.dictionary === dictionary) { return tagGroup; }
+        }
+        const newTagGroup = {dictionary, tagNames: []};
+        tagGroups.push(newTagGroup);
+        return newTagGroup;
+    }
+
+    /**
+     * @param {import('translator').TagGroup} tagGroup
+     * @param {string[]} newTagNames
+     */
+    _addUniqueTags(tagGroup, newTagNames) {
+        const {tagNames} = tagGroup;
+        for (const tagName of newTagNames) {
+            if (tagNames.includes(tagName)) { continue; }
+            tagNames.push(tagName);
+        }
+    }
 }
diff --git a/ext/js/media/audio-downloader.js b/ext/js/media/audio-downloader.js
index 32048553db..d0b04e9e04 100644
--- a/ext/js/media/audio-downloader.js
+++ b/ext/js/media/audio-downloader.js
@@ -25,11 +25,18 @@
  */
 
 class AudioDownloader {
+    /**
+     * @param {{japaneseUtil: JapaneseUtil, requestBuilder: RequestBuilder}} details
+     */
     constructor({japaneseUtil, requestBuilder}) {
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = japaneseUtil;
+        /** @type {RequestBuilder} */
         this._requestBuilder = requestBuilder;
+        /** @type {?JsonSchema} */
         this._customAudioListSchema = null;
-        this._getInfoHandlers = new Map([
+        /** @type {Map<import('settings').AudioSourceType, import('audio-downloader').GetInfoHandler>} */
+        this._getInfoHandlers = new Map(/** @type {[name: import('settings').AudioSourceType, handler: import('audio-downloader').GetInfoHandler][]} */ ([
             ['jpod101', this._getInfoJpod101.bind(this)],
             ['jpod101-alternate', this._getInfoJpod101Alternate.bind(this)],
             ['jisho', this._getInfoJisho.bind(this)],
@@ -37,9 +44,15 @@ class AudioDownloader {
             ['text-to-speech-reading', this._getInfoTextToSpeechReading.bind(this)],
             ['custom', this._getInfoCustom.bind(this)],
             ['custom-json', this._getInfoCustomJson.bind(this)]
-        ]);
+        ]));
     }
 
+    /**
+     * @param {import('audio').AudioSourceInfo} source
+     * @param {string} term
+     * @param {string} reading
+     * @returns {Promise<import('audio-downloader').Info[]>}
+     */
     async getTermAudioInfoList(source, term, reading) {
         const handler = this._getInfoHandlers.get(source.type);
         if (typeof handler === 'function') {
@@ -52,6 +65,14 @@ class AudioDownloader {
         return [];
     }
 
+    /**
+     * @param {import('audio').AudioSourceInfo[]} sources
+     * @param {?number} preferredAudioIndex
+     * @param {string} term
+     * @param {string} reading
+     * @param {?number} idleTimeout
+     * @returns {Promise<import('audio-downloader').AudioBinaryBase64>}
+     */
     async downloadTermAudio(sources, preferredAudioIndex, term, reading, idleTimeout) {
         const errors = [];
         for (const source of sources) {
@@ -72,28 +93,34 @@ class AudioDownloader {
             }
         }
 
-        const error = new Error('Could not download audio');
+        const error = new ExtensionError('Could not download audio');
         error.data = {errors};
         throw error;
     }
 
     // Private
 
+    /**
+     * @param {string} url
+     * @param {string} base
+     * @returns {string}
+     */
     _normalizeUrl(url, base) {
         return new URL(url, base).href;
     }
 
+    /** @type {import('audio-downloader').GetInfoHandler} */
     async _getInfoJpod101(term, reading) {
         if (reading === term && this._japaneseUtil.isStringEntirelyKana(term)) {
             reading = term;
-            term = null;
+            term = '';
         }
 
         const params = new URLSearchParams();
-        if (term) {
+        if (term.length > 0) {
             params.set('kanji', term);
         }
-        if (reading) {
+        if (reading.length > 0) {
             params.set('kana', reading);
         }
 
@@ -101,6 +128,7 @@ class AudioDownloader {
         return [{type: 'url', url}];
     }
 
+    /** @type {import('audio-downloader').GetInfoHandler} */
     async _getInfoJpod101Alternate(term, reading) {
         const fetchUrl = 'https://www.japanesepod101.com/learningcenter/reference/dictionary_post';
         const data = new URLSearchParams({
@@ -151,6 +179,7 @@ class AudioDownloader {
         throw new Error('Failed to find audio URL');
     }
 
+    /** @type {import('audio-downloader').GetInfoHandler} */
     async _getInfoJisho(term, reading) {
         const fetchUrl = `https://jisho.org/search/${term}`;
         const response = await this._requestBuilder.fetchAnonymous(fetchUrl, {
@@ -183,26 +212,52 @@ class AudioDownloader {
         throw new Error('Failed to find audio URL');
     }
 
-    async _getInfoTextToSpeech(term, reading, {voice}) {
-        if (!voice) {
-            throw new Error('No voice');
+    /** @type {import('audio-downloader').GetInfoHandler} */
+    async _getInfoTextToSpeech(term, reading, details) {
+        if (typeof details !== 'object' || details === null) {
+            throw new Error('Invalid arguments');
+        }
+        const {voice} = details;
+        if (typeof voice !== 'string') {
+            throw new Error('Invalid voice');
         }
         return [{type: 'tts', text: term, voice: voice}];
     }
 
-    async _getInfoTextToSpeechReading(term, reading, {voice}) {
-        if (!voice) {
-            throw new Error('No voice');
+    /** @type {import('audio-downloader').GetInfoHandler} */
+    async _getInfoTextToSpeechReading(term, reading, details) {
+        if (typeof details !== 'object' || details === null) {
+            throw new Error('Invalid arguments');
+        }
+        const {voice} = details;
+        if (typeof voice !== 'string') {
+            throw new Error('Invalid voice');
         }
         return [{type: 'tts', text: reading, voice: voice}];
     }
 
-    async _getInfoCustom(term, reading, {url}) {
+    /** @type {import('audio-downloader').GetInfoHandler} */
+    async _getInfoCustom(term, reading, details) {
+        if (typeof details !== 'object' || details === null) {
+            throw new Error('Invalid arguments');
+        }
+        let {url} = details;
+        if (typeof url !== 'string') {
+            throw new Error('Invalid url');
+        }
         url = this._getCustomUrl(term, reading, url);
         return [{type: 'url', url}];
     }
 
-    async _getInfoCustomJson(term, reading, {url}) {
+    /** @type {import('audio-downloader').GetInfoHandler} */
+    async _getInfoCustomJson(term, reading, details) {
+        if (typeof details !== 'object' || details === null) {
+            throw new Error('Invalid arguments');
+        }
+        let {url} = details;
+        if (typeof url !== 'string') {
+            throw new Error('Invalid url');
+        }
         url = this._getCustomUrl(term, reading, url);
 
         const response = await this._requestBuilder.fetchAnonymous(url, {
@@ -222,12 +277,14 @@ class AudioDownloader {
 
         if (this._customAudioListSchema === null) {
             const schema = await this._getCustomAudioListSchema();
-            this._customAudioListSchema = new JsonSchema(schema);
+            this._customAudioListSchema = new JsonSchema(/** @type {import('json-schema').Schema} */ (schema));
         }
         this._customAudioListSchema.validate(responseJson);
 
+        /** @type {import('audio-downloader').Info[]} */
         const results = [];
         for (const {url: url2, name} of responseJson.audioSources) {
+            /** @type {import('audio-downloader').Info1} */
             const info = {type: 'url', url: url2};
             if (typeof name === 'string') { info.name = name; }
             results.push(info);
@@ -235,17 +292,32 @@ class AudioDownloader {
         return results;
     }
 
+    /**
+     * @param {string} term
+     * @param {string} reading
+     * @param {string} url
+     * @returns {string}
+     * @throws {Error}
+     */
     _getCustomUrl(term, reading, url) {
         if (typeof url !== 'string') {
             throw new Error('No custom URL defined');
         }
         const data = {term, reading};
-        return url.replace(/\{([^}]*)\}/g, (m0, m1) => (Object.prototype.hasOwnProperty.call(data, m1) ? `${data[m1]}` : m0));
+        return url.replace(/\{([^}]*)\}/g, (m0, m1) => (Object.prototype.hasOwnProperty.call(data, m1) ? `${data[/** @type {'term'|'reading'} */ (m1)]}` : m0));
     }
 
+    /**
+     * @param {string} url
+     * @param {import('settings').AudioSourceType} sourceType
+     * @param {?number} idleTimeout
+     * @returns {Promise<import('audio-downloader').AudioBinaryBase64>}
+     */
     async _downloadAudioFromUrl(url, sourceType, idleTimeout) {
         let signal;
+        /** @type {?(done: boolean) => void} */
         let onProgress = null;
+        /** @type {?number} */
         let idleTimer = null;
         if (typeof idleTimeout === 'number') {
             const abortController = new AbortController();
@@ -254,7 +326,9 @@ class AudioDownloader {
                 abortController.abort('Idle timeout');
             };
             onProgress = (done) => {
-                clearTimeout(idleTimer);
+                if (idleTimer !== null) {
+                    clearTimeout(idleTimer);
+                }
                 idleTimer = done ? null : setTimeout(onIdleTimeout, idleTimeout);
             };
             idleTimer = setTimeout(onIdleTimeout, idleTimeout);
@@ -289,6 +363,11 @@ class AudioDownloader {
         return {data, contentType};
     }
 
+    /**
+     * @param {ArrayBuffer} arrayBuffer
+     * @param {import('settings').AudioSourceType} sourceType
+     * @returns {Promise<boolean>}
+     */
     async _isAudioBinaryValid(arrayBuffer, sourceType) {
         switch (sourceType) {
             case 'jpod101':
@@ -306,6 +385,10 @@ class AudioDownloader {
         }
     }
 
+    /**
+     * @param {ArrayBuffer} arrayBuffer
+     * @returns {Promise<string>}
+     */
     async _arrayBufferDigest(arrayBuffer) {
         const hash = new Uint8Array(await crypto.subtle.digest('SHA-256', new Uint8Array(arrayBuffer)));
         let digest = '';
@@ -315,6 +398,11 @@ class AudioDownloader {
         return digest;
     }
 
+    /**
+     * @param {string} content
+     * @returns {import('simple-dom-parser').ISimpleDomParser}
+     * @throws {Error}
+     */
     _createSimpleDOMParser(content) {
         if (typeof NativeSimpleDOMParser !== 'undefined' && NativeSimpleDOMParser.isSupported()) {
             return new NativeSimpleDOMParser(content);
@@ -325,6 +413,9 @@ class AudioDownloader {
         }
     }
 
+    /**
+     * @returns {Promise<unknown>}
+     */
     async _getCustomAudioListSchema() {
         const url = chrome.runtime.getURL('/data/schemas/custom-audio-list-schema.json');
         const response = await fetch(url, {
diff --git a/ext/js/media/audio-system.js b/ext/js/media/audio-system.js
index d8b78fdc6a..5c389755d9 100644
--- a/ext/js/media/audio-system.js
+++ b/ext/js/media/audio-system.js
@@ -20,12 +20,19 @@
  * TextToSpeechAudio
  */
 
+/**
+ * @augments EventDispatcher<import('audio-system').EventType>
+ */
 class AudioSystem extends EventDispatcher {
     constructor() {
         super();
+        /** @type {?HTMLAudioElement} */
         this._fallbackAudio = null;
     }
 
+    /**
+     * @returns {void}
+     */
     prepare() {
         // speechSynthesis.getVoices() will not be populated unless some API call is made.
         if (
@@ -36,6 +43,9 @@ class AudioSystem extends EventDispatcher {
         }
     }
 
+    /**
+     * @returns {HTMLAudioElement}
+     */
     getFallbackAudio() {
         if (this._fallbackAudio === null) {
             this._fallbackAudio = new Audio('/data/audio/button.mp3');
@@ -43,6 +53,11 @@ class AudioSystem extends EventDispatcher {
         return this._fallbackAudio;
     }
 
+    /**
+     * @param {string} url
+     * @param {import('settings').AudioSourceType} sourceType
+     * @returns {Promise<HTMLAudioElement>}
+     */
     async createAudio(url, sourceType) {
         const audio = new Audio(url);
         await this._waitForData(audio);
@@ -52,6 +67,12 @@ class AudioSystem extends EventDispatcher {
         return audio;
     }
 
+    /**
+     * @param {string} text
+     * @param {string} voiceUri
+     * @returns {TextToSpeechAudio}
+     * @throws {Error}
+     */
     createTextToSpeechAudio(text, voiceUri) {
         const voice = this._getTextToSpeechVoiceFromVoiceUri(voiceUri);
         if (voice === null) {
@@ -62,10 +83,17 @@ class AudioSystem extends EventDispatcher {
 
     // Private
 
-    _onVoicesChanged(e) {
-        this.trigger('voiceschanged', e);
+    /**
+     * @param {Event} event
+     */
+    _onVoicesChanged(event) {
+        this.trigger('voiceschanged', event);
     }
 
+    /**
+     * @param {HTMLAudioElement} audio
+     * @returns {Promise<void>}
+     */
     _waitForData(audio) {
         return new Promise((resolve, reject) => {
             audio.addEventListener('loadeddata', () => resolve());
@@ -73,6 +101,11 @@ class AudioSystem extends EventDispatcher {
         });
     }
 
+    /**
+     * @param {HTMLAudioElement} audio
+     * @param {import('settings').AudioSourceType} sourceType
+     * @returns {boolean}
+     */
     _isAudioValid(audio, sourceType) {
         switch (sourceType) {
             case 'jpod101':
@@ -88,6 +121,10 @@ class AudioSystem extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} voiceUri
+     * @returns {?SpeechSynthesisVoice}
+     */
     _getTextToSpeechVoiceFromVoiceUri(voiceUri) {
         try {
             for (const voice of speechSynthesis.getVoices()) {
diff --git a/ext/js/media/media-util.js b/ext/js/media/media-util.js
index eb7f95f84a..1276bd0fb6 100644
--- a/ext/js/media/media-util.js
+++ b/ext/js/media/media-util.js
@@ -103,7 +103,7 @@ class MediaUtil {
     /**
      * Gets the file extension for a corresponding media type.
      * @param {string} mediaType The media type to use.
-     * @returns {string} A file extension including the dot for the media type,
+     * @returns {?string} A file extension including the dot for the media type,
      *   otherwise `null`.
      */
     static getFileExtensionFromAudioMediaType(mediaType) {
diff --git a/ext/js/media/text-to-speech-audio.js b/ext/js/media/text-to-speech-audio.js
index 35a0b9b12c..bcc066178e 100644
--- a/ext/js/media/text-to-speech-audio.js
+++ b/ext/js/media/text-to-speech-audio.js
@@ -17,13 +17,22 @@
  */
 
 class TextToSpeechAudio {
+    /**
+     * @param {string} text
+     * @param {SpeechSynthesisVoice} voice
+     */
     constructor(text, voice) {
+        /** @type {string} */
         this._text = text;
+        /** @type {SpeechSynthesisVoice} */
         this._voice = voice;
+        /** @type {?SpeechSynthesisUtterance} */
         this._utterance = null;
+        /** @type {number} */
         this._volume = 1;
     }
 
+    /** @type {number} */
     get currentTime() {
         return 0;
     }
@@ -32,6 +41,7 @@ class TextToSpeechAudio {
         // NOP
     }
 
+    /** @type {number} */
     get volume() {
         return this._volume;
     }
@@ -43,6 +53,9 @@ class TextToSpeechAudio {
         }
     }
 
+    /**
+     * @returns {Promise<void>}
+     */
     async play() {
         try {
             if (this._utterance === null) {
@@ -59,6 +72,9 @@ class TextToSpeechAudio {
         }
     }
 
+    /**
+     * @returns {void}
+     */
     pause() {
         try {
             speechSynthesis.cancel();
diff --git a/ext/js/pages/action-popup-main.js b/ext/js/pages/action-popup-main.js
index 9af5f64baf..bf7582b75b 100644
--- a/ext/js/pages/action-popup-main.js
+++ b/ext/js/pages/action-popup-main.js
@@ -23,10 +23,13 @@
 
 class DisplayController {
     constructor() {
+        /** @type {?import('settings').Options} */
         this._optionsFull = null;
+        /** @type {PermissionsUtil} */
         this._permissionsUtil = new PermissionsUtil();
     }
 
+    /** */
     async prepare() {
         const manifest = chrome.runtime.getManifest();
 
@@ -40,7 +43,12 @@ class DisplayController {
 
         this._setupHotkeys();
 
-        const optionsPageUrl = manifest.options_ui.page;
+        const optionsPageUrl = (
+            typeof manifest.options_ui === 'object' &&
+            manifest.options_ui !== null &&
+            typeof manifest.options_ui.page === 'string' ?
+            manifest.options_ui.page : ''
+        );
         this._setupButtonEvents('.action-open-settings', 'openSettingsPage', chrome.runtime.getURL(optionsPageUrl));
         this._setupButtonEvents('.action-open-permissions', null, chrome.runtime.getURL('/permissions.html'));
 
@@ -50,7 +58,7 @@ class DisplayController {
             this._setupOptions(primaryProfile);
         }
 
-        document.querySelector('.action-select-profile').hidden = (profiles.length <= 1);
+        /** @type {HTMLElement} */ (document.querySelector('.action-select-profile')).hidden = (profiles.length <= 1);
 
         this._updateProfileSelect(profiles, profileCurrent);
 
@@ -61,13 +69,18 @@ class DisplayController {
 
     // Private
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onSearchClick(e) {
         if (!e.shiftKey) { return; }
         e.preventDefault();
         location.href = '/search.html?action-popup=true';
-        return false;
     }
 
+    /**
+     * @param {chrome.runtime.Manifest} manifest
+     */
     _showExtensionInfo(manifest) {
         const node = document.getElementById('extension-info');
         if (node === null) { return; }
@@ -75,11 +88,21 @@ class DisplayController {
         node.textContent = `${manifest.name} v${manifest.version}`;
     }
 
+    /**
+     * @param {string} selector
+     * @param {?string} command
+     * @param {string} url
+     * @param {(event: MouseEvent) => void} [customHandler]
+     */
     _setupButtonEvents(selector, command, url, customHandler) {
+        /** @type {NodeListOf<HTMLAnchorElement>} */
         const nodes = document.querySelectorAll(selector);
         for (const node of nodes) {
             if (typeof command === 'string') {
-                node.addEventListener('click', (e) => {
+                /**
+                 * @param {MouseEvent} e
+                 */
+                const onClick = (e) => {
                     if (e.button !== 0) { return; }
                     if (typeof customHandler === 'function') {
                         const result = customHandler(e);
@@ -87,12 +110,17 @@ class DisplayController {
                     }
                     yomichan.api.commandExec(command, {mode: e.ctrlKey ? 'newTab' : 'existingOrNewTab'});
                     e.preventDefault();
-                }, false);
-                node.addEventListener('auxclick', (e) => {
+                };
+                /**
+                 * @param {MouseEvent} e
+                 */
+                const onAuxClick = (e) => {
                     if (e.button !== 1) { return; }
                     yomichan.api.commandExec(command, {mode: 'newTab'});
                     e.preventDefault();
-                }, false);
+                };
+                node.addEventListener('click', onClick, false);
+                node.addEventListener('auxclick', onAuxClick, false);
             }
 
             if (typeof url === 'string') {
@@ -103,6 +131,7 @@ class DisplayController {
         }
     }
 
+    /** */
     async _setupEnvironment() {
         const urlSearchParams = new URLSearchParams(location.search);
         let mode = urlSearchParams.get('mode');
@@ -130,6 +159,9 @@ class DisplayController {
         document.documentElement.dataset.mode = mode;
     }
 
+    /**
+     * @returns {Promise<chrome.tabs.Tab|undefined>}
+     */
     _getCurrentTab() {
         return new Promise((resolve, reject) => {
             chrome.tabs.getCurrent((result) => {
@@ -143,10 +175,13 @@ class DisplayController {
         });
     }
 
+    /**
+     * @param {import('settings').Profile} profile
+     */
     _setupOptions({options}) {
         const extensionEnabled = options.general.enable;
         const onToggleChanged = () => yomichan.api.commandExec('toggleTextScanning');
-        for (const toggle of document.querySelectorAll('#enable-search,#enable-search2')) {
+        for (const toggle of /** @type {NodeListOf<HTMLInputElement>} */ (document.querySelectorAll('#enable-search,#enable-search2'))) {
             toggle.checked = extensionEnabled;
             toggle.addEventListener('change', onToggleChanged, false);
         }
@@ -154,11 +189,12 @@ class DisplayController {
         this._updatePermissionsWarnings(options);
     }
 
+    /** */
     async _setupHotkeys() {
         const hotkeyHelpController = new HotkeyHelpController();
         await hotkeyHelpController.prepare();
 
-        const {profiles, profileCurrent} = this._optionsFull;
+        const {profiles, profileCurrent} = /** @type {import('settings').Options} */ (this._optionsFull);
         const primaryProfile = (profileCurrent >= 0 && profileCurrent < profiles.length) ? profiles[profileCurrent] : null;
         if (primaryProfile !== null) {
             hotkeyHelpController.setOptions(primaryProfile.options);
@@ -167,9 +203,13 @@ class DisplayController {
         hotkeyHelpController.setupNode(document.documentElement);
     }
 
+    /**
+     * @param {import('settings').Profile[]} profiles
+     * @param {number} profileCurrent
+     */
     _updateProfileSelect(profiles, profileCurrent) {
-        const select = document.querySelector('#profile-select');
-        const optionGroup = document.querySelector('#profile-select-option-group');
+        const select = /** @type {HTMLSelectElement} */ (document.querySelector('#profile-select'));
+        const optionGroup = /** @type {HTMLElement} */ (document.querySelector('#profile-select-option-group'));
         const fragment = document.createDocumentFragment();
         for (let i = 0, ii = profiles.length; i < ii; ++i) {
             const {name} = profiles[i];
@@ -185,26 +225,37 @@ class DisplayController {
         select.addEventListener('change', this._onProfileSelectChange.bind(this), false);
     }
 
-    _onProfileSelectChange(e) {
-        const value = parseInt(e.currentTarget.value, 10);
-        if (typeof value === 'number' && Number.isFinite(value) && value >= 0 && value <= this._optionsFull.profiles.length) {
+    /**
+     * @param {Event} event
+     */
+    _onProfileSelectChange(event) {
+        const node = /** @type {HTMLInputElement} */ (event.currentTarget);
+        const value = parseInt(node.value, 10);
+        if (typeof value === 'number' && Number.isFinite(value) && value >= 0 && value <= /** @type {import('settings').Options} */ (this._optionsFull).profiles.length) {
             this._setPrimaryProfileIndex(value);
         }
     }
 
+    /**
+     * @param {number} value
+     */
     async _setPrimaryProfileIndex(value) {
-        return await yomichan.api.modifySettings(
-            [{
-                action: 'set',
-                path: 'profileCurrent',
-                value,
-                scope: 'global'
-            }]
-        );
+        /** @type {import('settings-modifications').ScopedModificationSet} */
+        const modification = {
+            action: 'set',
+            path: 'profileCurrent',
+            value,
+            scope: 'global',
+            optionsContext: null
+        };
+        await yomichan.api.modifySettings([modification], 'action-popup');
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     async _updateDictionariesEnabledWarnings(options) {
-        const noDictionariesEnabledWarnings = document.querySelectorAll('.no-dictionaries-enabled-warning');
+        const noDictionariesEnabledWarnings = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.no-dictionaries-enabled-warning'));
         const dictionaries = await yomichan.api.getDictionaryInfo();
 
         const enabledDictionaries = new Set();
@@ -227,16 +278,20 @@ class DisplayController {
         }
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     async _updatePermissionsWarnings(options) {
         const permissions = await this._permissionsUtil.getAllPermissions();
         if (this._permissionsUtil.hasRequiredPermissionsForOptions(permissions, options)) { return; }
 
-        const warnings = document.querySelectorAll('.action-open-permissions,.permissions-required-warning');
+        const warnings = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.action-open-permissions,.permissions-required-warning'));
         for (const node of warnings) {
             node.hidden = false;
         }
     }
 
+    /** @returns {Promise<boolean>} */
     async _isSafari() {
         const {browser} = await yomichan.api.getEnvironmentInfo();
         return browser === 'safari';
diff --git a/ext/js/pages/common/extension-content-controller.js b/ext/js/pages/common/extension-content-controller.js
index c50a6d237b..c286102fdc 100644
--- a/ext/js/pages/common/extension-content-controller.js
+++ b/ext/js/pages/common/extension-content-controller.js
@@ -21,6 +21,7 @@
  */
 
 class ExtensionContentController {
+    /** */
     prepare() {
         this._prepareSpecialUrls();
         this._prepareExtensionIdExamples();
@@ -29,6 +30,7 @@ class ExtensionContentController {
 
     // Private
 
+    /** */
     async _prepareEnvironmentInfo() {
         const {dataset} = document.documentElement;
         const {manifest_version: manifestVersion} = chrome.runtime.getManifest();
@@ -42,6 +44,7 @@ class ExtensionContentController {
         dataset.os = platform.os;
     }
 
+    /** */
     _prepareExtensionIdExamples() {
         const nodes = document.querySelectorAll('.extension-id-example');
         let url = '';
@@ -55,8 +58,9 @@ class ExtensionContentController {
         }
     }
 
+    /** */
     _prepareSpecialUrls() {
-        const nodes = document.querySelectorAll('[data-special-url]');
+        const nodes = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('[data-special-url]'));
         if (nodes.length === 0) { return; }
 
         let extensionId = '';
@@ -79,16 +83,27 @@ class ExtensionContentController {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onSpecialUrlLinkClick(e) {
         switch (e.button) {
             case 0:
             case 1:
-                e.preventDefault();
-                this._createTab(e.currentTarget.dataset.specialUrl, true);
+                {
+                    const element = /** @type {HTMLElement} */ (e.currentTarget);
+                    const {specialUrl} = element.dataset;
+                    if (typeof specialUrl !== 'string') { return; }
+                    e.preventDefault();
+                    this._createTab(specialUrl, true);
+                }
                 break;
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onSpecialUrlLinkMouseDown(e) {
         switch (e.button) {
             case 0:
@@ -98,10 +113,17 @@ class ExtensionContentController {
         }
     }
 
+    /**
+     * @param {string} url
+     * @param {boolean} useOpener
+     * @returns {Promise<chrome.tabs.Tab>}
+     */
     async _createTab(url, useOpener) {
+        /** @type {number|undefined} */
         let openerTabId;
         if (useOpener) {
             try {
+                /** @type {chrome.tabs.Tab|undefined} */
                 const tab = await new Promise((resolve, reject) => {
                     chrome.tabs.getCurrent((result) => {
                         const e = chrome.runtime.lastError;
@@ -112,7 +134,9 @@ class ExtensionContentController {
                         }
                     });
                 });
-                openerTabId = tab.id;
+                if (typeof tab !== 'undefined') {
+                    openerTabId = tab.id;
+                }
             } catch (e) {
                 // NOP
             }
diff --git a/ext/js/pages/info-main.js b/ext/js/pages/info-main.js
index 06ad10e891..1024983fe7 100644
--- a/ext/js/pages/info-main.js
+++ b/ext/js/pages/info-main.js
@@ -22,6 +22,10 @@
  * SettingsController
  */
 
+/**
+ * @param {import('environment').Browser} browser
+ * @returns {string}
+ */
 function getBrowserDisplayName(browser) {
     switch (browser) {
         case 'chrome': return 'Chrome';
@@ -29,10 +33,15 @@ function getBrowserDisplayName(browser) {
         case 'firefox-mobile': return 'Firefox for Android';
         case 'edge': return 'Edge';
         case 'edge-legacy': return 'Edge Legacy';
+        case 'safari': return 'Safari';
         default: return `${browser}`;
     }
 }
 
+/**
+ * @param {import('environment').OperatingSystem} os
+ * @returns {string}
+ */
 function getOperatingSystemDisplayName(os) {
     switch (os) {
         case 'mac': return 'Mac OS';
@@ -60,14 +69,15 @@ function getOperatingSystemDisplayName(os) {
         const {name, version} = manifest;
         const {browser, platform: {os}} = await yomichan.api.getEnvironmentInfo();
 
-        const thisVersionLink = document.querySelector('#release-notes-this-version-link');
-        thisVersionLink.href = thisVersionLink.dataset.hrefFormat.replace(/\{version\}/g, version);
+        const thisVersionLink = /** @type {HTMLLinkElement} */ (document.querySelector('#release-notes-this-version-link'));
+        const {hrefFormat} = thisVersionLink.dataset;
+        thisVersionLink.href = typeof hrefFormat === 'string' ? hrefFormat.replace(/\{version\}/g, version) : '';
 
-        document.querySelector('#version').textContent = `${name} ${version}`;
-        document.querySelector('#browser').textContent = getBrowserDisplayName(browser);
-        document.querySelector('#platform').textContent = getOperatingSystemDisplayName(os);
-        document.querySelector('#language').textContent = `${language}`;
-        document.querySelector('#user-agent').textContent = userAgent;
+        /** @type {HTMLElement} */ (document.querySelector('#version')).textContent = `${name} ${version}`;
+        /** @type {HTMLElement} */ (document.querySelector('#browser')).textContent = getBrowserDisplayName(browser);
+        /** @type {HTMLElement} */ (document.querySelector('#platform')).textContent = getOperatingSystemDisplayName(os);
+        /** @type {HTMLElement} */ (document.querySelector('#language')).textContent = `${language}`;
+        /** @type {HTMLElement} */ (document.querySelector('#user-agent')).textContent = userAgent;
 
         (async () => {
             let ankiConnectVersion = null;
@@ -77,9 +87,9 @@ function getOperatingSystemDisplayName(os) {
                 // NOP
             }
 
-            document.querySelector('#anki-connect-version').textContent = (ankiConnectVersion !== null ? `${ankiConnectVersion}` : 'Unknown');
-            document.querySelector('#anki-connect-version-container').hasError = `${ankiConnectVersion === null}`;
-            document.querySelector('#anki-connect-version-unknown-message').hidden = (ankiConnectVersion !== null);
+            /** @type {HTMLElement} */ (document.querySelector('#anki-connect-version')).textContent = (ankiConnectVersion !== null ? `${ankiConnectVersion}` : 'Unknown');
+            /** @type {HTMLElement} */ (document.querySelector('#anki-connect-version-container')).dataset.hasError = `${ankiConnectVersion === null}`;
+            /** @type {HTMLElement} */ (document.querySelector('#anki-connect-version-unknown-message')).hidden = (ankiConnectVersion !== null);
         })();
 
         (async () => {
@@ -105,8 +115,8 @@ function getOperatingSystemDisplayName(os) {
                 fragment.appendChild(node);
             }
 
-            document.querySelector('#installed-dictionaries-none').hidden = (dictionaryInfos.length !== 0);
-            const container = document.querySelector('#installed-dictionaries');
+            /** @type {HTMLElement} */ (document.querySelector('#installed-dictionaries-none')).hidden = (dictionaryInfos.length !== 0);
+            const container = /** @type {HTMLElement} */ (document.querySelector('#installed-dictionaries'));
             container.textContent = '';
             container.appendChild(fragment);
         })();
diff --git a/ext/js/pages/permissions-main.js b/ext/js/pages/permissions-main.js
index 57dbd2eed9..608f707b3f 100644
--- a/ext/js/pages/permissions-main.js
+++ b/ext/js/pages/permissions-main.js
@@ -27,6 +27,9 @@
  * SettingsDisplayController
  */
 
+/**
+ * @returns {Promise<void>}
+ */
 async function setupEnvironmentInfo() {
     const {manifest_version: manifestVersion} = chrome.runtime.getManifest();
     const {browser, platform} = await yomichan.api.getEnvironmentInfo();
@@ -35,20 +38,39 @@ async function setupEnvironmentInfo() {
     document.documentElement.dataset.manifestVersion = `${manifestVersion}`;
 }
 
+/**
+ * @returns {Promise<boolean>}
+ */
 async function isAllowedIncognitoAccess() {
     return await new Promise((resolve) => chrome.extension.isAllowedIncognitoAccess(resolve));
 }
 
+/**
+ * @returns {Promise<boolean>}
+ */
 async function isAllowedFileSchemeAccess() {
     return await new Promise((resolve) => chrome.extension.isAllowedFileSchemeAccess(resolve));
 }
 
+/**
+ * @returns {void}
+ */
 function setupPermissionsToggles() {
     const manifest = chrome.runtime.getManifest();
-    let optionalPermissions = manifest.optional_permissions;
-    if (!Array.isArray(optionalPermissions)) { optionalPermissions = []; }
-    optionalPermissions = new Set(optionalPermissions);
+    const optionalPermissions = manifest.optional_permissions;
+    /** @type {Set<string>} */
+    const optionalPermissionsSet = new Set(optionalPermissions);
+    if (Array.isArray(optionalPermissions)) {
+        for (const permission of optionalPermissions) {
+            optionalPermissionsSet.add(permission);
+        }
+    }
 
+    /**
+     * @param {Set<string>} set
+     * @param {string[]} values
+     * @returns {boolean}
+     */
     const hasAllPermisions = (set, values) => {
         for (const value of values) {
             if (!set.has(value)) { return false; }
@@ -56,10 +78,10 @@ function setupPermissionsToggles() {
         return true;
     };
 
-    for (const toggle of document.querySelectorAll('.permissions-toggle')) {
-        let permissions = toggle.dataset.requiredPermissions;
-        permissions = (typeof permissions === 'string' && permissions.length > 0 ? permissions.split(' ') : []);
-        toggle.disabled = !hasAllPermisions(optionalPermissions, permissions);
+    for (const toggle of /** @type {NodeListOf<HTMLInputElement>} */ (document.querySelectorAll('.permissions-toggle'))) {
+        const permissions = toggle.dataset.requiredPermissions;
+        const permissionsArray = (typeof permissions === 'string' && permissions.length > 0 ? permissions.split(' ') : []);
+        toggle.disabled = !hasAllPermisions(optionalPermissionsSet, permissionsArray);
     }
 }
 
@@ -77,9 +99,10 @@ function setupPermissionsToggles() {
 
         setupEnvironmentInfo();
 
+        /** @type {[HTMLInputElement, HTMLInputElement]} */
         const permissionsCheckboxes = [
-            document.querySelector('#permission-checkbox-allow-in-private-windows'),
-            document.querySelector('#permission-checkbox-allow-file-url-access')
+            /** @type {HTMLInputElement} */ (document.querySelector('#permission-checkbox-allow-in-private-windows')),
+            /** @type {HTMLInputElement} */ (document.querySelector('#permission-checkbox-allow-file-url-access'))
         ];
 
         const permissions = await Promise.all([
diff --git a/ext/js/pages/settings/anki-controller.js b/ext/js/pages/settings/anki-controller.js
index c66dfecef4..c5a090bd03 100644
--- a/ext/js/pages/settings/anki-controller.js
+++ b/ext/js/pages/settings/anki-controller.js
@@ -24,9 +24,15 @@
  */
 
 class AnkiController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {AnkiConnect} */
         this._ankiConnect = new AnkiConnect();
+        /** @type {SelectorObserver<AnkiCardController>} */
         this._selectorObserver = new SelectorObserver({
             selector: '.anki-card',
             ignoreSelector: null,
@@ -34,52 +40,74 @@ class AnkiController {
             onRemoved: this._removeCardController.bind(this),
             isStale: this._isCardControllerStale.bind(this)
         });
+        /** @type {Intl.Collator} */
         this._stringComparer = new Intl.Collator(); // Locale does not matter
+        /** @type {?Promise<import('anki-controller').AnkiData>} */
         this._getAnkiDataPromise = null;
+        /** @type {?HTMLElement} */
         this._ankiErrorContainer = null;
+        /** @type {?HTMLElement} */
         this._ankiErrorMessageNode = null;
+        /** @type {string} */
         this._ankiErrorMessageNodeDefaultContent = '';
+        /** @type {?HTMLElement} */
         this._ankiErrorMessageDetailsNode = null;
+        /** @type {?HTMLElement} */
         this._ankiErrorMessageDetailsContainer = null;
+        /** @type {?HTMLElement} */
         this._ankiErrorMessageDetailsToggle = null;
+        /** @type {?HTMLElement} */
         this._ankiErrorInvalidResponseInfo = null;
+        /** @type {?HTMLElement} */
         this._ankiCardPrimary = null;
+        /** @type {?Error} */
         this._ankiError = null;
+        /** @type {?import('core').TokenObject} */
         this._validateFieldsToken = null;
     }
 
+    /** @type {SettingsController} */
     get settingsController() {
         return this._settingsController;
     }
 
+    /** */
     async prepare() {
-        this._ankiErrorContainer = document.querySelector('#anki-error');
-        this._ankiErrorMessageNode = document.querySelector('#anki-error-message');
-        this._ankiErrorMessageNodeDefaultContent = this._ankiErrorMessageNode.textContent;
-        this._ankiErrorMessageDetailsNode = document.querySelector('#anki-error-message-details');
-        this._ankiErrorMessageDetailsContainer = document.querySelector('#anki-error-message-details-container');
-        this._ankiErrorMessageDetailsToggle = document.querySelector('#anki-error-message-details-toggle');
-        this._ankiErrorInvalidResponseInfo = document.querySelector('#anki-error-invalid-response-info');
-        this._ankiEnableCheckbox = document.querySelector('[data-setting="anki.enable"]');
-        this._ankiCardPrimary = document.querySelector('#anki-card-primary');
-        const ankiApiKeyInput = document.querySelector('#anki-api-key-input');
-        const ankiCardPrimaryTypeRadios = document.querySelectorAll('input[type=radio][name=anki-card-primary-type]');
+        this._ankiErrorContainer = /** @type {HTMLElement} */ (document.querySelector('#anki-error'));
+        this._ankiErrorMessageNode = /** @type {HTMLElement} */ (document.querySelector('#anki-error-message'));
+        const ankiErrorMessageNodeDefaultContent = this._ankiErrorMessageNode.textContent;
+        this._ankiErrorMessageNodeDefaultContent = typeof ankiErrorMessageNodeDefaultContent === 'string' ? ankiErrorMessageNodeDefaultContent : '';
+        this._ankiErrorMessageDetailsNode = /** @type {HTMLElement} */ (document.querySelector('#anki-error-message-details'));
+        this._ankiErrorMessageDetailsContainer = /** @type {HTMLElement} */ (document.querySelector('#anki-error-message-details-container'));
+        this._ankiErrorMessageDetailsToggle = /** @type {HTMLElement} */ (document.querySelector('#anki-error-message-details-toggle'));
+        this._ankiErrorInvalidResponseInfo = /** @type {HTMLElement} */ (document.querySelector('#anki-error-invalid-response-info'));
+        this._ankiEnableCheckbox = /** @type {?HTMLInputElement} */ (document.querySelector('[data-setting="anki.enable"]'));
+        this._ankiCardPrimary = /** @type {HTMLElement} */ (document.querySelector('#anki-card-primary'));
+        const ankiApiKeyInput = /** @type {HTMLElement} */ (document.querySelector('#anki-api-key-input'));
+        const ankiCardPrimaryTypeRadios = /** @type {NodeListOf<HTMLInputElement>} */ (document.querySelectorAll('input[type=radio][name=anki-card-primary-type]'));
+        const ankiErrorLog = /** @type {HTMLElement} */ (document.querySelector('#anki-error-log'));
 
         this._setupFieldMenus();
 
         this._ankiErrorMessageDetailsToggle.addEventListener('click', this._onAnkiErrorMessageDetailsToggleClick.bind(this), false);
-        if (this._ankiEnableCheckbox !== null) { this._ankiEnableCheckbox.addEventListener('settingChanged', this._onAnkiEnableChanged.bind(this), false); }
+        if (this._ankiEnableCheckbox !== null) {
+            this._ankiEnableCheckbox.addEventListener(
+                /** @type {string} */ ('settingChanged'),
+                /** @type {EventListener} */ (this._onAnkiEnableChanged.bind(this)),
+                false
+            );
+        }
         for (const input of ankiCardPrimaryTypeRadios) {
             input.addEventListener('change', this._onAnkiCardPrimaryTypeRadioChange.bind(this), false);
         }
 
-        const testAnkiNoteViewerButtons = document.querySelectorAll('.test-anki-note-viewer-button');
+        const testAnkiNoteViewerButtons = /** @type {NodeListOf<HTMLButtonElement>} */ (document.querySelectorAll('.test-anki-note-viewer-button'));
         const onTestAnkiNoteViewerButtonClick = this._onTestAnkiNoteViewerButtonClick.bind(this);
         for (const button of testAnkiNoteViewerButtons) {
             button.addEventListener('click', onTestAnkiNoteViewerButtonClick, false);
         }
 
-        document.querySelector('#anki-error-log').addEventListener('click', this._onAnkiErrorLogLinkClick.bind(this));
+        ankiErrorLog.addEventListener('click', this._onAnkiErrorLogLinkClick.bind(this));
 
         ankiApiKeyInput.addEventListener('focus', this._onApiKeyInputFocus.bind(this));
         ankiApiKeyInput.addEventListener('blur', this._onApiKeyInputBlur.bind(this));
@@ -94,6 +122,10 @@ class AnkiController {
         this._settingsController.on('optionsChanged', this._onOptionsChanged.bind(this));
     }
 
+    /**
+     * @param {string} type
+     * @returns {string[]}
+     */
     getFieldMarkers(type) {
         switch (type) {
             case 'terms':
@@ -154,6 +186,9 @@ class AnkiController {
         }
     }
 
+    /**
+     * @returns {Promise<import('anki-controller').AnkiData>}
+     */
     async getAnkiData() {
         let promise = this._getAnkiDataPromise;
         if (promise === null) {
@@ -164,23 +199,37 @@ class AnkiController {
         return promise;
     }
 
+    /**
+     * @param {string} model
+     * @returns {Promise<string[]>}
+     */
     async getModelFieldNames(model) {
         return await this._ankiConnect.getModelFieldNames(model);
     }
 
+    /**
+     * @param {string} fieldValue
+     * @returns {string[]}
+     */
     getRequiredPermissions(fieldValue) {
         return this._settingsController.permissionsUtil.getRequiredPermissionsForAnkiFieldValue(fieldValue);
     }
 
     // Private
 
+    /** */
     async _updateOptions() {
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     async _onOptionsChanged({options: {anki}}) {
-        let {apiKey} = anki;
+        /** @type {?string} */
+        let apiKey = anki.apiKey;
         if (apiKey === '') { apiKey = null; }
         this._ankiConnect.server = anki.server;
         this._ankiConnect.enabled = anki.enable;
@@ -190,44 +239,73 @@ class AnkiController {
         this._selectorObserver.observe(document.documentElement, true);
     }
 
+    /** */
     _onAnkiErrorMessageDetailsToggleClick() {
-        const node = this._ankiErrorMessageDetailsContainer;
+        const node = /** @type {HTMLElement} */ (this._ankiErrorMessageDetailsContainer);
         node.hidden = !node.hidden;
     }
 
+    /**
+     * @param {import('dom-data-binder').SettingChangedEvent} event
+     */
     _onAnkiEnableChanged({detail: {value}}) {
         if (this._ankiConnect.server === null) { return; }
-        this._ankiConnect.enabled = value;
+        this._ankiConnect.enabled = typeof value === 'boolean' && value;
 
         for (const cardController of this._selectorObserver.datas()) {
             cardController.updateAnkiState();
         }
     }
 
+    /**
+     * @param {Event} e
+     */
     _onAnkiCardPrimaryTypeRadioChange(e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         if (!node.checked) { return; }
-
-        this._setAnkiCardPrimaryType(node.dataset.value, node.dataset.ankiCardMenu);
+        const {value, ankiCardMenu} = node.dataset;
+        if (typeof value !== 'string') { return; }
+        this._setAnkiCardPrimaryType(value, ankiCardMenu);
     }
 
+    /** */
     _onAnkiErrorLogLinkClick() {
         if (this._ankiError === null) { return; }
         console.log({error: this._ankiError});
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onTestAnkiNoteViewerButtonClick(e) {
-        this._testAnkiNoteViewerSafe(e.currentTarget.dataset.mode);
+        const element = /** @type {HTMLElement} */ (e.currentTarget);
+        const {mode} = element.dataset;
+        if (typeof mode !== 'string') { return; }
+        const mode2 = this._normalizeAnkiNoteGuiMode(mode);
+        if (mode2 === null) { return; }
+        this._testAnkiNoteViewerSafe(mode2);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onApiKeyInputFocus(e) {
-        e.currentTarget.type = 'text';
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        element.type = 'text';
     }
 
+    /**
+     * @param {Event} e
+     */
     _onApiKeyInputBlur(e) {
-        e.currentTarget.type = 'password';
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        element.type = 'password';
     }
 
+    /**
+     * @param {string} ankiCardType
+     * @param {string} [ankiCardMenu]
+     */
     _setAnkiCardPrimaryType(ankiCardType, ankiCardMenu) {
         if (this._ankiCardPrimary === null) { return; }
         this._ankiCardPrimary.dataset.ankiCardType = ankiCardType;
@@ -238,28 +316,43 @@ class AnkiController {
         }
     }
 
+    /**
+     * @param {Element} node
+     * @returns {AnkiCardController}
+     */
     _createCardController(node) {
-        const cardController = new AnkiCardController(this._settingsController, this, node);
+        const cardController = new AnkiCardController(this._settingsController, this, /** @type {HTMLElement} */ (node));
         cardController.prepare();
         return cardController;
     }
 
-    _removeCardController(node, cardController) {
+    /**
+     * @param {Element} _node
+     * @param {AnkiCardController} cardController
+     */
+    _removeCardController(_node, cardController) {
         cardController.cleanup();
     }
 
-    _isCardControllerStale(node, cardController) {
+    /**
+     * @param {Element} _node
+     * @param {AnkiCardController} cardController
+     * @returns {boolean}
+     */
+    _isCardControllerStale(_node, cardController) {
         return cardController.isStale();
     }
 
+    /** */
     _setupFieldMenus() {
+        /** @type {[types: string[], selector: string][]} */
         const fieldMenuTargets = [
             [['terms'], '#anki-card-terms-field-menu-template'],
             [['kanji'], '#anki-card-kanji-field-menu-template'],
             [['terms', 'kanji'], '#anki-card-all-field-menu-template']
         ];
         for (const [types, selector] of fieldMenuTargets) {
-            const element = document.querySelector(selector);
+            const element = /** @type {HTMLTemplateElement} */ (document.querySelector(selector));
             if (element === null) { continue; }
 
             let markers = [];
@@ -284,6 +377,9 @@ class AnkiController {
         }
     }
 
+    /**
+     * @returns {Promise<import('anki-controller').AnkiData>}
+     */
     async _getAnkiData() {
         this._setAnkiStatusChanging();
         const [
@@ -305,85 +401,108 @@ class AnkiController {
         return {deckNames, modelNames};
     }
 
+    /**
+     * @returns {Promise<[deckNames: string[], error: ?Error]>}
+     */
     async _getDeckNames() {
         try {
             const result = await this._ankiConnect.getDeckNames();
             this._sortStringArray(result);
             return [result, null];
         } catch (e) {
-            return [[], e];
+            return [[], e instanceof Error ? e : new Error(`${e}`)];
         }
     }
 
+    /**
+     * @returns {Promise<[modelNames: string[], error: ?Error]>}
+     */
     async _getModelNames() {
         try {
             const result = await this._ankiConnect.getModelNames();
             this._sortStringArray(result);
             return [result, null];
         } catch (e) {
-            return [[], e];
+            return [[], e instanceof Error ? e : new Error(`${e}`)];
         }
     }
 
+    /** */
     _setAnkiStatusChanging() {
-        this._ankiErrorMessageNode.textContent = this._ankiErrorMessageNodeDefaultContent;
-        this._ankiErrorMessageNode.classList.remove('danger-text');
+        const ankiErrorMessageNode = /** @type {HTMLElement} */ (this._ankiErrorMessageNode);
+        ankiErrorMessageNode.textContent = this._ankiErrorMessageNodeDefaultContent;
+        ankiErrorMessageNode.classList.remove('danger-text');
     }
 
+    /** */
     _hideAnkiError() {
+        const ankiErrorMessageNode = /** @type {HTMLElement} */ (this._ankiErrorMessageNode);
         if (this._ankiErrorContainer !== null) {
             this._ankiErrorContainer.hidden = true;
         }
-        this._ankiErrorMessageDetailsContainer.hidden = true;
-        this._ankiErrorMessageDetailsToggle.hidden = true;
-        this._ankiErrorInvalidResponseInfo.hidden = true;
-        this._ankiErrorMessageNode.textContent = (this._ankiConnect.enabled ? 'Connected' : 'Not enabled');
-        this._ankiErrorMessageNode.classList.remove('danger-text');
-        this._ankiErrorMessageDetailsNode.textContent = '';
+        /** @type {HTMLElement} */ (this._ankiErrorMessageDetailsContainer).hidden = true;
+        /** @type {HTMLElement} */ (this._ankiErrorMessageDetailsToggle).hidden = true;
+        /** @type {HTMLElement} */ (this._ankiErrorInvalidResponseInfo).hidden = true;
+        ankiErrorMessageNode.textContent = (this._ankiConnect.enabled ? 'Connected' : 'Not enabled');
+        ankiErrorMessageNode.classList.remove('danger-text');
+        /** @type {HTMLElement} */ (this._ankiErrorMessageDetailsNode).textContent = '';
         this._ankiError = null;
     }
 
+    /**
+     * @param {Error} error
+     */
     _showAnkiError(error) {
+        const ankiErrorMessageNode = /** @type {HTMLElement} */ (this._ankiErrorMessageNode);
         this._ankiError = error;
 
         let errorString = typeof error === 'object' && error !== null ? error.message : null;
         if (!errorString) { errorString = `${error}`; }
         if (!/[.!?]$/.test(errorString)) { errorString += '.'; }
-        this._ankiErrorMessageNode.textContent = errorString;
-        this._ankiErrorMessageNode.classList.add('danger-text');
+        ankiErrorMessageNode.textContent = errorString;
+        ankiErrorMessageNode.classList.add('danger-text');
 
-        const data = error.data;
+        const data = error instanceof ExtensionError ? error.data : void 0;
         let details = '';
         if (typeof data !== 'undefined') {
             details += `${JSON.stringify(data, null, 4)}\n\n`;
         }
         details += `${error.stack}`.trimRight();
-        this._ankiErrorMessageDetailsNode.textContent = details;
+        /** @type {HTMLElement} */ (this._ankiErrorMessageDetailsNode).textContent = details;
 
         if (this._ankiErrorContainer !== null) {
             this._ankiErrorContainer.hidden = false;
         }
-        this._ankiErrorMessageDetailsContainer.hidden = true;
-        this._ankiErrorInvalidResponseInfo.hidden = (errorString.indexOf('Invalid response') < 0);
-        this._ankiErrorMessageDetailsToggle.hidden = false;
+        /** @type {HTMLElement} */ (this._ankiErrorMessageDetailsContainer).hidden = true;
+        /** @type {HTMLElement} */ (this._ankiErrorInvalidResponseInfo).hidden = (errorString.indexOf('Invalid response') < 0);
+        /** @type {HTMLElement} */ (this._ankiErrorMessageDetailsToggle).hidden = false;
     }
 
+    /**
+     * @param {string[]} array
+     */
     _sortStringArray(array) {
         const stringComparer = this._stringComparer;
         array.sort((a, b) => stringComparer.compare(a, b));
     }
 
+    /**
+     * @param {import('settings').AnkiNoteGuiMode} mode
+     */
     async _testAnkiNoteViewerSafe(mode) {
         this._setAnkiNoteViewerStatus(false, null);
         try {
             await this._testAnkiNoteViewer(mode);
         } catch (e) {
-            this._setAnkiNoteViewerStatus(true, e);
+            this._setAnkiNoteViewerStatus(true, e instanceof Error ? e : new Error(`${e}`));
             return;
         }
         this._setAnkiNoteViewerStatus(true, null);
     }
 
+    /**
+     * @param {import('settings').AnkiNoteGuiMode} mode
+     */
     async _testAnkiNoteViewer(mode) {
         const queries = [
             '"よむ" deck:current',
@@ -408,8 +527,12 @@ class AnkiController {
         await yomichan.api.noteView(noteId, mode, false);
     }
 
+    /**
+     * @param {boolean} visible
+     * @param {?Error} error
+     */
     _setAnkiNoteViewerStatus(visible, error) {
-        const node = document.querySelector('#test-anki-note-viewer-results');
+        const node = /** @type {HTMLElement} */ (document.querySelector('#test-anki-note-viewer-results'));
         if (visible) {
             const success = (error === null);
             node.textContent = success ? 'Success!' : error.message;
@@ -420,26 +543,61 @@ class AnkiController {
         }
         node.hidden = !visible;
     }
+
+    /**
+     * @param {string} value
+     * @returns {?import('settings').AnkiNoteGuiMode}
+     */
+    _normalizeAnkiNoteGuiMode(value) {
+        switch (value) {
+            case 'browse':
+            case 'edit':
+                return value;
+            default:
+                return null;
+        }
+    }
 }
 
 class AnkiCardController {
+    /**
+     * @param {SettingsController} settingsController
+     * @param {AnkiController} ankiController
+     * @param {HTMLElement} node
+     */
     constructor(settingsController, ankiController, node) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {AnkiController} */
         this._ankiController = ankiController;
+        /** @type {HTMLElement} */
         this._node = node;
-        this._cardType = node.dataset.ankiCardType;
+        const {ankiCardType} = node.dataset;
+        /** @type {string} */
+        this._cardType = typeof ankiCardType === 'string' ? ankiCardType : 'terms';
+        /** @type {string|undefined} */
         this._cardMenu = node.dataset.ankiCardMenu;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {EventListenerCollection} */
         this._fieldEventListeners = new EventListenerCollection();
-        this._fields = null;
+        /** @type {import('settings').AnkiNoteFields} */
+        this._fields = {};
+        /** @type {?string} */
         this._modelChangingTo = null;
+        /** @type {?Element} */
         this._ankiCardFieldsContainer = null;
+        /** @type {boolean} */
         this._cleaned = false;
+        /** @type {import('anki-controller').FieldEntry[]} */
         this._fieldEntries = [];
+        /** @type {AnkiCardSelectController} */
         this._deckController = new AnkiCardSelectController();
+        /** @type {AnkiCardSelectController} */
         this._modelController = new AnkiCardSelectController();
     }
 
+    /** */
     async prepare() {
         const options = await this._settingsController.getOptions();
         const ankiOptions = options.anki;
@@ -448,8 +606,8 @@ class AnkiCardController {
         const cardOptions = this._getCardOptions(ankiOptions, this._cardType);
         if (cardOptions === null) { return; }
         const {deck, model, fields} = cardOptions;
-        this._deckController.prepare(this._node.querySelector('.anki-card-deck'), deck);
-        this._modelController.prepare(this._node.querySelector('.anki-card-model'), model);
+        this._deckController.prepare(/** @type {HTMLSelectElement} */ (this._node.querySelector('.anki-card-deck')), deck);
+        this._modelController.prepare(/** @type {HTMLSelectElement} */ (this._node.querySelector('.anki-card-model')), model);
         this._fields = fields;
 
         this._ankiCardFieldsContainer = this._node.querySelector('.anki-card-fields');
@@ -463,12 +621,14 @@ class AnkiCardController {
         await this.updateAnkiState();
     }
 
+    /** */
     cleanup() {
         this._cleaned = true;
         this._fieldEntries = [];
         this._eventListeners.removeAllEventListeners();
     }
 
+    /** */
     async updateAnkiState() {
         if (this._fields === null) { return; }
         const {deckNames, modelNames} = await this._ankiController.getAnkiData();
@@ -477,41 +637,70 @@ class AnkiCardController {
         this._modelController.setOptionValues(modelNames);
     }
 
+    /**
+     * @returns {boolean}
+     */
     isStale() {
         return (this._cardType !== this._node.dataset.ankiCardType);
     }
 
     // Private
 
+    /**
+     * @param {Event} e
+     */
     _onCardDeckChange(e) {
-        this._setDeck(e.currentTarget.value);
+        const node = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        this._setDeck(node.value);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onCardModelChange(e) {
-        this._setModel(e.currentTarget.value);
+        const node = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        this._setModel(node.value);
     }
 
+    /**
+     * @param {number} index
+     * @param {Event} e
+     */
     _onFieldChange(index, e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         this._validateFieldPermissions(node, index, true);
         this._validateField(node, index);
     }
 
+    /**
+     * @param {number} index
+     * @param {Event} e
+     */
     _onFieldInput(index, e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         this._validateField(node, index);
     }
 
+    /**
+     * @param {number} index
+     * @param {import('dom-data-binder').SettingChangedEvent} e
+     */
     _onFieldSettingChanged(index, e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         this._validateFieldPermissions(node, index, false);
     }
 
-    _onFieldMenuOpen({currentTarget: button, detail: {menu}}) {
-        let {index, fieldName} = button.dataset;
-        index = Number.parseInt(index, 10);
-
-        const defaultValue = this._getDefaultFieldValue(fieldName, index, this._cardType, null);
+    /**
+     * @param {import('popup-menu').MenuOpenEvent} event
+     */
+    _onFieldMenuOpen(event) {
+        const button = /** @type {HTMLElement} */ (event.currentTarget);
+        const {menu} = event.detail;
+        const {index, fieldName} = button.dataset;
+        const indexNumber = typeof index === 'string' ? Number.parseInt(index, 10) : 0;
+        if (typeof fieldName !== 'string') { return; }
+
+        const defaultValue = this._getDefaultFieldValue(fieldName, indexNumber, this._cardType, null);
         if (defaultValue === '') { return; }
 
         const match = /^\{([\w\W]+)\}$/.exec(defaultValue);
@@ -524,14 +713,28 @@ class AnkiCardController {
         item.classList.add('popup-menu-item-bold');
     }
 
-    _onFieldMenuClose({currentTarget: button, detail: {action, item}}) {
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} event
+     */
+    _onFieldMenuClose(event) {
+        const button = /** @type {HTMLElement} */ (event.currentTarget);
+        const {action, item} = event.detail;
         switch (action) {
             case 'setFieldMarker':
-                this._setFieldMarker(button, item.dataset.marker);
+                if (item !== null) {
+                    const {marker} = item.dataset;
+                    if (typeof marker === 'string') {
+                        this._setFieldMarker(button, marker);
+                    }
+                }
                 break;
         }
     }
 
+    /**
+     * @param {HTMLInputElement} node
+     * @param {number} index
+     */
     _validateField(node, index) {
         let valid = (node.dataset.hasPermissions !== 'false');
         if (valid && index === 0 && !AnkiUtil.stringContainsAnyFieldMarker(node.value)) {
@@ -540,12 +743,23 @@ class AnkiCardController {
         node.dataset.invalid = `${!valid}`;
     }
 
+    /**
+     * @param {Element} element
+     * @param {string} marker
+     */
     _setFieldMarker(element, marker) {
-        const input = element.closest('.anki-card-field-value-container').querySelector('.anki-card-field-value');
+        const container = element.closest('.anki-card-field-value-container');
+        if (container === null) { return; }
+        const input = /** @type {HTMLInputElement} */ (container.querySelector('.anki-card-field-value'));
         input.value = `{${marker}}`;
         input.dispatchEvent(new Event('change'));
     }
 
+    /**
+     * @param {import('settings').AnkiOptions} ankiOptions
+     * @param {string} cardType
+     * @returns {?import('settings').AnkiNoteOptions}
+     */
     _getCardOptions(ankiOptions, cardType) {
         switch (cardType) {
             case 'terms': return ankiOptions.terms;
@@ -554,6 +768,7 @@ class AnkiCardController {
         }
     }
 
+    /** */
     _setupFields() {
         this._fieldEventListeners.removeAllEventListeners();
 
@@ -563,15 +778,15 @@ class AnkiCardController {
         for (const [fieldName, fieldValue] of Object.entries(this._fields)) {
             const content = this._settingsController.instantiateTemplateFragment('anki-card-field');
 
-            const fieldNameContainerNode = content.querySelector('.anki-card-field-name-container');
+            const fieldNameContainerNode = /** @type {HTMLElement} */ (content.querySelector('.anki-card-field-name-container'));
             fieldNameContainerNode.dataset.index = `${index}`;
-            const fieldNameNode = content.querySelector('.anki-card-field-name');
+            const fieldNameNode = /** @type {HTMLElement} */ (content.querySelector('.anki-card-field-name'));
             fieldNameNode.textContent = fieldName;
 
-            const valueContainer = content.querySelector('.anki-card-field-value-container');
+            const valueContainer = /** @type {HTMLElement} */ (content.querySelector('.anki-card-field-value-container'));
             valueContainer.dataset.index = `${index}`;
 
-            const inputField = content.querySelector('.anki-card-field-value');
+            const inputField = /** @type {HTMLInputElement} */ (content.querySelector('.anki-card-field-value'));
             inputField.value = fieldValue;
             inputField.dataset.setting = ObjectPropertyAccessor.getPathString(['anki', this._cardType, 'fields', fieldName]);
             this._validateFieldPermissions(inputField, index, false);
@@ -581,7 +796,7 @@ class AnkiCardController {
             this._fieldEventListeners.addEventListener(inputField, 'settingChanged', this._onFieldSettingChanged.bind(this, index), false);
             this._validateField(inputField, index);
 
-            const menuButton = content.querySelector('.anki-card-field-value-menu-button');
+            const menuButton = /** @type {?HTMLElement} */ (content.querySelector('.anki-card-field-value-menu-button'));
             if (menuButton !== null) {
                 if (typeof this._cardMenu !== 'undefined') {
                     menuButton.dataset.menu = this._cardMenu;
@@ -602,15 +817,18 @@ class AnkiCardController {
 
         const ELEMENT_NODE = Node.ELEMENT_NODE;
         const container = this._ankiCardFieldsContainer;
-        for (const node of [...container.childNodes]) {
-            if (node.nodeType === ELEMENT_NODE && node.dataset.persistent === 'true') { continue; }
-            container.removeChild(node);
+        if (container !== null) {
+            for (const node of [...container.childNodes]) {
+                if (node.nodeType === ELEMENT_NODE && node instanceof HTMLElement && node.dataset.persistent === 'true') { continue; }
+                container.removeChild(node);
+            }
+            container.appendChild(totalFragment);
         }
-        container.appendChild(totalFragment);
 
         this._validateFields();
     }
 
+    /** */
     async _validateFields() {
         const token = {};
         this._validateFieldsToken = token;
@@ -633,6 +851,9 @@ class AnkiCardController {
         }
     }
 
+    /**
+     * @param {string} value
+     */
     async _setDeck(value) {
         if (this._deckController.value === value) { return; }
         this._deckController.value = value;
@@ -644,6 +865,9 @@ class AnkiCardController {
         }]);
     }
 
+    /**
+     * @param {string} value
+     */
     async _setModel(value) {
         const select = this._modelController.select;
         if (this._modelChangingTo !== null) {
@@ -671,12 +895,14 @@ class AnkiCardController {
         const cardOptions = this._getCardOptions(options.anki, cardType);
         const oldFields = cardOptions !== null ? cardOptions.fields : null;
 
+        /** @type {import('settings').AnkiNoteFields} */
         const fields = {};
         for (let i = 0, ii = fieldNames.length; i < ii; ++i) {
             const fieldName = fieldNames[i];
             fields[fieldName] = this._getDefaultFieldValue(fieldName, i, cardType, oldFields);
         }
 
+        /** @type {import('settings-modifications').Modification[]} */
         const targets = [
             {
                 action: 'set',
@@ -698,6 +924,9 @@ class AnkiCardController {
         this._setupFields();
     }
 
+    /**
+     * @param {string[]} permissions
+     */
     async _requestPermissions(permissions) {
         try {
             await this._settingsController.permissionsUtil.setPermissionsGranted({permissions}, true);
@@ -706,6 +935,11 @@ class AnkiCardController {
         }
     }
 
+    /**
+     * @param {HTMLInputElement} node
+     * @param {number} index
+     * @param {boolean} request
+     */
     async _validateFieldPermissions(node, index, request) {
         const fieldValue = node.value;
         const permissions = this._ankiController.getRequiredPermissions(fieldValue);
@@ -725,16 +959,19 @@ class AnkiCardController {
         this._validateField(node, index);
     }
 
+    /**
+     * @param {import('settings-controller').PermissionsChangedEvent} details
+     */
     _onPermissionsChanged({permissions: {permissions}}) {
         const permissionsSet = new Set(permissions);
         for (let i = 0, ii = this._fieldEntries.length; i < ii; ++i) {
             const {inputField} = this._fieldEntries[i];
-            let {requiredPermission} = inputField.dataset;
+            const {requiredPermission} = inputField.dataset;
             if (typeof requiredPermission !== 'string') { continue; }
-            requiredPermission = (requiredPermission.length === 0 ? [] : requiredPermission.split(' '));
+            const requiredPermissionArray = (requiredPermission.length === 0 ? [] : requiredPermission.split(' '));
 
             let hasPermissions = true;
-            for (const permission of requiredPermission) {
+            for (const permission of requiredPermissionArray) {
                 if (!permissionsSet.has(permission)) {
                     hasPermissions = false;
                     break;
@@ -746,6 +983,13 @@ class AnkiCardController {
         }
     }
 
+    /**
+     * @param {string} fieldName
+     * @param {number} index
+     * @param {string} cardType
+     * @param {?import('settings').AnkiNoteFields} oldFields
+     * @returns {string}
+     */
     _getDefaultFieldValue(fieldName, index, cardType, oldFields) {
         if (
             typeof oldFields === 'object' &&
@@ -783,9 +1027,9 @@ class AnkiCardController {
                 pattern += name.replace(hyphenPattern, '[-_ ]*');
             }
             pattern += ')$';
-            pattern = new RegExp(pattern, 'i');
+            const patternRegExp = new RegExp(pattern, 'i');
 
-            if (pattern.test(fieldName)) {
+            if (patternRegExp.test(fieldName)) {
                 return `{${marker}}`;
             }
         }
@@ -796,14 +1040,21 @@ class AnkiCardController {
 
 class AnkiCardSelectController {
     constructor() {
+        /** @type {?string} */
         this._value = null;
+        /** @type {?HTMLSelectElement} */
         this._select = null;
-        this._optionValues = null;
+        /** @type {string[]} */
+        this._optionValues = [];
+        /** @type {boolean} */
         this._hasExtraOption = false;
+        /** @type {boolean} */
         this._selectNeedsUpdate = false;
     }
 
+    /** @type {string} */
     get value() {
+        if (this._value === null) { throw new Error('Invalid value'); }
         return this._value;
     }
 
@@ -812,16 +1063,25 @@ class AnkiCardSelectController {
         this._updateSelect();
     }
 
+    /** @type {HTMLSelectElement} */
     get select() {
+        if (this._select === null) { throw new Error('Invalid value'); }
         return this._select;
     }
 
+    /**
+     * @param {HTMLSelectElement} select
+     * @param {string} value
+     */
     prepare(select, value) {
         this._select = select;
         this._value = value;
         this._updateSelect();
     }
 
+    /**
+     * @param {string[]} optionValues
+     */
     setOptionValues(optionValues) {
         this._optionValues = optionValues;
         this._selectNeedsUpdate = true;
@@ -830,8 +1090,11 @@ class AnkiCardSelectController {
 
     // Private
 
+    /** */
     _updateSelect() {
+        const select = this._select;
         const value = this._value;
+        if (select === null || value === null) { return; }
         let optionValues = this._optionValues;
         const hasOptionValues = Array.isArray(optionValues) && optionValues.length > 0;
 
@@ -844,7 +1107,6 @@ class AnkiCardSelectController {
             optionValues = [...optionValues, value];
         }
 
-        const select = this._select;
         if (this._selectNeedsUpdate || hasExtraOption !== this._hasExtraOption) {
             this._setSelectOptions(select, optionValues);
             select.value = value;
@@ -859,6 +1121,10 @@ class AnkiCardSelectController {
         }
     }
 
+    /**
+     * @param {HTMLSelectElement} select
+     * @param {string[]} optionValues
+     */
     _setSelectOptions(select, optionValues) {
         const fragment = document.createDocumentFragment();
         for (const optionValue of optionValues) {
diff --git a/ext/js/pages/settings/anki-templates-controller.js b/ext/js/pages/settings/anki-templates-controller.js
index e66def9fed..0c4fafd45b 100644
--- a/ext/js/pages/settings/anki-templates-controller.js
+++ b/ext/js/pages/settings/anki-templates-controller.js
@@ -22,33 +22,51 @@
  */
 
 class AnkiTemplatesController {
+    /**
+     * @param {SettingsController} settingsController
+     * @param {ModalController} modalController
+     * @param {AnkiController} ankiController
+     */
     constructor(settingsController, modalController, ankiController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {ModalController} */
         this._modalController = modalController;
+        /** @type {AnkiController} */
         this._ankiController = ankiController;
+        /** @type {?import('dictionary').TermDictionaryEntry} */
         this._cachedDictionaryEntryValue = null;
+        /** @type {?string} */
         this._cachedDictionaryEntryText = null;
+        /** @type {?string} */
         this._defaultFieldTemplates = null;
+        /** @type {?HTMLTextAreaElement} */
         this._fieldTemplatesTextarea = null;
+        /** @type {?HTMLElement} */
         this._compileResultInfo = null;
+        /** @type {?HTMLInputElement} */
         this._renderFieldInput = null;
+        /** @type {?HTMLElement} */
         this._renderResult = null;
+        /** @type {?Modal} */
         this._fieldTemplateResetModal = null;
+        /** @type {AnkiNoteBuilder} */
         this._ankiNoteBuilder = new AnkiNoteBuilder({japaneseUtil: new JapaneseUtil(null)});
     }
 
+    /** */
     async prepare() {
         this._defaultFieldTemplates = await yomichan.api.getDefaultAnkiFieldTemplates();
 
-        this._fieldTemplatesTextarea = document.querySelector('#anki-card-templates-textarea');
-        this._compileResultInfo = document.querySelector('#anki-card-templates-compile-result');
-        this._renderFieldInput = document.querySelector('#anki-card-templates-test-field-input');
-        this._renderTextInput = document.querySelector('#anki-card-templates-test-text-input');
-        this._renderResult = document.querySelector('#anki-card-templates-render-result');
-        const menuButton = document.querySelector('#anki-card-templates-test-field-menu-button');
-        const testRenderButton = document.querySelector('#anki-card-templates-test-render-button');
-        const resetButton = document.querySelector('#anki-card-templates-reset-button');
-        const resetConfirmButton = document.querySelector('#anki-card-templates-reset-button-confirm');
+        this._fieldTemplatesTextarea = /** @type {HTMLTextAreaElement} */ (document.querySelector('#anki-card-templates-textarea'));
+        this._compileResultInfo = /** @type {HTMLElement} */ (document.querySelector('#anki-card-templates-compile-result'));
+        this._renderFieldInput = /** @type {HTMLInputElement} */ (document.querySelector('#anki-card-templates-test-field-input'));
+        this._renderTextInput = /** @type {HTMLInputElement} */ (document.querySelector('#anki-card-templates-test-text-input'));
+        this._renderResult = /** @type {HTMLElement} */ (document.querySelector('#anki-card-templates-render-result'));
+        const menuButton = /** @type {HTMLButtonElement} */ (document.querySelector('#anki-card-templates-test-field-menu-button'));
+        const testRenderButton = /** @type {HTMLButtonElement} */ (document.querySelector('#anki-card-templates-test-render-button'));
+        const resetButton = /** @type {HTMLButtonElement} */ (document.querySelector('#anki-card-templates-reset-button'));
+        const resetConfirmButton = /** @type {HTMLButtonElement} */ (document.querySelector('#anki-card-templates-reset-button-confirm'));
         this._fieldTemplateResetModal = this._modalController.getModal('anki-card-templates-reset');
 
         this._fieldTemplatesTextarea.addEventListener('change', this._onChanged.bind(this), false);
@@ -56,44 +74,71 @@ class AnkiTemplatesController {
         resetButton.addEventListener('click', this._onReset.bind(this), false);
         resetConfirmButton.addEventListener('click', this._onResetConfirm.bind(this), false);
         if (menuButton !== null) {
-            menuButton.addEventListener('menuClose', this._onFieldMenuClose.bind(this), false);
+            menuButton.addEventListener(
+                /** @type {string} */ ('menuClose'),
+                /** @type {EventListener} */ (this._onFieldMenuClose.bind(this)),
+                false
+            );
         }
 
         this._settingsController.on('optionsChanged', this._onOptionsChanged.bind(this));
 
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
     // Private
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         let templates = options.anki.fieldTemplates;
-        if (typeof templates !== 'string') { templates = this._defaultFieldTemplates; }
-        this._fieldTemplatesTextarea.value = templates;
+        if (typeof templates !== 'string') {
+            templates = this._defaultFieldTemplates;
+            if (typeof templates !== 'string') { templates = ''; }
+        }
+        /** @type {HTMLTextAreaElement} */ (this._fieldTemplatesTextarea).value = templates;
 
         this._onValidateCompile();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onReset(e) {
         e.preventDefault();
-        this._fieldTemplateResetModal.setVisible(true);
+        if (this._fieldTemplateResetModal !== null) {
+            this._fieldTemplateResetModal.setVisible(true);
+        }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onResetConfirm(e) {
         e.preventDefault();
 
-        this._fieldTemplateResetModal.setVisible(false);
+        if (this._fieldTemplateResetModal !== null) {
+            this._fieldTemplateResetModal.setVisible(false);
+        }
 
         const value = this._defaultFieldTemplates;
 
-        this._fieldTemplatesTextarea.value = value;
-        this._fieldTemplatesTextarea.dispatchEvent(new Event('change'));
+        const textarea = /** @type {HTMLTextAreaElement} */ (this._fieldTemplatesTextarea);
+        textarea.value = typeof value === 'string' ? value : '';
+        textarea.dispatchEvent(new Event('change'));
     }
 
+    /**
+     * @param {Event} e
+     */
     async _onChanged(e) {
         // Get value
-        let templates = e.currentTarget.value;
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        /** @type {?string} */
+        let templates = element.value;
         if (templates === this._defaultFieldTemplates) {
             // Default
             templates = null;
@@ -106,34 +151,55 @@ class AnkiTemplatesController {
         this._onValidateCompile();
     }
 
+    /** */
     _onValidateCompile() {
+        if (this._compileResultInfo === null) { return; }
         this._validate(this._compileResultInfo, '{expression}', 'term-kanji', false, true);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onRender(e) {
         e.preventDefault();
 
-        const field = this._renderFieldInput.value;
-        const infoNode = this._renderResult;
+        const field = /** @type {HTMLInputElement} */ (this._renderFieldInput).value;
+        const infoNode = /** @type {HTMLElement} */ (this._renderResult);
         infoNode.hidden = true;
         this._cachedDictionaryEntryText = null;
         this._validate(infoNode, field, 'term-kanji', true, false);
     }
 
-    _onFieldMenuClose({currentTarget: button, detail: {action, item}}) {
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} event
+     */
+    _onFieldMenuClose({detail: {action, item}}) {
         switch (action) {
             case 'setFieldMarker':
-                this._setFieldMarker(button, item.dataset.marker);
+                {
+                    const {marker} = /** @type {HTMLElement} */ (item).dataset;
+                    if (typeof marker === 'string') {
+                        this._setFieldMarker(marker);
+                    }
+                }
                 break;
         }
     }
 
-    _setFieldMarker(element, marker) {
-        const input = this._renderFieldInput;
+    /**
+     * @param {string} marker
+     */
+    _setFieldMarker(marker) {
+        const input = /** @type {HTMLInputElement} */ (this._renderFieldInput);
         input.value = `{${marker}}`;
         input.dispatchEvent(new Event('change'));
     }
 
+    /**
+     * @param {string} text
+     * @param {import('settings').OptionsContext} optionsContext
+     * @returns {Promise<?{dictionaryEntry: import('dictionary').TermDictionaryEntry, text: string}>}
+     */
     async _getDictionaryEntry(text, optionsContext) {
         if (this._cachedDictionaryEntryText !== text) {
             const {dictionaryEntries} = await yomichan.api.termsFind(text, {}, optionsContext);
@@ -143,19 +209,28 @@ class AnkiTemplatesController {
             this._cachedDictionaryEntryText = text;
         }
         return {
-            dictionaryEntry: this._cachedDictionaryEntryValue,
+            dictionaryEntry: /** @type {import('dictionary').TermDictionaryEntry} */ (this._cachedDictionaryEntryValue),
             text: this._cachedDictionaryEntryText
         };
     }
 
+    /**
+     * @param {HTMLElement} infoNode
+     * @param {string} field
+     * @param {import('anki-templates-internal').CreateModeNoTest} mode
+     * @param {boolean} showSuccessResult
+     * @param {boolean} invalidateInput
+     */
     async _validate(infoNode, field, mode, showSuccessResult, invalidateInput) {
+        /** @type {Error[]} */
         const allErrors = [];
-        const text = this._renderTextInput.value || '';
+        const text = /** @type {HTMLInputElement} */ (this._renderTextInput).value;
         let result = `No definition found for ${text}`;
         try {
             const optionsContext = this._settingsController.getOptionsContext();
-            const {dictionaryEntry, text: sentenceText} = await this._getDictionaryEntry(text, optionsContext);
-            if (dictionaryEntry !== null) {
+            const data = await this._getDictionaryEntry(text, optionsContext);
+            if (data !== null) {
+                const {dictionaryEntry, text: sentenceText} = data;
                 const options = await this._settingsController.getOptions();
                 const context = {
                     url: window.location.href,
@@ -170,7 +245,7 @@ class AnkiTemplatesController {
                 let template = options.anki.fieldTemplates;
                 if (typeof template !== 'string') { template = this._defaultFieldTemplates; }
                 const {general: {resultOutputMode, glossaryLayoutMode, compactTags}} = options;
-                const {note, errors} = await this._ankiNoteBuilder.createNote({
+                const {note, errors} = await this._ankiNoteBuilder.createNote(/** @type {import('anki-note-builder').CreateNoteDetails} */ ({
                     dictionaryEntry,
                     mode,
                     context,
@@ -183,28 +258,29 @@ class AnkiTemplatesController {
                     resultOutputMode,
                     glossaryLayoutMode,
                     compactTags
-                });
+                }));
                 result = note.fields.field;
                 allErrors.push(...errors);
             }
         } catch (e) {
-            allErrors.push(e);
+            allErrors.push(e instanceof Error ? e : new Error(`${e}`));
         }
 
+        /**
+         * @param {Error} e
+         * @returns {string}
+         */
         const errorToMessageString = (e) => {
-            if (isObject(e)) {
-                let v = e.data;
-                if (isObject(v)) {
-                    v = v.error;
-                    if (isObject(v)) {
-                        e = v;
+            if (e instanceof ExtensionError) {
+                const v = e.data;
+                if (typeof v === 'object' && v !== null) {
+                    const v2 = /** @type {import('core').UnknownObject} */ (v).error;
+                    if (v2 instanceof Error) {
+                        return v2.message;
                     }
                 }
-
-                v = e.message;
-                if (typeof v === 'string') { return v; }
             }
-            return `${e}`;
+            return e.message;
         };
 
         const hasError = allErrors.length > 0;
@@ -212,7 +288,7 @@ class AnkiTemplatesController {
         infoNode.textContent = hasError ? allErrors.map(errorToMessageString).join('\n') : (showSuccessResult ? result : '');
         infoNode.classList.toggle('text-danger', hasError);
         if (invalidateInput) {
-            this._fieldTemplatesTextarea.dataset.invalid = `${hasError}`;
+            /** @type {HTMLTextAreaElement} */ (this._fieldTemplatesTextarea).dataset.invalid = `${hasError}`;
         }
     }
 }
diff --git a/ext/js/pages/settings/audio-controller.js b/ext/js/pages/settings/audio-controller.js
index 82caff74ff..2730dddde3 100644
--- a/ext/js/pages/settings/audio-controller.js
+++ b/ext/js/pages/settings/audio-controller.js
@@ -20,48 +20,71 @@
  * AudioSystem
  */
 
+/**
+ * @augments EventDispatcher<import('audio-controller').EventType>
+ */
 class AudioController extends EventDispatcher {
+    /**
+     * @param {SettingsController} settingsController
+     * @param {ModalController} modalController
+     */
     constructor(settingsController, modalController) {
         super();
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {ModalController} */
         this._modalController = modalController;
+        /** @type {AudioSystem} */
         this._audioSystem = new AudioSystem();
+        /** @type {?HTMLElement} */
         this._audioSourceContainer = null;
+        /** @type {?HTMLButtonElement} */
         this._audioSourceAddButton = null;
+        /** @type {AudioSourceEntry[]} */
         this._audioSourceEntries = [];
+        /** @type {?HTMLInputElement} */
         this._voiceTestTextInput = null;
+        /** @type {import('audio-controller').VoiceInfo[]} */
         this._voices = [];
     }
 
+    /** @type {SettingsController} */
     get settingsController() {
         return this._settingsController;
     }
 
+    /** @type {ModalController} */
     get modalController() {
         return this._modalController;
     }
 
+    /** */
     async prepare() {
         this._audioSystem.prepare();
 
-        this._voiceTestTextInput = document.querySelector('#text-to-speech-voice-test-text');
-        this._audioSourceContainer = document.querySelector('#audio-source-list');
-        this._audioSourceAddButton = document.querySelector('#audio-source-add');
+        this._voiceTestTextInput = /** @type {HTMLInputElement} */ (document.querySelector('#text-to-speech-voice-test-text'));
+        this._audioSourceContainer = /** @type {HTMLElement} */ (document.querySelector('#audio-source-list'));
+        this._audioSourceAddButton = /** @type {HTMLButtonElement} */ (document.querySelector('#audio-source-add'));
         this._audioSourceContainer.textContent = '';
+        const testButton = /** @type {HTMLButtonElement} */ (document.querySelector('#text-to-speech-voice-test'));
 
         this._audioSourceAddButton.addEventListener('click', this._onAddAudioSource.bind(this), false);
 
-        this._audioSystem.on('voiceschanged', this._updateTextToSpeechVoices.bind(this), false);
+        this._audioSystem.on('voiceschanged', this._updateTextToSpeechVoices.bind(this));
         this._updateTextToSpeechVoices();
 
-        document.querySelector('#text-to-speech-voice-test').addEventListener('click', this._onTestTextToSpeech.bind(this), false);
+        testButton.addEventListener('click', this._onTestTextToSpeech.bind(this), false);
 
         this._settingsController.on('optionsChanged', this._onOptionsChanged.bind(this));
 
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
+    /**
+     * @param {AudioSourceEntry} entry
+     */
     async removeSource(entry) {
         const {index} = entry;
         this._audioSourceEntries.splice(index, 1);
@@ -79,16 +102,25 @@ class AudioController extends EventDispatcher {
         }]);
     }
 
+    /**
+     * @returns {import('audio-controller').VoiceInfo[]}
+     */
     getVoices() {
         return this._voices;
     }
 
+    /**
+     * @param {string} voice
+     */
     setTestVoice(voice) {
-        this._voiceTestTextInput.dataset.voice = voice;
+        /** @type {HTMLInputElement} */ (this._voiceTestTextInput).dataset.voice = voice;
     }
 
     // Private
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         for (const entry of this._audioSourceEntries) {
             entry.cleanup();
@@ -101,15 +133,18 @@ class AudioController extends EventDispatcher {
         }
     }
 
+    /** */
     _onAddAudioSource() {
         this._addAudioSource();
     }
 
+    /** */
     _onTestTextToSpeech() {
         try {
-            const text = this._voiceTestTextInput.value || '';
-            const voiceUri = this._voiceTestTextInput.dataset.voice;
-            const audio = this._audioSystem.createTextToSpeechAudio(text, voiceUri);
+            const input = /** @type {HTMLInputElement} */ (this._voiceTestTextInput);
+            const text = input.value || '';
+            const voiceUri = input.dataset.voice;
+            const audio = this._audioSystem.createTextToSpeechAudio(text, typeof voiceUri === 'string' ? voiceUri : '');
             audio.volume = 1.0;
             audio.play();
         } catch (e) {
@@ -117,6 +152,7 @@ class AudioController extends EventDispatcher {
         }
     }
 
+    /** */
     _updateTextToSpeechVoices() {
         const voices = (
             typeof speechSynthesis !== 'undefined' ?
@@ -132,6 +168,11 @@ class AudioController extends EventDispatcher {
         this.trigger('voicesUpdated');
     }
 
+    /**
+     * @param {import('audio-controller').VoiceInfo} a
+     * @param {import('audio-controller').VoiceInfo} b
+     * @returns {number}
+     */
     _textToSpeechVoiceCompare(a, b) {
         if (a.isJapanese) {
             if (!b.isJapanese) { return -1; }
@@ -148,6 +189,10 @@ class AudioController extends EventDispatcher {
         return a.index - b.index;
     }
 
+    /**
+     * @param {string} languageTag
+     * @returns {boolean}
+     */
     _languageTagIsJapanese(languageTag) {
         return (
             languageTag.startsWith('ja_') ||
@@ -156,15 +201,23 @@ class AudioController extends EventDispatcher {
         );
     }
 
+    /**
+     * @param {number} index
+     * @param {import('settings').AudioSourceOptions} source
+     */
     _createAudioSourceEntry(index, source) {
-        const node = this._settingsController.instantiateTemplate('audio-source');
+        const node = /** @type {HTMLElement} */ (this._settingsController.instantiateTemplate('audio-source'));
         const entry = new AudioSourceEntry(this, index, source, node);
         this._audioSourceEntries.push(entry);
-        this._audioSourceContainer.appendChild(node);
+        /** @type {HTMLElement} */ (this._audioSourceContainer).appendChild(node);
         entry.prepare();
     }
 
+    /**
+     * @returns {import('settings').AudioSourceType}
+     */
     _getUnusedAudioSourceType() {
+        /** @type {import('settings').AudioSourceType[]} */
         const typesAvailable = [
             'jpod101',
             'jpod101-alternate',
@@ -179,8 +232,10 @@ class AudioController extends EventDispatcher {
         return typesAvailable[0];
     }
 
+    /** */
     async _addAudioSource() {
         const type = this._getUnusedAudioSourceType();
+        /** @type {import('settings').AudioSourceOptions} */
         const source = {type, url: '', voice: ''};
         const index = this._audioSourceEntries.length;
         this._createAudioSourceEntry(index, source);
@@ -195,19 +250,36 @@ class AudioController extends EventDispatcher {
 }
 
 class AudioSourceEntry {
+    /**
+     * @param {AudioController} parent
+     * @param {number} index
+     * @param {import('settings').AudioSourceOptions} source
+     * @param {HTMLElement} node
+     */
     constructor(parent, index, source, node) {
+        /** @type {AudioController} */
         this._parent = parent;
+        /** @type {number} */
         this._index = index;
+        /** @type {import('settings').AudioSourceType} */
         this._type = source.type;
+        /** @type {string} */
         this._url = source.url;
+        /** @type {string} */
         this._voice = source.voice;
+        /** @type {HTMLElement} */
         this._node = node;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?HTMLSelectElement} */
         this._typeSelect = null;
+        /** @type {?HTMLInputElement} */
         this._urlInput = null;
+        /** @type {?HTMLSelectElement} */
         this._voiceSelect = null;
     }
 
+    /** @type {number} */
     get index() {
         return this._index;
     }
@@ -216,17 +288,19 @@ class AudioSourceEntry {
         this._index = value;
     }
 
+    /** @type {import('settings').AudioSourceType} */
     get type() {
         return this._type;
     }
 
+    /** */
     prepare() {
         this._updateTypeParameter();
 
-        const menuButton = this._node.querySelector('.audio-source-menu-button');
-        this._typeSelect = this._node.querySelector('.audio-source-type-select');
-        this._urlInput = this._node.querySelector('.audio-source-parameter-container[data-field=url] .audio-source-parameter');
-        this._voiceSelect = this._node.querySelector('.audio-source-parameter-container[data-field=voice] .audio-source-parameter');
+        const menuButton = /** @type {HTMLButtonElement} */ (this._node.querySelector('.audio-source-menu-button'));
+        this._typeSelect = /** @type {HTMLSelectElement} */ (this._node.querySelector('.audio-source-type-select'));
+        this._urlInput = /** @type {HTMLInputElement} */ (this._node.querySelector('.audio-source-parameter-container[data-field=url] .audio-source-parameter'));
+        this._voiceSelect = /** @type {HTMLSelectElement} */ (this._node.querySelector('.audio-source-parameter-container[data-field=voice] .audio-source-parameter'));
 
         this._typeSelect.value = this._type;
         this._urlInput.value = this._url;
@@ -240,6 +314,7 @@ class AudioSourceEntry {
         this._onVoicesUpdated();
     }
 
+    /** */
     cleanup() {
         if (this._node.parentNode !== null) {
             this._node.parentNode.removeChild(this._node);
@@ -249,7 +324,9 @@ class AudioSourceEntry {
 
     // Private
 
+    /** */
     _onVoicesUpdated() {
+        if (this._voiceSelect === null) { return; }
         const voices = this._parent.getVoices();
 
         const fragment = document.createDocumentFragment();
@@ -271,18 +348,35 @@ class AudioSourceEntry {
         this._voiceSelect.value = this._voice;
     }
 
+    /**
+     * @param {Event} e
+     */
     _onTypeSelectChange(e) {
-        this._setType(e.currentTarget.value);
+        const element = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        const value = this._normalizeAudioSourceType(element.value);
+        if (value === null) { return; }
+        this._setType(value);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onUrlInputChange(e) {
-        this._setUrl(e.currentTarget.value);
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        this._setUrl(element.value);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onVoiceSelectChange(e) {
-        this._setVoice(e.currentTarget.value);
+        const element = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        this._setVoice(element.value);
     }
 
+    /**
+     * @param {import('popup-menu').MenuOpenEvent} e
+     */
     _onMenuOpen(e) {
         const {menu} = e.detail;
 
@@ -296,9 +390,15 @@ class AudioSourceEntry {
                 break;
         }
 
-        menu.bodyNode.querySelector('.popup-menu-item[data-menu-action=help]').hidden = !hasHelp;
+        const helpNode = /** @type {?HTMLElement} */ (menu.bodyNode.querySelector('.popup-menu-item[data-menu-action=help]'));
+        if (helpNode !== null) {
+            helpNode.hidden = !hasHelp;
+        }
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuClose(e) {
         switch (e.detail.action) {
             case 'help':
@@ -310,22 +410,32 @@ class AudioSourceEntry {
         }
     }
 
+    /**
+     * @param {import('settings').AudioSourceType} value
+     */
     async _setType(value) {
         this._type = value;
         this._updateTypeParameter();
         await this._parent.settingsController.setProfileSetting(`audio.sources[${this._index}].type`, value);
     }
 
+    /**
+     * @param {string} value
+     */
     async _setUrl(value) {
         this._url = value;
         await this._parent.settingsController.setProfileSetting(`audio.sources[${this._index}].url`, value);
     }
 
+    /**
+     * @param {string} value
+     */
     async _setVoice(value) {
         this._voice = value;
         await this._parent.settingsController.setProfileSetting(`audio.sources[${this._index}].voice`, value);
     }
 
+    /** */
     _updateTypeParameter() {
         let field = null;
         switch (this._type) {
@@ -338,11 +448,14 @@ class AudioSourceEntry {
                 field = 'voice';
                 break;
         }
-        for (const node of this._node.querySelectorAll('.audio-source-parameter-container')) {
+        for (const node of /** @type {NodeListOf<HTMLElement>} */ (this._node.querySelectorAll('.audio-source-parameter-container'))) {
             node.hidden = (field === null || node.dataset.field !== field);
         }
     }
 
+    /**
+     * @param {import('settings').AudioSourceType} type
+     */
     _showHelp(type) {
         switch (type) {
             case 'custom':
@@ -359,7 +472,31 @@ class AudioSourceEntry {
         }
     }
 
+    /**
+     * @param {string} name
+     */
     _showModal(name) {
-        this._parent.modalController.getModal(name).setVisible(true);
+        const modal = this._parent.modalController.getModal(name);
+        if (modal === null) { return; }
+        modal.setVisible(true);
+    }
+
+    /**
+     * @param {string} value
+     * @returns {?import('settings').AudioSourceType}
+     */
+    _normalizeAudioSourceType(value) {
+        switch (value) {
+            case 'jpod101':
+            case 'jpod101-alternate':
+            case 'jisho':
+            case 'text-to-speech':
+            case 'text-to-speech-reading':
+            case 'custom':
+            case 'custom-json':
+                return value;
+            default:
+                return null;
+        }
     }
 }
diff --git a/ext/js/pages/settings/backup-controller.js b/ext/js/pages/settings/backup-controller.js
index b4de01bfd4..7de79f17a5 100644
--- a/ext/js/pages/settings/backup-controller.js
+++ b/ext/js/pages/settings/backup-controller.js
@@ -23,15 +23,28 @@
  */
 
 class BackupController {
+    /**
+     * @param {SettingsController} settingsController
+     * @param {?ModalController} modalController
+     */
     constructor(settingsController, modalController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?ModalController} */
         this._modalController = modalController;
+        /** @type {?import('core').TokenObject} */
         this._settingsExportToken = null;
+        /** @type {?() => void} */
         this._settingsExportRevoke = null;
+        /** @type {number} */
         this._currentVersion = 0;
+        /** @type {?Modal} */
         this._settingsResetModal = null;
+        /** @type {?Modal} */
         this._settingsImportErrorModal = null;
+        /** @type {?Modal} */
         this._settingsImportWarningModal = null;
+        /** @type {?OptionsUtil} */
         this._optionsUtil = null;
         try {
             this._optionsUtil = new OptionsUtil();
@@ -40,6 +53,7 @@ class BackupController {
         }
     }
 
+    /** */
     async prepare() {
         if (this._optionsUtil !== null) {
             await this._optionsUtil.prepare();
@@ -60,13 +74,27 @@ class BackupController {
 
     // Private
 
-    _addNodeEventListener(selector, ...args) {
+    /**
+     * @param {string} selector
+     * @param {string} eventName
+     * @param {(event: Event) => void} callback
+     * @param {boolean} capture
+     */
+    _addNodeEventListener(selector, eventName, callback, capture) {
         const node = document.querySelector(selector);
         if (node === null) { return; }
 
-        node.addEventListener(...args);
+        node.addEventListener(eventName, callback, capture);
     }
 
+    /**
+     * @param {Date} date
+     * @param {string} dateSeparator
+     * @param {string} dateTimeSeparator
+     * @param {string} timeSeparator
+     * @param {number} resolution
+     * @returns {string}
+     */
     _getSettingsExportDateString(date, dateSeparator, dateTimeSeparator, timeSeparator, resolution) {
         const values = [
             date.getUTCFullYear().toString(),
@@ -84,6 +112,10 @@ class BackupController {
         return values.slice(0, resolution * 2 - 1).join('');
     }
 
+    /**
+     * @param {Date} date
+     * @returns {Promise<import('backup-controller').BackupData>}
+     */
     async _getSettingsExportData(date) {
         const optionsFull = await this._settingsController.getOptionsFull();
         const environment = await yomichan.api.getEnvironmentInfo();
@@ -111,11 +143,19 @@ class BackupController {
         return data;
     }
 
+    /**
+     * @param {Blob} blob
+     * @param {string} fileName
+     */
     _saveBlob(blob, fileName) {
-        if (typeof navigator === 'object' && typeof navigator.msSaveBlob === 'function') {
-            if (navigator.msSaveBlob(blob)) {
-                return;
-            }
+        if (
+            typeof navigator === 'object' && navigator !== null &&
+            // @ts-ignore - call for legacy Edge
+            typeof navigator.msSaveBlob === 'function' &&
+            // @ts-ignore - call for legacy Edge
+            navigator.msSaveBlob(blob)
+        ) {
+            return;
         }
 
         const blobUrl = URL.createObjectURL(blob);
@@ -137,6 +177,7 @@ class BackupController {
         setTimeout(revoke, 60000);
     }
 
+    /** */
     async _onSettingsExportClick() {
         if (this._settingsExportRevoke !== null) {
             this._settingsExportRevoke();
@@ -145,6 +186,7 @@ class BackupController {
 
         const date = new Date(Date.now());
 
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._settingsExportToken = token;
         const data = await this._getSettingsExportData(date);
@@ -159,10 +201,14 @@ class BackupController {
         this._saveBlob(blob, fileName);
     }
 
+    /**
+     * @param {File} file
+     * @returns {Promise<ArrayBuffer>}
+     */
     _readFileArrayBuffer(file) {
         return new Promise((resolve, reject) => {
             const reader = new FileReader();
-            reader.onload = () => resolve(reader.result);
+            reader.onload = () => resolve(/** @type {ArrayBuffer} */ (reader.result));
             reader.onerror = () => reject(reader.error);
             reader.readAsArrayBuffer(file);
         });
@@ -170,19 +216,33 @@ class BackupController {
 
     // Importing
 
+    /**
+     * @param {import('settings').Options} optionsFull
+     */
     async _settingsImportSetOptionsFull(optionsFull) {
         await this._settingsController.setAllSettings(optionsFull);
     }
 
+    /**
+     * @param {Error} error
+     */
     _showSettingsImportError(error) {
         log.error(error);
-        document.querySelector('#settings-import-error-message').textContent = `${error}`;
-        this._settingsImportErrorModal.setVisible(true);
+        const element = /** @type {HTMLElement} */ (document.querySelector('#settings-import-error-message'));
+        element.textContent = `${error}`;
+        if (this._settingsImportErrorModal !== null) {
+            this._settingsImportErrorModal.setVisible(true);
+        }
     }
 
+    /**
+     * @param {Set<string>} warnings
+     * @returns {Promise<import('backup-controller').ShowSettingsImportWarningsResult>}
+     */
     async _showSettingsImportWarnings(warnings) {
         const modal = this._settingsImportWarningModal;
-        const buttons = document.querySelectorAll('.settings-import-warning-import-button');
+        if (modal === null) { return {result: false}; }
+        const buttons = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.settings-import-warning-import-button'));
         const messageContainer = document.querySelector('#settings-import-warning-message');
         if (buttons.length === 0 || messageContainer === null) {
             return {result: false};
@@ -203,20 +263,30 @@ class BackupController {
 
         // Wait for modal to close
         return new Promise((resolve) => {
+            /**
+             * @param {MouseEvent} e
+             */
             const onButtonClick = (e) => {
+                const element = /** @type {HTMLElement} */ (e.currentTarget);
                 e.preventDefault();
                 complete({
                     result: true,
-                    sanitize: e.currentTarget.dataset.importSanitize === 'true'
+                    sanitize: element.dataset.importSanitize === 'true'
                 });
                 modal.setVisible(false);
             };
+            /**
+             * @param {import('panel-element').VisibilityChangedEvent} details
+             */
             const onModalVisibilityChanged = ({visible}) => {
                 if (visible) { return; }
                 complete({result: false});
             };
 
             let completed = false;
+            /**
+             * @param {import('backup-controller').ShowSettingsImportWarningsResult} result
+             */
             const complete = (result) => {
                 if (completed) { return; }
                 completed = true;
@@ -237,6 +307,10 @@ class BackupController {
         });
     }
 
+    /**
+     * @param {string} urlString
+     * @returns {boolean}
+     */
     _isLocalhostUrl(urlString) {
         try {
             const url = new URL(urlString);
@@ -257,6 +331,11 @@ class BackupController {
         return false;
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     * @param {boolean} dryRun
+     * @returns {string[]}
+     */
     _settingsImportSanitizeProfileOptions(options, dryRun) {
         const warnings = [];
 
@@ -299,6 +378,11 @@ class BackupController {
         return warnings;
     }
 
+    /**
+     * @param {import('settings').Options} optionsFull
+     * @param {boolean} dryRun
+     * @returns {Set<string>}
+     */
     _settingsImportSanitizeOptions(optionsFull, dryRun) {
         const warnings = new Set();
 
@@ -319,7 +403,12 @@ class BackupController {
         return warnings;
     }
 
+    /**
+     * @param {File} file
+     */
     async _importSettingsFile(file) {
+        if (this._optionsUtil === null) { throw new Error('OptionsUtil invalid'); }
+
         const dataString = ArrayBufferUtil.arrayBufferUtf8Decode(await this._readFileArrayBuffer(file));
         const data = JSON.parse(dataString);
 
@@ -374,31 +463,44 @@ class BackupController {
         await this._settingsImportSetOptionsFull(optionsFull);
     }
 
+    /** */
     _onSettingsImportClick() {
-        document.querySelector('#settings-import-file').click();
+        const element = /** @type {HTMLElement} */ (document.querySelector('#settings-import-file'));
+        element.click();
     }
 
+    /**
+     * @param {Event} e
+     */
     async _onSettingsImportFileChange(e) {
-        const files = e.target.files;
-        if (files.length === 0) { return; }
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        const files = element.files;
+        if (files === null || files.length === 0) { return; }
 
         const file = files[0];
-        e.target.value = null;
+        element.value = '';
         try {
             await this._importSettingsFile(file);
         } catch (error) {
-            this._showSettingsImportError(error);
+            this._showSettingsImportError(error instanceof Error ? error : new Error(`${error}`));
         }
     }
 
     // Resetting
 
+    /** */
     _onSettingsResetClick() {
+        if (this._settingsResetModal === null) { return; }
         this._settingsResetModal.setVisible(true);
     }
 
+    /** */
     async _onSettingsResetConfirmClick() {
-        this._settingsResetModal.setVisible(false);
+        if (this._optionsUtil === null) { throw new Error('OptionsUtil invalid'); }
+
+        if (this._settingsResetModal !== null) {
+            this._settingsResetModal.setVisible(false);
+        }
 
         // Get default options
         const optionsFull = this._optionsUtil.getDefault();
diff --git a/ext/js/pages/settings/collapsible-dictionary-controller.js b/ext/js/pages/settings/collapsible-dictionary-controller.js
index 949df0de1e..14879c085b 100644
--- a/ext/js/pages/settings/collapsible-dictionary-controller.js
+++ b/ext/js/pages/settings/collapsible-dictionary-controller.js
@@ -17,18 +17,29 @@
  */
 
 class CollapsibleDictionaryController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?import('core').TokenObject} */
         this._getDictionaryInfoToken = null;
+        /** @type {Map<string, import('dictionary-importer').Summary>} */
         this._dictionaryInfoMap = new Map();
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?HTMLElement} */
         this._container = null;
+        /** @type {HTMLSelectElement[]} */
         this._selects = [];
+        /** @type {?HTMLSelectElement} */
         this._allSelect = null;
     }
 
+    /** */
     async prepare() {
-        this._container = document.querySelector('#collapsible-dictionary-list');
+        this._container = /** @type {HTMLElement} */ (document.querySelector('#collapsible-dictionary-list'));
 
         await this._onDatabaseUpdated();
 
@@ -39,7 +50,9 @@ class CollapsibleDictionaryController {
 
     // Private
 
+    /** */
     async _onDatabaseUpdated() {
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._getDictionaryInfoToken = token;
         const dictionaries = await this._settingsController.getDictionaryInfo();
@@ -51,10 +64,12 @@ class CollapsibleDictionaryController {
             this._dictionaryInfoMap.set(entry.title, entry);
         }
 
-        const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        await this._onDictionarySettingsReordered();
     }
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         this._eventListeners.removeAllEventListeners();
         this._selects = [];
@@ -76,25 +91,37 @@ class CollapsibleDictionaryController {
             this._selects.push(select);
         }
 
-        this._container.textContent = '';
-        this._container.appendChild(fragment);
+        const container = /** @type {HTMLElement} */ (this._container);
+        container.textContent = '';
+        container.appendChild(fragment);
     }
 
+    /** */
     _onDefinitionsCollapsibleChange() {
         this._updateAllSelectFresh();
     }
 
+    /**
+     * @param {Event} e
+     */
     _onAllSelectChange(e) {
-        const {value} = e.currentTarget;
-        if (value === 'varies') { return; }
-        this._setDefinitionsCollapsibleAll(value);
+        const {value} = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        const value2 = this._normalizeDictionaryDefinitionsCollapsible(value);
+        if (value2 === null) { return; }
+        this._setDefinitionsCollapsibleAll(value2);
     }
 
+    /** */
     async _onDictionarySettingsReordered() {
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
+    /**
+     * @param {DocumentFragment} fragment
+     * @param {import('settings').ProfileOptions} options
+     */
     _setupAllSelect(fragment, options) {
         const select = this._addSelect(fragment, 'All', '');
 
@@ -110,23 +137,33 @@ class CollapsibleDictionaryController {
         this._updateAllSelect(options);
     }
 
+    /**
+     * @param {DocumentFragment} fragment
+     * @param {string} dictionary
+     * @param {string} version
+     * @returns {HTMLSelectElement}
+     */
     _addSelect(fragment, dictionary, version) {
         const node = this._settingsController.instantiateTemplate('collapsible-dictionary-item');
         fragment.appendChild(node);
 
-        const nameNode = node.querySelector('.dictionary-title');
+        const nameNode = /** @type {HTMLElement} */ (node.querySelector('.dictionary-title'));
         nameNode.textContent = dictionary;
 
-        const versionNode = node.querySelector('.dictionary-version');
+        const versionNode = /** @type {HTMLElement} */ (node.querySelector('.dictionary-version'));
         versionNode.textContent = version;
 
-        return node.querySelector('.definitions-collapsible');
+        return /** @type {HTMLSelectElement} */ (node.querySelector('.definitions-collapsible'));
     }
 
+    /** */
     async _updateAllSelectFresh() {
         this._updateAllSelect(await this._settingsController.getOptions());
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     _updateAllSelect(options) {
         let value = null;
         let varies = false;
@@ -139,11 +176,17 @@ class CollapsibleDictionaryController {
             }
         }
 
-        this._allSelect.value = (varies || value === null ? 'varies' : value);
+        if (this._allSelect !== null) {
+            this._allSelect.value = (varies || value === null ? 'varies' : value);
+        }
     }
 
+    /**
+     * @param {import('settings').DictionaryDefinitionsCollapsible} value
+     */
     async _setDefinitionsCollapsibleAll(value) {
         const options = await this._settingsController.getOptions();
+        /** @type {import('settings-modifications').Modification[]} */
         const targets = [];
         const {dictionaries} = options;
         for (let i = 0, ii = dictionaries.length; i < ii; ++i) {
@@ -155,4 +198,21 @@ class CollapsibleDictionaryController {
             select.value = value;
         }
     }
+
+    /**
+     * @param {string} value
+     * @returns {?import('settings').DictionaryDefinitionsCollapsible}
+     */
+    _normalizeDictionaryDefinitionsCollapsible(value) {
+        switch (value) {
+            case 'not-collapsible':
+            case 'expanded':
+            case 'collapsed':
+            case 'force-collapsed':
+            case 'force-expanded':
+                return value;
+            default:
+                return null;
+        }
+    }
 }
\ No newline at end of file
diff --git a/ext/js/pages/settings/dictionary-controller.js b/ext/js/pages/settings/dictionary-controller.js
index 3a70a61419..7c4aae5e79 100644
--- a/ext/js/pages/settings/dictionary-controller.js
+++ b/ext/js/pages/settings/dictionary-controller.js
@@ -21,27 +21,49 @@
  */
 
 class DictionaryEntry {
+    /**
+     * @param {DictionaryController} dictionaryController
+     * @param {DocumentFragment} fragment
+     * @param {number} index
+     * @param {import('dictionary-importer').Summary} dictionaryInfo
+     */
     constructor(dictionaryController, fragment, index, dictionaryInfo) {
+        /** @type {DictionaryController} */
         this._dictionaryController = dictionaryController;
+        /** @type {number} */
         this._index = index;
+        /** @type {import('dictionary-importer').Summary} */
         this._dictionaryInfo = dictionaryInfo;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?import('dictionary-database').DictionaryCountGroup} */
         this._counts = null;
+        /** @type {ChildNode[]} */
         this._nodes = [...fragment.childNodes];
-        this._enabledCheckbox = fragment.querySelector('.dictionary-enabled');
-        this._priorityInput = fragment.querySelector('.dictionary-priority');
-        this._menuButton = fragment.querySelector('.dictionary-menu-button');
-        this._outdatedButton = fragment.querySelector('.dictionary-outdated-button');
-        this._integrityButton = fragment.querySelector('.dictionary-integrity-button');
-        this._titleNode = fragment.querySelector('.dictionary-title');
-        this._versionNode = fragment.querySelector('.dictionary-version');
-        this._titleContainer = fragment.querySelector('.dictionary-item-title-container');
-    }
-
+        /** @type {HTMLInputElement} */
+        this._enabledCheckbox = /** @type {HTMLInputElement} */ (fragment.querySelector('.dictionary-enabled'));
+        /** @type {HTMLInputElement} */
+        this._priorityInput = /** @type {HTMLInputElement} */ (fragment.querySelector('.dictionary-priority'));
+        /** @type {HTMLButtonElement} */
+        this._menuButton = /** @type {HTMLButtonElement} */ (fragment.querySelector('.dictionary-menu-button'));
+        /** @type {HTMLButtonElement} */
+        this._outdatedButton = /** @type {HTMLButtonElement} */ (fragment.querySelector('.dictionary-outdated-button'));
+        /** @type {HTMLButtonElement} */
+        this._integrityButton = /** @type {HTMLButtonElement} */ (fragment.querySelector('.dictionary-integrity-button'));
+        /** @type {HTMLElement} */
+        this._titleNode = /** @type {HTMLElement} */ (fragment.querySelector('.dictionary-title'));
+        /** @type {HTMLElement} */
+        this._versionNode = /** @type {HTMLElement} */ (fragment.querySelector('.dictionary-version'));
+        /** @type {HTMLElement} */
+        this._titleContainer = /** @type {HTMLElement} */ (fragment.querySelector('.dictionary-item-title-container'));
+    }
+
+    /** @type {string} */
     get dictionaryTitle() {
         return this._dictionaryInfo.title;
     }
 
+    /** */
     prepare() {
         const index = this._index;
         const {title, revision, version} = this._dictionaryInfo;
@@ -58,6 +80,7 @@ class DictionaryEntry {
         this._eventListeners.addEventListener(this._integrityButton, 'click', this._onIntegrityButtonClick.bind(this), false);
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
         for (const node of this._nodes) {
@@ -68,17 +91,26 @@ class DictionaryEntry {
         this._nodes = [];
     }
 
+    /**
+     * @param {import('dictionary-database').DictionaryCountGroup} counts
+     */
     setCounts(counts) {
         this._counts = counts;
         this._integrityButton.hidden = false;
     }
 
+    /**
+     * @param {boolean} value
+     */
     setEnabled(value) {
         this._enabledCheckbox.checked = value;
     }
 
     // Private
 
+    /**
+     * @param {import('popup-menu').MenuOpenEvent} e
+     */
     _onMenuOpen(e) {
         const bodyNode = e.detail.menu.bodyNode;
         const count = this._dictionaryController.dictionaryOptionCount;
@@ -87,6 +119,9 @@ class DictionaryEntry {
         this._setMenuActionEnabled(bodyNode, 'moveTo', count > 1);
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuClose(e) {
         switch (e.detail.action) {
             case 'delete':
@@ -107,36 +142,48 @@ class DictionaryEntry {
         }
     }
 
+    /**
+     * @param {import('dom-data-binder').SettingChangedEvent} e
+     */
     _onEnabledChanged(e) {
         const {detail: {value}} = e;
         this._titleContainer.dataset.enabled = `${value}`;
         this._dictionaryController.updateDictionariesEnabled();
     }
 
+    /** */
     _onOutdatedButtonClick() {
         this._showDetails();
     }
 
+    /** */
     _onIntegrityButtonClick() {
         this._showDetails();
     }
 
+    /** */
     _showDetails() {
         const {title, revision, version, prefixWildcardsSupported} = this._dictionaryInfo;
 
         const modal = this._dictionaryController.modalController.getModal('dictionary-details');
+        if (modal === null) { return; }
 
-        modal.node.querySelector('.dictionary-title').textContent = title;
-        modal.node.querySelector('.dictionary-version').textContent = `rev.${revision}`;
-        modal.node.querySelector('.dictionary-outdated-notification').hidden = (version >= 3);
-        modal.node.querySelector('.dictionary-counts').textContent = this._counts !== null ? JSON.stringify(this._counts, null, 4) : '';
-        modal.node.querySelector('.dictionary-prefix-wildcard-searches-supported').checked = prefixWildcardsSupported;
-        this._setupDetails(modal.node.querySelector('.dictionary-details-table'));
+        /** @type {HTMLElement} */ (modal.node.querySelector('.dictionary-title')).textContent = title;
+        /** @type {HTMLElement} */ (modal.node.querySelector('.dictionary-version')).textContent = `rev.${revision}`;
+        /** @type {HTMLElement} */ (modal.node.querySelector('.dictionary-outdated-notification')).hidden = (version >= 3);
+        /** @type {HTMLElement} */ (modal.node.querySelector('.dictionary-counts')).textContent = this._counts !== null ? JSON.stringify(this._counts, null, 4) : '';
+        /** @type {HTMLInputElement} */ (modal.node.querySelector('.dictionary-prefix-wildcard-searches-supported')).checked = prefixWildcardsSupported;
+        this._setupDetails(/** @type {HTMLElement} */ (modal.node.querySelector('.dictionary-details-table')));
 
         modal.setVisible(true);
     }
 
+    /**
+     * @param {Element} detailsTable
+     * @returns {boolean}
+     */
     _setupDetails(detailsTable) {
+        /** @type {[label: string, key: 'author'|'url'|'description'|'attribution'][]} */
         const targets = [
             ['Author', 'author'],
             ['URL', 'url'],
@@ -151,10 +198,10 @@ class DictionaryEntry {
             const info = dictionaryInfo[key];
             if (typeof info !== 'string') { continue; }
 
-            const details = this._dictionaryController.instantiateTemplate('dictionary-details-entry');
+            const details = /** @type {HTMLElement} */ (this._dictionaryController.instantiateTemplate('dictionary-details-entry'));
             details.dataset.type = key;
-            details.querySelector('.dictionary-details-entry-label').textContent = `${label}:`;
-            details.querySelector('.dictionary-details-entry-info').textContent = info;
+            /** @type {HTMLElement} */ (details.querySelector('.dictionary-details-entry-label')).textContent = `${label}:`;
+            /** @type {HTMLElement} */ (details.querySelector('.dictionary-details-entry-info')).textContent = info;
             fragment.appendChild(details);
 
             any = true;
@@ -165,28 +212,40 @@ class DictionaryEntry {
         return any;
     }
 
+    /** */
     _delete() {
         this._dictionaryController.deleteDictionary(this.dictionaryTitle);
     }
 
+    /**
+     * @param {number} offset
+     */
     _move(offset) {
         this._dictionaryController.moveDictionaryOptions(this._index, this._index + offset);
     }
 
+    /**
+     * @param {Element} menu
+     * @param {string} action
+     * @param {boolean} enabled
+     */
     _setMenuActionEnabled(menu, action, enabled) {
-        const element = menu.querySelector(`[data-menu-action="${action}"]`);
+        const element = /** @type {?HTMLButtonElement} */ (menu.querySelector(`[data-menu-action="${action}"]`));
         if (element === null) { return; }
         element.disabled = !enabled;
     }
 
+    /** */
     _showMoveToModal() {
         const {title} = this._dictionaryInfo;
         const count = this._dictionaryController.dictionaryOptionCount;
         const modal = this._dictionaryController.modalController.getModal('dictionary-move-location');
-        const input = modal.node.querySelector('#dictionary-move-location');
+        if (modal === null) { return; }
+        const input = /** @type {HTMLInputElement} */ (modal.node.querySelector('#dictionary-move-location'));
+        const titleNode = /** @type {HTMLElement} */ (modal.node.querySelector('.dictionary-title'));
 
         modal.node.dataset.index = `${this._index}`;
-        modal.node.querySelector('.dictionary-title').textContent = title;
+        titleNode.textContent = title;
         input.value = `${this._index + 1}`;
         input.max = `${count}`;
 
@@ -195,25 +254,45 @@ class DictionaryEntry {
 }
 
 class DictionaryExtraInfo {
+    /**
+     * @param {DictionaryController} parent
+     * @param {import('dictionary-database').DictionaryCountGroup} totalCounts
+     * @param {import('dictionary-database').DictionaryCountGroup} remainders
+     * @param {number} totalRemainder
+     */
     constructor(parent, totalCounts, remainders, totalRemainder) {
+        /** @type {DictionaryController} */
         this._parent = parent;
+        /** @type {import('dictionary-database').DictionaryCountGroup} */
         this._totalCounts = totalCounts;
+        /** @type {import('dictionary-database').DictionaryCountGroup} */
         this._remainders = remainders;
+        /** @type {number} */
         this._totalRemainder = totalRemainder;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
-        this._nodes = null;
+        /** @type {ChildNode[]} */
+        this._nodes = [];
     }
 
+    /**
+     * @param {HTMLElement} container
+     */
     prepare(container) {
         const fragment = this._parent.instantiateTemplateFragment('dictionary-extra');
-        this._nodes = [...fragment.childNodes];
+        for (const node of fragment.childNodes) {
+            this._nodes.push(node);
+        }
+
+        const dictionaryIntegrityButton = /** @type {HTMLButtonElement} */ (fragment.querySelector('.dictionary-integrity-button'));
 
         this._setTitle(fragment.querySelector('.dictionary-total-count'));
-        this._eventListeners.addEventListener(fragment.querySelector('.dictionary-integrity-button'), 'click', this._onIntegrityButtonClick.bind(this), false);
+        this._eventListeners.addEventListener(dictionaryIntegrityButton, 'click', this._onIntegrityButtonClick.bind(this), false);
 
         container.appendChild(fragment);
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
         for (const node of this._nodes) {
@@ -221,74 +300,110 @@ class DictionaryExtraInfo {
                 node.parentNode.removeChild(node);
             }
         }
-        this._nodes = [];
+        this._nodes.length =0;
     }
 
     // Private
 
+    /** */
     _onIntegrityButtonClick() {
         this._showDetails();
     }
 
+    /** */
     _showDetails() {
         const modal = this._parent.modalController.getModal('dictionary-extra-data');
+        if (modal === null) { return; }
+
+        const dictionaryCounts = /** @type {HTMLElement} */ (modal.node.querySelector('.dictionary-counts'));
 
         const info = {counts: this._totalCounts, remainders: this._remainders};
-        modal.node.querySelector('.dictionary-counts').textContent = JSON.stringify(info, null, 4);
+        dictionaryCounts.textContent = JSON.stringify(info, null, 4);
         this._setTitle(modal.node.querySelector('.dictionary-total-count'));
 
         modal.setVisible(true);
     }
 
+    /**
+     * @param {?Element} node
+     */
     _setTitle(node) {
+        if (node === null) { return; }
         node.textContent = `${this._totalRemainder} item${this._totalRemainder !== 1 ? 's' : ''}`;
     }
 }
 
 class DictionaryController {
+    /**
+     * @param {SettingsController} settingsController
+     * @param {ModalController} modalController
+     * @param {StatusFooter} statusFooter
+     */
     constructor(settingsController, modalController, statusFooter) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {ModalController} */
         this._modalController = modalController;
+        /** @type {StatusFooter} */
         this._statusFooter = statusFooter;
+        /** @type {?import('dictionary-importer').Summary[]} */
         this._dictionaries = null;
+        /** @type {DictionaryEntry[]} */
         this._dictionaryEntries = [];
+        /** @type {?import('core').TokenObject} */
         this._databaseStateToken = null;
+        /** @type {boolean} */
         this._checkingIntegrity = false;
+        /** @type {?HTMLButtonElement} */
         this._checkIntegrityButton = null;
+        /** @type {?HTMLElement} */
         this._dictionaryEntryContainer = null;
+        /** @type {?HTMLElement} */
         this._dictionaryInstallCountNode = null;
+        /** @type {?HTMLElement} */
         this._dictionaryEnabledCountNode = null;
+        /** @type {?NodeListOf<HTMLElement>} */
         this._noDictionariesInstalledWarnings = null;
+        /** @type {?NodeListOf<HTMLElement>} */
         this._noDictionariesEnabledWarnings = null;
+        /** @type {?Modal} */
         this._deleteDictionaryModal = null;
+        /** @type {?HTMLInputElement} */
         this._allCheckbox = null;
+        /** @type {?DictionaryExtraInfo} */
         this._extraInfo = null;
+        /** @type {boolean} */
         this._isDeleting = false;
     }
 
+    /** @type {ModalController} */
     get modalController() {
         return this._modalController;
     }
 
+    /** @type {number} */
     get dictionaryOptionCount() {
         return this._dictionaryEntries.length;
     }
 
+    /** */
     async prepare() {
-        this._checkIntegrityButton = document.querySelector('#dictionary-check-integrity');
-        this._dictionaryEntryContainer = document.querySelector('#dictionary-list');
-        this._dictionaryInstallCountNode = document.querySelector('#dictionary-install-count');
-        this._dictionaryEnabledCountNode = document.querySelector('#dictionary-enabled-count');
-        this._noDictionariesInstalledWarnings = document.querySelectorAll('.no-dictionaries-installed-warning');
-        this._noDictionariesEnabledWarnings = document.querySelectorAll('.no-dictionaries-enabled-warning');
+        this._checkIntegrityButton = /** @type {HTMLButtonElement} */ (document.querySelector('#dictionary-check-integrity'));
+        this._dictionaryEntryContainer = /** @type {HTMLElement} */ (document.querySelector('#dictionary-list'));
+        this._dictionaryInstallCountNode = /** @type {HTMLElement} */ (document.querySelector('#dictionary-install-count'));
+        this._dictionaryEnabledCountNode = /** @type {HTMLElement} */ (document.querySelector('#dictionary-enabled-count'));
+        this._noDictionariesInstalledWarnings = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.no-dictionaries-installed-warning'));
+        this._noDictionariesEnabledWarnings = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.no-dictionaries-enabled-warning'));
         this._deleteDictionaryModal = this._modalController.getModal('dictionary-confirm-delete');
-        this._allCheckbox = document.querySelector('#all-dictionaries-enabled');
+        this._allCheckbox = /** @type {HTMLInputElement} */ (document.querySelector('#all-dictionaries-enabled'));
+        const dictionaryDeleteButton = /** @type {HTMLButtonElement} */ (document.querySelector('#dictionary-confirm-delete-button'));
+        const dictionaryMoveButton = /** @type {HTMLButtonElement} */ (document.querySelector('#dictionary-move-button'));
 
         yomichan.on('databaseUpdated', this._onDatabaseUpdated.bind(this));
         this._settingsController.on('optionsChanged', this._onOptionsChanged.bind(this));
         this._allCheckbox.addEventListener('change', this._onAllCheckboxChange.bind(this), false);
-        document.querySelector('#dictionary-confirm-delete-button').addEventListener('click', this._onDictionaryConfirmDelete.bind(this), false);
-        document.querySelector('#dictionary-move-button').addEventListener('click', this._onDictionaryMoveButtonClick.bind(this), false);
+        dictionaryDeleteButton.addEventListener('click', this._onDictionaryConfirmDelete.bind(this), false);
+        dictionaryMoveButton.addEventListener('click', this._onDictionaryMoveButtonClick.bind(this), false);
         if (this._checkIntegrityButton !== null) {
             this._checkIntegrityButton.addEventListener('click', this._onCheckIntegrityButtonClick.bind(this), false);
         }
@@ -298,14 +413,22 @@ class DictionaryController {
         await this._onDatabaseUpdated();
     }
 
+    /**
+     * @param {string} dictionaryTitle
+     */
     deleteDictionary(dictionaryTitle) {
         if (this._isDeleting) { return; }
-        const modal = this._deleteDictionaryModal;
+        const modal = /** @type {Modal} */ (this._deleteDictionaryModal);
         modal.node.dataset.dictionaryTitle = dictionaryTitle;
-        modal.node.querySelector('#dictionary-confirm-delete-name').textContent = dictionaryTitle;
+        const nameElement = /** @type {Element} */ (modal.node.querySelector('#dictionary-confirm-delete-name'));
+        nameElement.textContent = dictionaryTitle;
         modal.setVisible(true);
     }
 
+    /**
+     * @param {number} currentIndex
+     * @param {number} targetIndex
+     */
     async moveDictionaryOptions(currentIndex, targetIndex) {
         const options = await this._settingsController.getOptions();
         const {dictionaries} = options;
@@ -326,24 +449,40 @@ class DictionaryController {
             value: dictionaries
         }]);
 
-        this._settingsController.trigger('dictionarySettingsReordered', {source: this});
+        /** @type {import('settings-controller').DictionarySettingsReorderedEvent} */
+        const event = {source: this};
+        this._settingsController.trigger('dictionarySettingsReordered', event);
 
         await this._updateEntries();
     }
 
+    /**
+     * @param {string} name
+     * @returns {Element}
+     */
     instantiateTemplate(name) {
         return this._settingsController.instantiateTemplate(name);
     }
 
+    /**
+     * @param {string} name
+     * @returns {DocumentFragment}
+     */
     instantiateTemplateFragment(name) {
         return this._settingsController.instantiateTemplateFragment(name);
     }
 
+    /** */
     async updateDictionariesEnabled() {
         const options = await this._settingsController.getOptions();
         this._updateDictionariesEnabledWarnings(options);
     }
 
+    /**
+     * @param {string} name
+     * @param {boolean} enabled
+     * @returns {import('settings').DictionaryOptions}
+     */
     static createDefaultDictionarySettings(name, enabled) {
         return {
             name,
@@ -354,6 +493,13 @@ class DictionaryController {
         };
     }
 
+    /**
+     * @param {SettingsController} settingsController
+     * @param {import('dictionary-importer').Summary[]|undefined} dictionaries
+     * @param {import('settings').Options|undefined} optionsFull
+     * @param {boolean} modifyGlobalSettings
+     * @param {boolean} newDictionariesEnabled
+     */
     static async ensureDictionarySettings(settingsController, dictionaries, optionsFull, modifyGlobalSettings, newDictionariesEnabled) {
         if (typeof dictionaries === 'undefined') {
             dictionaries = await settingsController.getDictionaryInfo();
@@ -367,6 +513,7 @@ class DictionaryController {
             installedDictionaries.add(title);
         }
 
+        /** @type {import('settings-modifications').Modification[]} */
         const targets = [];
         const {profiles} = optionsFull;
         for (let i = 0, ii = profiles.length; i < ii; ++i) {
@@ -405,6 +552,9 @@ class DictionaryController {
 
     // Private
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         this._updateDictionariesEnabledWarnings(options);
         if (this._dictionaries !== null) {
@@ -412,7 +562,9 @@ class DictionaryController {
         }
     }
 
+    /** */
     async _onDatabaseUpdated() {
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._databaseStateToken = token;
         this._dictionaries = null;
@@ -423,14 +575,18 @@ class DictionaryController {
         await this._updateEntries();
     }
 
+    /** */
     _onAllCheckboxChange() {
-        const value = this._allCheckbox.checked;
-        this._allCheckbox.checked = !value;
+        const allCheckbox = /** @type {HTMLInputElement} */ (this._allCheckbox);
+        const value = allCheckbox.checked;
+        allCheckbox.checked = !value;
         this._setAllDictionariesEnabled(value);
     }
 
+    /** */
     async _updateEntries() {
         const dictionaries = this._dictionaries;
+        if (dictionaries === null) { return; }
         this._updateMainDictionarySelectOptions(dictionaries);
 
         for (const entry of this._dictionaryEntries) {
@@ -444,7 +600,7 @@ class DictionaryController {
         }
 
         const hasDictionary = (dictionaries.length > 0);
-        for (const node of this._noDictionariesInstalledWarnings) {
+        for (const node of /** @type {NodeListOf<HTMLElement>} */ (this._noDictionariesInstalledWarnings)) {
             node.hidden = hasDictionary;
         }
 
@@ -453,8 +609,9 @@ class DictionaryController {
         const options = await this._settingsController.getOptions();
         this._updateDictionariesEnabledWarnings(options);
 
+        /** @type {Map<string, import('dictionary-importer').Summary>} */
         const dictionaryInfoMap = new Map();
-        for (const dictionary of this._dictionaries) {
+        for (const dictionary of dictionaries) {
             dictionaryInfoMap.set(dictionary.title, dictionary);
         }
 
@@ -467,6 +624,9 @@ class DictionaryController {
         }
     }
 
+    /**
+     * @param {import('settings').ProfileOptions} options
+     */
     _updateDictionariesEnabledWarnings(options) {
         const {dictionaries} = options;
         let enabledDictionaryCountValid = 0;
@@ -489,7 +649,7 @@ class DictionaryController {
         }
 
         const hasEnabledDictionary = (enabledDictionaryCountValid > 0);
-        for (const node of this._noDictionariesEnabledWarnings) {
+        for (const node of /** @type {NodeListOf<HTMLElement>} */ (this._noDictionariesEnabledWarnings)) {
             node.hidden = hasEnabledDictionary;
         }
 
@@ -497,7 +657,7 @@ class DictionaryController {
             this._dictionaryEnabledCountNode.textContent = `${enabledDictionaryCountValid}`;
         }
 
-        this._allCheckbox.checked = (enabledDictionaryCount >= dictionaryCount);
+        /** @type {HTMLInputElement} */ (this._allCheckbox).checked = (enabledDictionaryCount >= dictionaryCount);
 
         const entries = this._dictionaryEntries;
         for (let i = 0, ii = Math.min(entries.length, dictionaryCount); i < ii; ++i) {
@@ -505,10 +665,13 @@ class DictionaryController {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onDictionaryConfirmDelete(e) {
         e.preventDefault();
 
-        const modal = this._deleteDictionaryModal;
+        const modal = /** @type {Modal} */ (this._deleteDictionaryModal);
         modal.setVisible(false);
 
         const title = modal.node.dataset.dictionaryTitle;
@@ -518,24 +681,32 @@ class DictionaryController {
         this._deleteDictionary(title);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onCheckIntegrityButtonClick(e) {
         e.preventDefault();
         this._checkIntegrity();
     }
 
+    /** */
     _onDictionaryMoveButtonClick() {
-        const modal = this._modalController.getModal('dictionary-move-location');
-        let {index} = modal.node.dataset;
-        index = Number.parseInt(index, 10);
+        const modal = /** @type {Modal} */ (this._modalController.getModal('dictionary-move-location'));
+        const {index} = modal.node.dataset;
+        if (typeof index !== 'number') { return; }
+        const indexNumber = Number.parseInt(index, 10);
 
-        let target = document.querySelector('#dictionary-move-location').value;
-        target = Number.parseInt(target, 10) - 1;
+        const targetString = /** @type {HTMLInputElement} */ (document.querySelector('#dictionary-move-location')).value;
+        const target = Number.parseInt(targetString, 10) - 1;
 
-        if (!Number.isFinite(target) || !Number.isFinite(index) || index === target) { return; }
+        if (!Number.isFinite(target) || !Number.isFinite(indexNumber) || indexNumber === target) { return; }
 
-        this.moveDictionaryOptions(index, target);
+        this.moveDictionaryOptions(indexNumber, target);
     }
 
+    /**
+     * @param {import('dictionary-importer').Summary[]} dictionaries
+     */
     _updateMainDictionarySelectOptions(dictionaries) {
         for (const select of document.querySelectorAll('[data-setting="general.mainDictionary"]')) {
             const fragment = document.createDocumentFragment();
@@ -559,6 +730,7 @@ class DictionaryController {
         }
     }
 
+    /** */
     async _checkIntegrity() {
         if (this._dictionaries === null || this._checkingIntegrity || this._isDeleting) { return; }
 
@@ -576,13 +748,17 @@ class DictionaryController {
                 entry.setCounts(counts[i]);
             }
 
-            this._setCounts(counts, total);
+            this._setCounts(counts, /** @type {import('dictionary-database').DictionaryCountGroup} */ (total));
         } finally {
             this._setButtonsEnabled(true);
             this._checkingIntegrity = false;
         }
     }
 
+    /**
+     * @param {import('dictionary-database').DictionaryCountGroup[]} dictionaryCounts
+     * @param {import('dictionary-database').DictionaryCountGroup} totalCounts
+     */
     _setCounts(dictionaryCounts, totalCounts) {
         const remainders = Object.assign({}, totalCounts);
         const keys = Object.keys(remainders);
@@ -603,12 +779,16 @@ class DictionaryController {
             this._extraInfo = null;
         }
 
-        if (totalRemainder > 0) {
+        if (totalRemainder > 0 && this._dictionaryEntryContainer !== null) {
             this._extraInfo = new DictionaryExtraInfo(this, totalCounts, remainders, totalRemainder);
             this._extraInfo.prepare(this._dictionaryEntryContainer);
         }
     }
 
+    /**
+     * @param {number} index
+     * @param {import('dictionary-importer').Summary} dictionaryInfo
+     */
     _createDictionaryEntry(index, dictionaryInfo) {
         const fragment = this.instantiateTemplateFragment('dictionary');
 
@@ -616,13 +796,16 @@ class DictionaryController {
         this._dictionaryEntries.push(entry);
         entry.prepare();
 
-        const container = this._dictionaryEntryContainer;
+        const container = /** @type {HTMLElement} */ (this._dictionaryEntryContainer);
         const relative = container.querySelector('.dictionary-item-bottom');
         container.insertBefore(fragment, relative);
 
         this._updateDictionaryEntryCount();
     }
 
+    /**
+     * @param {string} dictionaryTitle
+     */
     async _deleteDictionary(dictionaryTitle) {
         if (this._isDeleting || this._checkingIntegrity) { return; }
 
@@ -631,15 +814,18 @@ class DictionaryController {
 
         const statusFooter = this._statusFooter;
         const progressSelector = '.dictionary-delete-progress';
-        const progressContainers = document.querySelectorAll(`#dictionaries-modal ${progressSelector}`);
-        const progressBars = document.querySelectorAll(`${progressSelector} .progress-bar`);
-        const infoLabels = document.querySelectorAll(`${progressSelector} .progress-info`);
-        const statusLabels = document.querySelectorAll(`${progressSelector} .progress-status`);
+        const progressContainers = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll(`#dictionaries-modal ${progressSelector}`));
+        const progressBars = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll(`${progressSelector} .progress-bar`));
+        const infoLabels = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll(`${progressSelector} .progress-info`));
+        const statusLabels = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll(`${progressSelector} .progress-status`));
         const prevention = this._settingsController.preventPageExit();
         try {
             this._isDeleting = true;
             this._setButtonsEnabled(false);
 
+            /**
+             * @param {import('dictionary-database').DeleteDictionaryProgressData} details
+             */
             const onProgress = ({processed, count, storeCount, storesProcesed}) => {
                 const percent = (
                     (count > 0 && storesProcesed > 0) ?
@@ -672,21 +858,32 @@ class DictionaryController {
         }
     }
 
+    /**
+     * @param {boolean} value
+     */
     _setButtonsEnabled(value) {
         value = !value;
-        for (const node of document.querySelectorAll('.dictionary-database-mutating-input')) {
+        for (const node of /** @type {NodeListOf<HTMLInputElement>} */ (document.querySelectorAll('.dictionary-database-mutating-input'))) {
             node.disabled = value;
         }
     }
 
+    /**
+     * @param {string} dictionaryTitle
+     * @param {import('dictionary-worker').DeleteProgressCallback} onProgress
+     */
     async _deleteDictionaryInternal(dictionaryTitle, onProgress) {
         await new DictionaryWorker().deleteDictionary(dictionaryTitle, onProgress);
         yomichan.api.triggerDatabaseUpdated('dictionary', 'delete');
     }
 
+    /**
+     * @param {string} dictionaryTitle
+     */
     async _deleteDictionarySettings(dictionaryTitle) {
         const optionsFull = await this._settingsController.getOptionsFull();
         const {profiles} = optionsFull;
+        /** @type {import('settings-modifications').Modification[]} */
         const targets = [];
         for (let i = 0, ii = profiles.length; i < ii; ++i) {
             const {options: {dictionaries}} = profiles[i];
@@ -705,18 +902,24 @@ class DictionaryController {
         await this._settingsController.modifyGlobalSettings(targets);
     }
 
+    /** */
     _triggerStorageChanged() {
         yomichan.trigger('storageChanged');
     }
 
+    /** */
     _updateDictionaryEntryCount() {
-        this._dictionaryEntryContainer.dataset.count = `${this._dictionaryEntries.length}`;
+        /** @type {HTMLElement} */ (this._dictionaryEntryContainer).dataset.count = `${this._dictionaryEntries.length}`;
     }
 
+    /**
+     * @param {boolean} value
+     */
     async _setAllDictionariesEnabled(value) {
         const options = await this._settingsController.getOptions();
         const {dictionaries} = options;
 
+        /** @type {import('settings-modifications').Modification[]} */
         const targets = [];
         for (let i = 0, ii = dictionaries.length; i < ii; ++i) {
             targets.push({
diff --git a/ext/js/pages/settings/dictionary-import-controller.js b/ext/js/pages/settings/dictionary-import-controller.js
index 4708ee5f32..8ee06a6483 100644
--- a/ext/js/pages/settings/dictionary-import-controller.js
+++ b/ext/js/pages/settings/dictionary-import-controller.js
@@ -22,19 +22,37 @@
  */
 
 class DictionaryImportController {
+    /**
+     * @param {SettingsController} settingsController
+     * @param {ModalController} modalController
+     * @param {StatusFooter} statusFooter
+     */
     constructor(settingsController, modalController, statusFooter) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {ModalController} */
         this._modalController = modalController;
+        /** @type {StatusFooter} */
         this._statusFooter = statusFooter;
+        /** @type {boolean} */
         this._modifying = false;
+        /** @type {?HTMLButtonElement} */
         this._purgeButton = null;
+        /** @type {?HTMLButtonElement} */
         this._purgeConfirmButton = null;
+        /** @type {?HTMLButtonElement} */
         this._importFileButton = null;
+        /** @type {?HTMLInputElement} */
         this._importFileInput = null;
+        /** @type {?Modal} */
         this._purgeConfirmModal = null;
+        /** @type {?HTMLElement} */
         this._errorContainer = null;
+        /** @type {?HTMLElement} */
         this._spinner = null;
+        /** @type {?HTMLElement} */
         this._purgeNotification = null;
+        /** @type {[originalMessage: string, newMessage: string][]} */
         this._errorToStringOverrides = [
             [
                 'A mutation operation was attempted on a database that did not allow mutations.',
@@ -47,15 +65,16 @@ class DictionaryImportController {
         ];
     }
 
+    /** */
     async prepare() {
-        this._purgeButton = document.querySelector('#dictionary-delete-all-button');
-        this._purgeConfirmButton = document.querySelector('#dictionary-confirm-delete-all-button');
-        this._importFileButton = document.querySelector('#dictionary-import-file-button');
-        this._importFileInput = document.querySelector('#dictionary-import-file-input');
+        this._purgeButton = /** @type {HTMLButtonElement} */ (document.querySelector('#dictionary-delete-all-button'));
+        this._purgeConfirmButton = /** @type {HTMLButtonElement} */ (document.querySelector('#dictionary-confirm-delete-all-button'));
+        this._importFileButton = /** @type {HTMLButtonElement} */ (document.querySelector('#dictionary-import-file-button'));
+        this._importFileInput = /** @type {HTMLInputElement} */ (document.querySelector('#dictionary-import-file-input'));
         this._purgeConfirmModal = this._modalController.getModal('dictionary-confirm-delete-all');
-        this._errorContainer = document.querySelector('#dictionary-error');
-        this._spinner = document.querySelector('#dictionary-spinner');
-        this._purgeNotification = document.querySelector('#dictionary-delete-all-status');
+        this._errorContainer = /** @type {HTMLElement} */ (document.querySelector('#dictionary-error'));
+        this._spinner = /** @type {HTMLElement} */ (document.querySelector('#dictionary-spinner'));
+        this._purgeNotification = /** @type {HTMLElement} */ (document.querySelector('#dictionary-delete-all-status'));
 
         this._purgeButton.addEventListener('click', this._onPurgeButtonClick.bind(this), false);
         this._purgeConfirmButton.addEventListener('click', this._onPurgeConfirmButtonClick.bind(this), false);
@@ -65,28 +84,41 @@ class DictionaryImportController {
 
     // Private
 
+    /** */
     _onImportButtonClick() {
-        this._importFileInput.click();
+        /** @type {HTMLInputElement} */ (this._importFileInput).click();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onPurgeButtonClick(e) {
         e.preventDefault();
-        this._purgeConfirmModal.setVisible(true);
+        /** @type {Modal} */ (this._purgeConfirmModal).setVisible(true);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onPurgeConfirmButtonClick(e) {
         e.preventDefault();
-        this._purgeConfirmModal.setVisible(false);
+        /** @type {Modal} */ (this._purgeConfirmModal).setVisible(false);
         this._purgeDatabase();
     }
 
+    /**
+     * @param {Event} e
+     */
     _onImportFileChange(e) {
-        const node = e.currentTarget;
-        const files = [...node.files];
-        node.value = null;
-        this._importDictionaries(files);
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
+        const {files} = node;
+        if (files === null) { return; }
+        const files2 = [...files];
+        node.value = '';
+        this._importDictionaries(files2);
     }
 
+    /** */
     async _purgeDatabase() {
         if (this._modifying) { return; }
 
@@ -106,7 +138,7 @@ class DictionaryImportController {
                 this._showErrors(errors);
             }
         } catch (error) {
-            this._showErrors([error]);
+            this._showErrors([error instanceof Error ? error : new Error(`${error}`)]);
         } finally {
             prevention.end();
             if (purgeNotification !== null) { purgeNotification.hidden = true; }
@@ -116,16 +148,19 @@ class DictionaryImportController {
         }
     }
 
+    /**
+     * @param {File[]} files
+     */
     async _importDictionaries(files) {
         if (this._modifying) { return; }
 
         const statusFooter = this._statusFooter;
-        const importInfo = document.querySelector('#dictionary-import-info');
+        const importInfo = /** @type {HTMLElement} */ (document.querySelector('#dictionary-import-info'));
         const progressSelector = '.dictionary-import-progress';
-        const progressContainers = document.querySelectorAll(`#dictionaries-modal ${progressSelector}`);
-        const progressBars = document.querySelectorAll(`${progressSelector} .progress-bar`);
-        const infoLabels = document.querySelectorAll(`${progressSelector} .progress-info`);
-        const statusLabels = document.querySelectorAll(`${progressSelector} .progress-status`);
+        const progressContainers = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll(`#dictionaries-modal ${progressSelector}`));
+        const progressBars = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll(`${progressSelector} .progress-bar`));
+        const infoLabels = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll(`${progressSelector} .progress-info`));
+        const statusLabels = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll(`${progressSelector} .progress-status`));
 
         const prevention = this._preventPageExit();
 
@@ -143,6 +178,7 @@ class DictionaryImportController {
 
             let statusPrefix = '';
             let stepIndex = -2;
+            /** @type {import('dictionary-worker').ImportProgressCallback} */
             const onProgress = (data) => {
                 const {stepIndex: stepIndex2, index, count} = data;
                 if (stepIndex !== stepIndex2) {
@@ -184,7 +220,7 @@ class DictionaryImportController {
                 await this._importDictionary(files[i], importDetails, onProgress);
             }
         } catch (err) {
-            this._showErrors([err]);
+            this._showErrors([err instanceof Error ? err : new Error(`${err}`)]);
         } finally {
             prevention.end();
             for (const progress of progressContainers) { progress.hidden = true; }
@@ -199,6 +235,10 @@ class DictionaryImportController {
         }
     }
 
+    /**
+     * @param {number} stepIndex
+     * @returns {string}
+     */
     _getImportLabel(stepIndex) {
         switch (stepIndex) {
             case -1:
@@ -212,6 +252,11 @@ class DictionaryImportController {
         }
     }
 
+    /**
+     * @param {File} file
+     * @param {import('dictionary-importer').ImportDetails} importDetails
+     * @param {import('dictionary-worker').ImportProgressCallback} onProgress
+     */
     async _importDictionary(file, importDetails, onProgress) {
         const archiveContent = await this._readFile(file);
         const {result, errors} = await new DictionaryWorker().importDictionary(archiveContent, importDetails, onProgress);
@@ -225,8 +270,14 @@ class DictionaryImportController {
         }
     }
 
+    /**
+     * @param {boolean} sequenced
+     * @param {string} title
+     * @returns {Promise<Error[]>}
+     */
     async _addDictionarySettings(sequenced, title) {
         const optionsFull = await this._settingsController.getOptionsFull();
+        /** @type {import('settings-modifications').Modification[]} */
         const targets = [];
         const profileCount = optionsFull.profiles.length;
         for (let i = 0; i < profileCount; ++i) {
@@ -243,8 +294,12 @@ class DictionaryImportController {
         return await this._modifyGlobalSettings(targets);
     }
 
+    /**
+     * @returns {Promise<Error[]>}
+     */
     async _clearDictionarySettings() {
         const optionsFull = await this._settingsController.getOptionsFull();
+        /** @type {import('settings-modifications').Modification[]} */
         const targets = [];
         const profileCount = optionsFull.profiles.length;
         for (let i = 0; i < profileCount; ++i) {
@@ -256,16 +311,25 @@ class DictionaryImportController {
         return await this._modifyGlobalSettings(targets);
     }
 
+    /**
+     * @param {boolean} visible
+     */
     _setSpinnerVisible(visible) {
         if (this._spinner !== null) {
             this._spinner.hidden = !visible;
         }
     }
 
+    /**
+     * @returns {import('settings-controller').PageExitPrevention}
+     */
     _preventPageExit() {
         return this._settingsController.preventPageExit();
     }
 
+    /**
+     * @param {Error[]} errors
+     */
     _showErrors(errors) {
         const uniqueErrors = new Map();
         for (const error of errors) {
@@ -292,59 +356,81 @@ class DictionaryImportController {
             fragment.appendChild(div);
         }
 
-        this._errorContainer.appendChild(fragment);
-        this._errorContainer.hidden = false;
+        const errorContainer = /** @type {HTMLElement} */ (this._errorContainer);
+        errorContainer.appendChild(fragment);
+        errorContainer.hidden = false;
     }
 
+    /** */
     _hideErrors() {
-        this._errorContainer.textContent = '';
-        this._errorContainer.hidden = true;
+        const errorContainer = /** @type {HTMLElement} */ (this._errorContainer);
+        errorContainer.textContent = '';
+        errorContainer.hidden = true;
     }
 
+    /**
+     * @param {File} file
+     * @returns {Promise<ArrayBuffer>}
+     */
     _readFile(file) {
         return new Promise((resolve, reject) => {
             const reader = new FileReader();
-            reader.onload = () => resolve(reader.result);
+            reader.onload = () => resolve(/** @type {ArrayBuffer} */ (reader.result));
             reader.onerror = () => reject(reader.error);
             reader.readAsArrayBuffer(file);
         });
     }
 
+    /**
+     * @param {Error} error
+     * @returns {string}
+     */
     _errorToString(error) {
-        error = (typeof error.toString === 'function' ? error.toString() : `${error}`);
+        const errorMessage = error.toString();
 
         for (const [match, newErrorString] of this._errorToStringOverrides) {
-            if (error.includes(match)) {
+            if (errorMessage.includes(match)) {
                 return newErrorString;
             }
         }
 
-        return error;
+        return errorMessage;
     }
 
+    /**
+     * @param {boolean} value
+     */
     _setModifying(value) {
         this._modifying = value;
         this._setButtonsEnabled(!value);
     }
 
+    /**
+     * @param {boolean} value
+     */
     _setButtonsEnabled(value) {
         value = !value;
-        for (const node of document.querySelectorAll('.dictionary-database-mutating-input')) {
+        for (const node of /** @type {NodeListOf<HTMLInputElement>} */ (document.querySelectorAll('.dictionary-database-mutating-input'))) {
             node.disabled = value;
         }
     }
 
+    /**
+     * @param {import('settings-modifications').Modification[]} targets
+     * @returns {Promise<Error[]>}
+     */
     async _modifyGlobalSettings(targets) {
         const results = await this._settingsController.modifyGlobalSettings(targets);
         const errors = [];
         for (const {error} of results) {
             if (typeof error !== 'undefined') {
-                errors.push(deserializeError(error));
+                errors.push(ExtensionError.deserialize(error));
             }
         }
         return errors;
     }
 
+    /** */
     _triggerStorageChanged() {
         yomichan.trigger('storageChanged');
     }
diff --git a/ext/js/pages/settings/extension-keyboard-shortcuts-controller.js b/ext/js/pages/settings/extension-keyboard-shortcuts-controller.js
index 3ac036a3c3..009d304e8d 100644
--- a/ext/js/pages/settings/extension-keyboard-shortcuts-controller.js
+++ b/ext/js/pages/settings/extension-keyboard-shortcuts-controller.js
@@ -22,24 +22,36 @@
  */
 
 class ExtensionKeyboardShortcutController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?HTMLButtonElement} */
         this._resetButton = null;
+        /** @type {?HTMLButtonElement} */
         this._clearButton = null;
+        /** @type {?HTMLElement} */
         this._listContainer = null;
+        /** @type {HotkeyUtil} */
         this._hotkeyUtil = new HotkeyUtil();
+        /** @type {?import('environment').OperatingSystem} */
         this._os = null;
+        /** @type {ExtensionKeyboardShortcutHotkeyEntry[]} */
         this._entries = [];
     }
 
+    /** @type {HotkeyUtil} */
     get hotkeyUtil() {
         return this._hotkeyUtil;
     }
 
+    /** */
     async prepare() {
-        this._resetButton = document.querySelector('#extension-hotkey-list-reset-all');
-        this._clearButton = document.querySelector('#extension-hotkey-list-clear-all');
-        this._listContainer = document.querySelector('#extension-hotkey-list');
+        this._resetButton = /** @type {HTMLButtonElement} */ (document.querySelector('#extension-hotkey-list-reset-all'));
+        this._clearButton = /** @type {HTMLButtonElement} */ (document.querySelector('#extension-hotkey-list-clear-all'));
+        this._listContainer = /** @type {HTMLElement} */ (document.querySelector('#extension-hotkey-list'));
 
         const canResetCommands = this.canResetCommands();
         const canModifyCommands = this.canModifyCommands();
@@ -61,10 +73,16 @@ class ExtensionKeyboardShortcutController {
         this._setupCommands(commands);
     }
 
+    /**
+     * @param {string} name
+     * @returns {Promise<{key: ?string, modifiers: import('input').Modifier[]}>}
+     */
     async resetCommand(name) {
         await this._resetCommand(name);
 
+        /** @type {?string} */
         let key = null;
+        /** @type {import('input').Modifier[]} */
         let modifiers = [];
 
         const commands = await this._getCommands();
@@ -78,32 +96,60 @@ class ExtensionKeyboardShortcutController {
         return {key, modifiers};
     }
 
+    /**
+     * @param {string} name
+     * @param {?string} key
+     * @param {import('input').Modifier[]} modifiers
+     */
     async updateCommand(name, key, modifiers) {
         // Firefox-only; uses Promise API
         const shortcut = this._hotkeyUtil.convertInputToCommand(key, modifiers);
-        return await chrome.commands.update({name, shortcut});
+        await browser.commands.update({name, shortcut});
     }
 
+    /**
+     * @returns {boolean}
+     */
     canResetCommands() {
-        return isObject(chrome.commands) && typeof chrome.commands.reset === 'function';
+        return (
+            typeof browser === 'object' && browser !== null &&
+            typeof browser.commands === 'object' && browser.commands !== null &&
+            typeof browser.commands.reset === 'function'
+        );
     }
 
+    /**
+     * @returns {boolean}
+     */
     canModifyCommands() {
-        return isObject(chrome.commands) && typeof chrome.commands.update === 'function';
+        return (
+            typeof browser === 'object' && browser !== null &&
+            typeof browser.commands === 'object' && browser.commands !== null &&
+            typeof browser.commands.update === 'function'
+        );
     }
 
     // Add
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onResetClick(e) {
         e.preventDefault();
         this._resetAllCommands();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onClearClick(e) {
         e.preventDefault();
         this._clearAllCommands();
     }
 
+    /**
+     * @returns {Promise<chrome.commands.Command[]>}
+     */
     _getCommands() {
         return new Promise((resolve, reject) => {
             if (!(isObject(chrome.commands) && typeof chrome.commands.getAll === 'function')) {
@@ -122,6 +168,9 @@ class ExtensionKeyboardShortcutController {
         });
     }
 
+    /**
+     * @param {chrome.commands.Command[]} commands
+     */
     _setupCommands(commands) {
         for (const entry of this._entries) {
             entry.cleanup();
@@ -131,7 +180,7 @@ class ExtensionKeyboardShortcutController {
         const fragment = document.createDocumentFragment();
 
         for (const {name, description, shortcut} of commands) {
-            if (name.startsWith('_')) { continue; }
+            if (typeof name !== 'string' || name.startsWith('_')) { continue; }
 
             const {key, modifiers} = this._hotkeyUtil.convertCommandToInput(shortcut);
 
@@ -143,10 +192,12 @@ class ExtensionKeyboardShortcutController {
             this._entries.push(entry);
         }
 
-        this._listContainer.textContent = '';
-        this._listContainer.appendChild(fragment);
+        const listContainer = /** @type {HTMLElement} */ (this._listContainer);
+        listContainer.textContent = '';
+        listContainer.appendChild(fragment);
     }
 
+    /** */
     async _resetAllCommands() {
         if (!this.canModifyCommands()) { return; }
 
@@ -154,7 +205,7 @@ class ExtensionKeyboardShortcutController {
         const promises = [];
 
         for (const {name} of commands) {
-            if (name.startsWith('_')) { continue; }
+            if (typeof name !== 'string' || name.startsWith('_')) { continue; }
             promises.push(this._resetCommand(name));
         }
 
@@ -164,6 +215,7 @@ class ExtensionKeyboardShortcutController {
         this._setupCommands(commands);
     }
 
+    /** */
     async _clearAllCommands() {
         if (!this.canModifyCommands()) { return; }
 
@@ -171,7 +223,7 @@ class ExtensionKeyboardShortcutController {
         const promises = [];
 
         for (const {name} of commands) {
-            if (name.startsWith('_')) { continue; }
+            if (typeof name !== 'string' || name.startsWith('_')) { continue; }
             promises.push(this.updateCommand(name, null, []));
         }
 
@@ -181,31 +233,55 @@ class ExtensionKeyboardShortcutController {
         this._setupCommands(commands);
     }
 
+    /**
+     * @param {string} name
+     */
     async _resetCommand(name) {
         // Firefox-only; uses Promise API
-        return await chrome.commands.reset(name);
+        await browser.commands.reset(name);
     }
 }
 
 class ExtensionKeyboardShortcutHotkeyEntry {
+    /**
+     * @param {ExtensionKeyboardShortcutController} parent
+     * @param {Element} node
+     * @param {string} name
+     * @param {string|undefined} description
+     * @param {?string} key
+     * @param {import('input').Modifier[]} modifiers
+     * @param {?import('environment').OperatingSystem} os
+     */
     constructor(parent, node, name, description, key, modifiers, os) {
+        /** @type {ExtensionKeyboardShortcutController} */
         this._parent = parent;
+        /** @type {Element} */
         this._node = node;
+        /** @type {string} */
         this._name = name;
+        /** @type {string|undefined} */
         this._description = description;
+        /** @type {?string} */
         this._key = key;
+        /** @type {import('input').Modifier[]} */
         this._modifiers = modifiers;
+        /** @type {?import('environment').OperatingSystem} */
         this._os = os;
+        /** @type {?HTMLInputElement} */
         this._input = null;
+        /** @type {?KeyboardMouseInputField} */
         this._inputField = null;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
     }
 
+    /** */
     prepare() {
-        this._node.querySelector('.settings-item-label').textContent = this._description || this._name;
+        const label = /** @type {HTMLElement} */ (this._node.querySelector('.settings-item-label'));
+        label.textContent = this._description || this._name;
 
-        const button = this._node.querySelector('.extension-hotkey-list-item-button');
-        const input = this._node.querySelector('input');
+        const button = /** @type {HTMLButtonElement} */ (this._node.querySelector('.extension-hotkey-list-item-button'));
+        const input = /** @type {HTMLInputElement} */ (this._node.querySelector('input'));
 
         this._input = input;
 
@@ -222,6 +298,7 @@ class ExtensionKeyboardShortcutHotkeyEntry {
         }
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
         if (this._node.parentNode !== null) {
@@ -235,15 +312,22 @@ class ExtensionKeyboardShortcutHotkeyEntry {
 
     // Private
 
+    /**
+     * @param {import('keyboard-mouse-input-field').ChangeEvent} e
+     */
     _onInputFieldChange(e) {
         const {key, modifiers} = e;
         this._tryUpdateInput(key, modifiers, false);
     }
 
+    /** */
     _onInputFieldBlur() {
         this._updateInput();
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuClose(e) {
         switch (e.detail.action) {
             case 'clearInput':
@@ -255,11 +339,19 @@ class ExtensionKeyboardShortcutHotkeyEntry {
         }
     }
 
+    /** */
     _updateInput() {
-        this._inputField.setInput(this._key, this._modifiers);
-        delete this._input.dataset.invalid;
+        /** @type {KeyboardMouseInputField} */ (this._inputField).setInput(this._key, this._modifiers);
+        if (this._input !== null) {
+            delete this._input.dataset.invalid;
+        }
     }
 
+    /**
+     * @param {?string} key
+     * @param {import('input').Modifier[]} modifiers
+     * @param {boolean} updateInput
+     */
     async _tryUpdateInput(key, modifiers, updateInput) {
         let okay = (key === null ? (modifiers.length === 0) : (modifiers.length !== 0));
         if (okay) {
@@ -273,9 +365,13 @@ class ExtensionKeyboardShortcutHotkeyEntry {
         if (okay) {
             this._key = key;
             this._modifiers = modifiers;
-            delete this._input.dataset.invalid;
+            if (this._input !== null) {
+                delete this._input.dataset.invalid;
+            }
         } else {
-            this._input.dataset.invalid = 'true';
+            if (this._input !== null) {
+                this._input.dataset.invalid = 'true';
+            }
         }
 
         if (updateInput) {
@@ -283,6 +379,7 @@ class ExtensionKeyboardShortcutHotkeyEntry {
         }
     }
 
+    /** */
     async _resetInput() {
         const {key, modifiers} = await this._parent.resetCommand(this._name);
         this._key = key;
diff --git a/ext/js/pages/settings/generic-setting-controller.js b/ext/js/pages/settings/generic-setting-controller.js
index c416d1a767..4886529103 100644
--- a/ext/js/pages/settings/generic-setting-controller.js
+++ b/ext/js/pages/settings/generic-setting-controller.js
@@ -22,9 +22,15 @@
  */
 
 class GenericSettingController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {import('settings-modifications').OptionsScopeType} */
         this._defaultScope = 'profile';
+        /** @type {DOMDataBinder<import('generic-setting-controller').ElementMetadata>} */
         this._dataBinder = new DOMDataBinder({
             selector: '[data-setting]',
             createElementMetadata: this._createElementMetadata.bind(this),
@@ -32,7 +38,8 @@ class GenericSettingController {
             getValues: this._getValues.bind(this),
             setValues: this._setValues.bind(this)
         });
-        this._transforms = new Map([
+        /** @type {Map<import('generic-setting-controller').TransformType, import('generic-setting-controller').TransformFunction>} */
+        this._transforms = new Map(/** @type {[key: import('generic-setting-controller').TransformType, value: import('generic-setting-controller').TransformFunction][]} */ ([
             ['setAttribute', this._setAttribute.bind(this)],
             ['setVisibility', this._setVisibility.bind(this)],
             ['splitTags', this._splitTags.bind(this)],
@@ -41,41 +48,49 @@ class GenericSettingController {
             ['toBoolean', this._toBoolean.bind(this)],
             ['toString', this._toString.bind(this)],
             ['conditionalConvert', this._conditionalConvert.bind(this)]
-        ]);
+        ]));
     }
 
+    /** */
     async prepare() {
         this._dataBinder.observe(document.body);
         this._settingsController.on('optionsChanged', this._onOptionsChanged.bind(this));
     }
 
+    /** */
     async refresh() {
         await this._dataBinder.refresh();
     }
 
     // Private
 
+    /** */
     _onOptionsChanged() {
         this._dataBinder.refresh();
     }
 
+    /**
+     * @param {Element} element
+     * @returns {import('generic-setting-controller').ElementMetadata|undefined}
+     */
     _createElementMetadata(element) {
-        const {dataset: {setting: path, scope, transform: transformRaw}} = element;
-        let transforms;
-        if (typeof transformRaw === 'string') {
-            transforms = JSON.parse(transformRaw);
-            if (!Array.isArray(transforms)) { transforms = [transforms]; }
-        } else {
-            transforms = [];
-        }
+        if (!(element instanceof HTMLElement)) { return void 0; }
+        const {setting: path, scope, transform: transformRaw} = element.dataset;
+        if (typeof path !== 'string') { return void 0; }
+        const scope2 = this._normalizeScope(scope);
         return {
             path,
-            scope,
-            transforms,
+            scope: scope2 !== null ? scope2 : this._defaultScope,
+            transforms: this._getTransformDataArray(transformRaw),
             transformRaw
         };
     }
 
+    /**
+     * @param {import('generic-setting-controller').ElementMetadata} metadata1
+     * @param {import('generic-setting-controller').ElementMetadata} metadata2
+     * @returns {boolean}
+     */
     _compareElementMetadata(metadata1, metadata2) {
         return (
             metadata1.path === metadata2.path &&
@@ -84,45 +99,71 @@ class GenericSettingController {
         );
     }
 
+    /**
+     * @param {import('dom-data-binder').GetValuesDetails<import('generic-setting-controller').ElementMetadata>[]} targets
+     * @returns {Promise<import('dom-data-binder').TaskResult[]>}
+     */
     async _getValues(targets) {
         const defaultScope = this._defaultScope;
+        /** @type {import('settings-modifications').ScopedRead[]} */
         const settingsTargets = [];
         for (const {metadata: {path, scope}} of targets) {
+            /** @type {import('settings-modifications').ScopedRead} */
             const target = {
                 path,
-                scope: scope || defaultScope
+                scope: typeof scope === 'string' ? scope : defaultScope,
+                optionsContext: null
             };
             settingsTargets.push(target);
         }
         return this._transformResults(await this._settingsController.getSettings(settingsTargets), targets);
     }
 
+    /**
+     * @param {import('dom-data-binder').SetValuesDetails<import('generic-setting-controller').ElementMetadata>[]} targets
+     * @returns {Promise<import('dom-data-binder').TaskResult[]>}
+     */
     async _setValues(targets) {
         const defaultScope = this._defaultScope;
+        /** @type {import('settings-modifications').ScopedModification[]} */
         const settingsTargets = [];
         for (const {metadata: {path, scope, transforms}, value, element} of targets) {
             const transformedValue = this._applyTransforms(value, transforms, 'pre', element);
+            /** @type {import('settings-modifications').ScopedModification} */
             const target = {
                 path,
-                scope: scope || defaultScope,
+                scope: typeof scope === 'string' ? scope : defaultScope,
                 action: 'set',
-                value: transformedValue
+                value: transformedValue,
+                optionsContext: null
             };
             settingsTargets.push(target);
         }
         return this._transformResults(await this._settingsController.modifySettings(settingsTargets), targets);
     }
 
+    /**
+     * @param {import('settings-controller').ModifyResult[]} values
+     * @param {import('dom-data-binder').GetValuesDetails<import('generic-setting-controller').ElementMetadata>[]|import('dom-data-binder').SetValuesDetails<import('generic-setting-controller').ElementMetadata>[]} targets
+     * @returns {import('dom-data-binder').TaskResult[]}
+     */
     _transformResults(values, targets) {
         return values.map((value, i) => {
             const error = value.error;
-            if (error) { return deserializeError(error); }
+            if (error) { return {error: ExtensionError.deserialize(error)}; }
             const {metadata: {transforms}, element} = targets[i];
             const result = this._applyTransforms(value.result, transforms, 'post', element);
             return {result};
         });
     }
 
+    /**
+     * @param {unknown} value
+     * @param {import('generic-setting-controller').TransformData[]} transforms
+     * @param {import('generic-setting-controller').TransformStep} step
+     * @param {Element} element
+     * @returns {unknown}
+     */
     _applyTransforms(value, transforms, step, element) {
         for (const transform of transforms) {
             const transformStep = transform.step;
@@ -136,6 +177,11 @@ class GenericSettingController {
         return value;
     }
 
+    /**
+     * @param {?Node} node
+     * @param {number} ancestorDistance
+     * @returns {?Node}
+     */
     _getAncestor(node, ancestorDistance) {
         if (ancestorDistance < 0) {
             return document.documentElement;
@@ -146,6 +192,12 @@ class GenericSettingController {
         return node;
     }
 
+    /**
+     * @param {?Node} node
+     * @param {number|undefined} ancestorDistance
+     * @param {string|undefined} selector
+     * @returns {?Node}
+     */
     _getRelativeElement(node, ancestorDistance, selector) {
         const selectorRoot = (
             typeof ancestorDistance === 'number' ?
@@ -155,12 +207,17 @@ class GenericSettingController {
         if (selectorRoot === null) { return null; }
 
         return (
-            typeof selector === 'string' ?
+            typeof selector === 'string' && (selectorRoot instanceof Element || selectorRoot instanceof Document) ?
             selectorRoot.querySelector(selector) :
             (selectorRoot === document ? document.documentElement : selectorRoot)
         );
     }
 
+    /**
+     * @param {import('generic-setting-controller').OperationData} operationData
+     * @param {unknown} lhs
+     * @returns {unknown}
+     */
     _evaluateSimpleOperation(operationData, lhs) {
         const {op: operation, value: rhs} = operationData;
         switch (operation) {
@@ -168,18 +225,18 @@ class GenericSettingController {
             case '!!': return !!lhs;
             case '===': return lhs === rhs;
             case '!==': return lhs !== rhs;
-            case '>=': return lhs >= rhs;
-            case '<=': return lhs <= rhs;
-            case '>': return lhs > rhs;
-            case '<': return lhs < rhs;
+            case '>=': return /** @type {number} */ (lhs) >= /** @type {number} */ (rhs);
+            case '<=': return /** @type {number} */ (lhs) <= /** @type {number} */ (rhs);
+            case '>': return /** @type {number} */ (lhs) > /** @type {number} */ (rhs);
+            case '<': return /** @type {number} */ (lhs) < /** @type {number} */ (rhs);
             case '&&':
-                for (const operationData2 of rhs) {
+                for (const operationData2 of /** @type {import('generic-setting-controller').OperationData[]} */ (rhs)) {
                     const result = this._evaluateSimpleOperation(operationData2, lhs);
                     if (!result) { return result; }
                 }
                 return true;
             case '||':
-                for (const operationData2 of rhs) {
+                for (const operationData2 of /** @type {import('generic-setting-controller').OperationData[]} */ (rhs)) {
                     const result = this._evaluateSimpleOperation(operationData2, lhs);
                     if (result) { return result; }
                 }
@@ -189,48 +246,112 @@ class GenericSettingController {
         }
     }
 
+    /**
+     * @param {string|undefined} value
+     * @returns {?import('settings-modifications').OptionsScopeType}
+     */
+    _normalizeScope(value) {
+        switch (value) {
+            case 'profile':
+            case 'global':
+                return value;
+            default:
+                return null;
+        }
+    }
+
+    /**
+     * @param {string|undefined} transformRaw
+     * @returns {import('generic-setting-controller').TransformData[]}
+     */
+    _getTransformDataArray(transformRaw) {
+        if (typeof transformRaw === 'string') {
+            const transforms = JSON.parse(transformRaw);
+            return Array.isArray(transforms) ? transforms : [transforms];
+        }
+        return [];
+    }
+
     // Transforms
 
+    /**
+     * @param {unknown} value
+     * @param {import('generic-setting-controller').SetAttributeTransformData} data
+     * @param {Element} element
+     * @returns {unknown}
+     */
     _setAttribute(value, data, element) {
         const {ancestorDistance, selector, attribute} = data;
         const relativeElement = this._getRelativeElement(element, ancestorDistance, selector);
-        if (relativeElement !== null) {
+        if (relativeElement !== null && relativeElement instanceof Element) {
             relativeElement.setAttribute(attribute, `${value}`);
         }
         return value;
     }
 
+    /**
+     * @param {unknown} value
+     * @param {import('generic-setting-controller').SetVisibilityTransformData} data
+     * @param {Element} element
+     * @returns {unknown}
+     */
     _setVisibility(value, data, element) {
         const {ancestorDistance, selector, condition} = data;
         const relativeElement = this._getRelativeElement(element, ancestorDistance, selector);
-        if (relativeElement !== null) {
+        if (relativeElement !== null && relativeElement instanceof HTMLElement) {
             relativeElement.hidden = !this._evaluateSimpleOperation(condition, value);
         }
         return value;
     }
 
+    /**
+     * @param {unknown} value
+     * @returns {string[]}
+     */
     _splitTags(value) {
         return `${value}`.split(/[,; ]+/).filter((v) => !!v);
     }
 
+    /**
+     * @param {unknown} value
+     * @returns {string}
+     */
     _joinTags(value) {
-        return value.join(' ');
+        return Array.isArray(value) ? value.join(' ') : '';
     }
 
+    /**
+     * @param {unknown} value
+     * @param {import('generic-setting-controller').ToNumberConstraintsTransformData} data
+     * @returns {number}
+     */
     _toNumber(value, data) {
-        let {constraints} = data;
-        if (!isObject(constraints)) { constraints = {}; }
-        return DocumentUtil.convertElementValueToNumber(value, constraints);
+        /** @type {import('document-util').ToNumberConstraints} */
+        const constraints = typeof data.constraints === 'object' && data.constraints !== null ? data.constraints : {};
+        return typeof value === 'string' ? DocumentUtil.convertElementValueToNumber(value, constraints) : 0;
     }
 
+    /**
+     * @param {string} value
+     * @returns {boolean}
+     */
     _toBoolean(value) {
         return (value === 'true');
     }
 
+    /**
+     * @param {unknown} value
+     * @returns {string}
+     */
     _toString(value) {
         return `${value}`;
     }
 
+    /**
+     * @param {unknown} value
+     * @param {import('generic-setting-controller').ConditionalConvertTransformData} data
+     * @returns {unknown}
+     */
     _conditionalConvert(value, data) {
         const {cases} = data;
         if (Array.isArray(cases)) {
diff --git a/ext/js/pages/settings/keyboard-mouse-input-field.js b/ext/js/pages/settings/keyboard-mouse-input-field.js
index d4680eb1dc..c565827991 100644
--- a/ext/js/pages/settings/keyboard-mouse-input-field.js
+++ b/ext/js/pages/settings/keyboard-mouse-input-field.js
@@ -21,31 +21,58 @@
  * HotkeyUtil
  */
 
+/**
+ * @augments EventDispatcher<import('keyboard-mouse-input-field').EventType>
+ */
 class KeyboardMouseInputField extends EventDispatcher {
+    /**
+     * @param {HTMLInputElement} inputNode
+     * @param {?HTMLButtonElement} mouseButton
+     * @param {?import('environment').OperatingSystem} os
+     * @param {?(pointerType: string) => boolean} [isPointerTypeSupported]
+     */
     constructor(inputNode, mouseButton, os, isPointerTypeSupported=null) {
         super();
+        /** @type {HTMLInputElement} */
         this._inputNode = inputNode;
+        /** @type {?HTMLButtonElement} */
         this._mouseButton = mouseButton;
+        /** @type {?(pointerType: string) => boolean} */
         this._isPointerTypeSupported = isPointerTypeSupported;
+        /** @type {HotkeyUtil} */
         this._hotkeyUtil = new HotkeyUtil(os);
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?string} */
         this._key = null;
+        /** @type {import('input').Modifier[]} */
         this._modifiers = [];
+        /** @type {Set<number>} */
         this._penPointerIds = new Set();
+        /** @type {boolean} */
         this._mouseModifiersSupported = false;
+        /** @type {boolean} */
         this._keySupported = false;
     }
 
+    /** @type {import('input').Modifier[]} */
     get modifiers() {
         return this._modifiers;
     }
 
+    /**
+     * @param {?string} key
+     * @param {import('input').Modifier[]} modifiers
+     * @param {boolean} [mouseModifiersSupported]
+     * @param {boolean} [keySupported]
+     */
     prepare(key, modifiers, mouseModifiersSupported=false, keySupported=false) {
         this.cleanup();
 
         this._mouseModifiersSupported = mouseModifiersSupported;
         this._keySupported = keySupported;
         this.setInput(key, modifiers);
+        /** @type {import('event-listener-collection').AddEventListenerArgs[]} */
         const events = [
             [this._inputNode, 'keydown', this._onModifierKeyDown.bind(this), false],
             [this._inputNode, 'keyup', this._onModifierKeyUp.bind(this), false]
@@ -66,12 +93,17 @@ class KeyboardMouseInputField extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {?string} key
+     * @param {import('input').Modifier[]} modifiers
+     */
     setInput(key, modifiers) {
         this._key = key;
         this._modifiers = this._sortModifiers(modifiers);
         this._updateDisplayString();
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
         this._modifiers = [];
@@ -81,21 +113,31 @@ class KeyboardMouseInputField extends EventDispatcher {
         this._penPointerIds.clear();
     }
 
+    /** */
     clearInputs() {
         this._updateModifiers([], null);
     }
 
     // Private
 
+    /**
+     * @param {import('input').Modifier[]} modifiers
+     * @returns {import('input').Modifier[]}
+     */
     _sortModifiers(modifiers) {
         return this._hotkeyUtil.sortModifiers(modifiers);
     }
 
+    /** */
     _updateDisplayString() {
         const displayValue = this._hotkeyUtil.getInputDisplayValue(this._key, this._modifiers);
         this._inputNode.value = displayValue;
     }
 
+    /**
+     * @param {KeyboardEvent} e
+     * @returns {Set<import('input').ModifierKey>}
+     */
     _getModifierKeys(e) {
         const modifiers = new Set(DocumentUtil.getActiveModifiers(e));
         // https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent/metaKey
@@ -116,6 +158,10 @@ class KeyboardMouseInputField extends EventDispatcher {
         return modifiers;
     }
 
+    /**
+     * @param {string|undefined} keyName
+     * @returns {boolean}
+     */
     _isModifierKey(keyName) {
         switch (keyName) {
             case 'AltLeft':
@@ -134,9 +180,13 @@ class KeyboardMouseInputField extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {KeyboardEvent} e
+     */
     _onModifierKeyDown(e) {
         e.preventDefault();
 
+        /** @type {string|undefined} */
         let key = e.code;
         if (key === 'Unidentified' || key === '') { key = void 0; }
         if (this._keySupported) {
@@ -154,15 +204,24 @@ class KeyboardMouseInputField extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {KeyboardEvent} e
+     */
     _onModifierKeyUp(e) {
         e.preventDefault();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMouseButtonMouseDown(e) {
         e.preventDefault();
         this._addModifiers(DocumentUtil.getActiveButtons(e));
     }
 
+    /**
+     * @param {PointerEvent} e
+     */
     _onMouseButtonPointerDown(e) {
         if (!e.isPrimary) { return; }
 
@@ -180,6 +239,9 @@ class KeyboardMouseInputField extends EventDispatcher {
         this._addModifiers(DocumentUtil.getActiveButtons(e));
     }
 
+    /**
+     * @param {PointerEvent} e
+     */
     _onMouseButtonPointerOver(e) {
         const {pointerType, pointerId} = e;
         if (pointerType === 'pen') {
@@ -187,23 +249,39 @@ class KeyboardMouseInputField extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {PointerEvent} e
+     */
     _onMouseButtonPointerOut(e) {
         const {pointerId} = e;
         this._penPointerIds.delete(pointerId);
     }
 
+    /**
+     * @param {PointerEvent} e
+     */
     _onMouseButtonPointerCancel(e) {
         this._onMouseButtonPointerOut(e);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMouseButtonMouseUp(e) {
         e.preventDefault();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMouseButtonContextMenu(e) {
         e.preventDefault();
     }
 
+    /**
+     * @param {Iterable<import('input').Modifier>} newModifiers
+     * @param {?string} [newKey]
+     */
     _addModifiers(newModifiers, newKey) {
         const modifiers = new Set(this._modifiers);
         for (const modifier of newModifiers) {
@@ -212,6 +290,10 @@ class KeyboardMouseInputField extends EventDispatcher {
         this._updateModifiers([...modifiers], newKey);
     }
 
+    /**
+     * @param {import('input').Modifier[]} modifiers
+     * @param {?string} [newKey]
+     */
     _updateModifiers(modifiers, newKey) {
         modifiers = this._sortModifiers(modifiers);
 
@@ -227,10 +309,18 @@ class KeyboardMouseInputField extends EventDispatcher {
 
         this._updateDisplayString();
         if (changed) {
-            this.trigger('change', {modifiers: this._modifiers, key: this._key});
+            /** @type {import('keyboard-mouse-input-field').ChangeEvent} */
+            const event = {modifiers: this._modifiers, key: this._key};
+            this.trigger('change', event);
         }
     }
 
+    /**
+     * @template T
+     * @param {T[]} array1
+     * @param {T[]} array2
+     * @returns {boolean}
+     */
     _areArraysEqual(array1, array2) {
         const length = array1.length;
         if (length !== array2.length) { return false; }
diff --git a/ext/js/pages/settings/keyboard-shortcuts-controller.js b/ext/js/pages/settings/keyboard-shortcuts-controller.js
index e1c000807c..cb8feb4378 100644
--- a/ext/js/pages/settings/keyboard-shortcuts-controller.js
+++ b/ext/js/pages/settings/keyboard-shortcuts-controller.js
@@ -23,16 +23,29 @@
  */
 
 class KeyboardShortcutController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {KeyboardShortcutHotkeyEntry[]} */
         this._entries = [];
+        /** @type {?import('environment').OperatingSystem} */
         this._os = null;
+        /** @type {?HTMLButtonElement} */
         this._addButton = null;
+        /** @type {?HTMLButtonElement} */
         this._resetButton = null;
+        /** @type {?HTMLElement} */
         this._listContainer = null;
+        /** @type {?HTMLElement} */
         this._emptyIndicator = null;
+        /** @type {Intl.Collator} */
         this._stringComparer = new Intl.Collator('en-US'); // Invariant locale
+        /** @type {?HTMLElement} */
         this._scrollContainer = null;
+        /** @type {Map<string, import('keyboard-shortcut-controller').ActionDetails>} */
         this._actionDetails = new Map([
             ['',                                 {scopes: new Set()}],
             ['close',                            {scopes: new Set(['popup', 'search'])}],
@@ -58,19 +71,21 @@ class KeyboardShortcutController {
         ]);
     }
 
+    /** @type {SettingsController} */
     get settingsController() {
         return this._settingsController;
     }
 
+    /** */
     async prepare() {
         const {platform: {os}} = await yomichan.api.getEnvironmentInfo();
         this._os = os;
 
-        this._addButton = document.querySelector('#hotkey-list-add');
-        this._resetButton = document.querySelector('#hotkey-list-reset');
-        this._listContainer = document.querySelector('#hotkey-list');
-        this._emptyIndicator = document.querySelector('#hotkey-list-empty');
-        this._scrollContainer = document.querySelector('#keyboard-shortcuts-modal .modal-body');
+        this._addButton = /** @type {HTMLButtonElement} */ (document.querySelector('#hotkey-list-add'));
+        this._resetButton = /** @type {HTMLButtonElement} */ (document.querySelector('#hotkey-list-reset'));
+        this._listContainer = /** @type {HTMLElement} */ (document.querySelector('#hotkey-list'));
+        this._emptyIndicator = /** @type {HTMLElement} */ (document.querySelector('#hotkey-list-empty'));
+        this._scrollContainer = /** @type {HTMLElement} */ (document.querySelector('#keyboard-shortcuts-modal .modal-body'));
 
         this._addButton.addEventListener('click', this._onAddClick.bind(this));
         this._resetButton.addEventListener('click', this._onResetClick.bind(this));
@@ -79,6 +94,9 @@ class KeyboardShortcutController {
         await this._updateOptions();
     }
 
+    /**
+     * @param {import('settings').InputsHotkeyOptions} terminationCharacterEntry
+     */
     async addEntry(terminationCharacterEntry) {
         const options = await this._settingsController.getOptions();
         const {inputs: {hotkeys}} = options;
@@ -92,9 +110,14 @@ class KeyboardShortcutController {
         }]);
 
         await this._updateOptions();
-        this._scrollContainer.scrollTop = this._scrollContainer.scrollHeight;
+        const scrollContainer = /** @type {HTMLElement} */ (this._scrollContainer);
+        scrollContainer.scrollTop = scrollContainer.scrollHeight;
     }
 
+    /**
+     * @param {number} index
+     * @returns {Promise<boolean>}
+     */
     async deleteEntry(index) {
         const options = await this._settingsController.getOptions();
         const {inputs: {hotkeys}} = options;
@@ -113,55 +136,79 @@ class KeyboardShortcutController {
         return true;
     }
 
+    /**
+     * @param {import('settings-modifications').Modification[]} targets
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async modifyProfileSettings(targets) {
         return await this._settingsController.modifyProfileSettings(targets);
     }
 
+    /**
+     * @returns {Promise<import('settings').InputsHotkeyOptions[]>}
+     */
     async getDefaultHotkeys() {
         const defaultOptions = await this._settingsController.getDefaultOptions();
         return defaultOptions.profiles[0].options.inputs.hotkeys;
     }
 
+    /**
+     * @param {string} action
+     * @returns {import('keyboard-shortcut-controller').ActionDetails|undefined}
+     */
     getActionDetails(action) {
         return this._actionDetails.get(action);
     }
 
     // Private
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         for (const entry of this._entries) {
             entry.cleanup();
         }
 
         this._entries = [];
+        const os = /** @type {import('environment').OperatingSystem} */ (this._os);
         const {inputs: {hotkeys}} = options;
         const fragment = document.createDocumentFragment();
 
         for (let i = 0, ii = hotkeys.length; i < ii; ++i) {
             const hotkeyEntry = hotkeys[i];
-            const node = this._settingsController.instantiateTemplate('hotkey-list-item');
+            const node = /** @type {HTMLElement} */ (this._settingsController.instantiateTemplate('hotkey-list-item'));
             fragment.appendChild(node);
-            const entry = new KeyboardShortcutHotkeyEntry(this, hotkeyEntry, i, node, this._os, this._stringComparer);
+            const entry = new KeyboardShortcutHotkeyEntry(this, hotkeyEntry, i, node, os, this._stringComparer);
             this._entries.push(entry);
             entry.prepare();
         }
 
-        this._listContainer.appendChild(fragment);
-        this._listContainer.hidden = (hotkeys.length === 0);
-        this._emptyIndicator.hidden = (hotkeys.length !== 0);
+        const listContainer = /** @type {HTMLElement} */ (this._listContainer);
+        listContainer.appendChild(fragment);
+        listContainer.hidden = (hotkeys.length === 0);
+        /** @type {HTMLElement} */ (this._emptyIndicator).hidden = (hotkeys.length !== 0);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onAddClick(e) {
         e.preventDefault();
         this._addNewEntry();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onResetClick(e) {
         e.preventDefault();
         this._reset();
     }
 
+    /** */
     async _addNewEntry() {
+        /** @type {import('settings').InputsHotkeyOptions} */
         const newEntry = {
             action: '',
             argument: '',
@@ -170,14 +217,17 @@ class KeyboardShortcutController {
             scopes: ['popup', 'search'],
             enabled: true
         };
-        return await this.addEntry(newEntry);
+        await this.addEntry(newEntry);
     }
 
+    /** */
     async _updateOptions() {
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
+    /** */
     async _reset() {
         const value = await this.getDefaultHotkeys();
         await this._settingsController.setProfileSetting('inputs.hotkeys', value);
@@ -186,34 +236,59 @@ class KeyboardShortcutController {
 }
 
 class KeyboardShortcutHotkeyEntry {
+    /**
+     * @param {KeyboardShortcutController} parent
+     * @param {import('settings').InputsHotkeyOptions} data
+     * @param {number} index
+     * @param {HTMLElement} node
+     * @param {import('environment').OperatingSystem} os
+     * @param {Intl.Collator} stringComparer
+     */
     constructor(parent, data, index, node, os, stringComparer) {
+        /** @type {KeyboardShortcutController} */
         this._parent = parent;
+        /** @type {import('settings').InputsHotkeyOptions} */
         this._data = data;
+        /** @type {number} */
         this._index = index;
+        /** @type {HTMLElement} */
         this._node = node;
+        /** @type {import('environment').OperatingSystem} */
         this._os = os;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?KeyboardMouseInputField} */
         this._inputField = null;
+        /** @type {?HTMLSelectElement} */
         this._actionSelect = null;
+        /** @type {string} */
         this._basePath = `inputs.hotkeys[${this._index}]`;
+        /** @type {Intl.Collator} */
         this._stringComparer = stringComparer;
+        /** @type {?HTMLButtonElement} */
         this._enabledButton = null;
+        /** @type {?PopupMenu} */
         this._scopeMenu = null;
+        /** @type {EventListenerCollection} */
         this._scopeMenuEventListeners = new EventListenerCollection();
+        /** @type {?HTMLElement} */
         this._argumentContainer = null;
+        /** @type {?HTMLInputElement} */
         this._argumentInput = null;
+        /** @type {EventListenerCollection} */
         this._argumentEventListeners = new EventListenerCollection();
     }
 
+    /** */
     prepare() {
         const node = this._node;
 
-        const menuButton = node.querySelector('.hotkey-list-item-button');
-        const input = node.querySelector('.hotkey-list-item-input');
-        const action = node.querySelector('.hotkey-list-item-action');
-        const enabledToggle = node.querySelector('.hotkey-list-item-enabled');
-        const scopesButton = node.querySelector('.hotkey-list-item-scopes-button');
-        const enabledButton = node.querySelector('.hotkey-list-item-enabled-button');
+        const menuButton = /** @type {HTMLButtonElement} */ (node.querySelector('.hotkey-list-item-button'));
+        const input = /** @type {HTMLInputElement} */ (node.querySelector('.hotkey-list-item-input'));
+        const action = /** @type {HTMLSelectElement} */ (node.querySelector('.hotkey-list-item-action'));
+        const enabledToggle = /** @type {HTMLInputElement} */ (node.querySelector('.hotkey-list-item-enabled'));
+        const scopesButton = /** @type {HTMLButtonElement} */ (node.querySelector('.hotkey-list-item-scopes-button'));
+        const enabledButton = /** @type {HTMLButtonElement} */ (node.querySelector('.hotkey-list-item-enabled-button'));
 
         this._actionSelect = action;
         this._enabledButton = enabledButton;
@@ -238,9 +313,10 @@ class KeyboardShortcutHotkeyEntry {
         this._eventListeners.on(this._inputField, 'change', this._onInputFieldChange.bind(this));
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
-        this._inputField.cleanup();
+        /** @type {KeyboardMouseInputField} */ (this._inputField).cleanup();
         this._clearScopeMenu();
         this._clearArgumentEventListeners();
         if (this._node.parentNode !== null) {
@@ -250,11 +326,14 @@ class KeyboardShortcutHotkeyEntry {
 
     // Private
 
+    /**
+     * @param {import('popup-menu').MenuOpenEvent} e
+     */
     _onMenuOpen(e) {
         const {action} = this._data;
 
         const {menu} = e.detail;
-        const resetArgument = menu.bodyNode.querySelector('.popup-menu-item[data-menu-action="resetArgument"]');
+        const resetArgument = /** @type {HTMLElement} */ (menu.bodyNode.querySelector('.popup-menu-item[data-menu-action="resetArgument"]'));
 
         const details = this._parent.getActionDetails(action);
         const argumentDetails = typeof details !== 'undefined' ? details.argument : void 0;
@@ -262,13 +341,16 @@ class KeyboardShortcutHotkeyEntry {
         resetArgument.hidden = (typeof argumentDetails === 'undefined');
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuClose(e) {
         switch (e.detail.action) {
             case 'delete':
                 this._delete();
                 break;
             case 'clearInputs':
-                this._inputField.clearInputs();
+                /** @type {KeyboardMouseInputField} */ (this._inputField).clearInputs();
                 break;
             case 'resetInput':
                 this._resetInput();
@@ -279,10 +361,13 @@ class KeyboardShortcutHotkeyEntry {
         }
     }
 
+    /**
+     * @param {import('popup-menu').MenuOpenEvent} e
+     */
     _onScopesMenuOpen(e) {
         const {menu} = e.detail;
         const validScopes = this._getValidScopesForAction(this._data.action);
-        if (validScopes.size === 0) {
+        if (validScopes === null || validScopes.size === 0) {
             menu.close();
             return;
         }
@@ -291,6 +376,9 @@ class KeyboardShortcutHotkeyEntry {
         this._updateDisplay(menu.containerNode); // Fix a animation issue due to changing checkbox values
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onScopesMenuClose(e) {
         const {menu, action} = e.detail;
         if (action === 'toggleScope') {
@@ -302,24 +390,45 @@ class KeyboardShortcutHotkeyEntry {
         }
     }
 
+    /**
+     * @param {import('keyboard-mouse-input-field').ChangeEvent} details
+     */
     _onInputFieldChange({key, modifiers}) {
-        this._setKeyAndModifiers(key, modifiers);
+        /** @type {import('input').ModifierKey[]} */
+        const modifiers2 = [];
+        for (const modifier of modifiers) {
+            const modifier2 = DocumentUtil.normalizeModifierKey(modifier);
+            if (modifier2 === null) { continue; }
+            modifiers2.push(modifier2);
+        }
+        this._setKeyAndModifiers(key, modifiers2);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onScopeCheckboxChange(e) {
-        const node = e.currentTarget;
-        const {scope} = node.dataset;
-        if (typeof scope !== 'string') { return; }
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
+        const scope = this._normalizeScope(node.dataset.scope);
+        if (scope === null) { return; }
         this._setScopeEnabled(scope, node.checked);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onActionSelectChange(e) {
-        const value = e.currentTarget.value;
+        const node = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        const value = node.value;
         this._setAction(value);
     }
 
+    /**
+     * @param {string} template
+     * @param {Event} e
+     */
     _onArgumentValueChange(template, e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         let value = this._getArgumentInputValue(node);
         switch (template) {
             case 'hotkey-argument-move-offset':
@@ -329,10 +438,15 @@ class KeyboardShortcutHotkeyEntry {
         this._setArgument(value);
     }
 
+    /** */
     async _delete() {
         this._parent.deleteEntry(this._index);
     }
 
+    /**
+     * @param {?string} key
+     * @param {import('input').ModifierKey[]} modifiers
+     */
     async _setKeyAndModifiers(key, modifiers) {
         this._data.key = key;
         this._data.modifiers = modifiers;
@@ -350,6 +464,10 @@ class KeyboardShortcutHotkeyEntry {
         ]);
     }
 
+    /**
+     * @param {import('settings').InputsHotkeyScope} scope
+     * @param {boolean} enabled
+     */
     async _setScopeEnabled(scope, enabled) {
         const scopes = this._data.scopes;
         const index = scopes.indexOf(scope);
@@ -372,10 +490,15 @@ class KeyboardShortcutHotkeyEntry {
         this._updateScopesButton();
     }
 
+    /**
+     * @param {import('settings-modifications').Modification[]} targets
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async _modifyProfileSettings(targets) {
         return await this._parent.settingsController.modifyProfileSettings(targets);
     }
 
+    /** */
     async _resetInput() {
         const defaultHotkeys = await this._parent.getDefaultHotkeys();
         const defaultValue = this._getDefaultKeyAndModifiers(defaultHotkeys, this._data.action);
@@ -383,9 +506,10 @@ class KeyboardShortcutHotkeyEntry {
 
         const {key, modifiers} = defaultValue;
         await this._setKeyAndModifiers(key, modifiers);
-        this._inputField.setInput(key, modifiers);
+        /** @type {KeyboardMouseInputField} */ (this._inputField).setInput(key, modifiers);
     }
 
+    /** */
     async _resetArgument() {
         const {action} = this._data;
         const details = this._parent.getActionDetails(action);
@@ -395,6 +519,11 @@ class KeyboardShortcutHotkeyEntry {
         await this._setArgument(argumentDefault);
     }
 
+    /**
+     * @param {import('settings').InputsHotkeyOptions[]} defaultHotkeys
+     * @param {string} action
+     * @returns {?{modifiers: import('settings').InputsHotkeyModifier[], key: ?string}}
+     */
     _getDefaultKeyAndModifiers(defaultHotkeys, action) {
         for (const {action: action2, key, modifiers} of defaultHotkeys) {
             if (action2 !== action) { continue; }
@@ -403,16 +532,18 @@ class KeyboardShortcutHotkeyEntry {
         return null;
     }
 
+    /**
+     * @param {string} value
+     */
     async _setAction(value) {
         const validScopesOld = this._getValidScopesForAction(this._data.action);
 
         const scopes = this._data.scopes;
 
         let details = this._parent.getActionDetails(value);
-        if (typeof details === 'undefined') { details = {}; }
+        if (typeof details === 'undefined') { details = {scopes: new Set()}; }
 
-        let validScopes = details.scopes;
-        if (typeof validScopes === 'undefined') { validScopes = new Set(); }
+        const validScopes = details.scopes;
 
         const {argument: argumentDetails} = details;
         let defaultArgument = typeof argumentDetails !== 'undefined' ? argumentDetails.default : '';
@@ -462,6 +593,9 @@ class KeyboardShortcutHotkeyEntry {
         this._updateActionArgument();
     }
 
+    /**
+     * @param {string} value
+     */
     async _setArgument(value) {
         this._data.argument = value;
 
@@ -479,16 +613,24 @@ class KeyboardShortcutHotkeyEntry {
         }]);
     }
 
+    /** */
     _updateScopesMenu() {
         if (this._scopeMenu === null) { return; }
         this._updateScopeMenuItems(this._scopeMenu);
     }
 
+    /**
+     * @param {string} action
+     * @returns {?Set<import('settings').InputsHotkeyScope>}
+     */
     _getValidScopesForAction(action) {
         const details = this._parent.getActionDetails(action);
         return typeof details !== 'undefined' ? details.scopes : null;
     }
 
+    /**
+     * @param {PopupMenu} menu
+     */
     _updateScopeMenuItems(menu) {
         this._scopeMenuEventListeners.removeAllEventListeners();
 
@@ -496,14 +638,15 @@ class KeyboardShortcutHotkeyEntry {
         const validScopes = this._getValidScopesForAction(this._data.action);
 
         const bodyNode = menu.bodyNode;
-        const menuItems = bodyNode.querySelectorAll('.popup-menu-item');
+        const menuItems = /** @type {NodeListOf<HTMLElement>} */ (bodyNode.querySelectorAll('.popup-menu-item'));
         for (const menuItem of menuItems) {
             if (menuItem.dataset.menuAction !== 'toggleScope') { continue; }
 
-            const {scope} = menuItem.dataset;
+            const scope = this._normalizeScope(menuItem.dataset.scope);
+            if (scope === null) { continue; }
             menuItem.hidden = !(validScopes === null || validScopes.has(scope));
 
-            const checkbox = menuItem.querySelector('.hotkey-scope-checkbox');
+            const checkbox = /** @type {HTMLInputElement} */ (menuItem.querySelector('.hotkey-scope-checkbox'));
             if (checkbox !== null) {
                 checkbox.checked = scopes.includes(scope);
                 this._scopeMenuEventListeners.addEventListener(checkbox, 'change', this._onScopeCheckboxChange.bind(this), false);
@@ -511,16 +654,23 @@ class KeyboardShortcutHotkeyEntry {
         }
     }
 
+    /** */
     _clearScopeMenu() {
         this._scopeMenuEventListeners.removeAllEventListeners();
         this._scopeMenu = null;
     }
 
+    /** */
     _updateScopesButton() {
         const {scopes} = this._data;
-        this._enabledButton.dataset.scopeCount = `${scopes.length}`;
+        if (this._enabledButton !== null) {
+            this._enabledButton.dataset.scopeCount = `${scopes.length}`;
+        }
     }
 
+    /**
+     * @param {HTMLElement} node
+     */
     _updateDisplay(node) {
         const {style} = node;
         const {display} = style;
@@ -529,49 +679,64 @@ class KeyboardShortcutHotkeyEntry {
         style.display = display;
     }
 
+    /** */
     _updateActionArgument() {
         this._clearArgumentEventListeners();
 
         const {action, argument} = this._data;
         const details = this._parent.getActionDetails(action);
-        const {argument: argumentDetails} = typeof details !== 'undefined' ? details : {};
+        const argumentDetails = typeof details !== 'undefined' ? details.argument : void 0;
 
-        this._argumentContainer.textContent = '';
+        if (this._argumentContainer !== null) {
+            this._argumentContainer.textContent = '';
+        }
         if (typeof argumentDetails !== 'undefined') {
             const {template} = argumentDetails;
             const node = this._parent.settingsController.instantiateTemplate(template);
             const inputSelector = '.hotkey-argument-input';
-            const inputNode = node.matches(inputSelector) ? node : node.querySelector(inputSelector);
+            const inputNode = /** @type {HTMLInputElement} */ (node.matches(inputSelector) ? node : node.querySelector(inputSelector));
             if (inputNode !== null) {
                 this._setArgumentInputValue(inputNode, argument);
                 this._argumentInput = inputNode;
                 this._updateArgumentInputValidity();
                 this._argumentEventListeners.addEventListener(inputNode, 'change', this._onArgumentValueChange.bind(this, template), false);
             }
-            this._argumentContainer.appendChild(node);
+            if (this._argumentContainer !== null) {
+                this._argumentContainer.appendChild(node);
+            }
         }
     }
 
+    /** */
     _clearArgumentEventListeners() {
         this._argumentEventListeners.removeAllEventListeners();
         this._argumentInput = null;
     }
 
+    /**
+     * @param {HTMLInputElement} node
+     * @returns {string}
+     */
     _getArgumentInputValue(node) {
         return node.value;
     }
 
+    /**
+     * @param {HTMLInputElement} node
+     * @param {string} value
+     */
     _setArgumentInputValue(node, value) {
         node.value = value;
     }
 
+    /** */
     async _updateArgumentInputValidity() {
         if (this._argumentInput === null) { return; }
 
         let okay = true;
         const {action, argument} = this._data;
         const details = this._parent.getActionDetails(action);
-        const {argument: argumentDetails} = typeof details !== 'undefined' ? details : {};
+        const argumentDetails = typeof details !== 'undefined' ? details.argument : void 0;
 
         if (typeof argumentDetails !== 'undefined') {
             const {template} = argumentDetails;
@@ -585,6 +750,10 @@ class KeyboardShortcutHotkeyEntry {
         this._argumentInput.dataset.invalid = `${!okay}`;
     }
 
+    /**
+     * @param {string} path
+     * @returns {Promise<boolean>}
+     */
     async _isHotkeyArgumentSettingPathValid(path) {
         if (path.length === 0) { return true; }
 
@@ -601,4 +770,19 @@ class KeyboardShortcutHotkeyEntry {
         }
         return false;
     }
+
+    /**
+     * @param {string|undefined} value
+     * @returns {?import('settings').InputsHotkeyScope}
+     */
+    _normalizeScope(value) {
+        switch (value) {
+            case 'popup':
+            case 'search':
+            case 'web':
+                return value;
+            default:
+                return null;
+        }
+    }
 }
diff --git a/ext/js/pages/settings/mecab-controller.js b/ext/js/pages/settings/mecab-controller.js
index 8b00c72d39..fe66dcfb53 100644
--- a/ext/js/pages/settings/mecab-controller.js
+++ b/ext/js/pages/settings/mecab-controller.js
@@ -17,48 +17,61 @@
  */
 
 class MecabController {
-    constructor(settingsController) {
-        this._settingsController = settingsController;
+    constructor() {
+        /** @type {?HTMLButtonElement} */
         this._testButton = null;
+        /** @type {?HTMLElement} */
         this._resultsContainer = null;
+        /** @type {boolean} */
         this._testActive = false;
     }
 
+    /** */
     prepare() {
-        this._testButton = document.querySelector('#test-mecab-button');
-        this._resultsContainer = document.querySelector('#test-mecab-results');
+        this._testButton = /** @type {HTMLButtonElement} */ (document.querySelector('#test-mecab-button'));
+        this._resultsContainer = /** @type {HTMLElement} */ (document.querySelector('#test-mecab-results'));
 
         this._testButton.addEventListener('click', this._onTestButtonClick.bind(this), false);
     }
 
     // Private
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onTestButtonClick(e) {
         e.preventDefault();
         this._testMecab();
     }
 
+    /** */
     async _testMecab() {
         if (this._testActive) { return; }
 
         try {
             this._testActive = true;
-            this._testButton.disabled = true;
-            this._resultsContainer.textContent = '';
-            this._resultsContainer.hidden = true;
+            const resultsContainer = /** @type {HTMLElement} */ (this._resultsContainer);
+            /** @type {HTMLButtonElement} */ (this._testButton).disabled = true;
+            resultsContainer.textContent = '';
+            resultsContainer.hidden = true;
             await yomichan.api.testMecab();
             this._setStatus('Connection was successful', false);
         } catch (e) {
-            this._setStatus(e.message, true);
+            this._setStatus(e instanceof Error ? e.message : `${e}`, true);
         } finally {
             this._testActive = false;
-            this._testButton.disabled = false;
+            /** @type {HTMLButtonElement} */ (this._testButton).disabled = false;
         }
     }
 
+    /**
+     * @param {string} message
+     * @param {boolean} isError
+     */
     _setStatus(message, isError) {
-        this._resultsContainer.textContent = message;
-        this._resultsContainer.hidden = false;
-        this._resultsContainer.classList.toggle('danger-text', isError);
+        const resultsContainer = /** @type {HTMLElement} */ (this._resultsContainer);
+        resultsContainer.textContent = message;
+        resultsContainer.hidden = false;
+        resultsContainer.classList.toggle('danger-text', isError);
     }
 }
diff --git a/ext/js/pages/settings/modal-controller.js b/ext/js/pages/settings/modal-controller.js
index 645485d563..f9f018e928 100644
--- a/ext/js/pages/settings/modal-controller.js
+++ b/ext/js/pages/settings/modal-controller.js
@@ -22,13 +22,16 @@
 
 class ModalController {
     constructor() {
+        /** @type {Modal[]} */
         this._modals = [];
+        /** @type {Map<string|Element, Modal>} */
         this._modalMap = new Map();
     }
 
+    /** */
     prepare() {
         const idSuffix = '-modal';
-        for (const node of document.querySelectorAll('.modal')) {
+        for (const node of /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.modal'))) {
             let {id} = node;
             if (typeof id !== 'string') { continue; }
 
@@ -44,11 +47,18 @@ class ModalController {
         }
     }
 
+    /**
+     * @param {string|Element} nameOrNode
+     * @returns {?Modal}
+     */
     getModal(nameOrNode) {
         const modal = this._modalMap.get(nameOrNode);
         return (typeof modal !== 'undefined' ? modal : null);
     }
 
+    /**
+     * @returns {?Modal}
+     */
     getTopVisibleModal() {
         for (let i = this._modals.length - 1; i >= 0; --i) {
             const modal = this._modals[i];
diff --git a/ext/js/pages/settings/modal.js b/ext/js/pages/settings/modal.js
index 74e22fa4a4..25a924c3d1 100644
--- a/ext/js/pages/settings/modal.js
+++ b/ext/js/pages/settings/modal.js
@@ -21,40 +21,55 @@
  */
 
 class Modal extends PanelElement {
+    /**
+     * @param {HTMLElement} node
+     */
     constructor(node) {
         super({
             node,
             closingAnimationDuration: 375 // Milliseconds; includes buffer
         });
+        /** @type {?Element} */
         this._contentNode = null;
+        /** @type {boolean} */
         this._canCloseOnClick = false;
     }
 
+    /** */
     prepare() {
         const node = this.node;
         this._contentNode = node.querySelector('.modal-content');
-        let dimmerNode = node.querySelector('.modal-content-dimmer');
+        let dimmerNode = /** @type {?HTMLElement} */ (node.querySelector('.modal-content-dimmer'));
         if (dimmerNode === null) { dimmerNode = node; }
         dimmerNode.addEventListener('mousedown', this._onModalContainerMouseDown.bind(this), false);
         dimmerNode.addEventListener('mouseup', this._onModalContainerMouseUp.bind(this), false);
         dimmerNode.addEventListener('click', this._onModalContainerClick.bind(this), false);
 
-        for (const actionNode of node.querySelectorAll('[data-modal-action]')) {
+        for (const actionNode of /** @type {NodeListOf<HTMLElement>} */ (node.querySelectorAll('[data-modal-action]'))) {
             actionNode.addEventListener('click', this._onActionNodeClick.bind(this), false);
         }
     }
 
     // Private
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onModalContainerMouseDown(e) {
         this._canCloseOnClick = (e.currentTarget === e.target);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onModalContainerMouseUp(e) {
         if (!this._canCloseOnClick) { return; }
         this._canCloseOnClick = (e.currentTarget === e.target);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onModalContainerClick(e) {
         if (!this._canCloseOnClick) { return; }
         this._canCloseOnClick = false;
@@ -62,8 +77,12 @@ class Modal extends PanelElement {
         this.setVisible(false);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onActionNodeClick(e) {
-        const {modalAction} = e.currentTarget.dataset;
+        const element = /** @type {HTMLElement} */ (e.currentTarget);
+        const {modalAction} = element.dataset;
         switch (modalAction) {
             case 'expand':
                 this._setExpanded(true);
@@ -74,6 +93,9 @@ class Modal extends PanelElement {
         }
     }
 
+    /**
+     * @param {boolean} expanded
+     */
     _setExpanded(expanded) {
         if (this._contentNode === null) { return; }
         this._contentNode.classList.toggle('modal-content-full', expanded);
diff --git a/ext/js/pages/settings/nested-popups-controller.js b/ext/js/pages/settings/nested-popups-controller.js
index a46c8f1607..fac609a050 100644
--- a/ext/js/pages/settings/nested-popups-controller.js
+++ b/ext/js/pages/settings/nested-popups-controller.js
@@ -21,50 +21,79 @@
  */
 
 class NestedPopupsController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {number} */
         this._popupNestingMaxDepth = 0;
+        /** @type {?HTMLInputElement} */
+        this._nestedPopupsEnabled = null;
+        /** @type {?HTMLInputElement} */
+        this._nestedPopupsCount = null;
+        /** @type {?HTMLElement} */
+        this._nestedPopupsEnabledMoreOptions = null;
     }
 
+    /** */
     async prepare() {
-        this._nestedPopupsEnabled = document.querySelector('#nested-popups-enabled');
-        this._nestedPopupsCount = document.querySelector('#nested-popups-count');
-        this._nestedPopupsEnabledMoreOptions = document.querySelector('#nested-popups-enabled-more-options');
+        this._nestedPopupsEnabled = /** @type {HTMLInputElement} */ (document.querySelector('#nested-popups-enabled'));
+        this._nestedPopupsCount = /** @type {HTMLInputElement} */ (document.querySelector('#nested-popups-count'));
+        this._nestedPopupsEnabledMoreOptions = /** @type {HTMLElement} */ (document.querySelector('#nested-popups-enabled-more-options'));
 
         const options = await this._settingsController.getOptions();
+        const optionsContext = this._settingsController.getOptionsContext();
 
         this._nestedPopupsEnabled.addEventListener('change', this._onNestedPopupsEnabledChange.bind(this), false);
         this._nestedPopupsCount.addEventListener('change', this._onNestedPopupsCountChange.bind(this), false);
         this._settingsController.on('optionsChanged', this._onOptionsChanged.bind(this));
-        this._onOptionsChanged({options});
+        this._onOptionsChanged({options, optionsContext});
     }
 
     // Private
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         this._updatePopupNestingMaxDepth(options.scanning.popupNestingMaxDepth);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onNestedPopupsEnabledChange(e) {
-        const value = e.currentTarget.checked;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
+        const value = node.checked;
         if (value && this._popupNestingMaxDepth > 0) { return; }
         this._setPopupNestingMaxDepth(value ? 1 : 0);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onNestedPopupsCountChange(e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         const value = Math.max(1, DocumentUtil.convertElementValueToNumber(node.value, node));
         this._setPopupNestingMaxDepth(value);
     }
 
+    /**
+     * @param {number} value
+     */
     _updatePopupNestingMaxDepth(value) {
         const enabled = (value > 0);
         this._popupNestingMaxDepth = value;
-        this._nestedPopupsEnabled.checked = enabled;
-        this._nestedPopupsCount.value = `${value}`;
-        this._nestedPopupsEnabledMoreOptions.hidden = !enabled;
+        /** @type {HTMLInputElement} */ (this._nestedPopupsEnabled).checked = enabled;
+        /** @type {HTMLInputElement} */ (this._nestedPopupsCount).value = `${value}`;
+        /** @type {HTMLElement} */ (this._nestedPopupsEnabledMoreOptions).hidden = !enabled;
     }
 
+    /**
+     * @param {number} value
+     */
     async _setPopupNestingMaxDepth(value) {
         this._updatePopupNestingMaxDepth(value);
         await this._settingsController.setProfileSetting('scanning.popupNestingMaxDepth', value);
diff --git a/ext/js/pages/settings/permissions-origin-controller.js b/ext/js/pages/settings/permissions-origin-controller.js
index e31f75d185..c8940d1f50 100644
--- a/ext/js/pages/settings/permissions-origin-controller.js
+++ b/ext/js/pages/settings/permissions-origin-controller.js
@@ -17,24 +17,36 @@
  */
 
 class PermissionsOriginController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?HTMLElement} */
         this._originContainer = null;
+        /** @type {?HTMLElement} */
         this._originEmpty = null;
+        /** @type {?NodeListOf<HTMLInputElement>} */
         this._originToggleNodes = null;
+        /** @type {?HTMLInputElement} */
         this._addOriginInput = null;
+        /** @type {?HTMLElement} */
         this._errorContainer = null;
+        /** @type {ChildNode[]} */
         this._originContainerChildren = [];
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
     }
 
+    /** */
     async prepare() {
-        this._originContainer = document.querySelector('#permissions-origin-list');
-        this._originEmpty = document.querySelector('#permissions-origin-list-empty');
-        this._originToggleNodes = document.querySelectorAll('.permissions-origin-toggle');
-        this._addOriginInput = document.querySelector('#permissions-origin-new-input');
-        this._errorContainer = document.querySelector('#permissions-origin-list-error');
-        const addButton = document.querySelector('#permissions-origin-add');
+        this._originContainer = /** @type {HTMLElement} */ (document.querySelector('#permissions-origin-list'));
+        this._originEmpty = /** @type {HTMLElement} */ (document.querySelector('#permissions-origin-list-empty'));
+        this._originToggleNodes = /** @type {NodeListOf<HTMLInputElement>} */ (document.querySelectorAll('.permissions-origin-toggle'));
+        this._addOriginInput = /** @type {HTMLInputElement} */ (document.querySelector('#permissions-origin-new-input'));
+        this._errorContainer = /** @type {HTMLElement} */ (document.querySelector('#permissions-origin-list-error'));
+        const addButton = /** @type {HTMLButtonElement} */ (document.querySelector('#permissions-origin-add'));
 
         for (const node of this._originToggleNodes) {
             node.addEventListener('change', this._onOriginToggleChange.bind(this), false);
@@ -47,6 +59,9 @@ class PermissionsOriginController {
 
     // Private
 
+    /**
+     * @param {import('settings-controller').PermissionsChangedEvent} details
+     */
     _onPermissionsChanged({permissions}) {
         this._eventListeners.removeAllEventListeners();
         for (const node of this._originContainerChildren) {
@@ -55,9 +70,11 @@ class PermissionsOriginController {
         }
         this._originContainerChildren = [];
 
+        /** @type {Set<string>} */
         const originsSet = new Set(permissions.origins);
-        for (const node of this._originToggleNodes) {
-            node.checked = originsSet.has(node.dataset.origin);
+        for (const node of /** @type {NodeListOf<HTMLInputElement>} */ (this._originToggleNodes)) {
+            const {origin} = node.dataset;
+            node.checked = typeof origin === 'string' && originsSet.has(origin);
         }
 
         let any = false;
@@ -65,60 +82,78 @@ class PermissionsOriginController {
             '<all_urls>'
         ]);
         const fragment = document.createDocumentFragment();
-        for (const origin of permissions.origins) {
+        for (const origin of originsSet) {
             if (excludeOrigins.has(origin)) { continue; }
             const node = this._settingsController.instantiateTemplateFragment('permissions-origin');
-            const input = node.querySelector('.permissions-origin-input');
-            const menuButton = node.querySelector('.permissions-origin-button');
+            const input = /** @type {HTMLInputElement} */ (node.querySelector('.permissions-origin-input'));
+            const menuButton = /** @type {HTMLElement} */ (node.querySelector('.permissions-origin-button'));
             input.value = origin;
             this._eventListeners.addEventListener(menuButton, 'menuClose', this._onOriginMenuClose.bind(this, origin), false);
             this._originContainerChildren.push(...node.childNodes);
             fragment.appendChild(node);
             any = true;
         }
-        this._originContainer.insertBefore(fragment, this._originContainer.firstChild);
-        this._originEmpty.hidden = any;
+        const container = /** @type {HTMLElement} */ (this._originContainer);
+        container.insertBefore(fragment, container.firstChild);
+        /** @type {HTMLElement} */ (this._originEmpty).hidden = any;
 
-        this._errorContainer.hidden = true;
+        /** @type {HTMLElement} */ (this._errorContainer).hidden = true;
     }
 
+    /**
+     * @param {Event} e
+     */
     _onOriginToggleChange(e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         const value = node.checked;
         node.checked = !value;
 
         const {origin} = node.dataset;
+        if (typeof origin !== 'string') { return; }
         this._setOriginPermissionEnabled(origin, value);
     }
 
+    /**
+     * @param {string} origin
+     */
     _onOriginMenuClose(origin) {
         this._setOriginPermissionEnabled(origin, false);
     }
 
+    /** */
     _onAddButtonClick() {
         this._addOrigin();
     }
 
+    /** */
     async _addOrigin() {
-        const origin = this._addOriginInput.value;
+        const input = /** @type {HTMLInputElement} */ (this._addOriginInput);
+        const origin = input.value;
         const added = await this._setOriginPermissionEnabled(origin, true);
         if (added) {
-            this._addOriginInput.value = '';
+            input.value = '';
         }
     }
 
+    /** */
     async _updatePermissions() {
         const permissions = await this._settingsController.permissionsUtil.getAllPermissions();
         this._onPermissionsChanged({permissions});
     }
 
+    /**
+     * @param {string} origin
+     * @param {boolean} enabled
+     * @returns {Promise<boolean>}
+     */
     async _setOriginPermissionEnabled(origin, enabled) {
         let added = false;
         try {
             added = await this._settingsController.permissionsUtil.setPermissionsGranted({origins: [origin]}, enabled);
         } catch (e) {
-            this._errorContainer.hidden = false;
-            this._errorContainer.textContent = e.message;
+            const errorContainer = /** @type {HTMLElement} */ (this._errorContainer);
+            errorContainer.hidden = false;
+            errorContainer.textContent = e instanceof Error ? e.message : `${e}`;
         }
         if (!added) { return false; }
         await this._updatePermissions();
diff --git a/ext/js/pages/settings/permissions-toggle-controller.js b/ext/js/pages/settings/permissions-toggle-controller.js
index 8bf9dc1816..9fe7107a74 100644
--- a/ext/js/pages/settings/permissions-toggle-controller.js
+++ b/ext/js/pages/settings/permissions-toggle-controller.js
@@ -21,11 +21,17 @@
  */
 
 class PermissionsToggleController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?NodeListOf<HTMLInputElement>} */
         this._toggles = null;
     }
 
+    /** */
     async prepare() {
         this._toggles = document.querySelectorAll('.permissions-toggle');
 
@@ -36,14 +42,18 @@ class PermissionsToggleController {
         this._settingsController.on('permissionsChanged', this._onPermissionsChanged.bind(this));
 
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
     // Private
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         let accessor = null;
-        for (const toggle of this._toggles) {
+        for (const toggle of /** @type {NodeListOf<HTMLInputElement>} */ (this._toggles)) {
             const {permissionsSetting} = toggle.dataset;
             if (typeof permissionsSetting !== 'string') { continue; }
 
@@ -63,8 +73,11 @@ class PermissionsToggleController {
         this._updateValidity();
     }
 
+    /**
+     * @param {Event} e
+     */
     async _onPermissionsToggleChange(e) {
-        const toggle = e.currentTarget;
+        const toggle = /** @type {HTMLInputElement} */ (e.currentTarget);
         let value = toggle.checked;
         const valuePre = !value;
         const {permissionsSetting} = toggle.dataset;
@@ -92,9 +105,13 @@ class PermissionsToggleController {
         }
     }
 
-    _onPermissionsChanged({permissions: {permissions}}) {
-        const permissionsSet = new Set(permissions);
-        for (const toggle of this._toggles) {
+    /**
+     * @param {import('settings-controller').PermissionsChangedEvent} details
+     */
+    _onPermissionsChanged({permissions}) {
+        const permissions2 = permissions.permissions;
+        const permissionsSet = new Set(typeof permissions2 !== 'undefined' ? permissions2 : []);
+        for (const toggle of /** @type {NodeListOf<HTMLInputElement>} */ (this._toggles)) {
             const {permissionsSetting} = toggle.dataset;
             const hasPermissions = this._hasAll(permissionsSet, this._getRequiredPermissions(toggle));
 
@@ -107,17 +124,27 @@ class PermissionsToggleController {
         }
     }
 
+    /**
+     * @param {HTMLInputElement} toggle
+     * @param {boolean} valid
+     */
     _setToggleValid(toggle, valid) {
-        const relative = toggle.closest('.settings-item');
+        const relative = /** @type {?HTMLElement} */ (toggle.closest('.settings-item'));
         if (relative === null) { return; }
         relative.dataset.invalid = `${!valid}`;
     }
 
+    /** */
     async _updateValidity() {
         const permissions = await this._settingsController.permissionsUtil.getAllPermissions();
         this._onPermissionsChanged({permissions});
     }
 
+    /**
+     * @param {Set<string>} set
+     * @param {string[]} values
+     * @returns {boolean}
+     */
     _hasAll(set, values) {
         for (const value of values) {
             if (!set.has(value)) { return false; }
@@ -125,6 +152,10 @@ class PermissionsToggleController {
         return true;
     }
 
+    /**
+     * @param {HTMLInputElement} toggle
+     * @returns {string[]}
+     */
     _getRequiredPermissions(toggle) {
         const requiredPermissions = toggle.dataset.requiredPermissions;
         return (typeof requiredPermissions === 'string' && requiredPermissions.length > 0 ? requiredPermissions.split(' ') : []);
diff --git a/ext/js/pages/settings/persistent-storage-controller.js b/ext/js/pages/settings/persistent-storage-controller.js
index 4516924077..1b3c35a651 100644
--- a/ext/js/pages/settings/persistent-storage-controller.js
+++ b/ext/js/pages/settings/persistent-storage-controller.js
@@ -18,22 +18,27 @@
 
 class PersistentStorageController {
     constructor() {
-        this._persistentStorageCheckbox = false;
+        /** @type {?HTMLInputElement} */
+        this._persistentStorageCheckbox = null;
     }
 
+    /** */
     async prepare() {
-        this._persistentStorageCheckbox = document.querySelector('#storage-persistent-checkbox');
+        this._persistentStorageCheckbox = /** @type {HTMLInputElement} */ (document.querySelector('#storage-persistent-checkbox'));
         this._persistentStorageCheckbox.addEventListener('change', this._onPersistentStorageCheckboxChange.bind(this), false);
 
         if (!this._isPersistentStorageSupported()) { return; }
 
-        const info = document.querySelector('#storage-persistent-info');
+        const info = /** @type {?HTMLElement} */ (document.querySelector('#storage-persistent-info'));
         if (info !== null) { info.hidden = false; }
 
         const isStoragePeristent = await this.isStoragePeristent();
         this._updateCheckbox(isStoragePeristent);
     }
 
+    /**
+     * @returns {Promise<boolean>}
+     */
     async isStoragePeristent() {
         try {
             return await navigator.storage.persisted();
@@ -45,8 +50,11 @@ class PersistentStorageController {
 
     // Private
 
+    /**
+     * @param {Event} e
+     */
     _onPersistentStorageCheckboxChange(e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         if (node.checked) {
             node.checked = false;
             this._attemptPersistStorage();
@@ -55,6 +63,7 @@ class PersistentStorageController {
         }
     }
 
+    /** */
     async _attemptPersistStorage() {
         let isStoragePeristent = false;
         try {
@@ -65,18 +74,24 @@ class PersistentStorageController {
 
         this._updateCheckbox(isStoragePeristent);
 
-        const node = document.querySelector('#storage-persistent-fail-warning');
+        const node = /** @type {?HTMLElement} */ (document.querySelector('#storage-persistent-fail-warning'));
         if (node !== null) { node.hidden = isStoragePeristent; }
 
         yomichan.trigger('storageChanged');
     }
 
+    /**
+     * @returns {boolean}
+     */
     _isPersistentStorageSupported() {
         return isObject(navigator.storage) && typeof navigator.storage.persist === 'function';
     }
 
+    /**
+     * @param {boolean} isStoragePeristent
+     */
     _updateCheckbox(isStoragePeristent) {
-        this._persistentStorageCheckbox.checked = isStoragePeristent;
-        this._persistentStorageCheckbox.readOnly = isStoragePeristent;
+        /** @type {HTMLInputElement} */ (this._persistentStorageCheckbox).checked = isStoragePeristent;
+        /** @type {HTMLInputElement} */ (this._persistentStorageCheckbox).readOnly = isStoragePeristent;
     }
 }
diff --git a/ext/js/pages/settings/popup-preview-controller.js b/ext/js/pages/settings/popup-preview-controller.js
index 6f52613b4e..227fff23b3 100644
--- a/ext/js/pages/settings/popup-preview-controller.js
+++ b/ext/js/pages/settings/popup-preview-controller.js
@@ -17,22 +17,32 @@
  */
 
 class PopupPreviewController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {string} */
         this._targetOrigin = chrome.runtime.getURL('/').replace(/\/$/, '');
+        /** @type {?HTMLIFrameElement} */
         this._frame = null;
+        /** @type {?HTMLTextAreaElement} */
         this._customCss = null;
+        /** @type {?HTMLTextAreaElement} */
         this._customOuterCss = null;
+        /** @type {?HTMLElement} */
         this._previewFrameContainer = null;
     }
 
+    /** */
     async prepare() {
         if (new URLSearchParams(location.search).get('popup-preview') === 'false') { return; }
 
-        this._frame = document.querySelector('#popup-preview-frame');
-        this._customCss = document.querySelector('#custom-popup-css');
-        this._customOuterCss = document.querySelector('#custom-popup-outer-css');
-        this._previewFrameContainer = document.querySelector('.preview-frame-container');
+        this._frame = /** @type {HTMLIFrameElement} */ (document.querySelector('#popup-preview-frame'));
+        this._customCss = /** @type {HTMLTextAreaElement} */ (document.querySelector('#custom-popup-css'));
+        this._customOuterCss = /** @type {HTMLTextAreaElement} */ (document.querySelector('#custom-popup-outer-css'));
+        this._previewFrameContainer = /** @type {HTMLElement} */ (document.querySelector('.preview-frame-container'));
 
         this._customCss.addEventListener('input', this._onCustomCssChange.bind(this), false);
         this._customCss.addEventListener('settingChanged', this._onCustomCssChange.bind(this), false);
@@ -46,25 +56,35 @@ class PopupPreviewController {
 
     // Private
 
+    /** */
     _onFrameLoad() {
         this._onOptionsContextChange();
         this._onCustomCssChange();
         this._onCustomOuterCssChange();
     }
 
+    /** */
     _onCustomCssChange() {
-        this._invoke('PopupPreviewFrame.setCustomCss', {css: this._customCss.value});
+        const css = /** @type {HTMLTextAreaElement} */ (this._customCss).value;
+        this._invoke('PopupPreviewFrame.setCustomCss', {css});
     }
 
+    /** */
     _onCustomOuterCssChange() {
-        this._invoke('PopupPreviewFrame.setCustomOuterCss', {css: this._customOuterCss.value});
+        const css = /** @type {HTMLTextAreaElement} */ (this._customOuterCss).value;
+        this._invoke('PopupPreviewFrame.setCustomOuterCss', {css});
     }
 
+    /** */
     _onOptionsContextChange() {
         const optionsContext = this._settingsController.getOptionsContext();
         this._invoke('PopupPreviewFrame.updateOptionsContext', {optionsContext});
     }
 
+    /**
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     */
     _invoke(action, params) {
         if (this._frame === null || this._frame.contentWindow === null) { return; }
         this._frame.contentWindow.postMessage({action, params}, this._targetOrigin);
diff --git a/ext/js/pages/settings/popup-preview-frame-main.js b/ext/js/pages/settings/popup-preview-frame-main.js
index 4a2e5fdac7..f167411aa5 100644
--- a/ext/js/pages/settings/popup-preview-frame-main.js
+++ b/ext/js/pages/settings/popup-preview-frame-main.js
@@ -27,6 +27,12 @@
         await yomichan.prepare();
 
         const {tabId, frameId} = await yomichan.api.frameInformationGet();
+        if (typeof tabId === 'undefined') {
+            throw new Error('Failed to get tabId');
+        }
+        if (typeof frameId === 'undefined') {
+            throw new Error('Failed to get frameId');
+        }
 
         const hotkeyHandler = new HotkeyHandler();
         hotkeyHandler.prepare();
diff --git a/ext/js/pages/settings/popup-preview-frame.js b/ext/js/pages/settings/popup-preview-frame.js
index f24e1485cc..c5d0d2cd52 100644
--- a/ext/js/pages/settings/popup-preview-frame.js
+++ b/ext/js/pages/settings/popup-preview-frame.js
@@ -23,32 +23,53 @@
  */
 
 class PopupPreviewFrame {
+    /**
+     * @param {number} tabId
+     * @param {number} frameId
+     * @param {PopupFactory} popupFactory
+     * @param {HotkeyHandler} hotkeyHandler
+     */
     constructor(tabId, frameId, popupFactory, hotkeyHandler) {
+        /** @type {number} */
         this._tabId = tabId;
+        /** @type {number} */
         this._frameId = frameId;
+        /** @type {PopupFactory} */
         this._popupFactory = popupFactory;
+        /** @type {HotkeyHandler} */
         this._hotkeyHandler = hotkeyHandler;
+        /** @type {?Frontend} */
         this._frontend = null;
+        /** @type {?(optionsContext: import('settings').OptionsContext) => Promise<import('settings').ProfileOptions>} */
         this._apiOptionsGetOld = null;
+        /** @type {boolean} */
         this._popupShown = false;
+        /** @type {?number} */
         this._themeChangeTimeout = null;
+        /** @type {?import('text-source').TextSource} */
         this._textSource = null;
+        /** @type {?import('settings').OptionsContext} */
         this._optionsContext = null;
+        /** @type {?HTMLElement} */
         this._exampleText = null;
+        /** @type {?HTMLInputElement} */
         this._exampleTextInput = null;
+        /** @type {string} */
         this._targetOrigin = chrome.runtime.getURL('/').replace(/\/$/, '');
 
-        this._windowMessageHandlers = new Map([
+        /** @type {Map<string, (params: import('core').SerializableObjectAny) => void>} */
+        this._windowMessageHandlers = new Map(/** @type {[key: string, handler: (params: import('core').SerializableObjectAny) => void][]} */ ([
             ['PopupPreviewFrame.setText',              this._onSetText.bind(this)],
             ['PopupPreviewFrame.setCustomCss',         this._setCustomCss.bind(this)],
             ['PopupPreviewFrame.setCustomOuterCss',    this._setCustomOuterCss.bind(this)],
             ['PopupPreviewFrame.updateOptionsContext', this._updateOptionsContext.bind(this)]
-        ]);
+        ]));
     }
 
+    /** */
     async prepare() {
-        this._exampleText = document.querySelector('#example-text');
-        this._exampleTextInput = document.querySelector('#example-text-input');
+        this._exampleText = /** @type {HTMLElement} */ (document.querySelector('#example-text'));
+        this._exampleTextInput = /** @type {HTMLInputElement} */ (document.querySelector('#example-text-input'));
 
         if (this._exampleTextInput !== null && typeof wanakana !== 'undefined') {
             wanakana.bind(this._exampleTextInput);
@@ -57,12 +78,14 @@ class PopupPreviewFrame {
         window.addEventListener('message', this._onMessage.bind(this), false);
 
         // Setup events
-        document.querySelector('#theme-dark-checkbox').addEventListener('change', this._onThemeDarkCheckboxChanged.bind(this), false);
+        const darkThemeCheckbox = /** @type {HTMLInputElement} */ (document.querySelector('#theme-dark-checkbox'));
+        darkThemeCheckbox.addEventListener('change', this._onThemeDarkCheckboxChanged.bind(this), false);
         this._exampleText.addEventListener('click', this._onExampleTextClick.bind(this), false);
         this._exampleTextInput.addEventListener('blur', this._onExampleTextInputBlur.bind(this), false);
         this._exampleTextInput.addEventListener('input', this._onExampleTextInputInput.bind(this), false);
 
         // Overwrite API functions
+        /** @type {?(optionsContext: import('settings').OptionsContext) => Promise<import('settings').ProfileOptions>} */
         this._apiOptionsGetOld = yomichan.api.optionsGet.bind(yomichan.api);
         yomichan.api.optionsGet = this._apiOptionsGet.bind(this);
 
@@ -85,7 +108,10 @@ class PopupPreviewFrame {
         await this._frontend.prepare();
         this._frontend.setDisabledOverride(true);
         this._frontend.canClearSelection = false;
-        this._frontend.popup.on('customOuterCssChanged', this._onCustomOuterCssChanged.bind(this));
+        const {popup} = this._frontend;
+        if (popup !== null) {
+            popup.on('customOuterCssChanged', this._onCustomOuterCssChanged.bind(this));
+        }
 
         // Update search
         this._updateSearch();
@@ -93,8 +119,12 @@ class PopupPreviewFrame {
 
     // Private
 
-    async _apiOptionsGet(...args) {
-        const options = await this._apiOptionsGetOld(...args);
+    /**
+     * @param {import('settings').OptionsContext} optionsContext
+     * @returns {Promise<import('settings').ProfileOptions>}
+     */
+    async _apiOptionsGet(optionsContext) {
+        const options = await /** @type {(optionsContext: import('settings').OptionsContext) => Promise<import('settings').ProfileOptions>} */ (this._apiOptionsGetOld)(optionsContext);
         options.general.enable = true;
         options.general.debugInfo = false;
         options.general.popupWidth = 400;
@@ -109,16 +139,24 @@ class PopupPreviewFrame {
         return options;
     }
 
+    /**
+     * @param {import('popup').CustomOuterCssChangedEvent} details
+     */
     _onCustomOuterCssChanged({node, inShadow}) {
         if (node === null || inShadow) { return; }
 
         const node2 = document.querySelector('#popup-outer-css');
         if (node2 === null) { return; }
+        const {parentNode} = node2;
+        if (parentNode === null) { return; }
 
         // This simulates the stylesheet priorities when injecting using the web extension API.
-        node2.parentNode.insertBefore(node, node2);
+        parentNode.insertBefore(node, node2);
     }
 
+    /**
+     * @param {MessageEvent<{action: string, params: import('core').SerializableObject}>} e
+     */
     _onMessage(e) {
         if (e.origin !== this._targetOrigin) { return; }
 
@@ -129,19 +167,24 @@ class PopupPreviewFrame {
         handler(params);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onThemeDarkCheckboxChanged(e) {
-        document.documentElement.classList.toggle('dark', e.target.checked);
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        document.documentElement.classList.toggle('dark', element.checked);
         if (this._themeChangeTimeout !== null) {
             clearTimeout(this._themeChangeTimeout);
         }
         this._themeChangeTimeout = setTimeout(() => {
             this._themeChangeTimeout = null;
-            const popup = this._frontend.popup;
+            const popup = /** @type {Frontend} */ (this._frontend).popup;
             if (popup === null) { return; }
             popup.updateTheme();
         }, 300);
     }
 
+    /** */
     _onExampleTextClick() {
         if (this._exampleTextInput === null) { return; }
         const visible = this._exampleTextInput.hidden;
@@ -151,19 +194,31 @@ class PopupPreviewFrame {
         this._exampleTextInput.select();
     }
 
+    /** */
     _onExampleTextInputBlur() {
         if (this._exampleTextInput === null) { return; }
         this._exampleTextInput.hidden = true;
     }
 
+    /**
+     * @param {Event} e
+     */
     _onExampleTextInputInput(e) {
-        this._setText(e.currentTarget.value);
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        this._setText(element.value, false);
     }
 
+    /**
+     * @param {{text: string}} details
+     */
     _onSetText({text}) {
         this._setText(text, true);
     }
 
+    /**
+     * @param {string} text
+     * @param {boolean} setInput
+     */
     _setText(text, setInput) {
         if (setInput && this._exampleTextInput !== null) {
             this._exampleTextInput.value = text;
@@ -176,6 +231,9 @@ class PopupPreviewFrame {
         this._updateSearch();
     }
 
+    /**
+     * @param {boolean} visible
+     */
     _setInfoVisible(visible) {
         const node = document.querySelector('.placeholder-info');
         if (node === null) { return; }
@@ -183,6 +241,9 @@ class PopupPreviewFrame {
         node.classList.toggle('placeholder-info-visible', visible);
     }
 
+    /**
+     * @param {{css: string}} details
+     */
     _setCustomCss({css}) {
         if (this._frontend === null) { return; }
         const popup = this._frontend.popup;
@@ -190,6 +251,9 @@ class PopupPreviewFrame {
         popup.setCustomCss(css);
     }
 
+    /**
+     * @param {{css: string}} details
+     */
     _setCustomOuterCss({css}) {
         if (this._frontend === null) { return; }
         const popup = this._frontend.popup;
@@ -197,7 +261,11 @@ class PopupPreviewFrame {
         popup.setCustomOuterCss(css, false);
     }
 
-    async _updateOptionsContext({optionsContext}) {
+    /**
+     * @param {{optionsContext: import('settings').OptionsContext}} details
+     */
+    async _updateOptionsContext(details) {
+        const {optionsContext} = details;
         this._optionsContext = optionsContext;
         if (this._frontend === null) { return; }
         this._frontend.setOptionsContextOverride(optionsContext);
@@ -205,6 +273,7 @@ class PopupPreviewFrame {
         await this._updateSearch();
     }
 
+    /** */
     async _updateSearch() {
         if (this._exampleText === null) { return; }
 
@@ -214,16 +283,17 @@ class PopupPreviewFrame {
         const range = document.createRange();
         range.selectNodeContents(textNode);
         const source = TextSourceRange.create(range);
+        const frontend = /** @type {Frontend} */ (this._frontend);
 
         try {
-            await this._frontend.setTextSource(source);
+            await frontend.setTextSource(source);
         } finally {
             source.cleanup();
         }
         this._textSource = source;
-        await this._frontend.showContentCompleted();
+        await frontend.showContentCompleted();
 
-        const popup = this._frontend.popup;
+        const popup = frontend.popup;
         if (popup !== null && popup.isVisibleSync()) {
             this._popupShown = true;
         }
diff --git a/ext/js/pages/settings/popup-window-controller.js b/ext/js/pages/settings/popup-window-controller.js
index af74de4bad..4bb61cb162 100644
--- a/ext/js/pages/settings/popup-window-controller.js
+++ b/ext/js/pages/settings/popup-window-controller.js
@@ -17,18 +17,23 @@
  */
 
 class PopupWindowController {
+    /** */
     prepare() {
-        const testLink = document.querySelector('#test-window-open-link');
+        const testLink = /** @type {HTMLElement} */ (document.querySelector('#test-window-open-link'));
         testLink.addEventListener('click', this._onTestWindowOpenLinkClick.bind(this), false);
     }
 
     // Private
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onTestWindowOpenLinkClick(e) {
         e.preventDefault();
         this._testWindowOpen();
     }
 
+    /** */
     async _testWindowOpen() {
         await yomichan.api.getOrCreateSearchPopup({focus: true});
     }
diff --git a/ext/js/pages/settings/profile-conditions-ui.js b/ext/js/pages/settings/profile-conditions-ui.js
index 6865f27b2b..52a9f3593b 100644
--- a/ext/js/pages/settings/profile-conditions-ui.js
+++ b/ext/js/pages/settings/profile-conditions-ui.js
@@ -17,24 +17,40 @@
  */
 
 /* global
+ * DocumentUtil
  * KeyboardMouseInputField
  */
 
+/**
+ * @augments EventDispatcher<import('profile-conditions-ui').EventType>
+ */
 class ProfileConditionsUI extends EventDispatcher {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
         super();
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?import('environment').OperatingSystem} */
         this._os = null;
+        /** @type {?HTMLElement} */
         this._conditionGroupsContainer = null;
+        /** @type {?HTMLElement} */
         this._addConditionGroupButton = null;
+        /** @type {ProfileConditionGroupUI[]} */
         this._children = [];
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {import('profile-conditions-ui').DescriptorType} */
         this._defaultType = 'popupLevel';
+        /** @type {number} */
         this._profileIndex = 0;
         const validateInteger = this._validateInteger.bind(this);
         const normalizeInteger = this._normalizeInteger.bind(this);
         const validateFlags = this._validateFlags.bind(this);
         const normalizeFlags = this._normalizeFlags.bind(this);
+        /** @type {Map<import('profile-conditions-ui').DescriptorType, import('profile-conditions-ui').Descriptor>} */
         this._descriptors = new Map([
             [
                 'popupLevel',
@@ -89,19 +105,23 @@ class ProfileConditionsUI extends EventDispatcher {
                 }
             ]
         ]);
+        /** @type {Set<string>} */
         this._validFlags = new Set([
             'clipboard'
         ]);
     }
 
+    /** @type {SettingsController} */
     get settingsController() {
         return this._settingsController;
     }
 
+    /** @type {number} */
     get profileIndex() {
         return this._profileIndex;
     }
 
+    /** @type {?import('environment').OperatingSystem} */
     get os() {
         return this._os;
     }
@@ -110,6 +130,9 @@ class ProfileConditionsUI extends EventDispatcher {
         this._os = value;
     }
 
+    /**
+     * @param {number} profileIndex
+     */
     async prepare(profileIndex) {
         const options = await this._settingsController.getOptionsFull();
         const {profiles} = options;
@@ -117,8 +140,8 @@ class ProfileConditionsUI extends EventDispatcher {
         const {conditionGroups} = profiles[profileIndex];
 
         this._profileIndex = profileIndex;
-        this._conditionGroupsContainer = document.querySelector('#profile-condition-groups');
-        this._addConditionGroupButton = document.querySelector('#profile-add-condition-group');
+        this._conditionGroupsContainer = /** @type {HTMLElement} */ (document.querySelector('#profile-condition-groups'));
+        this._addConditionGroupButton = /** @type {HTMLElement} */ (document.querySelector('#profile-add-condition-group'));
 
         for (let i = 0, ii = conditionGroups.length; i < ii; ++i) {
             this._addConditionGroup(conditionGroups[i], i);
@@ -127,6 +150,7 @@ class ProfileConditionsUI extends EventDispatcher {
         this._eventListeners.addEventListener(this._addConditionGroupButton, 'click', this._onAddConditionGroupButtonClick.bind(this), false);
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
 
@@ -139,10 +163,17 @@ class ProfileConditionsUI extends EventDispatcher {
         this._addConditionGroupButton = null;
     }
 
-    instantiateTemplate(names) {
-        return this._settingsController.instantiateTemplate(names);
+    /**
+     * @param {string} name
+     * @returns {HTMLElement}
+     */
+    instantiateTemplate(name) {
+        return /** @type {HTMLElement} */ (this._settingsController.instantiateTemplate(name));
     }
 
+    /**
+     * @returns {import('profile-conditions-ui').DescriptorInfo[]}
+     */
     getDescriptorTypes() {
         const results = [];
         for (const [name, {displayName}] of this._descriptors.entries()) {
@@ -151,6 +182,10 @@ class ProfileConditionsUI extends EventDispatcher {
         return results;
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     * @returns {import('profile-conditions-ui').OperatorInfo[]}
+     */
     getDescriptorOperators(type) {
         const info = this._descriptors.get(type);
         const results = [];
@@ -162,15 +197,27 @@ class ProfileConditionsUI extends EventDispatcher {
         return results;
     }
 
+    /**
+     * @returns {import('profile-conditions-ui').DescriptorType}
+     */
     getDefaultType() {
         return this._defaultType;
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     * @returns {string}
+     */
     getDefaultOperator(type) {
         const info = this._descriptors.get(type);
         return (typeof info !== 'undefined' ? info.defaultOperator : '');
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     * @param {string} operator
+     * @returns {import('profile-conditions-ui').Operator}
+     */
     getOperatorDetails(type, operator) {
         const info = this._getOperatorDetails(type, operator);
 
@@ -193,6 +240,9 @@ class ProfileConditionsUI extends EventDispatcher {
         };
     }
 
+    /**
+     * @returns {import('settings').ProfileCondition}
+     */
     getDefaultCondition() {
         const type = this.getDefaultType();
         const operator = this.getDefaultOperator(type);
@@ -200,6 +250,10 @@ class ProfileConditionsUI extends EventDispatcher {
         return {type, operator, value};
     }
 
+    /**
+     * @param {ProfileConditionGroupUI} child
+     * @returns {boolean}
+     */
     removeConditionGroup(child) {
         const index = child.index;
         if (index < 0 || index >= this._children.length) { return false; }
@@ -227,22 +281,53 @@ class ProfileConditionsUI extends EventDispatcher {
         return true;
     }
 
+    /**
+     * @param {string} value
+     * @returns {string[]}
+     */
     splitValue(value) {
         return value.split(/[,;\s]+/).map((v) => v.trim().toLowerCase()).filter((v) => v.length > 0);
     }
 
+    /**
+     * @param {string} property
+     * @returns {string}
+     */
     getPath(property) {
         property = (typeof property === 'string' ? `.${property}` : '');
         return `profiles[${this.profileIndex}]${property}`;
     }
 
+    /**
+     * @param {HTMLInputElement} inputNode
+     * @param {?HTMLButtonElement} mouseButton
+     * @returns {KeyboardMouseInputField}
+     */
     createKeyboardMouseInputField(inputNode, mouseButton) {
         return new KeyboardMouseInputField(inputNode, mouseButton, this._os);
     }
 
+    /**
+     * @param {string} value
+     * @returns {?import('settings').ProfileConditionType}
+     */
+    static normalizeProfileConditionType(value) {
+        switch (value) {
+            case 'popupLevel':
+            case 'url':
+            case 'modifierKeys':
+            case 'flags':
+                return value;
+            default:
+                return null;
+        }
+    }
+
     // Private
 
+    /** */
     _onAddConditionGroupButtonClick() {
+        /** @type {import('settings').ProfileConditionGroup} */
         const conditionGroup = {
             conditions: [this.getDefaultCondition()]
         };
@@ -261,28 +346,50 @@ class ProfileConditionsUI extends EventDispatcher {
         this._triggerConditionGroupCountChanged(this._children.length);
     }
 
+    /**
+     * @param {import('settings').ProfileConditionGroup} conditionGroup
+     * @param {number} index
+     * @returns {ProfileConditionGroupUI}
+     */
     _addConditionGroup(conditionGroup, index) {
         const child = new ProfileConditionGroupUI(this, index);
         child.prepare(conditionGroup);
         this._children.push(child);
-        this._conditionGroupsContainer.appendChild(child.node);
+        /** @type {HTMLElement} */ (this._conditionGroupsContainer).appendChild(child.node);
         return child;
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     * @param {string} operator
+     * @returns {import('profile-conditions-ui').OperatorInternal|undefined}
+     */
     _getOperatorDetails(type, operator) {
         const info = this._descriptors.get(type);
         return (typeof info !== 'undefined' ? info.operators.get(operator) : void 0);
     }
 
+    /**
+     * @param {string} value
+     * @returns {boolean}
+     */
     _validateInteger(value) {
         const number = Number.parseFloat(value);
         return Number.isFinite(number) && Math.floor(number) === number;
     }
 
+    /**
+     * @param {string} value
+     * @returns {boolean}
+     */
     _validateDomains(value) {
         return this.splitValue(value).length > 0;
     }
 
+    /**
+     * @param {string} value
+     * @returns {boolean}
+     */
     _validateRegExp(value) {
         try {
             new RegExp(value, 'i');
@@ -292,15 +399,27 @@ class ProfileConditionsUI extends EventDispatcher {
         }
     }
 
+    /**
+     * @param {string} value
+     * @returns {string}
+     */
     _normalizeInteger(value) {
         const number = Number.parseFloat(value);
         return `${number}`;
     }
 
+    /**
+     * @param {string} value
+     * @returns {string}
+     */
     _normalizeDomains(value) {
         return this.splitValue(value).join(', ');
     }
 
+    /**
+     * @param {string} value
+     * @returns {boolean}
+     */
     _validateFlags(value) {
         const flags = this.splitValue(value);
         for (const flag of flags) {
@@ -311,34 +430,57 @@ class ProfileConditionsUI extends EventDispatcher {
         return flags.length > 0;
     }
 
+    /**
+     * @param {string} value
+     * @returns {string}
+     */
     _normalizeFlags(value) {
         return [...new Set(this.splitValue(value))].join(', ');
     }
 
+    /**
+     * @param {number} count
+     */
     _triggerConditionGroupCountChanged(count) {
-        this.trigger('conditionGroupCountChanged', {count, profileIndex: this._profileIndex});
+        /** @type {import('profile-conditions-ui').ConditionGroupCountChangedEvent} */
+        const event = {count, profileIndex: this._profileIndex};
+        this.trigger('conditionGroupCountChanged', event);
     }
 }
 
 class ProfileConditionGroupUI {
+    /**
+     * @param {ProfileConditionsUI} parent
+     * @param {number} index
+     */
     constructor(parent, index) {
+        /** @type {ProfileConditionsUI} */
         this._parent = parent;
+        /** @type {number} */
         this._index = index;
-        this._node = null;
-        this._conditionContainer = null;
-        this._addConditionButton = null;
+        /** @type {HTMLElement} */
+        this._node = /** @type {HTMLElement} */ (this._parent.instantiateTemplate('profile-condition-group'));
+        /** @type {HTMLElement} */
+        this._conditionContainer = /** @type {HTMLElement} */ (this._node.querySelector('.profile-condition-list'));
+        /** @type {HTMLElement} */
+        this._addConditionButton = /** @type {HTMLElement} */ (this._node.querySelector('.profile-condition-add-button'));
+        /** @type {ProfileConditionUI[]} */
         this._children = [];
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
     }
 
+    /** @type {SettingsController} */
     get settingsController() {
         return this._parent.settingsController;
     }
 
+    /** @type {ProfileConditionsUI} */
     get parent() {
         return this._parent;
     }
 
+    /** @type {number} */
     get index() {
         return this._index;
     }
@@ -347,19 +489,20 @@ class ProfileConditionGroupUI {
         this._index = value;
     }
 
+    /** @type {HTMLElement} */
     get node() {
         return this._node;
     }
 
+    /** @type {number} */
     get childCount() {
         return this._children.length;
     }
 
+    /**
+     * @param {import('settings').ProfileConditionGroup} conditionGroup
+     */
     prepare(conditionGroup) {
-        this._node = this._parent.instantiateTemplate('profile-condition-group');
-        this._conditionContainer = this._node.querySelector('.profile-condition-list');
-        this._addConditionButton = this._node.querySelector('.profile-condition-add-button');
-
         const conditions = conditionGroup.conditions;
         for (let i = 0, ii = conditions.length; i < ii; ++i) {
             this._addCondition(conditions[i], i);
@@ -368,6 +511,7 @@ class ProfileConditionGroupUI {
         this._eventListeners.addEventListener(this._addConditionButton, 'click', this._onAddConditionButtonClick.bind(this), false);
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
 
@@ -379,15 +523,15 @@ class ProfileConditionGroupUI {
         if (this._node === null) { return; }
 
         const node = this._node;
-        this._node = null;
-        this._conditionContainer = null;
-        this._addConditionButton = null;
-
         if (node.parentNode !== null) {
             node.parentNode.removeChild(node);
         }
     }
 
+    /**
+     * @param {ProfileConditionUI} child
+     * @returns {boolean}
+     */
     removeCondition(child) {
         const index = child.index;
         if (index < 0 || index >= this._children.length) { return false; }
@@ -417,17 +561,23 @@ class ProfileConditionGroupUI {
         return true;
     }
 
+    /**
+     * @param {string} property
+     * @returns {string}
+     */
     getPath(property) {
         property = (typeof property === 'string' ? `.${property}` : '');
         return this._parent.getPath(`conditionGroups[${this._index}]${property}`);
     }
 
+    /** */
     removeSelf() {
         this._parent.removeConditionGroup(this);
     }
 
     // Private
 
+    /** */
     _onAddConditionButtonClick() {
         const condition = this._parent.getDefaultCondition();
         const index = this._children.length;
@@ -443,41 +593,73 @@ class ProfileConditionGroupUI {
         }]);
     }
 
+    /**
+     * @param {import('settings').ProfileCondition} condition
+     * @param {number} index
+     * @returns {ProfileConditionUI}
+     */
     _addCondition(condition, index) {
         const child = new ProfileConditionUI(this, index);
         child.prepare(condition);
         this._children.push(child);
-        this._conditionContainer.appendChild(child.node);
+        if (this._conditionContainer !== null) {
+            this._conditionContainer.appendChild(child.node);
+        }
         return child;
     }
 }
 
 class ProfileConditionUI {
+    /**
+     * @param {ProfileConditionGroupUI} parent
+     * @param {number} index
+     */
     constructor(parent, index) {
+        /** @type {ProfileConditionGroupUI} */
         this._parent = parent;
+        /** @type {number} */
         this._index = index;
-        this._node = null;
-        this._typeInput = null;
-        this._operatorInput = null;
-        this._valueInputContainer = null;
-        this._removeButton = null;
-        this._mouseButton = null;
-        this._mouseButtonContainer = null;
-        this._menuButton = null;
+        /** @type {HTMLElement} */
+        this._node = this._parent.parent.instantiateTemplate('profile-condition');
+        /** @type {HTMLSelectElement} */
+        this._typeInput = /** @type {HTMLSelectElement} */ (this._node.querySelector('.profile-condition-type'));
+        /** @type {HTMLSelectElement} */
+        this._operatorInput = /** @type {HTMLSelectElement} */ (this._node.querySelector('.profile-condition-operator'));
+        /** @type {HTMLButtonElement} */
+        this._removeButton = /** @type {HTMLButtonElement} */ (this._node.querySelector('.profile-condition-remove'));
+        /** @type {HTMLButtonElement} */
+        this._mouseButton = /** @type {HTMLButtonElement} */ (this._node.querySelector('.mouse-button'));
+        /** @type {HTMLElement} */
+        this._mouseButtonContainer = /** @type {HTMLElement} */ (this._node.querySelector('.mouse-button-container'));
+        /** @type {HTMLButtonElement} */
+        this._menuButton = /** @type {HTMLButtonElement} */ (this._node.querySelector('.profile-condition-menu-button'));
+        /** @type {HTMLElement} */
+        this._typeOptionContainer = /** @type {HTMLElement} */ (this._typeInput.querySelector('optgroup'));
+        /** @type {HTMLElement} */
+        this._operatorOptionContainer = /** @type {HTMLElement} */ (this._operatorInput.querySelector('optgroup'));
+        /** @type {HTMLInputElement} */
+        this._valueInput = /** @type {HTMLInputElement} */ (this._node.querySelector('.profile-condition-input'));
+        /** @type {string} */
         this._value = '';
+        /** @type {?KeyboardMouseInputField} */
         this._kbmInputField = null;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {EventListenerCollection} */
         this._inputEventListeners = new EventListenerCollection();
     }
 
+    /** @type {SettingsController} */
     get settingsController() {
         return this._parent.parent.settingsController;
     }
 
+    /** @type {ProfileConditionGroupUI} */
     get parent() {
         return this._parent;
     }
 
+    /** @type {number} */
     get index() {
         return this._index;
     }
@@ -486,24 +668,17 @@ class ProfileConditionUI {
         this._index = value;
     }
 
+    /** @type {HTMLElement} */
     get node() {
         return this._node;
     }
 
+    /**
+     * @param {import('settings').ProfileCondition} condition
+     */
     prepare(condition) {
         const {type, operator, value} = condition;
 
-        this._node = this._parent.parent.instantiateTemplate('profile-condition');
-        this._typeInput = this._node.querySelector('.profile-condition-type');
-        this._typeOptionContainer = this._typeInput.querySelector('optgroup');
-        this._operatorInput = this._node.querySelector('.profile-condition-operator');
-        this._operatorOptionContainer = this._operatorInput.querySelector('optgroup');
-        this._valueInput = this._node.querySelector('.profile-condition-input');
-        this._removeButton = this._node.querySelector('.profile-condition-remove');
-        this._mouseButton = this._node.querySelector('.mouse-button');
-        this._mouseButtonContainer = this._node.querySelector('.mouse-button-container');
-        this._menuButton = this._node.querySelector('.profile-condition-menu-button');
-
         const operatorDetails = this._getOperatorDetails(type, operator);
         this._updateTypes(type);
         this._updateOperators(type, operator);
@@ -518,6 +693,7 @@ class ProfileConditionUI {
         }
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
         this._value = '';
@@ -525,17 +701,15 @@ class ProfileConditionUI {
         if (this._node === null) { return; }
 
         const node = this._node;
-        this._node = null;
-        this._typeInput = null;
-        this._operatorInput = null;
-        this._valueInputContainer = null;
-        this._removeButton = null;
-
         if (node.parentNode !== null) {
             node.parentNode.removeChild(node);
         }
     }
 
+    /**
+     * @param {string} property
+     * @returns {string}
+     */
     getPath(property) {
         property = (typeof property === 'string' ? `.${property}` : '');
         return this._parent.getPath(`conditions[${this._index}]${property}`);
@@ -543,19 +717,33 @@ class ProfileConditionUI {
 
     // Private
 
+    /**
+     * @param {Event} e
+     */
     _onTypeChange(e) {
-        const type = e.currentTarget.value;
+        const element = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        const type = ProfileConditionsUI.normalizeProfileConditionType(element.value);
+        if (type === null) { return; }
         this._setType(type);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onOperatorChange(e) {
-        const type = this._typeInput.value;
-        const operator = e.currentTarget.value;
+        const element = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        const type = ProfileConditionsUI.normalizeProfileConditionType(this._typeInput.value);
+        if (type === null) { return; }
+        const operator = element.value;
         this._setOperator(type, operator);
     }
 
+    /**
+     * @param {import('profile-conditions-ui').InputData} details
+     * @param {Event} e
+     */
     _onValueInputChange({validate, normalize}, e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         const value = node.value;
         const okay = this._validateValue(value, validate);
         this._value = value;
@@ -566,8 +754,12 @@ class ProfileConditionUI {
         }
     }
 
-    _onModifierInputChange({validate, normalize}, {modifiers}) {
-        modifiers = this._joinModifiers(modifiers);
+    /**
+     * @param {import('profile-conditions-ui').InputData} details
+     * @param {import('keyboard-mouse-input-field').ChangeEvent} event
+     */
+    _onModifierInputChange({validate, normalize}, event) {
+        const modifiers = this._joinModifiers(event.modifiers);
         const okay = this._validateValue(modifiers, validate);
         this._value = modifiers;
         if (okay) {
@@ -576,18 +768,25 @@ class ProfileConditionUI {
         }
     }
 
+    /** */
     _onRemoveButtonClick() {
         this._removeSelf();
     }
 
+    /**
+     * @param {import('popup-menu').MenuOpenEvent} e
+     */
     _onMenuOpen(e) {
         const bodyNode = e.detail.menu.bodyNode;
-        const deleteGroup = bodyNode.querySelector('.popup-menu-item[data-menu-action="deleteGroup"]');
+        const deleteGroup = /** @type {HTMLElement} */ (bodyNode.querySelector('.popup-menu-item[data-menu-action="deleteGroup"]'));
         if (deleteGroup !== null) {
             deleteGroup.hidden = (this._parent.childCount <= 1);
         }
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuClose(e) {
         switch (e.detail.action) {
             case 'delete':
@@ -602,28 +801,53 @@ class ProfileConditionUI {
         }
     }
 
+    /**
+     * @returns {import('profile-conditions-ui').DescriptorInfo[]}
+     */
     _getDescriptorTypes() {
         return this._parent.parent.getDescriptorTypes();
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     * @returns {import('profile-conditions-ui').OperatorInfo[]}
+     */
     _getDescriptorOperators(type) {
         return this._parent.parent.getDescriptorOperators(type);
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     * @param {string} operator
+     * @returns {import('profile-conditions-ui').Operator}
+     */
     _getOperatorDetails(type, operator) {
         return this._parent.parent.getOperatorDetails(type, operator);
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     */
     _updateTypes(type) {
         const types = this._getDescriptorTypes();
         this._updateSelect(this._typeInput, this._typeOptionContainer, types, type);
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     * @param {string} operator
+     */
     _updateOperators(type, operator) {
         const operators = this._getDescriptorOperators(type);
         this._updateSelect(this._operatorInput, this._operatorOptionContainer, operators, operator);
     }
 
+    /**
+     * @param {HTMLSelectElement} select
+     * @param {HTMLElement} optionContainer
+     * @param {import('profile-conditions-ui').DescriptorInfo[]|import('profile-conditions-ui').OperatorInfo[]} values
+     * @param {string} value
+     */
     _updateSelect(select, optionContainer, values, value) {
         optionContainer.textContent = '';
         for (const {name, displayName} of values) {
@@ -635,6 +859,11 @@ class ProfileConditionUI {
         select.value = value;
     }
 
+    /**
+     * @param {string} value
+     * @param {import('profile-conditions-ui').Operator} operator
+     * @returns {boolean}
+     */
     _updateValueInput(value, {type, validate, normalize}) {
         this._inputEventListeners.removeAllEventListeners();
         if (this._kbmInputField !== null) {
@@ -643,10 +872,15 @@ class ProfileConditionUI {
         }
 
         let inputType = 'text';
+        /** @type {?string} */
         let inputValue = value;
         let inputStep = null;
         let showMouseButton = false;
-        const events = [];
+        /** @type {import('event-listener-collection').AddEventListenerArgs[]} */
+        const events1 = [];
+        /** @type {import('event-listener-collection').OnArgs[]} */
+        const events2 = [];
+        /** @type {import('profile-conditions-ui').InputData} */
         const inputData = {validate, normalize};
         const node = this._valueInput;
 
@@ -654,7 +888,7 @@ class ProfileConditionUI {
             case 'integer':
                 inputType = 'number';
                 inputStep = '1';
-                events.push(['addEventListener', node, 'change', this._onValueInputChange.bind(this, inputData), false]);
+                events1.push([node, 'change', this._onValueInputChange.bind(this, inputData), false]);
                 break;
             case 'modifierKeys':
             case 'modifierInputs':
@@ -662,10 +896,10 @@ class ProfileConditionUI {
                 showMouseButton = (type === 'modifierInputs');
                 this._kbmInputField = this._parent.parent.createKeyboardMouseInputField(node, this._mouseButton);
                 this._kbmInputField.prepare(null, this._splitModifiers(value), showMouseButton, false);
-                events.push(['on', this._kbmInputField, 'change', this._onModifierInputChange.bind(this, inputData), false]);
+                events2.push([this._kbmInputField, 'change', this._onModifierInputChange.bind(this, inputData)]);
                 break;
             default: // 'string'
-                events.push(['addEventListener', node, 'change', this._onValueInputChange.bind(this, inputData), false]);
+                events1.push([node, 'change', this._onValueInputChange.bind(this, inputData), false]);
                 break;
         }
 
@@ -681,35 +915,67 @@ class ProfileConditionUI {
             node.removeAttribute('step');
         }
         this._mouseButtonContainer.hidden = !showMouseButton;
-        for (const args of events) {
-            this._inputEventListeners.addGeneric(...args);
+        for (const args of events1) {
+            this._inputEventListeners.addEventListener(...args);
+        }
+        for (const args of events2) {
+            this._inputEventListeners.on(...args);
         }
 
-        this._validateValue(value, validate);
+        return this._validateValue(value, validate);
     }
 
+    /**
+     * @param {string} value
+     * @param {?import('profile-conditions-ui').ValidateFunction} validate
+     * @returns {boolean}
+     */
     _validateValue(value, validate) {
         const okay = (validate === null || validate(value));
         this._valueInput.dataset.invalid = `${!okay}`;
         return okay;
     }
 
+    /**
+     * @param {string} value
+     * @param {?import('profile-conditions-ui').NormalizeFunction} normalize
+     * @returns {value}
+     */
     _normalizeValue(value, normalize) {
         return (normalize !== null ? normalize(value) : value);
     }
 
+    /** */
     _removeSelf() {
         this._parent.removeCondition(this);
     }
 
+    /**
+     * @param {string} modifiersString
+     * @returns {import('input').Modifier[]}
+     */
     _splitModifiers(modifiersString) {
-        return modifiersString.split(/[,;\s]+/).map((v) => v.trim().toLowerCase()).filter((v) => v.length > 0);
+        /** @type {import('input').Modifier[]} */
+        const results = [];
+        for (const item of modifiersString.split(/[,;\s]+/)) {
+            const modifier = DocumentUtil.normalizeModifier(item.trim().toLowerCase());
+            if (modifier !== null) { results.push(modifier); }
+        }
+        return results;
     }
 
+    /**
+     * @param {import('input').Modifier[]} modifiersArray
+     * @returns {string}
+     */
     _joinModifiers(modifiersArray) {
         return modifiersArray.join(', ');
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     * @param {string} [operator]
+     */
     async _setType(type, operator) {
         const operators = this._getDescriptorOperators(type);
         if (typeof operator === 'undefined') {
@@ -726,8 +992,13 @@ class ProfileConditionUI {
         ]);
     }
 
+    /**
+     * @param {import('profile-conditions-ui').DescriptorType} type
+     * @param {string} operator
+     */
     async _setOperator(type, operator) {
         const operatorDetails = this._getOperatorDetails(type, operator);
+        /** @type {import('settings-modifications').Modification[]} */
         const settingsModifications = [{action: 'set', path: this.getPath('operator'), value: operator}];
         if (operatorDetails.resetDefaultOnChange) {
             const {defaultValue} = operatorDetails;
@@ -739,8 +1010,10 @@ class ProfileConditionUI {
         await this.settingsController.modifyGlobalSettings(settingsModifications);
     }
 
+    /** */
     async _resetValue() {
-        const type = this._typeInput.value;
+        const type = ProfileConditionsUI.normalizeProfileConditionType(this._typeInput.value);
+        if (type === null) { return; }
         const operator = this._operatorInput.value;
         await this._setType(type, operator);
     }
diff --git a/ext/js/pages/settings/profile-controller.js b/ext/js/pages/settings/profile-controller.js
index d9e25fcff4..f1ef4eb13a 100644
--- a/ext/js/pages/settings/profile-controller.js
+++ b/ext/js/pages/settings/profile-controller.js
@@ -21,50 +21,77 @@
  */
 
 class ProfileController {
+    /**
+     * @param {SettingsController} settingsController
+     * @param {ModalController} modalController
+     */
     constructor(settingsController, modalController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {ModalController} */
         this._modalController = modalController;
+        /** @type {ProfileConditionsUI} */
         this._profileConditionsUI = new ProfileConditionsUI(settingsController);
+        /** @type {?number} */
         this._profileConditionsIndex = null;
+        /** @type {?HTMLSelectElement} */
         this._profileActiveSelect = null;
+        /** @type {?HTMLSelectElement} */
         this._profileTargetSelect = null;
+        /** @type {?HTMLSelectElement} */
         this._profileCopySourceSelect = null;
+        /** @type {?HTMLElement} */
         this._removeProfileNameElement = null;
+        /** @type {?HTMLButtonElement} */
         this._profileAddButton = null;
+        /** @type {?HTMLButtonElement} */
         this._profileRemoveConfirmButton = null;
+        /** @type {?HTMLButtonElement} */
         this._profileCopyConfirmButton = null;
+        /** @type {?HTMLElement} */
         this._profileEntryListContainer = null;
+        /** @type {?HTMLElement} */
         this._profileConditionsProfileName = null;
+        /** @type {?Modal} */
         this._profileRemoveModal = null;
+        /** @type {?Modal} */
         this._profileCopyModal = null;
+        /** @type {?Modal} */
         this._profileConditionsModal = null;
+        /** @type {boolean} */
         this._profileEntriesSupported = false;
+        /** @type {ProfileEntry[]} */
         this._profileEntryList = [];
+        /** @type {import('settings').Profile[]} */
         this._profiles = [];
+        /** @type {number} */
         this._profileCurrent = 0;
     }
 
+    /** @type {number} */
     get profileCount() {
         return this._profiles.length;
     }
 
+    /** @type {number} */
     get profileCurrentIndex() {
         return this._profileCurrent;
     }
 
+    /** */
     async prepare() {
         const {platform: {os}} = await yomichan.api.getEnvironmentInfo();
         this._profileConditionsUI.os = os;
 
-        this._profileActiveSelect = document.querySelector('#profile-active-select');
-        this._profileTargetSelect = document.querySelector('#profile-target-select');
-        this._profileCopySourceSelect = document.querySelector('#profile-copy-source-select');
-        this._removeProfileNameElement = document.querySelector('#profile-remove-name');
-        this._profileAddButton = document.querySelector('#profile-add-button');
-        this._profileRemoveConfirmButton = document.querySelector('#profile-remove-confirm-button');
-        this._profileCopyConfirmButton = document.querySelector('#profile-copy-confirm-button');
-        this._profileEntryListContainer = document.querySelector('#profile-entry-list');
-        this._profileConditionsProfileName = document.querySelector('#profile-conditions-profile-name');
+        this._profileActiveSelect = /** @type {HTMLSelectElement} */ (document.querySelector('#profile-active-select'));
+        this._profileTargetSelect = /** @type {HTMLSelectElement} */ (document.querySelector('#profile-target-select'));
+        this._profileCopySourceSelect = /** @type {HTMLSelectElement} */ (document.querySelector('#profile-copy-source-select'));
+        this._removeProfileNameElement = /** @type {HTMLElement} */ (document.querySelector('#profile-remove-name'));
+        this._profileAddButton = /** @type {HTMLButtonElement} */ (document.querySelector('#profile-add-button'));
+        this._profileRemoveConfirmButton = /** @type {HTMLButtonElement} */ (document.querySelector('#profile-remove-confirm-button'));
+        this._profileCopyConfirmButton = /** @type {HTMLButtonElement} */ (document.querySelector('#profile-copy-confirm-button'));
+        this._profileEntryListContainer = /** @type {HTMLElement} */ (document.querySelector('#profile-entry-list'));
+        this._profileConditionsProfileName = /** @type {HTMLElement} */ (document.querySelector('#profile-conditions-profile-name'));
         this._profileRemoveModal = this._modalController.getModal('profile-remove');
         this._profileCopyModal = this._modalController.getModal('profile-copy');
         this._profileConditionsModal = this._modalController.getModal('profile-conditions');
@@ -82,6 +109,10 @@ class ProfileController {
         this._onOptionsChanged();
     }
 
+    /**
+     * @param {number} profileIndex
+     * @param {number} offset
+     */
     async moveProfile(profileIndex, offset) {
         if (this._getProfile(profileIndex) === null) { return; }
 
@@ -91,6 +122,10 @@ class ProfileController {
         await this.swapProfiles(profileIndex, profileIndexNew);
     }
 
+    /**
+     * @param {number} profileIndex
+     * @param {string} value
+     */
     async setProfileName(profileIndex, value) {
         const profile = this._getProfile(profileIndex);
         if (profile === null) { return; }
@@ -104,11 +139,14 @@ class ProfileController {
         await this._settingsController.setGlobalSetting(`profiles[${profileIndex}].name`, value);
     }
 
+    /**
+     * @param {number} profileIndex
+     */
     async setDefaultProfile(profileIndex) {
         const profile = this._getProfile(profileIndex);
         if (profile === null) { return; }
 
-        this._profileActiveSelect.value = `${profileIndex}`;
+        /** @type {HTMLSelectElement} */ (this._profileActiveSelect).value = `${profileIndex}`;
         this._profileCurrent = profileIndex;
 
         const profileEntry = this._getProfileEntry(profileIndex);
@@ -117,6 +155,10 @@ class ProfileController {
         await this._settingsController.setGlobalSetting('profileCurrent', profileIndex);
     }
 
+    /**
+     * @param {number} sourceProfileIndex
+     * @param {number} destinationProfileIndex
+     */
     async copyProfile(sourceProfileIndex, destinationProfileIndex) {
         const sourceProfile = this._getProfile(sourceProfileIndex);
         if (sourceProfile === null || !this._getProfile(destinationProfileIndex)) { return; }
@@ -140,9 +182,12 @@ class ProfileController {
         await this._settingsController.refresh();
     }
 
+    /**
+     * @param {number} profileIndex
+     */
     async duplicateProfile(profileIndex) {
         const profile = this._getProfile(profileIndex);
-        if (this.profile === null) { return; }
+        if (profile === null) { return; }
 
         // Create new profile
         const newProfile = clone(profile);
@@ -169,6 +214,9 @@ class ProfileController {
         this._settingsController.profileIndex = index;
     }
 
+    /**
+     * @param {number} profileIndex
+     */
     async deleteProfile(profileIndex) {
         const profile = this._getProfile(profileIndex);
         if (profile === null || this.profileCount <= 1) { return; }
@@ -178,6 +226,7 @@ class ProfileController {
         const settingsProfileIndex = this._settingsController.profileIndex;
 
         // Construct settings modifications
+        /** @type {import('settings-modifications').Modification[]} */
         const modifications = [{
             action: 'splice',
             path: 'profiles',
@@ -225,6 +274,10 @@ class ProfileController {
         await this._settingsController.modifyGlobalSettings(modifications);
     }
 
+    /**
+     * @param {number} index1
+     * @param {number} index2
+     */
     async swapProfiles(index1, index2) {
         const profile1 = this._getProfile(index1);
         const profile2 = this._getProfile(index2);
@@ -238,6 +291,7 @@ class ProfileController {
         const settingsProfileIndexNew = this._getSwappedValue(settingsProfileIndex, index1, index2);
 
         // Construct settings modifications
+        /** @type {import('settings-modifications').Modification[]} */
         const modifications = [{
             action: 'swap',
             path1: `profiles[${index1}]`,
@@ -278,15 +332,21 @@ class ProfileController {
         }
     }
 
+    /**
+     * @param {number} profileIndex
+     */
     openDeleteProfileModal(profileIndex) {
         const profile = this._getProfile(profileIndex);
         if (profile === null || this.profileCount <= 1) { return; }
 
-        this._removeProfileNameElement.textContent = profile.name;
-        this._profileRemoveModal.node.dataset.profileIndex = `${profileIndex}`;
-        this._profileRemoveModal.setVisible(true);
+        /** @type {HTMLElement} */ (this._removeProfileNameElement).textContent = profile.name;
+        /** @type {Modal} */ (this._profileRemoveModal).node.dataset.profileIndex = `${profileIndex}`;
+        /** @type {Modal} */ (this._profileRemoveModal).setVisible(true);
     }
 
+    /**
+     * @param {number} profileIndex
+     */
     openCopyProfileModal(profileIndex) {
         const profile = this._getProfile(profileIndex);
         if (profile === null || this.profileCount <= 1) { return; }
@@ -301,16 +361,20 @@ class ProfileController {
         }
 
         const profileIndexString = `${profileIndex}`;
-        for (const option of this._profileCopySourceSelect.querySelectorAll('option')) {
+        const select = /** @type {HTMLSelectElement} */ (this._profileCopySourceSelect);
+        for (const option of select.querySelectorAll('option')) {
             const {value} = option;
             option.disabled = (value === profileIndexString);
         }
-        this._profileCopySourceSelect.value = `${copyFromIndex}`;
+        select.value = `${copyFromIndex}`;
 
-        this._profileCopyModal.node.dataset.profileIndex = `${profileIndex}`;
-        this._profileCopyModal.setVisible(true);
+        /** @type {Modal} */ (this._profileCopyModal).node.dataset.profileIndex = `${profileIndex}`;
+        /** @type {Modal} */ (this._profileCopyModal).setVisible(true);
     }
 
+    /**
+     * @param {number} profileIndex
+     */
     openProfileConditionsModal(profileIndex) {
         const profile = this._getProfile(profileIndex);
         if (profile === null) { return; }
@@ -328,6 +392,7 @@ class ProfileController {
 
     // Private
 
+    /** */
     async _onOptionsChanged() {
         // Update state
         const {profiles, profileCurrent} = await this._settingsController.getOptionsFull();
@@ -339,8 +404,8 @@ class ProfileController {
         // Udpate UI
         this._updateProfileSelectOptions();
 
-        this._profileActiveSelect.value = `${profileCurrent}`;
-        this._profileTargetSelect.value = `${settingsProfileIndex}`;
+        /** @type {HTMLSelectElement} */ (this._profileActiveSelect).value = `${profileCurrent}`;
+        /** @type {HTMLSelectElement} */ (this._profileTargetSelect).value = `${settingsProfileIndex}`;
 
         // Update profile conditions
         this._profileConditionsUI.cleanup();
@@ -361,51 +426,65 @@ class ProfileController {
         }
     }
 
+    /**
+     * @param {Event} e
+     */
     _onProfileActiveChange(e) {
-        const value = this._tryGetValidProfileIndex(e.currentTarget.value);
+        const element = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        const value = this._tryGetValidProfileIndex(element.value);
         if (value === null) { return; }
         this.setDefaultProfile(value);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onProfileTargetChange(e) {
-        const value = this._tryGetValidProfileIndex(e.currentTarget.value);
+        const element = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        const value = this._tryGetValidProfileIndex(element.value);
         if (value === null) { return; }
         this._settingsController.profileIndex = value;
     }
 
+    /** */
     _onAdd() {
         this.duplicateProfile(this._settingsController.profileIndex);
     }
 
+    /** */
     _onDeleteConfirm() {
-        const modal = this._profileRemoveModal;
+        const modal = /** @type {Modal} */ (this._profileRemoveModal);
         modal.setVisible(false);
         const {node} = modal;
-        let profileIndex = node.dataset.profileIndex;
+        const profileIndex = node.dataset.profileIndex;
         delete node.dataset.profileIndex;
 
-        profileIndex = this._tryGetValidProfileIndex(profileIndex);
-        if (profileIndex === null) { return; }
+        const validProfileIndex = this._tryGetValidProfileIndex(profileIndex);
+        if (validProfileIndex === null) { return; }
 
-        this.deleteProfile(profileIndex);
+        this.deleteProfile(validProfileIndex);
     }
 
+    /** */
     _onCopyConfirm() {
-        const modal = this._profileCopyModal;
+        const modal = /** @type {Modal} */ (this._profileCopyModal);
         modal.setVisible(false);
         const {node} = modal;
-        let destinationProfileIndex = node.dataset.profileIndex;
+        const destinationProfileIndex = node.dataset.profileIndex;
         delete node.dataset.profileIndex;
 
-        destinationProfileIndex = this._tryGetValidProfileIndex(destinationProfileIndex);
-        if (destinationProfileIndex === null) { return; }
+        const validDestinationProfileIndex = this._tryGetValidProfileIndex(destinationProfileIndex);
+        if (validDestinationProfileIndex === null) { return; }
 
-        const sourceProfileIndex = this._tryGetValidProfileIndex(this._profileCopySourceSelect.value);
+        const sourceProfileIndex = this._tryGetValidProfileIndex(/** @type {HTMLSelectElement} */ (this._profileCopySourceSelect).value);
         if (sourceProfileIndex === null) { return; }
 
-        this.copyProfile(sourceProfileIndex, destinationProfileIndex);
+        this.copyProfile(sourceProfileIndex, validDestinationProfileIndex);
     }
 
+    /**
+     * @param {import('profile-conditions-ui').ConditionGroupCountChangedEvent} details
+     */
     _onConditionGroupCountChanged({count, profileIndex}) {
         if (profileIndex >= 0 && profileIndex < this._profileEntryList.length) {
             const profileEntry = this._profileEntryList[profileIndex];
@@ -413,15 +492,19 @@ class ProfileController {
         }
     }
 
+    /**
+     * @param {number} profileIndex
+     */
     _addProfileEntry(profileIndex) {
         const profile = this._profiles[profileIndex];
-        const node = this._settingsController.instantiateTemplate('profile-entry');
-        const entry = new ProfileEntry(this, node);
+        const node = /** @type {HTMLElement} */ (this._settingsController.instantiateTemplate('profile-entry'));
+        const entry = new ProfileEntry(this, node, profile, profileIndex);
         this._profileEntryList.push(entry);
-        entry.prepare(profile, profileIndex);
-        this._profileEntryListContainer.appendChild(node);
+        entry.prepare();
+        /** @type {HTMLElement} */ (this._profileEntryListContainer).appendChild(node);
     }
 
+    /** */
     _updateProfileSelectOptions() {
         for (const select of this._getAllProfileSelects()) {
             const fragment = document.createDocumentFragment();
@@ -437,6 +520,10 @@ class ProfileController {
         }
     }
 
+    /**
+     * @param {number} index
+     * @param {string} name
+     */
     _updateSelectName(index, name) {
         const optionValue = `${index}`;
         for (const select of this._getAllProfileSelects()) {
@@ -448,14 +535,21 @@ class ProfileController {
         }
     }
 
+    /**
+     * @returns {HTMLSelectElement[]}
+     */
     _getAllProfileSelects() {
         return [
-            this._profileActiveSelect,
-            this._profileTargetSelect,
-            this._profileCopySourceSelect
+            /** @type {HTMLSelectElement} */ (this._profileActiveSelect),
+            /** @type {HTMLSelectElement} */ (this._profileTargetSelect),
+            /** @type {HTMLSelectElement} */ (this._profileCopySourceSelect)
         ];
     }
 
+    /**
+     * @param {string|undefined} stringValue
+     * @returns {?number}
+     */
     _tryGetValidProfileIndex(stringValue) {
         if (typeof stringValue !== 'string') { return null; }
         const intValue = parseInt(stringValue, 10);
@@ -467,6 +561,12 @@ class ProfileController {
         );
     }
 
+    /**
+     * @param {string} name
+     * @param {import('settings').Profile[]} profiles
+     * @param {number} maxUniqueAttempts
+     * @returns {string}
+     */
     _createCopyName(name, profiles, maxUniqueAttempts) {
         let space, index, prefix, suffix;
         const match = /^([\w\W]*\(Copy)((\s+)(\d+))?(\)\s*)$/.exec(name);
@@ -502,44 +602,80 @@ class ProfileController {
         }
     }
 
+    /**
+     * @template T
+     * @param {T} currentValue
+     * @param {T} value1
+     * @param {T} value2
+     * @returns {T}
+     */
     _getSwappedValue(currentValue, value1, value2) {
         if (currentValue === value1) { return value2; }
         if (currentValue === value2) { return value1; }
         return currentValue;
     }
 
+    /**
+     * @param {number} profileIndex
+     * @returns {?import('settings').Profile}
+     */
     _getProfile(profileIndex) {
         return (profileIndex >= 0 && profileIndex < this._profiles.length ? this._profiles[profileIndex] : null);
     }
 
+    /**
+     * @param {number} profileIndex
+     * @returns {?ProfileEntry}
+     */
     _getProfileEntry(profileIndex) {
         return (profileIndex >= 0 && profileIndex < this._profileEntryList.length ? this._profileEntryList[profileIndex] : null);
     }
 
+    /**
+     * @param {Element} node1
+     * @param {Element} node2
+     */
     _swapDomNodes(node1, node2) {
         const parent1 = node1.parentNode;
         const parent2 = node2.parentNode;
         const next1 = node1.nextSibling;
         const next2 = node2.nextSibling;
-        if (node2 !== next1) { parent1.insertBefore(node2, next1); }
-        if (node1 !== next2) { parent2.insertBefore(node1, next2); }
+        if (node2 !== next1 && parent1 !== null) { parent1.insertBefore(node2, next1); }
+        if (node1 !== next2 && parent2 !== null) { parent2.insertBefore(node1, next2); }
     }
 }
 
 class ProfileEntry {
-    constructor(profileController, node) {
+    /**
+     * @param {ProfileController} profileController
+     * @param {HTMLElement} node
+     * @param {import('settings').Profile} profile
+     * @param {number} index
+     */
+    constructor(profileController, node, profile, index) {
+        /** @type {ProfileController} */
         this._profileController = profileController;
+        /** @type {HTMLElement} */
         this._node = node;
-        this._profile = null;
-        this._index = 0;
-        this._isDefaultRadio = null;
-        this._nameInput = null;
-        this._countLink = null;
-        this._countText = null;
-        this._menuButton = null;
+        /** @type {import('settings').Profile} */
+        this._profile = profile;
+        /** @type {number} */
+        this._index = index;
+        /** @type {HTMLInputElement} */
+        this._isDefaultRadio = /** @type {HTMLInputElement} */ (node.querySelector('.profile-entry-is-default-radio'));
+        /** @type {HTMLInputElement} */
+        this._nameInput = /** @type {HTMLInputElement} */ (node.querySelector('.profile-entry-name-input'));
+        /** @type {HTMLElement} */
+        this._countLink = /** @type {HTMLElement} */ (node.querySelector('.profile-entry-condition-count-link'));
+        /** @type {HTMLElement} */
+        this._countText = /** @type {HTMLElement} */ (node.querySelector('.profile-entry-condition-count'));
+        /** @type {HTMLButtonElement} */
+        this._menuButton = /** @type {HTMLButtonElement} */ (node.querySelector('.profile-entry-menu-button'));
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
     }
 
+    /** @type {number} */
     get index() {
         return this._index;
     }
@@ -548,21 +684,13 @@ class ProfileEntry {
         this._index = value;
     }
 
+    /** @type {HTMLElement} */
     get node() {
         return this._node;
     }
 
-    prepare(profile, index) {
-        this._profile = profile;
-        this._index = index;
-
-        const node = this._node;
-        this._isDefaultRadio = node.querySelector('.profile-entry-is-default-radio');
-        this._nameInput = node.querySelector('.profile-entry-name-input');
-        this._countLink = node.querySelector('.profile-entry-condition-count-link');
-        this._countText = node.querySelector('.profile-entry-condition-count');
-        this._menuButton = node.querySelector('.profile-entry-menu-button');
-
+    /** */
+    prepare() {
         this.updateState();
 
         this._eventListeners.addEventListener(this._isDefaultRadio, 'change', this._onIsDefaultRadioChange.bind(this), false);
@@ -572,6 +700,7 @@ class ProfileEntry {
         this._eventListeners.addEventListener(this._menuButton, 'menuClose', this._onMenuClose.bind(this), false);
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
         if (this._node.parentNode !== null) {
@@ -579,41 +708,63 @@ class ProfileEntry {
         }
     }
 
+    /**
+     * @param {string} value
+     */
     setName(value) {
         if (this._nameInput.value === value) { return; }
         this._nameInput.value = value;
     }
 
+    /**
+     * @param {boolean} value
+     */
     setIsDefault(value) {
         this._isDefaultRadio.checked = value;
     }
 
+    /** */
     updateState() {
         this._nameInput.value = this._profile.name;
         this._countText.textContent = `${this._profile.conditionGroups.length}`;
         this._isDefaultRadio.checked = (this._index === this._profileController.profileCurrentIndex);
     }
 
+    /**
+     * @param {number} count
+     */
     setConditionGroupsCount(count) {
         this._countText.textContent = `${count}`;
     }
 
     // Private
 
+    /**
+     * @param {Event} e
+     */
     _onIsDefaultRadioChange(e) {
-        if (!e.currentTarget.checked) { return; }
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        if (!element.checked) { return; }
         this._profileController.setDefaultProfile(this._index);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onNameInputInput(e) {
-        const name = e.currentTarget.value;
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        const name = element.value;
         this._profileController.setProfileName(this._index, name);
     }
 
+    /** */
     _onConditionsCountLinkClick() {
         this._profileController.openProfileConditionsModal(this._index);
     }
 
+    /**
+     * @param {import('popup-menu').MenuOpenEvent} e
+     */
     _onMenuOpen(e) {
         const bodyNode = e.detail.menu.bodyNode;
         const count = this._profileController.profileCount;
@@ -623,6 +774,9 @@ class ProfileEntry {
         this._setMenuActionEnabled(bodyNode, 'delete', count > 1);
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuClose(e) {
         switch (e.detail.action) {
             case 'moveUp':
@@ -646,8 +800,13 @@ class ProfileEntry {
         }
     }
 
+    /**
+     * @param {Element} menu
+     * @param {string} action
+     * @param {boolean} enabled
+     */
     _setMenuActionEnabled(menu, action, enabled) {
-        const element = menu.querySelector(`[data-menu-action="${action}"]`);
+        const element = /** @type {HTMLButtonElement} */ (menu.querySelector(`[data-menu-action="${action}"]`));
         if (element === null) { return; }
         element.disabled = !enabled;
     }
diff --git a/ext/js/pages/settings/scan-inputs-controller.js b/ext/js/pages/settings/scan-inputs-controller.js
index 3ee6aed0c4..0d946a0756 100644
--- a/ext/js/pages/settings/scan-inputs-controller.js
+++ b/ext/js/pages/settings/scan-inputs-controller.js
@@ -17,26 +17,37 @@
  */
 
 /* global
+ * DocumentUtil
  * KeyboardMouseInputField
  */
 
 class ScanInputsController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?import('environment').OperatingSystem} */
         this._os = null;
+        /** @type {?HTMLElement} */
         this._container = null;
+        /** @type {?HTMLButtonElement} */
         this._addButton = null;
+        /** @type {?NodeListOf<HTMLElement>} */
         this._scanningInputCountNodes = null;
+        /** @type {ScanInputField[]} */
         this._entries = [];
     }
 
+    /** */
     async prepare() {
         const {platform: {os}} = await yomichan.api.getEnvironmentInfo();
         this._os = os;
 
-        this._container = document.querySelector('#scan-input-list');
-        this._addButton = document.querySelector('#scan-input-add');
-        this._scanningInputCountNodes = document.querySelectorAll('.scanning-input-count');
+        this._container = /** @type {HTMLElement} */ (document.querySelector('#scan-input-list'));
+        this._addButton = /** @type {HTMLButtonElement} */ (document.querySelector('#scan-input-add'));
+        this._scanningInputCountNodes = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.scanning-input-count'));
 
         this._addButton.addEventListener('click', this._onAddButtonClick.bind(this), false);
         this._settingsController.on('scanInputsChanged', this._onScanInputsChanged.bind(this));
@@ -45,6 +56,10 @@ class ScanInputsController {
         this.refresh();
     }
 
+    /**
+     * @param {number} index
+     * @returns {boolean}
+     */
     removeInput(index) {
         if (index < 0 || index >= this._entries.length) { return false; }
         const input = this._entries[index];
@@ -64,6 +79,12 @@ class ScanInputsController {
         return true;
     }
 
+    /**
+     * @param {number} index
+     * @param {string} property
+     * @param {unknown} value
+     * @param {boolean} event
+     */
     async setProperty(index, property, value, event) {
         const path = `scanning.inputs[${index}].${property}`;
         await this._settingsController.setProfileSetting(path, value);
@@ -72,22 +93,34 @@ class ScanInputsController {
         }
     }
 
+    /**
+     * @param {string} name
+     * @returns {Element}
+     */
     instantiateTemplate(name) {
         return this._settingsController.instantiateTemplate(name);
     }
 
+    /** */
     async refresh() {
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
     // Private
 
+    /**
+     * @param {import('settings-controller').ScanInputsChangedEvent} details
+     */
     _onScanInputsChanged({source}) {
         if (source === this) { return; }
         this.refresh();
     }
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         const {inputs} = options.scanning;
 
@@ -103,6 +136,9 @@ class ScanInputsController {
         this._updateCounts();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onAddButtonClick(e) {
         e.preventDefault();
 
@@ -119,34 +155,51 @@ class ScanInputsController {
         }]);
 
         // Scroll to bottom
-        const button = e.currentTarget;
-        const modalContainer = button.closest('.modal');
-        const scrollContainer = modalContainer.querySelector('.modal-body');
+        const button = /** @type {HTMLElement} */ (e.currentTarget);
+        const modalContainer = /** @type {HTMLElement} */ (button.closest('.modal'));
+        const scrollContainer = /** @type {HTMLElement} */ (modalContainer.querySelector('.modal-body'));
         scrollContainer.scrollTop = scrollContainer.scrollHeight;
     }
 
+    /**
+     * @param {number} index
+     * @param {import('settings').ScanningInput} scanningInput
+     */
     _addOption(index, scanningInput) {
+        if (this._os === null || this._container === null) { return; }
         const field = new ScanInputField(this, index, this._os);
         this._entries.push(field);
         field.prepare(this._container, scanningInput);
     }
 
+    /** */
     _updateCounts() {
         const stringValue = `${this._entries.length}`;
-        for (const node of this._scanningInputCountNodes) {
+        for (const node of /** @type {NodeListOf<HTMLElement>} */ (this._scanningInputCountNodes)) {
             node.textContent = stringValue;
         }
     }
 
+    /**
+     * @param {import('settings-modifications').Modification[]} targets
+     */
     async _modifyProfileSettings(targets) {
         await this._settingsController.modifyProfileSettings(targets);
         this._triggerScanInputsChanged();
     }
 
+    /** */
     _triggerScanInputsChanged() {
-        this._settingsController.trigger('scanInputsChanged', {source: this});
+        /** @type {import('settings-controller').ScanInputsChangedEvent} */
+        const event = {source: this};
+        this._settingsController.trigger('scanInputsChanged', event);
     }
 
+    /**
+     * @param {string} include
+     * @param {string} exclude
+     * @returns {import('settings').ScanningInput}
+     */
     static createDefaultMouseInput(include, exclude) {
         return {
             include,
@@ -172,16 +225,29 @@ class ScanInputsController {
 }
 
 class ScanInputField {
+    /**
+     * @param {ScanInputsController} parent
+     * @param {number} index
+     * @param {import('environment').OperatingSystem} os
+     */
     constructor(parent, index, os) {
+        /** @type {ScanInputsController} */
         this._parent = parent;
+        /** @type {number} */
         this._index = index;
+        /** @type {import('environment').OperatingSystem} */
         this._os = os;
+        /** @type {?HTMLElement} */
         this._node = null;
+        /** @type {?KeyboardMouseInputField} */
         this._includeInputField = null;
+        /** @type {?KeyboardMouseInputField} */
         this._excludeInputField = null;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
     }
 
+    /** @type {number} */
     get index() {
         return this._index;
     }
@@ -191,16 +257,20 @@ class ScanInputField {
         this._updateDataSettingTargets();
     }
 
+    /**
+     * @param {HTMLElement} container
+     * @param {import('settings').ScanningInput} scanningInput
+     */
     prepare(container, scanningInput) {
         const {include, exclude, options: {showAdvanced}} = scanningInput;
 
-        const node = this._parent.instantiateTemplate('scan-input');
-        const includeInputNode = node.querySelector('.scan-input-field[data-property=include]');
-        const includeMouseButton = node.querySelector('.mouse-button[data-property=include]');
-        const excludeInputNode = node.querySelector('.scan-input-field[data-property=exclude]');
-        const excludeMouseButton = node.querySelector('.mouse-button[data-property=exclude]');
-        const removeButton = node.querySelector('.scan-input-remove');
-        const menuButton = node.querySelector('.scanning-input-menu-button');
+        const node = /** @type {HTMLElement} */ (this._parent.instantiateTemplate('scan-input'));
+        const includeInputNode = /** @type {HTMLInputElement} */ (node.querySelector('.scan-input-field[data-property=include]'));
+        const includeMouseButton = /** @type {HTMLButtonElement} */ (node.querySelector('.mouse-button[data-property=include]'));
+        const excludeInputNode = /** @type {HTMLInputElement} */ (node.querySelector('.scan-input-field[data-property=exclude]'));
+        const excludeMouseButton = /** @type {HTMLButtonElement} */ (node.querySelector('.mouse-button[data-property=exclude]'));
+        const removeButton = /** @type {HTMLButtonElement} */ (node.querySelector('.scan-input-remove'));
+        const menuButton = /** @type {HTMLButtonElement} */ (node.querySelector('.scanning-input-menu-button'));
 
         node.dataset.showAdvanced = `${showAdvanced}`;
 
@@ -226,6 +296,7 @@ class ScanInputField {
         this._updateDataSettingTargets();
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
         if (this._includeInputField !== null) {
@@ -241,26 +312,38 @@ class ScanInputField {
 
     // Private
 
+    /**
+     * @param {import('keyboard-mouse-input-field').ChangeEvent} details
+     */
     _onIncludeValueChange({modifiers}) {
-        modifiers = this._joinModifiers(modifiers);
-        this._parent.setProperty(this._index, 'include', modifiers, true);
+        const modifiers2 = this._joinModifiers(modifiers);
+        this._parent.setProperty(this._index, 'include', modifiers2, true);
     }
 
+    /**
+     * @param {import('keyboard-mouse-input-field').ChangeEvent} details
+     */
     _onExcludeValueChange({modifiers}) {
-        modifiers = this._joinModifiers(modifiers);
-        this._parent.setProperty(this._index, 'exclude', modifiers, true);
+        const modifiers2 = this._joinModifiers(modifiers);
+        this._parent.setProperty(this._index, 'exclude', modifiers2, true);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onRemoveClick(e) {
         e.preventDefault();
         this._removeSelf();
     }
 
+    /**
+     * @param {import('popup-menu').MenuOpenEvent} e
+     */
     _onMenuOpen(e) {
         const bodyNode = e.detail.menu.bodyNode;
-        const showAdvanced = bodyNode.querySelector('.popup-menu-item[data-menu-action="showAdvanced"]');
-        const hideAdvanced = bodyNode.querySelector('.popup-menu-item[data-menu-action="hideAdvanced"]');
-        const advancedVisible = (this._node.dataset.showAdvanced === 'true');
+        const showAdvanced = /** @type {?HTMLElement} */ (bodyNode.querySelector('.popup-menu-item[data-menu-action="showAdvanced"]'));
+        const hideAdvanced = /** @type {?HTMLElement} */ (bodyNode.querySelector('.popup-menu-item[data-menu-action="hideAdvanced"]'));
+        const advancedVisible = (this._node !== null && this._node.dataset.showAdvanced === 'true');
         if (showAdvanced !== null) {
             showAdvanced.hidden = advancedVisible;
         }
@@ -269,6 +352,9 @@ class ScanInputField {
         }
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuClose(e) {
         switch (e.detail.action) {
             case 'remove':
@@ -281,40 +367,67 @@ class ScanInputField {
                 this._setAdvancedOptionsVisible(false);
                 break;
             case 'clearInputs':
-                this._includeInputField.clearInputs();
-                this._excludeInputField.clearInputs();
+                /** @type {KeyboardMouseInputField} */ (this._includeInputField).clearInputs();
+                /** @type {KeyboardMouseInputField} */ (this._excludeInputField).clearInputs();
                 break;
         }
     }
 
+    /**
+     * @param {string} pointerType
+     * @returns {boolean}
+     */
     _isPointerTypeSupported(pointerType) {
         if (this._node === null) { return false; }
-        const node = this._node.querySelector(`input.scan-input-settings-checkbox[data-property="types.${pointerType}"]`);
+        const node = /** @type {?HTMLInputElement} */ (this._node.querySelector(`input.scan-input-settings-checkbox[data-property="types.${pointerType}"]`));
         return node !== null && node.checked;
     }
 
+    /** */
     _updateDataSettingTargets() {
+        if (this._node === null) { return; }
         const index = this._index;
-        for (const typeCheckbox of this._node.querySelectorAll('.scan-input-settings-checkbox')) {
+        for (const typeCheckbox of /** @type {NodeListOf<HTMLElement>} */ (this._node.querySelectorAll('.scan-input-settings-checkbox'))) {
             const {property} = typeCheckbox.dataset;
             typeCheckbox.dataset.setting = `scanning.inputs[${index}].${property}`;
         }
     }
 
+    /** */
     _removeSelf() {
         this._parent.removeInput(this._index);
     }
 
+    /**
+     * @param {boolean} showAdvanced
+     */
     _setAdvancedOptionsVisible(showAdvanced) {
         showAdvanced = !!showAdvanced;
-        this._node.dataset.showAdvanced = `${showAdvanced}`;
+        if (this._node !== null) {
+            this._node.dataset.showAdvanced = `${showAdvanced}`;
+        }
         this._parent.setProperty(this._index, 'options.showAdvanced', showAdvanced, false);
     }
 
+    /**
+     * @param {string} modifiersString
+     * @returns {import('input').Modifier[]}
+     */
     _splitModifiers(modifiersString) {
-        return modifiersString.split(/[,;\s]+/).map((v) => v.trim().toLowerCase()).filter((v) => v.length > 0);
+        /** @type {import('input').Modifier[]} */
+        const results = [];
+        for (const modifier of modifiersString.split(/[,;\s]+/)) {
+            const modifier2 = DocumentUtil.normalizeModifier(modifier.trim().toLowerCase());
+            if (modifier2 === null) { continue; }
+            results.push(modifier2);
+        }
+        return results;
     }
 
+    /**
+     * @param {import('input').Modifier[]} modifiersArray
+     * @returns {string}
+     */
     _joinModifiers(modifiersArray) {
         return modifiersArray.join(', ');
     }
diff --git a/ext/js/pages/settings/scan-inputs-simple-controller.js b/ext/js/pages/settings/scan-inputs-simple-controller.js
index 8edb9a8678..8110956985 100644
--- a/ext/js/pages/settings/scan-inputs-simple-controller.js
+++ b/ext/js/pages/settings/scan-inputs-simple-controller.js
@@ -22,17 +22,26 @@
  */
 
 class ScanInputsSimpleController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?HTMLInputElement} */
         this._middleMouseButtonScan = null;
+        /** @type {?HTMLSelectElement} */
         this._mainScanModifierKeyInput = null;
+        /** @type {boolean} */
         this._mainScanModifierKeyInputHasOther = false;
+        /** @type {HotkeyUtil} */
         this._hotkeyUtil = new HotkeyUtil();
     }
 
+    /** */
     async prepare() {
-        this._middleMouseButtonScan = document.querySelector('#middle-mouse-button-scan');
-        this._mainScanModifierKeyInput = document.querySelector('#main-scan-modifier-key');
+        this._middleMouseButtonScan = /** @type {HTMLInputElement} */ (document.querySelector('#middle-mouse-button-scan'));
+        this._mainScanModifierKeyInput = /** @type {HTMLSelectElement} */ (document.querySelector('#main-scan-modifier-key'));
 
         const {platform: {os}} = await yomichan.api.getEnvironmentInfo();
         this._hotkeyUtil.os = os;
@@ -41,27 +50,36 @@ class ScanInputsSimpleController {
         this._populateSelect(this._mainScanModifierKeyInput, this._mainScanModifierKeyInputHasOther);
 
         const options = await this._settingsController.getOptions();
+        const optionsContext = this._settingsController.getOptionsContext();
 
         this._middleMouseButtonScan.addEventListener('change', this.onMiddleMouseButtonScanChange.bind(this), false);
         this._mainScanModifierKeyInput.addEventListener('change', this._onMainScanModifierKeyInputChange.bind(this), false);
 
         this._settingsController.on('scanInputsChanged', this._onScanInputsChanged.bind(this));
         this._settingsController.on('optionsChanged', this._onOptionsChanged.bind(this));
-        this._onOptionsChanged({options});
+        this._onOptionsChanged({options, optionsContext});
     }
 
+    /** */
     async refresh() {
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
     // Private
 
+    /**
+     * @param {import('settings-controller').ScanInputsChangedEvent} details
+     */
     _onScanInputsChanged({source}) {
         if (source === this) { return; }
         this.refresh();
     }
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         const {scanning: {inputs}} = options;
         const middleMouseSupportedIndex = this._getIndexOfMiddleMouseButtonScanInput(inputs);
@@ -88,27 +106,39 @@ class ScanInputsSimpleController {
 
         this._setHasMainScanInput(hasMainScanInput);
 
-        this._middleMouseButtonScan.checked = middleMouseSupported;
-        this._mainScanModifierKeyInput.value = mainScanInput;
+        /** @type {HTMLInputElement} */ (this._middleMouseButtonScan).checked = middleMouseSupported;
+        /** @type {HTMLSelectElement} */ (this._mainScanModifierKeyInput).value = mainScanInput;
     }
 
+    /**
+     * @param {Event} e
+     */
     onMiddleMouseButtonScanChange(e) {
-        const middleMouseSupported = e.currentTarget.checked;
+        const element = /** @type {HTMLInputElement} */ (e.currentTarget);
+        const middleMouseSupported = element.checked;
         this._setMiddleMouseSuppported(middleMouseSupported);
     }
 
+    /**
+     * @param {Event} e
+     */
     _onMainScanModifierKeyInputChange(e) {
-        const mainScanKey = e.currentTarget.value;
+        const element = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        const mainScanKey = element.value;
         if (mainScanKey === 'other') { return; }
         const mainScanInputs = (mainScanKey === 'none' ? [] : [mainScanKey]);
         this._setMainScanInputs(mainScanInputs);
     }
 
+    /**
+     * @param {HTMLSelectElement} select
+     * @param {boolean} hasOther
+     */
     _populateSelect(select, hasOther) {
         const modifierKeys = [
             {value: 'none', name: 'No key'}
         ];
-        for (const value of ['alt', 'ctrl', 'shift', 'meta']) {
+        for (const value of /** @type {import('input').ModifierKey[]} */ (['alt', 'ctrl', 'shift', 'meta'])) {
             const name = this._hotkeyUtil.getModifierDisplayValue(value);
             modifierKeys.push({value, name});
         }
@@ -128,10 +158,17 @@ class ScanInputsSimpleController {
         select.appendChild(fragment);
     }
 
+    /**
+     * @param {string} value
+     * @returns {string[]}
+     */
     _splitValue(value) {
         return value.split(/[,;\s]+/).map((v) => v.trim().toLowerCase()).filter((v) => v.length > 0);
     }
 
+    /**
+     * @param {boolean} value
+     */
     async _setMiddleMouseSuppported(value) {
         // Find target index
         const options = await this._settingsController.getOptions();
@@ -164,8 +201,11 @@ class ScanInputsSimpleController {
         }
     }
 
+    /**
+     * @param {string[]} value
+     */
     async _setMainScanInputs(value) {
-        value = value.join(', ');
+        const value2 = value.join(', ');
 
         // Find target index
         const options = await this._settingsController.getOptions();
@@ -176,7 +216,7 @@ class ScanInputsSimpleController {
 
         if (index < 0) {
             // Add new
-            const input = ScanInputsController.createDefaultMouseInput(value, 'mouse0');
+            const input = ScanInputsController.createDefaultMouseInput(value2, 'mouse0');
             await this._modifyProfileSettings([{
                 action: 'splice',
                 path: 'scanning.inputs',
@@ -189,16 +229,25 @@ class ScanInputsSimpleController {
             await this._modifyProfileSettings([{
                 action: 'set',
                 path: `scanning.inputs[${index}].include`,
-                value
+                value: value2
             }]);
         }
     }
 
+    /**
+     * @param {import('settings-modifications').Modification[]} targets
+     */
     async _modifyProfileSettings(targets) {
         await this._settingsController.modifyProfileSettings(targets);
-        this._settingsController.trigger('scanInputsChanged', {source: this});
+        /** @type {import('settings-controller').ScanInputsChangedEvent} */
+        const event = {source: this};
+        this._settingsController.trigger('scanInputsChanged', event);
     }
 
+    /**
+     * @param {import('settings').ScanningInput[]} inputs
+     * @returns {number}
+     */
     _getIndexOfMainScanInput(inputs) {
         for (let i = 0, ii = inputs.length; i < ii; ++i) {
             const {include, exclude, types: {mouse}} = inputs[i];
@@ -219,6 +268,10 @@ class ScanInputsSimpleController {
         return -1;
     }
 
+    /**
+     * @param {import('settings').ScanningInput[]} inputs
+     * @returns {number}
+     */
     _getIndexOfMiddleMouseButtonScanInput(inputs) {
         for (let i = 0, ii = inputs.length; i < ii; ++i) {
             const {include, exclude, types: {mouse}} = inputs[i];
@@ -235,13 +288,22 @@ class ScanInputsSimpleController {
         return -1;
     }
 
+    /**
+     * @param {string} input
+     * @returns {boolean}
+     */
     _isMouseInput(input) {
         return /^mouse\d+$/.test(input);
     }
 
+    /**
+     * @param {boolean} hasMainScanInput
+     */
     _setHasMainScanInput(hasMainScanInput) {
         if (this._mainScanModifierKeyInputHasOther !== hasMainScanInput) { return; }
         this._mainScanModifierKeyInputHasOther = !hasMainScanInput;
-        this._populateSelect(this._mainScanModifierKeyInput, this._mainScanModifierKeyInputHasOther);
+        if (this._mainScanModifierKeyInput !== null) {
+            this._populateSelect(this._mainScanModifierKeyInput, this._mainScanModifierKeyInputHasOther);
+        }
     }
 }
\ No newline at end of file
diff --git a/ext/js/pages/settings/secondary-search-dictionary-controller.js b/ext/js/pages/settings/secondary-search-dictionary-controller.js
index f8e2fb781e..f21186c683 100644
--- a/ext/js/pages/settings/secondary-search-dictionary-controller.js
+++ b/ext/js/pages/settings/secondary-search-dictionary-controller.js
@@ -17,16 +17,25 @@
  */
 
 class SecondarySearchDictionaryController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?import('core').TokenObject} */
         this._getDictionaryInfoToken = null;
+        /** @type {Map<string, import('dictionary-importer').Summary>} */
         this._dictionaryInfoMap = new Map();
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?HTMLElement} */
         this._container = null;
     }
 
+    /** */
     async prepare() {
-        this._container = document.querySelector('#secondary-search-dictionary-list');
+        this._container = /** @type {HTMLElement} */ (document.querySelector('#secondary-search-dictionary-list'));
 
         await this._onDatabaseUpdated();
 
@@ -37,7 +46,9 @@ class SecondarySearchDictionaryController {
 
     // Private
 
+    /** */
     async _onDatabaseUpdated() {
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._getDictionaryInfoToken = token;
         const dictionaries = await this._settingsController.getDictionaryInfo();
@@ -49,10 +60,12 @@ class SecondarySearchDictionaryController {
             this._dictionaryInfoMap.set(entry.title, entry);
         }
 
-        const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        await this._onDictionarySettingsReordered();
     }
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         this._eventListeners.removeAllEventListeners();
 
@@ -64,31 +77,38 @@ class SecondarySearchDictionaryController {
             const dictionaryInfo = this._dictionaryInfoMap.get(name);
             if (typeof dictionaryInfo === 'undefined') { continue; }
 
-            const node = this._settingsController.instantiateTemplate('secondary-search-dictionary');
+            const node = /** @type {HTMLElement} */ (this._settingsController.instantiateTemplate('secondary-search-dictionary'));
             fragment.appendChild(node);
 
-            const nameNode = node.querySelector('.dictionary-title');
+            const nameNode = /** @type {HTMLElement} */ (node.querySelector('.dictionary-title'));
             nameNode.textContent = name;
 
-            const versionNode = node.querySelector('.dictionary-version');
+            const versionNode = /** @type {HTMLElement} */ (node.querySelector('.dictionary-version'));
             versionNode.textContent = `rev.${dictionaryInfo.revision}`;
 
-            const toggle = node.querySelector('.dictionary-allow-secondary-searches');
+            const toggle = /** @type {HTMLElement} */ (node.querySelector('.dictionary-allow-secondary-searches'));
             toggle.dataset.setting = `dictionaries[${i}].allowSecondarySearches`;
             this._eventListeners.addEventListener(toggle, 'settingChanged', this._onEnabledChanged.bind(this, node), false);
         }
 
-        this._container.textContent = '';
-        this._container.appendChild(fragment);
+        const container = /** @type {HTMLElement} */ (this._container);
+        container.textContent = '';
+        container.appendChild(fragment);
     }
 
+    /**
+     * @param {HTMLElement} node
+     * @param {import('dom-data-binder').SettingChangedEvent} e
+     */
     _onEnabledChanged(node, e) {
         const {detail: {value}} = e;
         node.dataset.enabled = `${value}`;
     }
 
+    /** */
     async _onDictionarySettingsReordered() {
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 }
\ No newline at end of file
diff --git a/ext/js/pages/settings/sentence-termination-characters-controller.js b/ext/js/pages/settings/sentence-termination-characters-controller.js
index a243d2f813..4607aa7856 100644
--- a/ext/js/pages/settings/sentence-termination-characters-controller.js
+++ b/ext/js/pages/settings/sentence-termination-characters-controller.js
@@ -17,26 +17,38 @@
  */
 
 class SentenceTerminationCharactersController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {SentenceTerminationCharacterEntry[]} */
         this._entries = [];
+        /** @type {?HTMLButtonElement} */
         this._addButton = null;
+        /** @type {?HTMLButtonElement} */
         this._resetButton = null;
+        /** @type {?HTMLElement} */
         this._listTable = null;
+        /** @type {?HTMLElement} */
         this._listContainer = null;
+        /** @type {?HTMLElement} */
         this._emptyIndicator = null;
     }
 
+    /** @type {SettingsController} */
     get settingsController() {
         return this._settingsController;
     }
 
+    /** */
     async prepare() {
-        this._addButton = document.querySelector('#sentence-termination-character-list-add');
-        this._resetButton = document.querySelector('#sentence-termination-character-list-reset');
-        this._listTable = document.querySelector('#sentence-termination-character-list-table');
-        this._listContainer = document.querySelector('#sentence-termination-character-list');
-        this._emptyIndicator = document.querySelector('#sentence-termination-character-list-empty');
+        this._addButton = /** @type {HTMLButtonElement} */ (document.querySelector('#sentence-termination-character-list-add'));
+        this._resetButton = /** @type {HTMLButtonElement} */ (document.querySelector('#sentence-termination-character-list-reset'));
+        this._listTable = /** @type {HTMLElement} */ (document.querySelector('#sentence-termination-character-list-table'));
+        this._listContainer = /** @type {HTMLElement} */ (document.querySelector('#sentence-termination-character-list'));
+        this._emptyIndicator = /** @type {HTMLElement} */ (document.querySelector('#sentence-termination-character-list-empty'));
 
         this._addButton.addEventListener('click', this._onAddClick.bind(this));
         this._resetButton.addEventListener('click', this._onResetClick.bind(this));
@@ -45,6 +57,9 @@ class SentenceTerminationCharactersController {
         await this._updateOptions();
     }
 
+    /**
+     * @param {import('settings').SentenceParsingTerminationCharacterOption} terminationCharacterEntry
+     */
     async addEntry(terminationCharacterEntry) {
         const options = await this._settingsController.getOptions();
         const {sentenceParsing: {terminationCharacters}} = options;
@@ -60,6 +75,10 @@ class SentenceTerminationCharactersController {
         await this._updateOptions();
     }
 
+    /**
+     * @param {number} index
+     * @returns {Promise<boolean>}
+     */
     async deleteEntry(index) {
         const options = await this._settingsController.getOptions();
         const {sentenceParsing: {terminationCharacters}} = options;
@@ -78,12 +97,19 @@ class SentenceTerminationCharactersController {
         return true;
     }
 
+    /**
+     * @param {import('settings-modifications').Modification[]} targets
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async modifyProfileSettings(targets) {
         return await this._settingsController.modifyProfileSettings(targets);
     }
 
     // Private
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         for (const entry of this._entries) {
             entry.cleanup();
@@ -92,29 +118,37 @@ class SentenceTerminationCharactersController {
         this._entries = [];
         const {sentenceParsing: {terminationCharacters}} = options;
 
+        const listContainer = /** @type {HTMLElement} */ (this._listContainer);
         for (let i = 0, ii = terminationCharacters.length; i < ii; ++i) {
             const terminationCharacterEntry = terminationCharacters[i];
-            const node = this._settingsController.instantiateTemplate('sentence-termination-character-entry');
-            this._listContainer.appendChild(node);
+            const node = /** @type {HTMLElement} */ (this._settingsController.instantiateTemplate('sentence-termination-character-entry'));
+            listContainer.appendChild(node);
             const entry = new SentenceTerminationCharacterEntry(this, terminationCharacterEntry, i, node);
             this._entries.push(entry);
             entry.prepare();
         }
 
-        this._listTable.hidden = (terminationCharacters.length === 0);
-        this._emptyIndicator.hidden = (terminationCharacters.length !== 0);
+        /** @type {HTMLElement} */ (this._listTable).hidden = (terminationCharacters.length === 0);
+        /** @type {HTMLElement} */ (this._emptyIndicator).hidden = (terminationCharacters.length !== 0);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onAddClick(e) {
         e.preventDefault();
         this._addNewEntry();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onResetClick(e) {
         e.preventDefault();
         this._reset();
     }
 
+    /** */
     async _addNewEntry() {
         const newEntry = {
             enabled: true,
@@ -123,14 +157,17 @@ class SentenceTerminationCharactersController {
             includeCharacterAtStart: false,
             includeCharacterAtEnd: false
         };
-        return await this.addEntry(newEntry);
+        await this.addEntry(newEntry);
     }
 
+    /** */
     async _updateOptions() {
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
+    /** */
     async _reset() {
         const defaultOptions = await this._settingsController.getDefaultOptions();
         const value = defaultOptions.profiles[0].options.sentenceParsing.terminationCharacters;
@@ -140,28 +177,43 @@ class SentenceTerminationCharactersController {
 }
 
 class SentenceTerminationCharacterEntry {
+    /**
+     * @param {SentenceTerminationCharactersController} parent
+     * @param {import('settings').SentenceParsingTerminationCharacterOption} data
+     * @param {number} index
+     * @param {HTMLElement} node
+     */
     constructor(parent, data, index, node) {
+        /** @type {SentenceTerminationCharactersController} */
         this._parent = parent;
+        /** @type {import('settings').SentenceParsingTerminationCharacterOption} */
         this._data = data;
+        /** @type {number} */
         this._index = index;
+        /** @type {HTMLElement} */
         this._node = node;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?HTMLInputElement} */
         this._character1Input = null;
+        /** @type {?HTMLInputElement} */
         this._character2Input = null;
+        /** @type {string} */
         this._basePath = `sentenceParsing.terminationCharacters[${this._index}]`;
     }
 
+    /** */
     prepare() {
         const {enabled, character1, character2, includeCharacterAtStart, includeCharacterAtEnd} = this._data;
         const node = this._node;
 
-        const enabledToggle = node.querySelector('.sentence-termination-character-enabled');
-        const typeSelect = node.querySelector('.sentence-termination-character-type');
-        const character1Input = node.querySelector('.sentence-termination-character-input1');
-        const character2Input = node.querySelector('.sentence-termination-character-input2');
-        const includeAtStartCheckbox = node.querySelector('.sentence-termination-character-include-at-start');
-        const includeAtEndheckbox = node.querySelector('.sentence-termination-character-include-at-end');
-        const menuButton = node.querySelector('.sentence-termination-character-entry-button');
+        const enabledToggle = /** @type {HTMLInputElement} */ (node.querySelector('.sentence-termination-character-enabled'));
+        const typeSelect = /** @type {HTMLSelectElement} */ (node.querySelector('.sentence-termination-character-type'));
+        const character1Input = /** @type {HTMLInputElement} */ (node.querySelector('.sentence-termination-character-input1'));
+        const character2Input = /** @type {HTMLInputElement} */ (node.querySelector('.sentence-termination-character-input2'));
+        const includeAtStartCheckbox = /** @type {HTMLInputElement} */ (node.querySelector('.sentence-termination-character-include-at-start'));
+        const includeAtEndheckbox = /** @type {HTMLInputElement} */ (node.querySelector('.sentence-termination-character-include-at-end'));
+        const menuButton = /** @type {HTMLButtonElement} */ (node.querySelector('.sentence-termination-character-entry-button'));
 
         this._character1Input = character1Input;
         this._character2Input = character2Input;
@@ -186,6 +238,7 @@ class SentenceTerminationCharacterEntry {
         this._eventListeners.addEventListener(menuButton, 'menuClose', this._onMenuClose.bind(this), false);
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
         if (this._node.parentNode !== null) {
@@ -195,12 +248,20 @@ class SentenceTerminationCharacterEntry {
 
     // Private
 
+    /**
+     * @param {Event} e
+     */
     _onTypeSelectChange(e) {
-        this._setHasCharacter2(e.currentTarget.value === 'quote');
+        const element = /** @type {HTMLSelectElement} */ (e.currentTarget);
+        this._setHasCharacter2(element.value === 'quote');
     }
 
+    /**
+     * @param {1|2} characterNumber
+     * @param {Event} e
+     */
     _onCharacterChange(characterNumber, e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLInputElement} */ (e.currentTarget);
         if (characterNumber === 2 && this._data.character2 === null) {
             node.value = '';
         }
@@ -209,6 +270,9 @@ class SentenceTerminationCharacterEntry {
         this._setCharacterValue(node, characterNumber, value);
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuClose(e) {
         switch (e.detail.action) {
             case 'delete':
@@ -217,11 +281,16 @@ class SentenceTerminationCharacterEntry {
         }
     }
 
+    /** */
     async _delete() {
         this._parent.deleteEntry(this._index);
     }
 
+    /**
+     * @param {boolean} has
+     */
     async _setHasCharacter2(has) {
+        if (this._character2Input === null) { return; }
         const okay = await this._setCharacterValue(this._character2Input, 2, has ? this._data.character1 : null);
         if (okay) {
             const type = (!has ? 'terminator' : 'quote');
@@ -229,14 +298,24 @@ class SentenceTerminationCharacterEntry {
         }
     }
 
+    /**
+     * @param {HTMLInputElement} inputNode
+     * @param {1|2} characterNumber
+     * @param {?string} value
+     * @returns {Promise<boolean>}
+     */
     async _setCharacterValue(inputNode, characterNumber, value) {
-        const pathEnd = `character${characterNumber}`;
-        const r = await this._parent.settingsController.setProfileSetting(`${this._basePath}.${pathEnd}`, value);
+        if (characterNumber === 1 && typeof value !== 'string') { value = ''; }
+        const r = await this._parent.settingsController.setProfileSetting(`${this._basePath}.character${characterNumber}`, value);
         const okay = !r[0].error;
         if (okay) {
-            this._data[pathEnd] = value;
+            if (characterNumber === 1) {
+                this._data.character1 = /** @type {string} */ (value);
+            } else {
+                this._data.character2 = value;
+            }
         } else {
-            value = this._data[pathEnd];
+            value = characterNumber === 1 ? this._data.character1 : this._data.character2;
         }
         inputNode.value = (value !== null ? value : '');
         return okay;
diff --git a/ext/js/pages/settings/settings-controller.js b/ext/js/pages/settings/settings-controller.js
index f27135c4cf..eefd04a914 100644
--- a/ext/js/pages/settings/settings-controller.js
+++ b/ext/js/pages/settings/settings-controller.js
@@ -22,21 +22,33 @@
  * PermissionsUtil
  */
 
+/**
+ * @augments EventDispatcher<import('settings-controller').EventType>
+ */
 class SettingsController extends EventDispatcher {
     constructor() {
         super();
+        /** @type {number} */
         this._profileIndex = 0;
+        /** @type {string} */
         this._source = generateId(16);
+        /** @type {Set<import('settings-controller').PageExitPrevention>} */
         this._pageExitPreventions = new Set();
+        /** @type {EventListenerCollection} */
         this._pageExitPreventionEventListeners = new EventListenerCollection();
-        this._templates = new HtmlTemplateCollection(document);
+        /** @type {HtmlTemplateCollection} */
+        this._templates = new HtmlTemplateCollection();
+        this._templates.load(document);
+        /** @type {PermissionsUtil} */
         this._permissionsUtil = new PermissionsUtil();
     }
 
+    /** @type {string} */
     get source() {
         return this._source;
     }
 
+    /** @type {number} */
     get profileIndex() {
         return this._profileIndex;
     }
@@ -46,10 +58,12 @@ class SettingsController extends EventDispatcher {
         this._setProfileIndex(value, true);
     }
 
+    /** @type {PermissionsUtil} */
     get permissionsUtil() {
         return this._permissionsUtil;
     }
 
+    /** */
     async prepare() {
         yomichan.on('optionsUpdated', this._onOptionsUpdated.bind(this));
         if (this._canObservePermissionsChanges()) {
@@ -63,67 +77,121 @@ class SettingsController extends EventDispatcher {
         }
     }
 
+    /** */
     async refresh() {
         await this._onOptionsUpdatedInternal(true);
     }
 
+    /**
+     * @returns {Promise<import('settings').ProfileOptions>}
+     */
     async getOptions() {
         const optionsContext = this.getOptionsContext();
         return await yomichan.api.optionsGet(optionsContext);
     }
 
+    /**
+     * @returns {Promise<import('settings').Options>}
+     */
     async getOptionsFull() {
         return await yomichan.api.optionsGetFull();
     }
 
+    /**
+     * @param {import('settings').Options} value
+     */
     async setAllSettings(value) {
         const profileIndex = value.profileCurrent;
         await yomichan.api.setAllSettings(value, this._source);
         this._setProfileIndex(profileIndex, true);
     }
 
+    /**
+     * @param {import('settings-modifications').ScopedRead[]} targets
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async getSettings(targets) {
-        return await this._getSettings(targets, {});
+        return await this._getSettings(targets, null);
     }
 
+    /**
+     * @param {import('settings-modifications').Read[]} targets
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async getGlobalSettings(targets) {
-        return await this._getSettings(targets, {scope: 'global'});
+        return await this._getSettings(targets, {scope: 'global', optionsContext: null});
     }
 
+    /**
+     * @param {import('settings-modifications').Read[]} targets
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async getProfileSettings(targets) {
-        return await this._getSettings(targets, {scope: 'profile'});
+        return await this._getSettings(targets, {scope: 'profile', optionsContext: null});
     }
 
+    /**
+     * @param {import('settings-modifications').ScopedModification[]} targets
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async modifySettings(targets) {
-        return await this._modifySettings(targets, {});
+        return await this._modifySettings(targets, null);
     }
 
+    /**
+     * @param {import('settings-modifications').Modification[]} targets
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async modifyGlobalSettings(targets) {
-        return await this._modifySettings(targets, {scope: 'global'});
+        return await this._modifySettings(targets, {scope: 'global', optionsContext: null});
     }
 
+    /**
+     * @param {import('settings-modifications').Modification[]} targets
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async modifyProfileSettings(targets) {
-        return await this._modifySettings(targets, {scope: 'profile'});
+        return await this._modifySettings(targets, {scope: 'profile', optionsContext: null});
     }
 
+    /**
+     * @param {string} path
+     * @param {unknown} value
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async setGlobalSetting(path, value) {
         return await this.modifyGlobalSettings([{action: 'set', path, value}]);
     }
 
+    /**
+     * @param {string} path
+     * @param {unknown} value
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async setProfileSetting(path, value) {
         return await this.modifyProfileSettings([{action: 'set', path, value}]);
     }
 
+    /**
+     * @returns {Promise<import('dictionary-importer').Summary[]>}
+     */
     async getDictionaryInfo() {
         return await yomichan.api.getDictionaryInfo();
     }
 
+    /**
+     * @returns {import('settings').OptionsContext}
+     */
     getOptionsContext() {
         return {index: this._profileIndex};
     }
 
+    /**
+     * @returns {import('settings-controller').PageExitPrevention}
+     */
     preventPageExit() {
-        const obj = {end: null};
+        /** @type {import('settings-controller').PageExitPrevention} */
+        const obj = {};
         obj.end = this._endPreventPageExit.bind(this, obj);
         if (this._pageExitPreventionEventListeners.size === 0) {
             this._pageExitPreventionEventListeners.addEventListener(window, 'beforeunload', this._onBeforeUnload.bind(this), false);
@@ -132,14 +200,25 @@ class SettingsController extends EventDispatcher {
         return obj;
     }
 
+    /**
+     * @param {string} name
+     * @returns {Element}
+     */
     instantiateTemplate(name) {
         return this._templates.instantiate(name);
     }
 
+    /**
+     * @param {string} name
+     * @returns {DocumentFragment}
+     */
     instantiateTemplateFragment(name) {
         return this._templates.instantiateFragment(name);
     }
 
+    /**
+     * @returns {Promise<import('settings').Options>}
+     */
     async getDefaultOptions() {
         const optionsUtil = new OptionsUtil();
         await optionsUtil.prepare();
@@ -149,22 +228,34 @@ class SettingsController extends EventDispatcher {
 
     // Private
 
+    /**
+     * @param {number} value
+     * @param {boolean} canUpdateProfileIndex
+     */
     _setProfileIndex(value, canUpdateProfileIndex) {
         this._profileIndex = value;
         this.trigger('optionsContextChanged');
         this._onOptionsUpdatedInternal(canUpdateProfileIndex);
     }
 
+    /**
+     * @param {{source: string}} details
+     */
     _onOptionsUpdated({source}) {
         if (source === this._source) { return; }
         this._onOptionsUpdatedInternal(true);
     }
 
+    /**
+     * @param {boolean} canUpdateProfileIndex
+     */
     async _onOptionsUpdatedInternal(canUpdateProfileIndex) {
         const optionsContext = this.getOptionsContext();
         try {
             const options = await this.getOptions();
-            this.trigger('optionsChanged', {options, optionsContext});
+            /** @type {import('settings-controller').OptionsChangedEvent} */
+            const event = {options, optionsContext};
+            this.trigger('optionsChanged', event);
         } catch (e) {
             if (canUpdateProfileIndex) {
                 this._setProfileIndex(0, false);
@@ -174,26 +265,49 @@ class SettingsController extends EventDispatcher {
         }
     }
 
-    _setupTargets(targets, extraFields) {
-        return targets.map((target) => {
-            target = Object.assign({}, extraFields, target);
-            if (target.scope === 'profile') {
-                target.optionsContext = this.getOptionsContext();
-            }
-            return target;
-        });
+    /**
+     * @param {import('settings-modifications').OptionsScope} target
+     */
+    _modifyOptionsScope(target) {
+        if (target.scope === 'profile') {
+            target.optionsContext = this.getOptionsContext();
+        }
     }
 
+    /**
+     * @template {boolean} THasScope
+     * @param {import('settings-controller').SettingsRead<THasScope>[]} targets
+     * @param {import('settings-controller').SettingsExtraFields<THasScope>} extraFields
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async _getSettings(targets, extraFields) {
-        targets = this._setupTargets(targets, extraFields);
-        return await yomichan.api.getSettings(targets);
+        const targets2 = targets.map((target) => {
+            const target2 = /** @type {import('settings-controller').SettingsRead<true>} */ (Object.assign({}, extraFields, target));
+            this._modifyOptionsScope(target2);
+            return target2;
+        });
+        return await yomichan.api.getSettings(targets2);
     }
 
+    /**
+     * @template {boolean} THasScope
+     * @param {import('settings-controller').SettingsModification<THasScope>[]} targets
+     * @param {import('settings-controller').SettingsExtraFields<THasScope>} extraFields
+     * @returns {Promise<import('settings-controller').ModifyResult[]>}
+     */
     async _modifySettings(targets, extraFields) {
-        targets = this._setupTargets(targets, extraFields);
-        return await yomichan.api.modifySettings(targets, this._source);
+        const targets2 = targets.map((target) => {
+            const target2 = /** @type {import('settings-controller').SettingsModification<true>} */ (Object.assign({}, extraFields, target));
+            this._modifyOptionsScope(target2);
+            return target2;
+        });
+        return await yomichan.api.modifySettings(targets2, this._source);
     }
 
+    /**
+     * @param {BeforeUnloadEvent} e
+     * @returns {string|undefined}
+     */
     _onBeforeUnload(e) {
         if (this._pageExitPreventions.size === 0) {
             return;
@@ -204,6 +318,9 @@ class SettingsController extends EventDispatcher {
         return '';
     }
 
+    /**
+     * @param {import('settings-controller').PageExitPrevention} obj
+     */
     _endPreventPageExit(obj) {
         this._pageExitPreventions.delete(obj);
         if (this._pageExitPreventions.size === 0) {
@@ -211,18 +328,25 @@ class SettingsController extends EventDispatcher {
         }
     }
 
+    /** */
     _onPermissionsChanged() {
         this._triggerPermissionsChanged();
     }
 
+    /** */
     async _triggerPermissionsChanged() {
-        const event = 'permissionsChanged';
-        if (!this.hasListeners(event)) { return; }
+        const eventName = 'permissionsChanged';
+        if (!this.hasListeners(eventName)) { return; }
 
         const permissions = await this._permissionsUtil.getAllPermissions();
-        this.trigger(event, {permissions});
+        /** @type {import('settings-controller').PermissionsChangedEvent} */
+        const event = {permissions};
+        this.trigger(eventName, event);
     }
 
+    /**
+     * @returns {boolean}
+     */
     _canObservePermissionsChanges() {
         return isObject(chrome.permissions) && isObject(chrome.permissions.onAdded) && isObject(chrome.permissions.onRemoved);
     }
diff --git a/ext/js/pages/settings/settings-display-controller.js b/ext/js/pages/settings/settings-display-controller.js
index 3f1f6b6b68..14bc321bfa 100644
--- a/ext/js/pages/settings/settings-display-controller.js
+++ b/ext/js/pages/settings/settings-display-controller.js
@@ -23,44 +23,54 @@
  */
 
 class SettingsDisplayController {
+    /**
+     * @param {SettingsController} settingsController
+     * @param {ModalController} modalController
+     */
     constructor(settingsController, modalController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {ModalController} */
         this._modalController = modalController;
+        /** @type {?HTMLElement} */
         this._contentNode = null;
+        /** @type {?HTMLElement} */
         this._menuContainer = null;
-        this._onMoreToggleClickBind = null;
-        this._onMenuButtonClickBind = null;
+        /** @type {(event: MouseEvent) => void} */
+        this._onMoreToggleClickBind = this._onMoreToggleClick.bind(this);
+        /** @type {(event: MouseEvent) => void} */
+        this._onMenuButtonClickBind = this._onMenuButtonClick.bind(this);
     }
 
+    /** */
     prepare() {
-        this._contentNode = document.querySelector('.content');
-        this._menuContainer = document.querySelector('#popup-menus');
+        this._contentNode = /** @type {HTMLElement} */ (document.querySelector('.content'));
+        this._menuContainer = /** @type {HTMLElement} */ (document.querySelector('#popup-menus'));
 
         const onFabButtonClick = this._onFabButtonClick.bind(this);
-        for (const fabButton of document.querySelectorAll('.fab-button')) {
+        for (const fabButton of /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.fab-button'))) {
             fabButton.addEventListener('click', onFabButtonClick, false);
         }
 
         const onModalAction = this._onModalAction.bind(this);
-        for (const node of document.querySelectorAll('[data-modal-action]')) {
+        for (const node of /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('[data-modal-action]'))) {
             node.addEventListener('click', onModalAction, false);
         }
 
         const onSelectOnClickElementClick = this._onSelectOnClickElementClick.bind(this);
-        for (const node of document.querySelectorAll('[data-select-on-click]')) {
+        for (const node of /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('[data-select-on-click]'))) {
             node.addEventListener('click', onSelectOnClickElementClick, false);
         }
 
         const onInputTabActionKeyDown = this._onInputTabActionKeyDown.bind(this);
-        for (const node of document.querySelectorAll('[data-tab-action]')) {
+        for (const node of /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('[data-tab-action]'))) {
             node.addEventListener('keydown', onInputTabActionKeyDown, false);
         }
 
-        for (const node of document.querySelectorAll('.defer-load-iframe')) {
+        for (const node of /** @type {NodeListOf<HTMLIFrameElement>} */ (document.querySelectorAll('.defer-load-iframe'))) {
             this._setupDeferLoadIframe(node);
         }
 
-        this._onMoreToggleClickBind = this._onMoreToggleClick.bind(this);
         const moreSelectorObserver = new SelectorObserver({
             selector: '.more-toggle',
             onAdded: this._onMoreSetup.bind(this),
@@ -68,7 +78,6 @@ class SettingsDisplayController {
         });
         moreSelectorObserver.observe(document.documentElement, false);
 
-        this._onMenuButtonClickBind = this._onMenuButtonClick.bind(this);
         const menuSelectorObserver = new SelectorObserver({
             selector: '[data-menu]',
             onAdded: this._onMenuSetup.bind(this),
@@ -83,32 +92,54 @@ class SettingsDisplayController {
 
     // Private
 
+    /**
+     * @param {Element} element
+     * @returns {null}
+     */
     _onMoreSetup(element) {
-        element.addEventListener('click', this._onMoreToggleClickBind, false);
+        /** @type {HTMLElement} */ (element).addEventListener('click', this._onMoreToggleClickBind, false);
         return null;
     }
 
+    /**
+     * @param {Element} element
+     */
     _onMoreCleanup(element) {
-        element.removeEventListener('click', this._onMoreToggleClickBind, false);
+        /** @type {HTMLElement} */ (element).removeEventListener('click', this._onMoreToggleClickBind, false);
     }
 
+    /**
+     * @param {Element} element
+     * @returns {null}
+     */
     _onMenuSetup(element) {
-        element.addEventListener('click', this._onMenuButtonClickBind, false);
+        /** @type {HTMLElement} */ (element).addEventListener('click', this._onMenuButtonClickBind, false);
         return null;
     }
 
+    /**
+     * @param {Element} element
+     */
     _onMenuCleanup(element) {
-        element.removeEventListener('click', this._onMenuButtonClickBind, false);
+        /** @type {HTMLElement} */ (element).removeEventListener('click', this._onMenuButtonClickBind, false);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMenuButtonClick(e) {
-        const element = e.currentTarget;
+        const element = /** @type {HTMLElement} */ (e.currentTarget);
         const {menu} = element.dataset;
+        if (typeof menu === 'undefined') { return; }
         this._showMenu(element, menu);
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onFabButtonClick(e) {
-        const action = e.currentTarget.dataset.action;
+        const element = /** @type {HTMLElement} */ (e.currentTarget);
+        const action = element.dataset.action;
         switch (action) {
             case 'toggle-sidebar':
                 document.body.classList.toggle('sidebar-visible');
@@ -119,16 +150,20 @@ class SettingsDisplayController {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onMoreToggleClick(e) {
-        const container = this._getMoreContainer(e.currentTarget);
+        const node = /** @type {HTMLElement} */ (e.currentTarget);
+        const container = this._getMoreContainer(node);
         if (container === null) { return; }
 
-        const more = container.querySelector('.more');
+        const more = /** @type {?HTMLElement} */ (container.querySelector('.more'));
         if (more === null) { return; }
 
         const moreVisible = more.hidden;
         more.hidden = !moreVisible;
-        for (const moreToggle of container.querySelectorAll('.more-toggle')) {
+        for (const moreToggle of /** @type {NodeListOf<HTMLElement>} */ (container.querySelectorAll('.more-toggle'))) {
             const container2 = this._getMoreContainer(moreToggle);
             if (container2 === null) { continue; }
 
@@ -139,13 +174,16 @@ class SettingsDisplayController {
         }
 
         e.preventDefault();
-        return false;
     }
 
+    /** */
     _onPopState() {
         this._updateScrollTarget();
     }
 
+    /**
+     * @param {KeyboardEvent} e
+     */
     _onKeyDown(e) {
         switch (e.code) {
             case 'Escape':
@@ -157,12 +195,18 @@ class SettingsDisplayController {
         }
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onModalAction(e) {
-        const node = e.currentTarget;
+        const node = /** @type {HTMLElement} */ (e.currentTarget);
         const {modalAction} = node.dataset;
         if (typeof modalAction !== 'string') { return; }
 
-        let [action, target] = modalAction.split(',');
+        const modalActionArray = modalAction.split(',');
+        const action = modalActionArray[0];
+        /** @type {string|Element|undefined} */
+        let target = modalActionArray[1];
         if (typeof target === 'undefined') {
             const currentModal = node.closest('.modal');
             if (currentModal === null) { return; }
@@ -187,26 +231,33 @@ class SettingsDisplayController {
         e.preventDefault();
     }
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onSelectOnClickElementClick(e) {
         if (e.button !== 0) { return; }
 
-        const node = e.currentTarget;
+        const node = /** @type {HTMLElement} */ (e.currentTarget);
         const range = document.createRange();
         range.selectNode(node);
 
         const selection = window.getSelection();
-        selection.removeAllRanges();
-        selection.addRange(range);
+        if (selection !== null) {
+            selection.removeAllRanges();
+            selection.addRange(range);
+        }
 
         e.preventDefault();
         e.stopPropagation();
-        return false;
     }
 
+    /**
+     * @param {KeyboardEvent} e
+     */
     _onInputTabActionKeyDown(e) {
         if (e.key !== 'Tab' || e.ctrlKey) { return; }
 
-        const node = e.currentTarget;
+        const node = /** @type {HTMLElement} */ (e.currentTarget);
         const {tabAction} = node.dataset;
         if (typeof tabAction !== 'string') { return; }
 
@@ -222,6 +273,7 @@ class SettingsDisplayController {
         }
     }
 
+    /** */
     _updateScrollTarget() {
         const hash = window.location.hash;
         if (!hash.startsWith('#!')) { return; }
@@ -235,18 +287,25 @@ class SettingsDisplayController {
         content.scrollTop += rect2.top - rect1.top;
     }
 
+    /**
+     * @param {HTMLElement} link
+     * @returns {?Element}
+     */
     _getMoreContainer(link) {
         const v = link.dataset.parentDistance;
         const distance = v ? parseInt(v, 10) : 1;
         if (Number.isNaN(distance)) { return null; }
 
+        /** @type {?Element} */
+        let result = link;
         for (let i = 0; i < distance; ++i) {
-            link = link.parentNode;
-            if (link === null) { break; }
+            if (result === null) { break; }
+            result = /** @type {?Element} */ (result.parentNode);
         }
-        return link;
+        return result;
     }
 
+    /** */
     _closeTopMenuOrModal() {
         for (const popupMenu of PopupMenu.openMenus) {
             popupMenu.close();
@@ -259,17 +318,27 @@ class SettingsDisplayController {
         }
     }
 
+    /**
+     * @param {HTMLElement} element
+     * @param {string} menuName
+     */
     _showMenu(element, menuName) {
-        const menu = this._settingsController.instantiateTemplate(menuName);
-        if (menu === null) { return; }
+        const menu = /** @type {HTMLElement} */ (this._settingsController.instantiateTemplate(menuName));
 
-        this._menuContainer.appendChild(menu);
+        /** @type {HTMLElement} */ (this._menuContainer).appendChild(menu);
 
         const popupMenu = new PopupMenu(element, menu);
         popupMenu.prepare();
     }
 
+    /**
+     * @param {KeyboardEvent} e
+     * @param {HTMLElement} node
+     * @param {string[]} args
+     */
     _indentInput(e, node, args) {
+        if (!(node instanceof HTMLTextAreaElement)) { return; }
+
         let indent = '\t';
         if (args.length > 1) {
             const count = parseInt(args[1], 10);
@@ -278,7 +347,8 @@ class SettingsDisplayController {
 
         const {selectionStart: start, selectionEnd: end, value} = node;
         const lineStart = value.substring(0, start).lastIndexOf('\n') + 1;
-        const lineWhitespace = /^[ \t]*/.exec(value.substring(lineStart))[0];
+        const lineWhitespaceMatch = /^[ \t]*/.exec(value.substring(lineStart));
+        const lineWhitespace = lineWhitespaceMatch !== null ? lineWhitespaceMatch[0] : '';
 
         if (e.shiftKey) {
             const whitespaceLength = Math.max(0, Math.floor((lineWhitespace.length - 1) / 4) * 4);
@@ -300,17 +370,23 @@ class SettingsDisplayController {
         }
     }
 
+    /**
+     * @param {HTMLIFrameElement} element
+     */
     _setupDeferLoadIframe(element) {
         const parent = this._getMoreContainer(element);
         if (parent === null) { return; }
 
+        /** @type {?MutationObserver} */
         let mutationObserver = null;
         const callback = () => {
             if (!this._isElementVisible(element)) { return false; }
 
             const src = element.dataset.src;
             delete element.dataset.src;
-            element.src = src;
+            if (typeof src === 'string') {
+                element.src = src;
+            }
 
             if (mutationObserver === null) { return true; }
 
@@ -325,6 +401,10 @@ class SettingsDisplayController {
         mutationObserver.observe(parent, {attributes: true});
     }
 
+    /**
+     * @param {HTMLElement} element
+     * @returns {boolean}
+     */
     _isElementVisible(element) {
         return (element.offsetParent !== null);
     }
diff --git a/ext/js/pages/settings/settings-main.js b/ext/js/pages/settings/settings-main.js
index a4832220f7..f826d912ef 100644
--- a/ext/js/pages/settings/settings-main.js
+++ b/ext/js/pages/settings/settings-main.js
@@ -49,6 +49,9 @@
  * TranslationTextReplacementsController
  */
 
+/**
+ * @param {GenericSettingController} genericSettingController
+ */
 async function setupGenericSettingsController(genericSettingController) {
     await genericSettingController.prepare();
     await genericSettingController.refresh();
@@ -62,10 +65,11 @@ async function setupGenericSettingsController(genericSettingController) {
         const extensionContentController = new ExtensionContentController();
         extensionContentController.prepare();
 
-        const statusFooter = new StatusFooter(document.querySelector('.status-footer-container'));
+        const statusFooter = new StatusFooter(/** @type {HTMLElement} */ (document.querySelector('.status-footer-container')));
         statusFooter.prepare();
 
-        let prepareTimer = setTimeout(() => {
+        /** @type {?number} */
+        let prepareTimer = window.setTimeout(() => {
             prepareTimer = null;
             document.documentElement.dataset.loadingStalled = 'true';
         }, 1000);
diff --git a/ext/js/pages/settings/sort-frequency-dictionary-controller.js b/ext/js/pages/settings/sort-frequency-dictionary-controller.js
index 9a3fc23736..36e9f6f7df 100644
--- a/ext/js/pages/settings/sort-frequency-dictionary-controller.js
+++ b/ext/js/pages/settings/sort-frequency-dictionary-controller.js
@@ -17,20 +17,30 @@
  */
 
 class SortFrequencyDictionaryController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?HTMLSelectElement} */
         this._sortFrequencyDictionarySelect = null;
+        /** @type {?HTMLSelectElement} */
         this._sortFrequencyDictionaryOrderSelect = null;
+        /** @type {?HTMLButtonElement} */
         this._sortFrequencyDictionaryOrderAutoButton = null;
+        /** @type {?HTMLElement} */
         this._sortFrequencyDictionaryOrderContainerNode = null;
+        /** @type {?import('core').TokenObject} */
         this._getDictionaryInfoToken = null;
     }
 
+    /** */
     async prepare() {
-        this._sortFrequencyDictionarySelect = document.querySelector('#sort-frequency-dictionary');
-        this._sortFrequencyDictionaryOrderSelect = document.querySelector('#sort-frequency-dictionary-order');
-        this._sortFrequencyDictionaryOrderAutoButton = document.querySelector('#sort-frequency-dictionary-order-auto');
-        this._sortFrequencyDictionaryOrderContainerNode = document.querySelector('#sort-frequency-dictionary-order-container');
+        this._sortFrequencyDictionarySelect = /** @type {HTMLSelectElement} */ (document.querySelector('#sort-frequency-dictionary'));
+        this._sortFrequencyDictionaryOrderSelect = /** @type {HTMLSelectElement} */ (document.querySelector('#sort-frequency-dictionary-order'));
+        this._sortFrequencyDictionaryOrderAutoButton = /** @type {HTMLButtonElement} */ (document.querySelector('#sort-frequency-dictionary-order-auto'));
+        this._sortFrequencyDictionaryOrderContainerNode = /** @type {HTMLElement} */ (document.querySelector('#sort-frequency-dictionary-order-container'));
 
         await this._onDatabaseUpdated();
 
@@ -43,7 +53,9 @@ class SortFrequencyDictionaryController {
 
     // Private
 
+    /** */
     async _onDatabaseUpdated() {
+        /** @type {?import('core').TokenObject} */
         const token = {};
         this._getDictionaryInfoToken = token;
         const dictionaries = await this._settingsController.getDictionaryInfo();
@@ -53,33 +65,44 @@ class SortFrequencyDictionaryController {
         this._updateDictionaryOptions(dictionaries);
 
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         const {sortFrequencyDictionary, sortFrequencyDictionaryOrder} = options.general;
-        this._sortFrequencyDictionarySelect.value = (sortFrequencyDictionary !== null ? sortFrequencyDictionary : '');
-        this._sortFrequencyDictionaryOrderSelect.value = sortFrequencyDictionaryOrder;
-        this._sortFrequencyDictionaryOrderContainerNode.hidden = (sortFrequencyDictionary === null);
+        /** @type {HTMLSelectElement} */ (this._sortFrequencyDictionarySelect).value = (sortFrequencyDictionary !== null ? sortFrequencyDictionary : '');
+        /** @type {HTMLSelectElement} */ (this._sortFrequencyDictionaryOrderSelect).value = sortFrequencyDictionaryOrder;
+        /** @type {HTMLElement} */ (this._sortFrequencyDictionaryOrderContainerNode).hidden = (sortFrequencyDictionary === null);
     }
 
+    /** */
     _onSortFrequencyDictionarySelectChange() {
-        let {value} = this._sortFrequencyDictionarySelect;
-        if (value === '') { value = null; }
-        this._setSortFrequencyDictionaryValue(value);
+        const {value} = /** @type {HTMLSelectElement} */ (this._sortFrequencyDictionarySelect);
+        this._setSortFrequencyDictionaryValue(value !== '' ? value : null);
     }
 
+    /** */
     _onSortFrequencyDictionaryOrderSelectChange() {
-        const {value} = this._sortFrequencyDictionaryOrderSelect;
-        this._setSortFrequencyDictionaryOrderValue(value);
+        const {value} = /** @type {HTMLSelectElement} */ (this._sortFrequencyDictionaryOrderSelect);
+        const value2 = this._normalizeSortFrequencyDictionaryOrder(value);
+        if (value2 === null) { return; }
+        this._setSortFrequencyDictionaryOrderValue(value2);
     }
 
+    /** */
     _onSortFrequencyDictionaryOrderAutoButtonClick() {
-        const {value} = this._sortFrequencyDictionarySelect;
+        const {value} = /** @type {HTMLSelectElement} */ (this._sortFrequencyDictionarySelect);
         if (value === '') { return; }
         this._autoUpdateOrder(value);
     }
 
+    /**
+     * @param {import('dictionary-importer').Summary[]} dictionaries
+     */
     _updateDictionaryOptions(dictionaries) {
         const fragment = document.createDocumentFragment();
         let option = document.createElement('option');
@@ -93,30 +116,44 @@ class SortFrequencyDictionaryController {
             option.textContent = title;
             fragment.appendChild(option);
         }
-        this._sortFrequencyDictionarySelect.textContent = '';
-        this._sortFrequencyDictionarySelect.appendChild(fragment);
+        const select = /** @type {HTMLSelectElement} */ (this._sortFrequencyDictionarySelect);
+        select.textContent = '';
+        select.appendChild(fragment);
     }
 
+    /**
+     * @param {?string} value
+     */
     async _setSortFrequencyDictionaryValue(value) {
-        this._sortFrequencyDictionaryOrderContainerNode.hidden = (value === null);
+        /** @type {HTMLElement} */ (this._sortFrequencyDictionaryOrderContainerNode).hidden = (value === null);
         await this._settingsController.setProfileSetting('general.sortFrequencyDictionary', value);
         if (value !== null) {
             await this._autoUpdateOrder(value);
         }
     }
 
+    /**
+     * @param {import('settings').SortFrequencyDictionaryOrder} value
+     */
     async _setSortFrequencyDictionaryOrderValue(value) {
         await this._settingsController.setProfileSetting('general.sortFrequencyDictionaryOrder', value);
     }
 
+    /**
+     * @param {string} dictionary
+     */
     async _autoUpdateOrder(dictionary) {
         const order = await this._getFrequencyOrder(dictionary);
         if (order === 0) { return; }
         const value = (order > 0 ? 'descending' : 'ascending');
-        this._sortFrequencyDictionaryOrderSelect.value = value;
+        /** @type {HTMLSelectElement} */ (this._sortFrequencyDictionaryOrderSelect).value = value;
         await this._setSortFrequencyDictionaryOrderValue(value);
     }
 
+    /**
+     * @param {string} dictionary
+     * @returns {Promise<number>}
+     */
     async _getFrequencyOrder(dictionary) {
         const moreCommonTerms = ['来る', '言う', '出る', '入る', '方', '男', '女', '今', '何', '時'];
         const lessCommonTerms = ['行なう', '論じる', '過す', '行方', '人口', '猫', '犬', '滝', '理', '暁'];
@@ -127,6 +164,7 @@ class SortFrequencyDictionaryController {
             [dictionary]
         );
 
+        /** @type {Map<string, {hasValue: boolean, minValue: number, maxValue: number}>} */
         const termDetails = new Map();
         const moreCommonTermDetails = [];
         const lessCommonTermDetails = [];
@@ -142,7 +180,6 @@ class SortFrequencyDictionaryController {
         }
 
         for (const {term, frequency} of frequencies) {
-            if (typeof frequency !== 'number') { continue; }
             const details = termDetails.get(term);
             if (typeof details === 'undefined') { continue; }
             details.minValue = Math.min(details.minValue, frequency);
@@ -161,10 +198,28 @@ class SortFrequencyDictionaryController {
         return Math.sign(result);
     }
 
+    /**
+     * @param {import('dictionary-importer').SummaryCounts} counts
+     * @returns {boolean}
+     */
     _dictionaryHasNoFrequencies(counts) {
         if (typeof counts !== 'object' || counts === null) { return false; }
         const {termMeta} = counts;
         if (typeof termMeta !== 'object' || termMeta === null) { return false; }
         return termMeta.freq <= 0;
     }
+
+    /**
+     * @param {string} value
+     * @returns {?import('settings').SortFrequencyDictionaryOrder}
+     */
+    _normalizeSortFrequencyDictionaryOrder(value) {
+        switch (value) {
+            case 'ascending':
+            case 'descending':
+                return value;
+            default:
+                return null;
+        }
+    }
 }
diff --git a/ext/js/pages/settings/status-footer.js b/ext/js/pages/settings/status-footer.js
index 5c6ecbc802..a0a08a3f3f 100644
--- a/ext/js/pages/settings/status-footer.js
+++ b/ext/js/pages/settings/status-footer.js
@@ -21,34 +21,52 @@
  */
 
 class StatusFooter extends PanelElement {
+    /**
+     * @param {HTMLElement} node
+     */
     constructor(node) {
         super({
             node,
             closingAnimationDuration: 375 // Milliseconds; includes buffer
         });
-        this._body = node.querySelector('.status-footer');
+        /** @type {HTMLElement} */
+        this._body = /** @type {HTMLElement} */ (node.querySelector('.status-footer'));
     }
 
+    /** */
     prepare() {
-        this.on('closeCompleted', this._onCloseCompleted.bind(this), false);
-        this._body.querySelector('.status-footer-header-close').addEventListener('click', this._onCloseClick.bind(this), false);
+        const closeButton = /** @type {HTMLElement} */ (this._body.querySelector('.status-footer-header-close'));
+        this.on('closeCompleted', this._onCloseCompleted.bind(this));
+        closeButton.addEventListener('click', this._onCloseClick.bind(this), false);
     }
 
+    /**
+     * @param {string} selector
+     * @returns {?HTMLElement}
+     */
     getTaskContainer(selector) {
         return this._body.querySelector(selector);
     }
 
+    /**
+     * @param {string} selector
+     * @returns {boolean}
+     */
     isTaskActive(selector) {
         const target = this.getTaskContainer(selector);
-        return (target !== null && target.dataset.active);
+        return (target !== null && !!target.dataset.active);
     }
 
+    /**
+     * @param {string} selector
+     * @param {boolean} active
+     */
     setTaskActive(selector, active) {
         const target = this.getTaskContainer(selector);
         if (target === null) { return; }
 
         const activeElements = new Set();
-        for (const element of this._body.querySelectorAll('.status-footer-item')) {
+        for (const element of /** @type {NodeListOf<HTMLElement>} */ (this._body.querySelectorAll('.status-footer-item'))) {
             if (element.dataset.active) {
                 activeElements.add(element);
             }
@@ -70,13 +88,17 @@ class StatusFooter extends PanelElement {
 
     // Private
 
+    /**
+     * @param {MouseEvent} e
+     */
     _onCloseClick(e) {
         e.preventDefault();
         this.setVisible(false);
     }
 
+    /** */
     _onCloseCompleted() {
-        for (const element of this._body.querySelectorAll('.status-footer-item')) {
+        for (const element of /** @type {NodeListOf<HTMLElement>} */ (this._body.querySelectorAll('.status-footer-item'))) {
             if (!element.dataset.active) {
                 element.hidden = true;
             }
diff --git a/ext/js/pages/settings/storage-controller.js b/ext/js/pages/settings/storage-controller.js
index 49ee73611e..93cb4f8f6f 100644
--- a/ext/js/pages/settings/storage-controller.js
+++ b/ext/js/pages/settings/storage-controller.js
@@ -17,28 +17,43 @@
  */
 
 class StorageController {
+    /**
+     * @param {PersistentStorageController} persistentStorageController
+     */
     constructor(persistentStorageController) {
+    /** @type {PersistentStorageController} */
         this._persistentStorageController = persistentStorageController;
+        /** @type {?StorageEstimate} */
         this._mostRecentStorageEstimate = null;
+        /** @type {boolean} */
         this._storageEstimateFailed = false;
+        /** @type {boolean} */
         this._isUpdating = false;
-        this._storageUsageNode = null;
-        this._storageQuotaNode = null;
+        /** @type {?NodeListOf<HTMLElement>} */
+        this._storageUsageNodes = null;
+        /** @type {?NodeListOf<HTMLElement>} */
+        this._storageQuotaNodes = null;
+        /** @type {?NodeListOf<HTMLElement>} */
         this._storageUseFiniteNodes = null;
+        /** @type {?NodeListOf<HTMLElement>} */
         this._storageUseInfiniteNodes = null;
+        /** @type {?NodeListOf<HTMLElement>} */
         this._storageUseValidNodes = null;
+        /** @type {?NodeListOf<HTMLElement>} */
         this._storageUseInvalidNodes = null;
     }
 
+    /** */
     prepare() {
-        this._storageUsageNodes = document.querySelectorAll('.storage-usage');
-        this._storageQuotaNodes = document.querySelectorAll('.storage-quota');
-        this._storageUseFiniteNodes = document.querySelectorAll('.storage-use-finite');
-        this._storageUseInfiniteNodes = document.querySelectorAll('.storage-use-infinite');
-        this._storageUseValidNodes = document.querySelectorAll('.storage-use-valid');
-        this._storageUseInvalidNodes = document.querySelectorAll('.storage-use-invalid');
-
-        document.querySelector('#storage-refresh').addEventListener('click', this._onStorageRefreshButtonClick.bind(this), false);
+        this._storageUsageNodes = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.storage-usage'));
+        this._storageQuotaNodes = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.storage-quota'));
+        this._storageUseFiniteNodes = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.storage-use-finite'));
+        this._storageUseInfiniteNodes = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.storage-use-infinite'));
+        this._storageUseValidNodes = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.storage-use-valid'));
+        this._storageUseInvalidNodes = /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.storage-use-invalid'));
+        const storageRefreshButton = /** @type {HTMLButtonElement} */ (document.querySelector('#storage-refresh'));
+
+        storageRefreshButton.addEventListener('click', this._onStorageRefreshButtonClick.bind(this), false);
         yomichan.on('storageChanged', this._onStorageChanged.bind(this));
 
         this._updateStats();
@@ -46,14 +61,17 @@ class StorageController {
 
     // Private
 
+    /** */
     _onStorageRefreshButtonClick() {
         this._updateStats();
     }
 
+    /** */
     _onStorageChanged() {
         this._updateStats();
     }
 
+    /** */
     async _updateStats() {
         if (this._isUpdating) { return; }
 
@@ -64,13 +82,18 @@ class StorageController {
             const valid = (estimate !== null);
 
             // Firefox reports usage as 0 when persistent storage is enabled.
-            const finite = valid && (estimate.usage > 0 || !(await this._persistentStorageController.isStoragePeristent()));
+            const finite = valid && ((typeof estimate.usage === 'number' && estimate.usage > 0) || !(await this._persistentStorageController.isStoragePeristent()));
             if (finite) {
-                for (const node of this._storageUsageNodes) {
-                    node.textContent = this._bytesToLabeledString(estimate.usage);
+                let {usage, quota} = estimate;
+                if (typeof usage !== 'number') { usage = 0; }
+                if (typeof quota !== 'number') { quota = 0; }
+                const usageString = this._bytesToLabeledString(usage);
+                const quotaString = this._bytesToLabeledString(quota);
+                for (const node of /** @type {NodeListOf<HTMLElement>} */ (this._storageUsageNodes)) {
+                    node.textContent = usageString;
                 }
-                for (const node of this._storageQuotaNodes) {
-                    node.textContent = this._bytesToLabeledString(estimate.quota);
+                for (const node of /** @type {NodeListOf<HTMLElement>} */ (this._storageQuotaNodes)) {
+                    node.textContent = quotaString;
                 }
             }
 
@@ -78,8 +101,6 @@ class StorageController {
             this._setElementsVisible(this._storageUseInfiniteNodes, valid && !finite);
             this._setElementsVisible(this._storageUseValidNodes, valid);
             this._setElementsVisible(this._storageUseInvalidNodes, !valid);
-
-            return valid;
         } finally {
             this._isUpdating = false;
         }
@@ -87,6 +108,9 @@ class StorageController {
 
     // Private
 
+    /**
+     * @returns {Promise<?StorageEstimate>}
+     */
     async _storageEstimate() {
         if (this._storageEstimateFailed && this._mostRecentStorageEstimate === null) {
             return null;
@@ -101,6 +125,10 @@ class StorageController {
         return null;
     }
 
+    /**
+     * @param {number} size
+     * @returns {string}
+     */
     _bytesToLabeledString(size) {
         const base = 1000;
         const labels = [' bytes', 'KB', 'MB', 'GB', 'TB'];
@@ -114,7 +142,12 @@ class StorageController {
         return `${label}${labels[labelIndex]}`;
     }
 
+    /**
+     * @param {?NodeListOf<HTMLElement>} elements
+     * @param {boolean} visible
+     */
     _setElementsVisible(elements, visible) {
+        if (elements === null) { return; }
         visible = !visible;
         for (const element of elements) {
             element.hidden = visible;
diff --git a/ext/js/pages/settings/translation-text-replacements-controller.js b/ext/js/pages/settings/translation-text-replacements-controller.js
index 1a98c40604..1b67cc9827 100644
--- a/ext/js/pages/settings/translation-text-replacements-controller.js
+++ b/ext/js/pages/settings/translation-text-replacements-controller.js
@@ -17,15 +17,22 @@
  */
 
 class TranslationTextReplacementsController {
+    /**
+     * @param {SettingsController} settingsController
+     */
     constructor(settingsController) {
+        /** @type {SettingsController} */
         this._settingsController = settingsController;
+        /** @type {?HTMLElement} */
         this._entryContainer = null;
+        /** @type {TranslationTextReplacementsEntry[]} */
         this._entries = [];
     }
 
+    /** */
     async prepare() {
-        this._entryContainer = document.querySelector('#translation-text-replacement-list');
-        const addButton = document.querySelector('#translation-text-replacement-add');
+        this._entryContainer = /** @type {HTMLElement} */ (document.querySelector('#translation-text-replacement-list'));
+        const addButton = /** @type {HTMLButtonElement} */ (document.querySelector('#translation-text-replacement-add'));
 
         addButton.addEventListener('click', this._onAdd.bind(this), false);
         this._settingsController.on('optionsChanged', this._onOptionsChanged.bind(this));
@@ -33,11 +40,12 @@ class TranslationTextReplacementsController {
         await this._updateOptions();
     }
 
-
+    /** */
     async addGroup() {
         const options = await this._settingsController.getOptions();
         const {groups} = options.translation.textReplacements;
         const newEntry = this._createNewEntry();
+        /** @type {import('settings-modifications').Modification} */
         const target = (
             (groups.length === 0) ?
             {
@@ -60,6 +68,10 @@ class TranslationTextReplacementsController {
         await this._updateOptions();
     }
 
+    /**
+     * @param {number} index
+     * @returns {Promise<boolean>}
+     */
     async deleteGroup(index) {
         const options = await this._settingsController.getOptions();
         const {groups} = options.translation.textReplacements;
@@ -68,6 +80,7 @@ class TranslationTextReplacementsController {
         const group0 = groups[0];
         if (index < 0 || index >= group0.length) { return false; }
 
+        /** @type {import('settings-modifications').Modification} */
         const target = (
             (group0.length > 1) ?
             {
@@ -93,6 +106,9 @@ class TranslationTextReplacementsController {
 
     // Private
 
+    /**
+     * @param {import('settings-controller').OptionsChangedEvent} details
+     */
     _onOptionsChanged({options}) {
         for (const entry of this._entries) {
             entry.cleanup();
@@ -103,50 +119,70 @@ class TranslationTextReplacementsController {
         if (groups.length > 0) {
             const group0 = groups[0];
             for (let i = 0, ii = group0.length; i < ii; ++i) {
-                const data = group0[i];
-                const node = this._settingsController.instantiateTemplate('translation-text-replacement-entry');
-                this._entryContainer.appendChild(node);
-                const entry = new TranslationTextReplacementsEntry(this, node, i, data);
+                const node = /** @type {HTMLElement} */ (this._settingsController.instantiateTemplate('translation-text-replacement-entry'));
+                /** @type {HTMLElement} */ (this._entryContainer).appendChild(node);
+                const entry = new TranslationTextReplacementsEntry(this, node, i);
                 this._entries.push(entry);
                 entry.prepare();
             }
         }
     }
 
+    /** */
     _onAdd() {
         this.addGroup();
     }
 
+    /** */
     async _updateOptions() {
         const options = await this._settingsController.getOptions();
-        this._onOptionsChanged({options});
+        const optionsContext = this._settingsController.getOptionsContext();
+        this._onOptionsChanged({options, optionsContext});
     }
 
+    /**
+     * @returns {import('settings').TranslationTextReplacementGroup}
+     */
     _createNewEntry() {
         return {pattern: '', ignoreCase: false, replacement: ''};
     }
 }
 
 class TranslationTextReplacementsEntry {
+    /**
+     * @param {TranslationTextReplacementsController} parent
+     * @param {HTMLElement} node
+     * @param {number} index
+     */
     constructor(parent, node, index) {
+        /** @type {TranslationTextReplacementsController} */
         this._parent = parent;
+        /** @type {HTMLElement} */
         this._node = node;
+        /** @type {number} */
         this._index = index;
+        /** @type {EventListenerCollection} */
         this._eventListeners = new EventListenerCollection();
+        /** @type {?HTMLInputElement} */
         this._patternInput = null;
+        /** @type {?HTMLInputElement} */
         this._replacementInput = null;
+        /** @type {?HTMLInputElement} */
         this._ignoreCaseToggle = null;
+        /** @type {?HTMLInputElement} */
         this._testInput = null;
+        /** @type {?HTMLInputElement} */
         this._testOutput = null;
     }
 
+    /** */
     prepare() {
-        const patternInput = this._node.querySelector('.translation-text-replacement-pattern');
-        const replacementInput = this._node.querySelector('.translation-text-replacement-replacement');
-        const ignoreCaseToggle = this._node.querySelector('.translation-text-replacement-pattern-ignore-case');
-        const menuButton = this._node.querySelector('.translation-text-replacement-button');
-        const testInput = this._node.querySelector('.translation-text-replacement-test-input');
-        const testOutput = this._node.querySelector('.translation-text-replacement-test-output');
+        const patternInput = /** @type {HTMLInputElement} */ (this._node.querySelector('.translation-text-replacement-pattern'));
+        const replacementInput = /** @type {HTMLInputElement} */ (this._node.querySelector('.translation-text-replacement-replacement'));
+        const ignoreCaseToggle = /** @type {HTMLInputElement} */ (this._node.querySelector('.translation-text-replacement-pattern-ignore-case'));
+        const menuButton = /** @type {HTMLInputElement} */ (this._node.querySelector('.translation-text-replacement-button'));
+        const testInput = /** @type {HTMLInputElement} */ (this._node.querySelector('.translation-text-replacement-test-input'));
+        const testOutput = /** @type {HTMLInputElement} */ (this._node.querySelector('.translation-text-replacement-test-output'));
 
         this._patternInput = patternInput;
         this._replacementInput = replacementInput;
@@ -167,6 +203,7 @@ class TranslationTextReplacementsEntry {
         this._eventListeners.addEventListener(testInput, 'input', this._updateTestInput.bind(this), false);
     }
 
+    /** */
     cleanup() {
         this._eventListeners.removeAllEventListeners();
         if (this._node.parentNode !== null) {
@@ -176,13 +213,19 @@ class TranslationTextReplacementsEntry {
 
     // Private
 
+    /**
+     * @param {import('popup-menu').MenuOpenEvent} e
+     */
     _onMenuOpen(e) {
         const bodyNode = e.detail.menu.bodyNode;
         const testVisible = this._isTestVisible();
-        bodyNode.querySelector('[data-menu-action=showTest]').hidden = testVisible;
-        bodyNode.querySelector('[data-menu-action=hideTest]').hidden = !testVisible;
+        /** @type {HTMLElement} */ (bodyNode.querySelector('[data-menu-action=showTest]')).hidden = testVisible;
+        /** @type {HTMLElement} */ (bodyNode.querySelector('[data-menu-action=hideTest]')).hidden = !testVisible;
     }
 
+    /**
+     * @param {import('popup-menu').MenuCloseEvent} e
+     */
     _onMenuClose(e) {
         switch (e.detail.action) {
             case 'remove':
@@ -197,34 +240,58 @@ class TranslationTextReplacementsEntry {
         }
     }
 
+    /**
+     * @param {import('dom-data-binder').SettingChangedEvent} deatils
+     */
     _onPatternChanged({detail: {value}}) {
         this._validatePattern(value);
         this._updateTestInput();
     }
 
+    /**
+     * @param {unknown} value
+     */
     _validatePattern(value) {
         let okay = false;
         try {
-            new RegExp(value, 'g');
-            okay = true;
+            if (typeof value === 'string') {
+                new RegExp(value, 'g');
+                okay = true;
+            }
         } catch (e) {
             // NOP
         }
 
-        this._patternInput.dataset.invalid = `${!okay}`;
+        if (this._patternInput !== null) {
+            this._patternInput.dataset.invalid = `${!okay}`;
+        }
     }
 
+    /**
+     * @returns {boolean}
+     */
     _isTestVisible() {
         return this._node.dataset.testVisible === 'true';
     }
 
+    /**
+     * @param {boolean} visible
+     */
     _setTestVisible(visible) {
         this._node.dataset.testVisible = `${visible}`;
         this._updateTestInput();
     }
 
+    /** */
     _updateTestInput() {
-        if (!this._isTestVisible()) { return; }
+        if (
+            !this._isTestVisible() ||
+            this._ignoreCaseToggle === null ||
+            this._patternInput === null ||
+            this._replacementInput === null ||
+            this._testInput === null ||
+            this._testOutput === null
+        ) { return; }
 
         const ignoreCase = this._ignoreCaseToggle.checked;
         const pattern = this._patternInput.value;
diff --git a/ext/js/pages/welcome-main.js b/ext/js/pages/welcome-main.js
index eb8bd67589..eaf933bec0 100644
--- a/ext/js/pages/welcome-main.js
+++ b/ext/js/pages/welcome-main.js
@@ -29,6 +29,7 @@
  * StatusFooter
  */
 
+/** */
 async function setupEnvironmentInfo() {
     const {manifest_version: manifestVersion} = chrome.runtime.getManifest();
     const {browser, platform} = await yomichan.api.getEnvironmentInfo();
@@ -37,6 +38,9 @@ async function setupEnvironmentInfo() {
     document.documentElement.dataset.manifestVersion = `${manifestVersion}`;
 }
 
+/**
+ * @param {GenericSettingController} genericSettingController
+ */
 async function setupGenericSettingsController(genericSettingController) {
     await genericSettingController.prepare();
     await genericSettingController.refresh();
@@ -50,7 +54,7 @@ async function setupGenericSettingsController(genericSettingController) {
         const extensionContentController = new ExtensionContentController();
         extensionContentController.prepare();
 
-        const statusFooter = new StatusFooter(document.querySelector('.status-footer-container'));
+        const statusFooter = new StatusFooter(/** @type {HTMLElement} */ (document.querySelector('.status-footer-container')));
         statusFooter.prepare();
 
         await yomichan.prepare();
diff --git a/ext/js/script/dynamic-loader-sentinel.js b/ext/js/script/dynamic-loader-sentinel.js
index 9e049d7ab2..5f5ea3a0d8 100644
--- a/ext/js/script/dynamic-loader-sentinel.js
+++ b/ext/js/script/dynamic-loader-sentinel.js
@@ -16,4 +16,4 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-yomichan.trigger('dynamicLoaderSentinel', {script: document.currentScript});
+yomichan.trigger('dynamicLoaderSentinel', /** @type {import('dynamic-loader').DynamicLoaderSentinelDetails} */ ({script: document.currentScript}));
diff --git a/ext/js/script/dynamic-loader.js b/ext/js/script/dynamic-loader.js
index 7f3e77a4e2..a9fa39ab7f 100644
--- a/ext/js/script/dynamic-loader.js
+++ b/ext/js/script/dynamic-loader.js
@@ -17,9 +17,16 @@
  */
 
 const dynamicLoader = (() => {
+    /** @type {Map<string, ?HTMLStyleElement|HTMLLinkElement>} */
     const injectedStylesheets = new Map();
+    /** @type {WeakMap<Node, Map<string, ?HTMLStyleElement|HTMLLinkElement>>} */
     const injectedStylesheetsWithParent = new WeakMap();
 
+    /**
+     * @param {string} id
+     * @param {?Node} parentNode
+     * @returns {?HTMLStyleElement|HTMLLinkElement|undefined}
+     */
     function getInjectedStylesheet(id, parentNode) {
         if (parentNode === null) {
             return injectedStylesheets.get(id);
@@ -28,6 +35,11 @@ const dynamicLoader = (() => {
         return typeof map !== 'undefined' ? map.get(id) : void 0;
     }
 
+    /**
+     * @param {string} id
+     * @param {?Node} parentNode
+     * @param {?HTMLStyleElement|HTMLLinkElement} value
+     */
     function setInjectedStylesheet(id, parentNode, value) {
         if (parentNode === null) {
             injectedStylesheets.set(id, value);
@@ -41,6 +53,15 @@ const dynamicLoader = (() => {
         map.set(id, value);
     }
 
+    /**
+     * @param {string} id
+     * @param {'code'|'file'|'file-content'} type
+     * @param {string} value
+     * @param {boolean} [useWebExtensionApi]
+     * @param {?Node} [parentNode]
+     * @returns {Promise<?HTMLStyleElement|HTMLLinkElement>}
+     * @throws {Error}
+     */
     async function loadStyle(id, type, value, useWebExtensionApi=false, parentNode=null) {
         if (useWebExtensionApi && yomichan.isExtensionUrl(window.location.href)) {
             // Permissions error will occur if trying to use the WebExtension API to inject into an extension page
@@ -95,8 +116,8 @@ const dynamicLoader = (() => {
 
         // Update node style
         if (isFile) {
-            styleNode.rel = 'stylesheet';
-            styleNode.href = value;
+            /** @type {HTMLLinkElement} */ (styleNode).rel = 'stylesheet';
+            /** @type {HTMLLinkElement} */ (styleNode).href = value;
         } else {
             styleNode.textContent = value;
         }
@@ -111,6 +132,10 @@ const dynamicLoader = (() => {
         return styleNode;
     }
 
+    /**
+     * @param {string[]} urls
+     * @returns {Promise<void>}
+     */
     function loadScripts(urls) {
         return new Promise((resolve, reject) => {
             const parent = document.body;
@@ -133,10 +158,18 @@ const dynamicLoader = (() => {
         });
     }
 
+    /**
+     * @param {HTMLElement} parent
+     * @param {() => void} resolve
+     * @param {(reason?: unknown) => void} reject
+     */
     function loadScriptSentinel(parent, resolve, reject) {
         const script = document.createElement('script');
 
         const sentinelEventName = 'dynamicLoaderSentinel';
+        /**
+         * @param {import('dynamic-loader').DynamicLoaderSentinelDetails} e
+         */
         const sentinelEventCallback = (e) => {
             if (e.script !== script) { return; }
             yomichan.off(sentinelEventName, sentinelEventCallback);
@@ -155,6 +188,10 @@ const dynamicLoader = (() => {
         }
     }
 
+    /**
+     * @param {string} value
+     * @returns {string}
+     */
     function escapeCSSAttribute(value) {
         return value.replace(/['\\]/g, (character) => `\\${character}`);
     }
diff --git a/ext/js/templates/sandbox/anki-template-renderer-content-manager.js b/ext/js/templates/sandbox/anki-template-renderer-content-manager.js
index c51f01b31f..623ae8d1dc 100644
--- a/ext/js/templates/sandbox/anki-template-renderer-content-manager.js
+++ b/ext/js/templates/sandbox/anki-template-renderer-content-manager.js
@@ -16,18 +16,6 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-/**
- * A callback used when a media file has been loaded.
- * @callback AnkiTemplateRendererContentManager.OnLoadCallback
- * @param {string} url The URL of the media that was loaded.
- */
-
-/**
- * A callback used when a media file should be unloaded.
- * @callback AnkiTemplateRendererContentManager.OnUnloadCallback
- * @param {boolean} fullyLoaded Whether or not the media was fully loaded.
- */
-
 /**
  * The content manager which is used when generating content for Anki.
  */
@@ -35,12 +23,15 @@ class AnkiTemplateRendererContentManager {
     /**
      * Creates a new instance of the class.
      * @param {TemplateRendererMediaProvider} mediaProvider The media provider for the object.
-     * @param {object} data The data object passed to the Handlebars template renderer.
+     * @param {import('anki-templates').NoteData} data The data object passed to the Handlebars template renderer.
      *   See {@link AnkiNoteDataCreator.create}'s return value for structure information.
      */
     constructor(mediaProvider, data) {
+        /** @type {TemplateRendererMediaProvider} */
         this._mediaProvider = mediaProvider;
+        /** @type {import('anki-templates').NoteData} */
         this._data = data;
+        /** @type {import('anki-template-renderer-content-manager').OnUnloadCallback[]} */
         this._onUnloadCallbacks = [];
     }
 
@@ -48,9 +39,9 @@ class AnkiTemplateRendererContentManager {
      * Attempts to load the media file from a given dictionary.
      * @param {string} path The path to the media file in the dictionary.
      * @param {string} dictionary The name of the dictionary.
-     * @param {AnkiTemplateRendererContentManager.OnLoadCallback} onLoad The callback that is executed if the media was loaded successfully.
+     * @param {import('anki-template-renderer-content-manager').OnLoadCallback} onLoad The callback that is executed if the media was loaded successfully.
      *   No assumptions should be made about the synchronicity of this callback.
-     * @param {AnkiTemplateRendererContentManager.OnUnloadCallback} onUnload The callback that is executed when the media should be unloaded.
+     * @param {import('anki-template-renderer-content-manager').OnUnloadCallback} onUnload The callback that is executed when the media should be unloaded.
      */
     loadMedia(path, dictionary, onLoad, onUnload) {
         const imageUrl = this._mediaProvider.getMedia(this._data, ['dictionaryMedia', path], {dictionary, format: 'fileName', default: null});
@@ -73,7 +64,7 @@ class AnkiTemplateRendererContentManager {
 
     /**
      * Sets up attributes and events for a link element.
-     * @param {Element} element The link element.
+     * @param {HTMLAnchorElement} element The link element.
      * @param {string} href The URL.
      * @param {boolean} internal Whether or not the URL is an internal or external link.
      */
diff --git a/ext/js/templates/sandbox/anki-template-renderer.js b/ext/js/templates/sandbox/anki-template-renderer.js
index 789f094246..9d712be2cb 100644
--- a/ext/js/templates/sandbox/anki-template-renderer.js
+++ b/ext/js/templates/sandbox/anki-template-renderer.js
@@ -38,17 +38,29 @@ class AnkiTemplateRenderer {
      * Creates a new instance of the class.
      */
     constructor() {
+        /** @type {CssStyleApplier} */
         this._structuredContentStyleApplier = new CssStyleApplier('/data/structured-content-style.json');
+        /** @type {CssStyleApplier} */
         this._pronunciationStyleApplier = new CssStyleApplier('/data/pronunciation-style.json');
+        /** @type {RegExp} */
         this._structuredContentDatasetKeyIgnorePattern = /^sc([^a-z]|$)/;
+        /** @type {JapaneseUtil} */
         this._japaneseUtil = new JapaneseUtil(null);
+        /** @type {TemplateRenderer} */
         this._templateRenderer = new TemplateRenderer();
+        /** @type {AnkiNoteDataCreator} */
         this._ankiNoteDataCreator = new AnkiNoteDataCreator(this._japaneseUtil);
+        /** @type {TemplateRendererMediaProvider} */
         this._mediaProvider = new TemplateRendererMediaProvider();
+        /** @type {PronunciationGenerator} */
         this._pronunciationGenerator = new PronunciationGenerator(this._japaneseUtil);
+        /** @type {?(Map<string, unknown>[])} */
         this._stateStack = null;
+        /** @type {?import('anki-note-builder').Requirement[]} */
         this._requirements = null;
-        this._cleanupCallbacks = null;
+        /** @type {(() => void)[]} */
+        this._cleanupCallbacks = [];
+        /** @type {?HTMLElement} */
         this._temporaryElement = null;
     }
 
@@ -97,7 +109,7 @@ class AnkiTemplateRenderer {
         ]);
         this._templateRenderer.registerDataType('ankiNote', {
             modifier: ({marker, commonData}) => this._ankiNoteDataCreator.create(marker, commonData),
-            composeData: (marker, commonData) => ({marker, commonData})
+            composeData: ({marker}, commonData) => ({marker, commonData})
         });
         this._templateRenderer.setRenderCallbacks(
             this._onRenderSetup.bind(this),
@@ -111,36 +123,48 @@ class AnkiTemplateRenderer {
 
     // Private
 
+    /**
+     * @returns {{requirements: import('anki-note-builder').Requirement[]}}
+     */
     _onRenderSetup() {
+        /** @type {import('anki-note-builder').Requirement[]} */
         const requirements = [];
         this._stateStack = [new Map()];
         this._requirements = requirements;
         this._mediaProvider.requirements = requirements;
-        this._cleanupCallbacks = [];
         return {requirements};
     }
 
+    /**
+     * @returns {void}
+     */
     _onRenderCleanup() {
         for (const callback of this._cleanupCallbacks) { callback(); }
         this._stateStack = null;
         this._requirements = null;
         this._mediaProvider.requirements = null;
-        this._cleanupCallbacks = null;
+        this._cleanupCallbacks.length = 0;
     }
 
+    /**
+     * @param {string} text
+     * @returns {string}
+     */
     _escape(text) {
         return Handlebars.Utils.escapeExpression(text);
     }
 
     // Template helpers
 
-    _dumpObject(context, options) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _dumpObject(_args, context, options) {
         const dump = JSON.stringify(options.fn(context), null, 4);
         return this._escape(dump);
     }
 
-    _furigana(context, ...args) {
-        const {expression, reading} = this._getFuriganaExpressionAndReading(context, ...args);
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _furigana(args, context, options) {
+        const {expression, reading} = this._getFuriganaExpressionAndReading(args, context, options);
         const segs = this._japaneseUtil.distributeFurigana(expression, reading);
 
         let result = '';
@@ -155,8 +179,9 @@ class AnkiTemplateRenderer {
         return result;
     }
 
-    _furiganaPlain(context, ...args) {
-        const {expression, reading} = this._getFuriganaExpressionAndReading(context, ...args);
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _furiganaPlain(args, context, options) {
+        const {expression, reading} = this._getFuriganaExpressionAndReading(args, context, options);
         const segs = this._japaneseUtil.distributeFurigana(expression, reading);
 
         let result = '';
@@ -172,21 +197,29 @@ class AnkiTemplateRenderer {
         return result;
     }
 
-    _getFuriganaExpressionAndReading(context, ...args) {
-        const options = args[args.length - 1];
-        if (args.length >= 3) {
-            return {expression: args[0], reading: args[1]};
+    /**
+     * @type {import('template-renderer').HelperFunction<{expression: string, reading: string}>}
+     */
+    _getFuriganaExpressionAndReading(args, context, options) {
+        let expression;
+        let reading;
+        if (args.length >= 2) {
+            [expression, reading] = /** @type {[expression?: string, reading?: string]} */ (args);
         } else {
-            const {expression, reading} = options.fn(context);
-            return {expression, reading};
+            ({expression, reading} = /** @type {import('core').SerializableObject} */ (options.fn(context)));
         }
+        return {
+            expression: typeof expression === 'string' ? expression : '',
+            reading: typeof reading === 'string' ? reading : ''
+        };
     }
 
-    _kanjiLinks(context, options) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _kanjiLinks(_args, context, options) {
         const jp = this._japaneseUtil;
         let result = '';
-        for (const c of options.fn(context)) {
-            if (jp.isCodePointKanji(c.codePointAt(0))) {
+        for (const c of this._asString(options.fn(context))) {
+            if (jp.isCodePointKanji(/** @type {number} */ (c.codePointAt(0)))) {
                 result += `<a href="#" class="kanji-link">${c}</a>`;
             } else {
                 result += c;
@@ -196,36 +229,44 @@ class AnkiTemplateRenderer {
         return result;
     }
 
+    /**
+     * @param {string} string
+     * @returns {string}
+     */
     _stringToMultiLineHtml(string) {
         return string.split('\n').join('<br>');
     }
 
-    _multiLine(context, options) {
-        return this._stringToMultiLineHtml(options.fn(context));
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _multiLine(_args, context, options) {
+        return this._stringToMultiLineHtml(this._asString(options.fn(context)));
     }
 
-    _sanitizeCssClass(context, options) {
-        return options.fn(context).replace(/[^_a-z0-9\u00a0-\uffff]/ig, '_');
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _sanitizeCssClass(_args, context, options) {
+        return this._asString(options.fn(context)).replace(/[^_a-z0-9\u00a0-\uffff]/ig, '_');
     }
 
-    _regexReplace(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _regexReplace(args, context, options) {
         // Usage:
         // {{#regexReplace regex string [flags] [content]...}}content{{/regexReplace}}
         // regex: regular expression string
         // string: string to replace
         // flags: optional flags for regular expression
         //   e.g. "i" for case-insensitive, "g" for replace all
-        const argCount = args.length - 1;
-        const options = args[argCount];
-        let value = typeof options.fn === 'function' ? options.fn(context) : '';
+        const argCount = args.length;
+        let value = this._asString(options.fn(context));
         if (argCount > 3) {
             value = `${args.slice(3).join('')}${value}`;
         }
         if (argCount > 1) {
             try {
-                const flags = argCount > 2 ? args[2] : 'g';
-                const regex = new RegExp(args[0], flags);
-                value = value.replace(regex, args[1]);
+                const [pattern, replacement, flags] = args;
+                if (typeof pattern !== 'string') { throw new Error('Invalid pattern'); }
+                if (typeof replacement !== 'string') { throw new Error('Invalid replacement'); }
+                const regex = new RegExp(pattern, typeof flags === 'string' ? flags : 'g');
+                value = value.replace(regex, replacement);
             } catch (e) {
                 return `${e}`;
             }
@@ -233,24 +274,26 @@ class AnkiTemplateRenderer {
         return value;
     }
 
-    _regexMatch(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _regexMatch(args, context, options) {
         // Usage:
         // {{#regexMatch regex [flags] [content]...}}content{{/regexMatch}}
         // regex: regular expression string
         // flags: optional flags for regular expression
         //   e.g. "i" for case-insensitive, "g" for match all
-        const argCount = args.length - 1;
-        const options = args[argCount];
-        let value = typeof options.fn === 'function' ? options.fn(context) : '';
+        const argCount = args.length;
+        let value = this._asString(options.fn(context));
         if (argCount > 2) {
             value = `${args.slice(2).join('')}${value}`;
         }
         if (argCount > 0) {
             try {
-                const flags = argCount > 1 ? args[1] : '';
-                const regex = new RegExp(args[0], flags);
+                const [pattern, flags] = args;
+                if (typeof pattern !== 'string') { throw new Error('Invalid pattern'); }
+                const regex = new RegExp(pattern, typeof flags === 'string' ? flags : '');
+                /** @type {string[]} */
                 const parts = [];
-                value.replace(regex, (g0) => parts.push(g0));
+                value.replace(regex, (g0) => { parts.push(g0); return g0; });
                 value = parts.join('');
             } catch (e) {
                 return `${e}`;
@@ -259,11 +302,18 @@ class AnkiTemplateRenderer {
         return value;
     }
 
-    _mergeTags(context, object, isGroupMode, isMergeMode) {
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _mergeTags(args) {
+        const [object, isGroupMode, isMergeMode] = /** @type {[object: import('anki-templates').TermDictionaryEntry, isGroupMode: boolean, isMergeMode: boolean]} */ (args);
         const tagSources = [];
         if (isGroupMode || isMergeMode) {
-            for (const definition of object.definitions) {
-                tagSources.push(definition.definitionTags);
+            const {definitions} = object;
+            if (Array.isArray(definitions)) {
+                for (const definition of definitions) {
+                    tagSources.push(definition.definitionTags);
+                }
             }
         } else {
             tagSources.push(object.definitionTags);
@@ -280,7 +330,9 @@ class AnkiTemplateRenderer {
         return [...tags].join(', ');
     }
 
-    _eachUpTo(context, iterable, maxCount, options) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _eachUpTo(args, context, options) {
+        const [iterable, maxCount] = /** @type {[iterable: Iterable<unknown>, maxCount: number]} */ (args);
         if (iterable) {
             const results = [];
             let any = false;
@@ -294,14 +346,15 @@ class AnkiTemplateRenderer {
                 return results.join('');
             }
         }
-        return options.inverse(context);
+        return this._asString(options.inverse(context));
     }
 
-    _spread(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<unknown[]>} */
+    _spread(args) {
         const result = [];
-        for (let i = 0, ii = args.length - 1; i < ii; ++i) {
+        for (const array of /** @type {Iterable<unknown>[]} */ (args)) {
             try {
-                result.push(...args[i]);
+                result.push(...array);
             } catch (e) {
                 // NOP
             }
@@ -309,15 +362,22 @@ class AnkiTemplateRenderer {
         return result;
     }
 
-    _op(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _op(args) {
+        const [operator] = /** @type {[operator: string, operand1: import('core').SafeAny, operand2?: import('core').SafeAny, operand3?: import('core').SafeAny]} */ (args);
         switch (args.length) {
-            case 3: return this._evaluateUnaryExpression(args[0], args[1]);
-            case 4: return this._evaluateBinaryExpression(args[0], args[1], args[2]);
-            case 5: return this._evaluateTernaryExpression(args[0], args[1], args[2], args[3]);
+            case 2: return this._evaluateUnaryExpression(operator, args[1]);
+            case 3: return this._evaluateBinaryExpression(operator, args[1], args[2]);
+            case 4: return this._evaluateTernaryExpression(operator, args[1], args[2], args[3]);
             default: return void 0;
         }
     }
 
+    /**
+     * @param {string} operator
+     * @param {import('core').SafeAny} operand1
+     * @returns {unknown}
+     */
     _evaluateUnaryExpression(operator, operand1) {
         switch (operator) {
             case '+': return +operand1;
@@ -328,6 +388,12 @@ class AnkiTemplateRenderer {
         }
     }
 
+    /**
+     * @param {string} operator
+     * @param {import('core').SafeAny} operand1
+     * @param {import('core').SafeAny} operand2
+     * @returns {unknown}
+     */
     _evaluateBinaryExpression(operator, operand1, operand2) {
         switch (operator) {
             case '+': return operand1 + operand2;
@@ -356,6 +422,13 @@ class AnkiTemplateRenderer {
         }
     }
 
+    /**
+     * @param {string} operator
+     * @param {import('core').SafeAny} operand1
+     * @param {import('core').SafeAny} operand2
+     * @param {import('core').SafeAny} operand3
+     * @returns {unknown}
+     */
     _evaluateTernaryExpression(operator, operand1, operand2, operand3) {
         switch (operator) {
             case '?:': return operand1 ? operand2 : operand3;
@@ -363,8 +436,11 @@ class AnkiTemplateRenderer {
         }
     }
 
-    _get(context, key) {
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _get(args) {
+        const [key] = /** @type {[key: string]} */ (args);
         const stateStack = this._stateStack;
+        if (stateStack === null) { throw new Error('Invalid state'); }
         for (let i = stateStack.length; --i >= 0;) {
             const map = stateStack[i];
             if (map.has(key)) {
@@ -374,19 +450,21 @@ class AnkiTemplateRenderer {
         return void 0;
     }
 
-    _set(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _set(args, context, options) {
         const stateStack = this._stateStack;
+        if (stateStack === null) { throw new Error('Invalid state'); }
         switch (args.length) {
-            case 2:
+            case 1:
                 {
-                    const [key, options] = args;
+                    const [key] = /** @type {[key: string]} */ (args);
                     const value = options.fn(context);
                     stateStack[stateStack.length - 1].set(key, value);
                 }
                 break;
-            case 3:
+            case 2:
                 {
-                    const [key, value] = args;
+                    const [key, value] = /** @type {[key: string, value: unknown]} */ (args);
                     stateStack[stateStack.length - 1].set(key, value);
                 }
                 break;
@@ -394,8 +472,10 @@ class AnkiTemplateRenderer {
         return '';
     }
 
-    _scope(context, options) {
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _scope(_args, context, options) {
         const stateStack = this._stateStack;
+        if (stateStack === null) { throw new Error('Invalid state'); }
         try {
             stateStack.push(new Map());
             return options.fn(context);
@@ -406,14 +486,25 @@ class AnkiTemplateRenderer {
         }
     }
 
-    _property(context, ...args) {
-        const ii = args.length - 1;
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _property(args) {
+        const ii = args.length;
         if (ii <= 0) { return void 0; }
 
         try {
             let value = args[0];
             for (let i = 1; i < ii; ++i) {
-                value = value[args[i]];
+                if (typeof value !== 'object' || value === null) { throw new Error('Invalid object'); }
+                const key = args[i];
+                switch (typeof key) {
+                    case 'number':
+                    case 'string':
+                    case 'symbol':
+                        break;
+                    default:
+                        throw new Error('Invalid key');
+                }
+                value = /** @type {import('core').UnknownObject} */ (value)[key];
             }
             return value;
         } catch (e) {
@@ -421,38 +512,51 @@ class AnkiTemplateRenderer {
         }
     }
 
-    _noop(context, options) {
+    /** @type {import('template-renderer').HelperFunction<unknown>} */
+    _noop(_args, context, options) {
         return options.fn(context);
     }
 
-    _isMoraPitchHigh(context, index, position) {
+    /** @type {import('template-renderer').HelperFunction<boolean>} */
+    _isMoraPitchHigh(args) {
+        const [index, position] = /** @type {[index: number, position: number]} */ (args);
         return this._japaneseUtil.isMoraPitchHigh(index, position);
     }
 
-    _getKanaMorae(context, text) {
+    /** @type {import('template-renderer').HelperFunction<string[]>} */
+    _getKanaMorae(args) {
+        const [text] = /** @type {[text: string]} */ (args);
         return this._japaneseUtil.getKanaMorae(`${text}`);
     }
 
-    _getTypeof(context, ...args) {
-        const ii = args.length - 1;
-        const value = (ii > 0 ? args[0] : args[ii].fn(context));
+    /** @type {import('template-renderer').HelperFunction<import('core').TypeofResult>} */
+    _getTypeof(args, context, options) {
+        const ii = args.length;
+        const value = (ii > 0 ? args[0] : options.fn(context));
         return typeof value;
     }
 
-    _join(context, ...args) {
-        return args.length > 1 ? args.slice(1, args.length - 1).flat().join(args[0]) : '';
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _join(args) {
+        return args.length > 0 ? args.slice(1, args.length).flat().join(/** @type {string} */ (args[0])) : '';
     }
 
-    _concat(context, ...args) {
+    /** @type {import('template-renderer').HelperFunction<string>} */
+    _concat(args) {
         let result = '';
-        for (let i = 0, ii = args.length - 1; i < ii; ++i) {
+        for (let i = 0, ii = args.length; i < ii; ++i) {
             result += args[i];
         }
         return result;
     }
 
-    _pitchCategories(context, data) {
-        const {pronunciations, headwords} = data.dictionaryEntry;
+    /** @type {import('template-renderer').HelperFunction<string[]>} */
+    _pitchCategories(args) {
+        const [data] = /** @type {[data: import('anki-templates').NoteData]} */ (args);
+        const {dictionaryEntry} = data;
+        if (dictionaryEntry.type !== 'term') { return []; }
+        const {pronunciations, headwords} = dictionaryEntry;
+        /** @type {Set<string>} */
         const categories = new Set();
         for (const {headwordIndex, pitches} of pronunciations) {
             const {reading, wordClasses} = headwords[headwordIndex];
@@ -467,6 +571,9 @@ class AnkiTemplateRenderer {
         return [...categories];
     }
 
+    /**
+     * @returns {HTMLElement}
+     */
     _getTemporaryElement() {
         let element = this._temporaryElement;
         if (element === null) {
@@ -476,14 +583,28 @@ class AnkiTemplateRenderer {
         return element;
     }
 
+    /**
+     * @param {Element} node
+     * @returns {string}
+     */
     _getStructuredContentHtml(node) {
         return this._getHtml(node, this._structuredContentStyleApplier, this._structuredContentDatasetKeyIgnorePattern);
     }
 
+    /**
+     * @param {Element} node
+     * @returns {string}
+     */
     _getPronunciationHtml(node) {
         return this._getHtml(node, this._pronunciationStyleApplier, null);
     }
 
+    /**
+     * @param {Element} node
+     * @param {CssStyleApplier} styleApplier
+     * @param {?RegExp} datasetKeyIgnorePattern
+     * @returns {string}
+     */
     _getHtml(node, styleApplier, datasetKeyIgnorePattern) {
         const container = this._getTemporaryElement();
         container.appendChild(node);
@@ -493,20 +614,27 @@ class AnkiTemplateRenderer {
         return result;
     }
 
+    /**
+     * @param {Element} root
+     * @param {CssStyleApplier} styleApplier
+     * @param {?RegExp} datasetKeyIgnorePattern
+     */
     _normalizeHtml(root, styleApplier, datasetKeyIgnorePattern) {
         const {ELEMENT_NODE, TEXT_NODE} = Node;
         const treeWalker = document.createTreeWalker(root, NodeFilter.SHOW_ELEMENT | NodeFilter.SHOW_TEXT);
+        /** @type {HTMLElement[]} */
         const elements = [];
+        /** @type {Text[]} */
         const textNodes = [];
         while (true) {
             const node = treeWalker.nextNode();
             if (node === null) { break; }
             switch (node.nodeType) {
                 case ELEMENT_NODE:
-                    elements.push(node);
+                    elements.push(/** @type {HTMLElement} */ (node));
                     break;
                 case TEXT_NODE:
-                    textNodes.push(node);
+                    textNodes.push(/** @type {Text} */ (node));
                     break;
             }
         }
@@ -523,8 +651,11 @@ class AnkiTemplateRenderer {
         }
     }
 
+    /**
+     * @param {Text} textNode
+     */
     _replaceNewlines(textNode) {
-        const parts = textNode.nodeValue.split('\n');
+        const parts = /** @type {string} */ (textNode.nodeValue).split('\n');
         if (parts.length <= 1) { return; }
         const {parentNode} = textNode;
         if (parentNode === null) { return; }
@@ -536,6 +667,10 @@ class AnkiTemplateRenderer {
         parentNode.replaceChild(fragment, textNode);
     }
 
+    /**
+     * @param {import('anki-templates').NoteData} data
+     * @returns {StructuredContentGenerator}
+     */
     _createStructuredContentGenerator(data) {
         const contentManager = new AnkiTemplateRendererContentManager(this._mediaProvider, data);
         const instance = new StructuredContentGenerator(contentManager, this._japaneseUtil, document);
@@ -543,45 +678,65 @@ class AnkiTemplateRenderer {
         return instance;
     }
 
-    _formatGlossary(context, dictionary, options) {
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _formatGlossary(args, context, options) {
+        const [dictionary] = /** @type {[dictionary: string]} */ (args);
         const data = options.data.root;
-        const content = options.fn(context);
+        const content = /** @type {import('dictionary-data').TermGlossary} */ (options.fn(context));
         if (typeof content === 'string') { return this._stringToMultiLineHtml(this._escape(content)); }
         if (!(typeof content === 'object' && content !== null)) { return ''; }
         switch (content.type) {
             case 'image': return this._formatGlossaryImage(content, dictionary, data);
             case 'structured-content': return this._formatStructuredContent(content, dictionary, data);
+            case 'text': return this._stringToMultiLineHtml(this._escape(content.text));
         }
         return '';
     }
 
+    /**
+     * @param {import('dictionary-data').TermGlossaryImage} content
+     * @param {string} dictionary
+     * @param {import('anki-templates').NoteData} data
+     * @returns {string}
+     */
     _formatGlossaryImage(content, dictionary, data) {
         const structuredContentGenerator = this._createStructuredContentGenerator(data);
         const node = structuredContentGenerator.createDefinitionImage(content, dictionary);
         return this._getStructuredContentHtml(node);
     }
 
+    /**
+     * @param {import('dictionary-data').TermGlossaryStructuredContent} content
+     * @param {string} dictionary
+     * @param {import('anki-templates').NoteData} data
+     * @returns {string}
+     */
     _formatStructuredContent(content, dictionary, data) {
         const structuredContentGenerator = this._createStructuredContentGenerator(data);
         const node = structuredContentGenerator.createStructuredContent(content.content, dictionary);
         return node !== null ? this._getStructuredContentHtml(node) : '';
     }
 
-    _hasMedia(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
-        return this._mediaProvider.hasMedia(options.data.root, args.slice(0, ii), options.hash);
+    /**
+     * @type {import('template-renderer').HelperFunction<boolean>}
+     */
+    _hasMedia(args, _context, options) {
+        return this._mediaProvider.hasMedia(options.data.root, args, options.hash);
     }
 
-    _getMedia(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
-        return this._mediaProvider.getMedia(options.data.root, args.slice(0, ii), options.hash);
+    /**
+     * @type {import('template-renderer').HelperFunction<?string>}
+     */
+    _getMedia(args, _context, options) {
+        return this._mediaProvider.getMedia(options.data.root, args, options.hash);
     }
 
-    _pronunciation(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _pronunciation(_args, _context, options) {
         let {format, reading, downstepPosition, nasalPositions, devoicePositions} = options.hash;
 
         if (typeof reading !== 'string' || reading.length === 0) { return ''; }
@@ -602,18 +757,30 @@ class AnkiTemplateRenderer {
         }
     }
 
-    _hiragana(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _hiragana(args, context, options) {
+        const ii = args.length;
         const {keepProlongedSoundMarks} = options.hash;
         const value = (ii > 0 ? args[0] : options.fn(context));
-        return this._japaneseUtil.convertKatakanaToHiragana(value, keepProlongedSoundMarks === true);
+        return typeof value === 'string' ? this._japaneseUtil.convertKatakanaToHiragana(value, keepProlongedSoundMarks === true) : '';
     }
 
-    _katakana(context, ...args) {
-        const ii = args.length - 1;
-        const options = args[ii];
+    /**
+     * @type {import('template-renderer').HelperFunction<string>}
+     */
+    _katakana(args, context, options) {
+        const ii = args.length;
         const value = (ii > 0 ? args[0] : options.fn(context));
-        return this._japaneseUtil.convertHiraganaToKatakana(value);
+        return typeof value === 'string' ? this._japaneseUtil.convertHiraganaToKatakana(value) : '';
+    }
+
+    /**
+     * @param {unknown} value
+     * @returns {string}
+     */
+    _asString(value) {
+        return typeof value === 'string' ? value : `${value}`;
     }
 }
diff --git a/ext/js/templates/sandbox/template-renderer-frame-api.js b/ext/js/templates/sandbox/template-renderer-frame-api.js
index d8f2714b5c..141ce6f58c 100644
--- a/ext/js/templates/sandbox/template-renderer-frame-api.js
+++ b/ext/js/templates/sandbox/template-renderer-frame-api.js
@@ -17,15 +17,23 @@
  */
 
 class TemplateRendererFrameApi {
+    /**
+     * @param {TemplateRenderer} templateRenderer
+     */
     constructor(templateRenderer) {
+        /** @type {TemplateRenderer} */
         this._templateRenderer = templateRenderer;
-        this._windowMessageHandlers = new Map([
+        /** @type {import('core').MessageHandlerMap} */
+        this._windowMessageHandlers = new Map(/** @type {import('core').MessageHandlerArray} */ ([
             ['render', {async: false, handler: this._onRender.bind(this)}],
             ['renderMulti', {async: false, handler: this._onRenderMulti.bind(this)}],
             ['getModifiedData', {async: false, handler: this._onGetModifiedData.bind(this)}]
-        ]);
+        ]));
     }
 
+    /**
+     * @returns {void}
+     */
     prepare() {
         window.addEventListener('message', this._onWindowMessage.bind(this), false);
         this._postMessage(window.parent, 'ready', {}, null);
@@ -33,14 +41,24 @@ class TemplateRendererFrameApi {
 
     // Private
 
+    /**
+     * @param {MessageEvent<import('template-renderer-frame-api').MessageData>} e
+     */
     _onWindowMessage(e) {
         const {source, data: {action, params, id}} = e;
         const messageHandler = this._windowMessageHandlers.get(action);
         if (typeof messageHandler === 'undefined') { return; }
 
-        this._onWindowMessageInner(messageHandler, action, params, source, id);
+        this._onWindowMessageInner(messageHandler, action, params, /** @type {Window} */ (source), id);
     }
 
+    /**
+     * @param {import('core').MessageHandlerDetails} handlerItem
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     * @param {Window} source
+     * @param {?string} id
+     */
     async _onWindowMessageInner({handler, async}, action, params, source, id) {
         let response;
         try {
@@ -50,64 +68,54 @@ class TemplateRendererFrameApi {
             }
             response = {result};
         } catch (error) {
-            response = {error: this._serializeError(error)};
+            response = {error: ExtensionError.serialize(error)};
         }
 
         if (typeof id === 'undefined') { return; }
         this._postMessage(source, `${action}.response`, response, id);
     }
 
+    /**
+     * @param {{template: string, data: import('template-renderer').PartialOrCompositeRenderData, type: import('anki-templates').RenderMode}} event
+     * @returns {import('template-renderer').RenderResult}
+     */
     _onRender({template, data, type}) {
         return this._templateRenderer.render(template, data, type);
     }
 
+    /**
+     * @param {{items: import('template-renderer').RenderMultiItem[]}} event
+     * @returns {import('core').Response<import('template-renderer').RenderResult>[]}
+     */
     _onRenderMulti({items}) {
-        return this._serializeMulti(this._templateRenderer.renderMulti(items));
+        return this._templateRenderer.renderMulti(items);
     }
 
+    /**
+     * @param {{data: import('template-renderer').CompositeRenderData, type: import('anki-templates').RenderMode}} event
+     * @returns {import('anki-templates').NoteData}
+     */
     _onGetModifiedData({data, type}) {
         const result = this._templateRenderer.getModifiedData(data, type);
         return this._clone(result);
     }
 
-    _serializeError(error) {
-        try {
-            if (typeof error === 'object' && error !== null) {
-                const result = {
-                    name: error.name,
-                    message: error.message,
-                    stack: error.stack
-                };
-                if (Object.prototype.hasOwnProperty.call(error, 'data')) {
-                    result.data = error.data;
-                }
-                return result;
-            }
-        } catch (e) {
-            // NOP
-        }
-        return {
-            value: error,
-            hasValue: true
-        };
-    }
-
-    _serializeMulti(array) {
-        for (let i = 0, ii = array.length; i < ii; ++i) {
-            const value = array[i];
-            const {error} = value;
-            if (typeof error !== 'undefined') {
-                value.error = this._serializeError(error);
-            }
-        }
-        return array;
-    }
-
+    /**
+     * @template [T=unknown]
+     * @param {T} value
+     * @returns {T}
+     */
     _clone(value) {
         return JSON.parse(JSON.stringify(value));
     }
 
+    /**
+     * @param {Window} target
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     * @param {?string} id
+     */
     _postMessage(target, action, params, id) {
-        return target.postMessage({action, params, id}, '*');
+        target.postMessage(/** @type {import('template-renderer-frame-api').MessageData} */ ({action, params, id}), '*');
     }
 }
diff --git a/ext/js/templates/sandbox/template-renderer-media-provider.js b/ext/js/templates/sandbox/template-renderer-media-provider.js
index f430fa2757..b6aea2046e 100644
--- a/ext/js/templates/sandbox/template-renderer-media-provider.js
+++ b/ext/js/templates/sandbox/template-renderer-media-provider.js
@@ -22,9 +22,11 @@
 
 class TemplateRendererMediaProvider {
     constructor() {
+        /** @type {?import('anki-note-builder').Requirement[]} */
         this._requirements = null;
     }
 
+    /** @type {?import('anki-note-builder').Requirement[]} */
     get requirements() {
         return this._requirements;
     }
@@ -33,12 +35,24 @@ class TemplateRendererMediaProvider {
         this._requirements = value;
     }
 
+    /**
+     * @param {import('anki-templates').NoteData} root
+     * @param {unknown[]} args
+     * @param {import('core').SerializableObject} namedArgs
+     * @returns {boolean}
+     */
     hasMedia(root, args, namedArgs) {
         const {media} = root;
         const data = this._getMediaData(media, args, namedArgs);
         return (data !== null);
     }
 
+    /**
+     * @param {import('anki-templates').NoteData} root
+     * @param {unknown[]} args
+     * @param {import('core').SerializableObject} namedArgs
+     * @returns {?string}
+     */
     getMedia(root, args, namedArgs) {
         const {media} = root;
         const data = this._getMediaData(media, args, namedArgs);
@@ -47,16 +61,24 @@ class TemplateRendererMediaProvider {
             if (typeof result === 'string') { return result; }
         }
         const defaultValue = namedArgs.default;
-        return typeof defaultValue !== 'undefined' ? defaultValue : '';
+        return defaultValue === null || typeof defaultValue === 'string' ? defaultValue : '';
     }
 
     // Private
 
+    /**
+     * @param {import('anki-note-builder').Requirement} value
+     */
     _addRequirement(value) {
         if (this._requirements === null) { return; }
         this._requirements.push(value);
     }
 
+    /**
+     * @param {import('anki-templates').MediaObject} data
+     * @param {import('core').SerializableObject} namedArgs
+     * @returns {string}
+     */
     _getFormattedValue(data, namedArgs) {
         let {value} = data;
         const {escape=true} = namedArgs;
@@ -66,6 +88,12 @@ class TemplateRendererMediaProvider {
         return value;
     }
 
+    /**
+     * @param {import('anki-templates').Media} media
+     * @param {unknown[]} args
+     * @param {import('core').SerializableObject} namedArgs
+     * @returns {?(import('anki-templates').MediaObject)}
+     */
     _getMediaData(media, args, namedArgs) {
         const type = args[0];
         switch (type) {
@@ -80,6 +108,11 @@ class TemplateRendererMediaProvider {
         }
     }
 
+    /**
+     * @param {import('anki-templates').Media} media
+     * @param {import('anki-templates').MediaSimpleType} type
+     * @returns {?import('anki-templates').MediaObject}
+     */
     _getSimpleMediaData(media, type) {
         const result = media[type];
         if (typeof result === 'object' && result !== null) { return result; }
@@ -87,12 +120,19 @@ class TemplateRendererMediaProvider {
         return null;
     }
 
+    /**
+     * @param {import('anki-templates').Media} media
+     * @param {unknown} path
+     * @param {import('core').SerializableObject} namedArgs
+     * @returns {?import('anki-templates').MediaObject}
+     */
     _getDictionaryMedia(media, path, namedArgs) {
+        if (typeof path !== 'string') { return null; }
         const {dictionaryMedia} = media;
         const {dictionary} = namedArgs;
+        if (typeof dictionary !== 'string') { return null; }
         if (
             typeof dictionaryMedia !== 'undefined' &&
-            typeof dictionary === 'string' &&
             Object.prototype.hasOwnProperty.call(dictionaryMedia, dictionary)
         ) {
             const dictionaryMedia2 = dictionaryMedia[dictionary];
@@ -111,8 +151,15 @@ class TemplateRendererMediaProvider {
         return null;
     }
 
+    /**
+     * @param {import('anki-templates').Media} media
+     * @param {unknown} text
+     * @param {import('core').SerializableObject} namedArgs
+     * @returns {?import('anki-templates').MediaObject}
+     */
     _getTextFurigana(media, text, namedArgs) {
-        const {readingMode=null} = namedArgs;
+        if (typeof text !== 'string') { return null; }
+        const readingMode = this._normalizeReadingMode(namedArgs.readingMode);
         const {textFurigana} = media;
         if (Array.isArray(textFurigana)) {
             for (const entry of textFurigana) {
@@ -127,4 +174,18 @@ class TemplateRendererMediaProvider {
         });
         return null;
     }
+
+    /**
+     * @param {unknown} value
+     * @returns {?import('anki-templates').TextFuriganaReadingMode}
+     */
+    _normalizeReadingMode(value) {
+        switch (value) {
+            case 'hiragana':
+            case 'katakana':
+                return value;
+            default:
+                return null;
+        }
+    }
 }
diff --git a/ext/js/templates/sandbox/template-renderer.js b/ext/js/templates/sandbox/template-renderer.js
index 7179f3661a..5117d54b3e 100644
--- a/ext/js/templates/sandbox/template-renderer.js
+++ b/ext/js/templates/sandbox/template-renderer.js
@@ -23,48 +23,83 @@
 
 class TemplateRenderer {
     constructor() {
+        /** @type {Map<string, HandlebarsTemplateDelegate<import('anki-templates').NoteData>>} */
         this._cache = new Map();
+        /** @type {number} */
         this._cacheMaxSize = 5;
+        /** @type {Map<import('anki-templates').RenderMode, import('template-renderer').DataType>} */
         this._dataTypes = new Map();
+        /** @type {?((noteData: import('anki-templates').NoteData) => import('template-renderer').SetupCallbackResult)} */
         this._renderSetup = null;
+        /** @type {?((noteData: import('anki-templates').NoteData) => import('template-renderer').CleanupCallbackResult)} */
         this._renderCleanup = null;
     }
 
+    /**
+     * @param {import('template-renderer').HelperFunctionsDescriptor} helpers
+     */
     registerHelpers(helpers) {
-        Handlebars.partials = Handlebars.templates;
+        const {templates, partials} = Handlebars;
+        if (
+            typeof templates === 'object' && templates !== null &&
+            typeof partials === 'object' && partials !== null
+        ) {
+            for (const [key, value] of Object.entries(templates)) {
+                partials[key] = value;
+            }
+        }
         for (const [name, helper] of helpers) {
             this._registerHelper(name, helper);
         }
     }
 
-    registerDataType(name, {modifier=null, composeData=null}) {
+    /**
+     * @param {import('anki-templates').RenderMode} name
+     * @param {import('template-renderer').DataType} details
+     */
+    registerDataType(name, {modifier, composeData}) {
         this._dataTypes.set(name, {modifier, composeData});
     }
 
+    /**
+     * @param {?((noteData: import('anki-templates').NoteData) => import('template-renderer').SetupCallbackResult)} setup
+     * @param {?((noteData: import('anki-templates').NoteData) => import('template-renderer').CleanupCallbackResult)} cleanup
+     */
     setRenderCallbacks(setup, cleanup) {
         this._renderSetup = setup;
         this._renderCleanup = cleanup;
     }
 
+    /**
+     * @param {string} template
+     * @param {import('template-renderer').PartialOrCompositeRenderData} data
+     * @param {import('anki-templates').RenderMode} type
+     * @returns {import('template-renderer').RenderResult}
+     */
     render(template, data, type) {
         const instance = this._getTemplateInstance(template);
-        data = this._getModifiedData(data, void 0, type);
-        return this._renderTemplate(instance, data);
+        const modifiedData = this._getModifiedData(data, void 0, type);
+        return this._renderTemplate(instance, modifiedData);
     }
 
+    /**
+     * @param {import('template-renderer').RenderMultiItem[]} items
+     * @returns {import('core').Response<import('template-renderer').RenderResult>[]}
+     */
     renderMulti(items) {
+        /** @type {import('core').Response<import('template-renderer').RenderResult>[]} */
         const results = [];
         for (const {template, templateItems} of items) {
             const instance = this._getTemplateInstance(template);
             for (const {type, commonData, datas} of templateItems) {
-                for (let data of datas) {
+                for (const data of datas) {
                     let result;
                     try {
-                        data = this._getModifiedData(data, commonData, type);
-                        result = this._renderTemplate(instance, data);
-                        result = {result};
+                        const data2 = this._getModifiedData(data, commonData, type);
+                        const renderResult = this._renderTemplate(instance, data2);
+                        result = {result: renderResult};
                     } catch (error) {
-                        result = {error};
+                        result = {error: ExtensionError.serialize(error)};
                     }
                     results.push(result);
                 }
@@ -73,29 +108,50 @@ class TemplateRenderer {
         return results;
     }
 
+    /**
+     * @param {import('template-renderer').CompositeRenderData} data
+     * @param {import('anki-templates').RenderMode} type
+     * @returns {import('anki-templates').NoteData}
+     */
     getModifiedData(data, type) {
         return this._getModifiedData(data, void 0, type);
     }
 
     // Private
 
+    /**
+     * @param {string} template
+     * @returns {HandlebarsTemplateDelegate<import('anki-templates').NoteData>}
+     */
     _getTemplateInstance(template) {
         const cache = this._cache;
         let instance = cache.get(template);
         if (typeof instance === 'undefined') {
             this._updateCacheSize(this._cacheMaxSize - 1);
-            instance = Handlebars[handlebarsCompileFnName](template);
+            /** @type {string} */
+            // @ts-ignore - not defined in type declarations
+            const compileFnName = handlebarsCompileFnName;
+            // @ts-ignore - Handlebars[compileFnName] is 'any' type, which is not allowed
+            instance = /** @type {(input: string, options?: CompileOptions) => HandlebarsTemplateDelegate<import('anki-templates').NoteData>} */ (Handlebars[compileFnName])(template);
             cache.set(template, instance);
         }
 
         return instance;
     }
 
+    /**
+     * @param {HandlebarsTemplateDelegate<import('anki-templates').NoteData>} instance
+     * @param {import('anki-templates').NoteData} data
+     * @returns {import('template-renderer').RenderResult}
+     */
     _renderTemplate(instance, data) {
         const renderSetup = this._renderSetup;
         const renderCleanup = this._renderCleanup;
+        /** @type {string} */
         let result;
+        /** @type {?import('template-renderer').SetupCallbackResult} */
         let additions1;
+        /** @type {?import('template-renderer').CleanupCallbackResult} */
         let additions2;
         try {
             additions1 = (typeof renderSetup === 'function' ? renderSetup(data) : null);
@@ -103,28 +159,36 @@ class TemplateRenderer {
         } finally {
             additions2 = (typeof renderCleanup === 'function' ? renderCleanup(data) : null);
         }
-        return Object.assign({result}, additions1, additions2);
+        return /** @type {import('template-renderer').RenderResult} */ (Object.assign({result}, additions1, additions2));
     }
 
+    /**
+     * @param {import('template-renderer').PartialOrCompositeRenderData} data
+     * @param {import('anki-note-builder').CommonData|undefined} commonData
+     * @param {import('anki-templates').RenderMode} type
+     * @returns {import('anki-templates').NoteData}
+     * @throws {Error}
+     */
     _getModifiedData(data, commonData, type) {
         if (typeof type === 'string') {
             const typeInfo = this._dataTypes.get(type);
             if (typeof typeInfo !== 'undefined') {
                 if (typeof commonData !== 'undefined') {
                     const {composeData} = typeInfo;
-                    if (typeof composeData === 'function') {
-                        data = composeData(data, commonData);
-                    }
+                    data = composeData(data, commonData);
+                } else if (typeof data.commonData === 'undefined') {
+                    throw new Error('Incomplete data');
                 }
                 const {modifier} = typeInfo;
-                if (typeof modifier === 'function') {
-                    data = modifier(data);
-                }
+                return modifier(/** @type {import('template-renderer').CompositeRenderData} */ (data));
             }
         }
-        return data;
+        throw new Error(`Invalid type: ${type}`);
     }
 
+    /**
+     * @param {number} maxSize
+     */
     _updateCacheSize(maxSize) {
         const cache = this._cache;
         let removeCount = cache.size - maxSize;
@@ -136,9 +200,21 @@ class TemplateRenderer {
         }
     }
 
+    /**
+     * @param {string} name
+     * @param {import('template-renderer').HelperFunction} helper
+     */
     _registerHelper(name, helper) {
+        /**
+         * @this {unknown}
+         * @param {unknown[]} args
+         * @returns {unknown}
+         */
         function wrapper(...args) {
-            return helper(this, ...args);
+            const argCountM1 = Math.max(0, args.length - 1);
+            const options = /** @type {Handlebars.HelperOptions} */ (args[argCountM1]);
+            args.length = argCountM1;
+            return helper(args, this, options);
         }
         Handlebars.registerHelper(name, wrapper);
     }
diff --git a/ext/js/templates/template-patcher.js b/ext/js/templates/template-patcher.js
index 1e6b011011..666cb9e73b 100644
--- a/ext/js/templates/template-patcher.js
+++ b/ext/js/templates/template-patcher.js
@@ -18,12 +18,20 @@
 
 class TemplatePatcher {
     constructor() {
+        /** @type {RegExp} */
         this._diffPattern1 = /\n?\{\{<<<<<<<\}\}\n/g;
+        /** @type {RegExp} */
         this._diffPattern2 = /\n\{\{=======\}\}\n/g;
+        /** @type {RegExp} */
         this._diffPattern3 = /\n\{\{>>>>>>>\}\}\n*/g;
+        /** @type {RegExp} */
         this._lookupMarkerPattern = /[ \t]*\{\{~?>\s*\(\s*lookup\s*\.\s*"marker"\s*\)\s*~?\}\}/g;
     }
 
+    /**
+     * @param {string} content
+     * @returns {import('template-patcher').Patch}
+     */
     parsePatch(content) {
         const diffPattern1 = this._diffPattern1;
         const diffPattern2 = this._diffPattern2;
@@ -61,6 +69,11 @@ class TemplatePatcher {
         return {addition: content, modifications};
     }
 
+    /**
+     * @param {string} template
+     * @param {import('template-patcher').Patch} patch
+     * @returns {string}
+     */
     applyPatch(template, patch) {
         for (const {current, replacement} of patch.modifications) {
             let fromIndex = 0;
@@ -77,6 +90,11 @@ class TemplatePatcher {
 
     // Private
 
+    /**
+     * @param {string} template
+     * @param {string} addition
+     * @returns {string}
+     */
     _addFieldTemplatesBeforeEnd(template, addition) {
         if (addition.length === 0) { return template; }
         const newline = '\n';
diff --git a/ext/js/templates/template-renderer-proxy.js b/ext/js/templates/template-renderer-proxy.js
index b504daf27d..84e9c1f963 100644
--- a/ext/js/templates/template-renderer-proxy.js
+++ b/ext/js/templates/template-renderer-proxy.js
@@ -18,31 +18,55 @@
 
 class TemplateRendererProxy {
     constructor() {
+        /** @type {?HTMLIFrameElement} */
         this._frame = null;
+        /** @type {boolean} */
         this._frameNeedsLoad = true;
+        /** @type {boolean} */
         this._frameLoading = false;
+        /** @type {?Promise<void>} */
         this._frameLoadPromise = null;
+        /** @type {string} */
         this._frameUrl = chrome.runtime.getURL('/template-renderer.html');
+        /** @type {Set<{cancel: () => void}>} */
         this._invocations = new Set();
     }
 
+    /**
+     * @param {string} template
+     * @param {import('template-renderer').PartialOrCompositeRenderData} data
+     * @param {import('anki-templates').RenderMode} type
+     * @returns {Promise<import('template-renderer').RenderResult>}
+     */
     async render(template, data, type) {
         await this._prepareFrame();
-        return await this._invoke('render', {template, data, type});
+        return /** @type {import('template-renderer').RenderResult} */ (await this._invoke('render', {template, data, type}));
     }
 
+    /**
+     * @param {import('template-renderer').RenderMultiItem[]} items
+     * @returns {Promise<import('core').Response<import('template-renderer').RenderResult>[]>}
+     */
     async renderMulti(items) {
         await this._prepareFrame();
-        return await this._invoke('renderMulti', {items});
+        return /** @type {import('core').Response<import('template-renderer').RenderResult>[]} */ (await this._invoke('renderMulti', {items}));
     }
 
+    /**
+     * @param {import('template-renderer').CompositeRenderData} data
+     * @param {import('anki-templates').RenderMode} type
+     * @returns {Promise<import('anki-templates').NoteData>}
+     */
     async getModifiedData(data, type) {
         await this._prepareFrame();
-        return await this._invoke('getModifiedData', {data, type});
+        return /** @type {import('anki-templates').NoteData} */ (await this._invoke('getModifiedData', {data, type}));
     }
 
     // Private
 
+    /**
+     * @returns {Promise<void>}
+     */
     async _prepareFrame() {
         if (this._frame === null) {
             this._frame = document.createElement('iframe');
@@ -66,6 +90,12 @@ class TemplateRendererProxy {
         await this._frameLoadPromise;
     }
 
+    /**
+     * @param {HTMLIFrameElement} frame
+     * @param {string} url
+     * @param {number} [timeout]
+     * @returns {Promise<void>}
+     */
     _loadFrame(frame, url, timeout=5000) {
         return new Promise((resolve, reject) => {
             let state = 0x0; // 0x1 = frame added; 0x2 = frame loaded; 0x4 = frame ready
@@ -77,6 +107,9 @@ class TemplateRendererProxy {
                     timer = null;
                 }
             };
+            /**
+             * @param {number} flags
+             */
             const updateState = (flags) => {
                 state |= flags;
                 if (state !== 0x7) { return; }
@@ -87,16 +120,20 @@ class TemplateRendererProxy {
                 if ((state & 0x3) !== 0x1) { return; }
                 updateState(0x2);
             };
+            /**
+             * @param {MessageEvent<unknown>} e
+             */
             const onWindowMessage = (e) => {
                 if ((state & 0x5) !== 0x1) { return; }
                 const frameWindow = frame.contentWindow;
                 if (frameWindow === null || frameWindow !== e.source) { return; }
                 const {data} = e;
-                if (!(typeof data === 'object' && data !== null && data.action === 'ready')) { return; }
+                if (!(typeof data === 'object' && data !== null && /** @type {import('core').SerializableObject} */ (data).action === 'ready')) { return; }
                 updateState(0x4);
             };
 
-            let timer = setTimeout(() => {
+            /** @type {?number} */
+            let timer = window.setTimeout(() => {
                 timer = null;
                 cleanup();
                 reject(new Error('Timeout'));
@@ -109,7 +146,9 @@ class TemplateRendererProxy {
             try {
                 document.body.appendChild(frame);
                 state = 0x1;
-                frame.contentDocument.location.href = url;
+                const {contentDocument} = frame;
+                if (contentDocument === null) { throw new Error('Failed to initialize frame URL'); }
+                contentDocument.location.href = url;
             } catch (e) {
                 cleanup();
                 reject(e);
@@ -117,6 +156,12 @@ class TemplateRendererProxy {
         });
     }
 
+    /**
+     * @param {string} action
+     * @param {import('core').SerializableObject} params
+     * @param {?number} [timeout]
+     * @returns {Promise<unknown>}
+     */
     _invoke(action, params, timeout=null) {
         return new Promise((resolve, reject) => {
             const frameWindow = (this._frame !== null ? this._frame.contentWindow : null);
@@ -141,22 +186,30 @@ class TemplateRendererProxy {
                     timer = null;
                 }
             };
-            const onMessage = (e) => {
+            /**
+             * @param {MessageEvent<unknown>} event
+             */
+            const onMessage = (event) => {
+                if (event.source !== frameWindow) { return; }
+                const {data} = event;
                 if (
-                    e.source !== frameWindow ||
-                    e.data.id !== id ||
-                    e.data.action !== `${action}.response`
+                    typeof data !== 'object' ||
+                    data === null ||
+                    /** @type {import('core').SerializableObject} */ (data).id !== id ||
+                    /** @type {import('core').SerializableObject} */ (data).action !== `${action}.response`
                 ) {
                     return;
                 }
 
-                const response = e.data.params;
+                const response = /** @type {import('core').SerializableObject} */ (data).params;
+                if (typeof response !== 'object' || response === null) { return; }
+
                 cleanup();
-                const {error} = response;
+                const {error} = /** @type {import('core').Response} */ (response);
                 if (error) {
-                    reject(deserializeError(error));
+                    reject(ExtensionError.deserialize(error));
                 } else {
-                    resolve(response.result);
+                    resolve(/** @type {import('core').Response} */ (response).result);
                 }
             };
 
@@ -172,6 +225,9 @@ class TemplateRendererProxy {
         });
     }
 
+    /**
+     * @returns {void}
+     */
     _onFrameLoad() {
         if (this._frameLoading) { return; }
         this._frameNeedsLoad = true;
diff --git a/ext/js/yomichan.js b/ext/js/yomichan.js
index 6eea952ecd..65b65caeed 100644
--- a/ext/js/yomichan.js
+++ b/ext/js/yomichan.js
@@ -37,11 +37,13 @@ if ((() => {
     }
     return (hasBrowser && !hasChrome);
 })()) {
+    // @ts-ignore - objects should have roughly the same interface
     chrome = browser;
 }
 
 /**
  * The Yomichan class is a core component through which various APIs are handled and invoked.
+ * @augments EventDispatcher<import('extension').ExtensionEventType>
  */
 class Yomichan extends EventDispatcher {
     /**
@@ -50,38 +52,51 @@ class Yomichan extends EventDispatcher {
     constructor() {
         super();
 
+        /** @type {string} */
+        this._extensionName = 'Yomichan';
         try {
             const manifest = chrome.runtime.getManifest();
             this._extensionName = `${manifest.name} v${manifest.version}`;
         } catch (e) {
-            this._extensionName = 'Yomichan';
+            // NOP
         }
 
+        /** @type {?string} */
+        this._extensionUrlBase = null;
         try {
             this._extensionUrlBase = chrome.runtime.getURL('/');
         } catch (e) {
-            this._extensionUrlBase = null;
+            // NOP
         }
 
+        /** @type {?boolean} */
         this._isBackground = null;
+        /** @type {?API} */
         this._api = null;
+        /** @type {?CrossFrameAPI} */
         this._crossFrame = null;
+        /** @type {boolean} */
         this._isExtensionUnloaded = false;
+        /** @type {boolean} */
         this._isTriggeringExtensionUnloaded = false;
+        /** @type {boolean} */
         this._isReady = false;
 
-        const {promise, resolve} = deferPromise();
+        const {promise, resolve} = /** @type {import('core').DeferredPromiseDetails<void>} */ (deferPromise());
+        /** @type {Promise<void>} */
         this._isBackendReadyPromise = promise;
+        /** @type {?(() => void)} */
         this._isBackendReadyPromiseResolve = resolve;
 
-        this._messageHandlers = new Map([
+        /** @type {import('core').MessageHandlerMap} */
+        this._messageHandlers = new Map(/** @type {import('core').MessageHandlerArray} */ ([
             ['Yomichan.isReady',         {async: false, handler: this._onMessageIsReady.bind(this)}],
             ['Yomichan.backendReady',    {async: false, handler: this._onMessageBackendReady.bind(this)}],
             ['Yomichan.getUrl',          {async: false, handler: this._onMessageGetUrl.bind(this)}],
             ['Yomichan.optionsUpdated',  {async: false, handler: this._onMessageOptionsUpdated.bind(this)}],
             ['Yomichan.databaseUpdated', {async: false, handler: this._onMessageDatabaseUpdated.bind(this)}],
             ['Yomichan.zoomChanged',     {async: false, handler: this._onMessageZoomChanged.bind(this)}]
-        ]);
+        ]));
     }
 
     /**
@@ -89,7 +104,8 @@ class Yomichan extends EventDispatcher {
      * @type {boolean}
      */
     get isBackground() {
-        return this._isBackground;
+        if (this._isBackground === null) { throw new Error('Not prepared'); }
+        return /** @type {boolean} */ (this._isBackground);
     }
 
     /**
@@ -106,6 +122,7 @@ class Yomichan extends EventDispatcher {
      * @type {API}
      */
     get api() {
+        if (this._api === null) { throw new Error('Not prepared'); }
         return this._api;
     }
 
@@ -115,6 +132,7 @@ class Yomichan extends EventDispatcher {
      * @type {CrossFrameAPI}
      */
     get crossFrame() {
+        if (this._crossFrame === null) { throw new Error('Not prepared'); }
         return this._crossFrame;
     }
 
@@ -159,13 +177,13 @@ class Yomichan extends EventDispatcher {
 
     /**
      * Runs `chrome.runtime.sendMessage()` with additional exception handling events.
-     * @param {...*} args The arguments to be passed to `chrome.runtime.sendMessage()`.
-     * @returns {void} The result of the `chrome.runtime.sendMessage()` call.
+     * @param {import('extension').ChromeRuntimeSendMessageArgs} args The arguments to be passed to `chrome.runtime.sendMessage()`.
      * @throws {Error} Errors thrown by `chrome.runtime.sendMessage()` are re-thrown.
      */
     sendMessage(...args) {
         try {
-            return chrome.runtime.sendMessage(...args);
+            // @ts-ignore - issue with type conversion, somewhat difficult to resolve in pure JS
+            chrome.runtime.sendMessage(...args);
         } catch (e) {
             this.triggerExtensionUnloaded();
             throw e;
@@ -175,7 +193,7 @@ class Yomichan extends EventDispatcher {
     /**
      * Runs `chrome.runtime.connect()` with additional exception handling events.
      * @param {...*} args The arguments to be passed to `chrome.runtime.connect()`.
-     * @returns {Port} The resulting port.
+     * @returns {chrome.runtime.Port} The resulting port.
      * @throws {Error} Errors thrown by `chrome.runtime.connect()` are re-thrown.
      */
     connect(...args) {
@@ -203,49 +221,71 @@ class Yomichan extends EventDispatcher {
 
     // Private
 
+    /**
+     * @returns {string}
+     */
     _getUrl() {
         return location.href;
     }
 
-    _getLogContext() {
-        return {url: this._getUrl()};
-    }
-
+    /** @type {import('extension').ChromeRuntimeOnMessageCallback} */
     _onMessage({action, params}, sender, callback) {
         const messageHandler = this._messageHandlers.get(action);
         if (typeof messageHandler === 'undefined') { return false; }
         return invokeMessageHandler(messageHandler, params, callback, sender);
     }
 
+    /**
+     * @returns {boolean}
+     */
     _onMessageIsReady() {
         return this._isReady;
     }
 
+    /**
+     * @returns {void}
+     */
     _onMessageBackendReady() {
         if (this._isBackendReadyPromiseResolve === null) { return; }
         this._isBackendReadyPromiseResolve();
         this._isBackendReadyPromiseResolve = null;
     }
 
+    /**
+     * @returns {{url: string}}
+     */
     _onMessageGetUrl() {
         return {url: this._getUrl()};
     }
 
+    /**
+     * @param {{source: string}} params
+     */
     _onMessageOptionsUpdated({source}) {
         this.trigger('optionsUpdated', {source});
     }
 
+    /**
+     * @param {{type: string, cause: string}} params
+     */
     _onMessageDatabaseUpdated({type, cause}) {
         this.trigger('databaseUpdated', {type, cause});
     }
 
+    /**
+     * @param {{oldZoomFactor: number, newZoomFactor: number}} params
+     */
     _onMessageZoomChanged({oldZoomFactor, newZoomFactor}) {
         this.trigger('zoomChanged', {oldZoomFactor, newZoomFactor});
     }
 
+    /**
+     * @param {{error: unknown, level: import('log').LogLevel, context?: import('log').LogContext}} params
+     */
     async _onForwardLog({error, level, context}) {
         try {
-            await this._api.log(serializeError(error), level, context);
+            const api = /** @type {API} */ (this._api);
+            await api.log(ExtensionError.serialize(error), level, context);
         } catch (e) {
             // NOP
         }
diff --git a/ext/manifest.json b/ext/manifest.json
index 018a4a0b5b..3ce4cf0ebb 100644
--- a/ext/manifest.json
+++ b/ext/manifest.json
@@ -41,6 +41,7 @@
             "all_frames": true,
             "js": [
                 "js/core.js",
+                "js/core/extension-error.js",
                 "js/yomichan.js",
                 "js/app/frontend.js",
                 "js/app/popup.js",
diff --git a/ext/permissions.html b/ext/permissions.html
index b76b1fb02a..2ad3069a3e 100644
--- a/ext/permissions.html
+++ b/ext/permissions.html
@@ -267,6 +267,7 @@ <h2 id="permissions"></h2>
 
 <!-- Scripts -->
 <script src="/js/core.js"></script>
+<script src="/js/core/extension-error.js"></script>
 
 <script src="/js/yomichan.js"></script>
 
diff --git a/ext/popup-preview.html b/ext/popup-preview.html
index 62d657a611..e5935735d0 100644
--- a/ext/popup-preview.html
+++ b/ext/popup-preview.html
@@ -38,6 +38,7 @@
 <script src="/lib/wanakana.min.js"></script>
 
 <script src="/js/core.js"></script>
+<script src="/js/core/extension-error.js"></script>
 
 <script src="/js/yomichan.js"></script>
 
diff --git a/ext/popup.html b/ext/popup.html
index 02248b1771..6d846c08cf 100644
--- a/ext/popup.html
+++ b/ext/popup.html
@@ -94,6 +94,7 @@ <h3>Default Profile</h3>
 
 <!-- Scripts -->
 <script src="/js/core.js"></script>
+<script src="/js/core/extension-error.js"></script>
 
 <script src="/js/yomichan.js"></script>
 
diff --git a/ext/search.html b/ext/search.html
index be2959378a..ee2393853c 100644
--- a/ext/search.html
+++ b/ext/search.html
@@ -81,6 +81,7 @@ <h1>Yomitan Search</h1>
 <script src="/lib/wanakana.min.js"></script>
 
 <script src="/js/core.js"></script>
+<script src="/js/core/extension-error.js"></script>
 
 <script src="/js/yomichan.js"></script>
 
diff --git a/ext/settings.html b/ext/settings.html
index 62e06e983f..e76d7acd89 100644
--- a/ext/settings.html
+++ b/ext/settings.html
@@ -3806,6 +3806,7 @@ <h1>Yomitan Settings</h1>
 <script src="/lib/wanakana.min.js"></script>
 
 <script src="/js/core.js"></script>
+<script src="/js/core/extension-error.js"></script>
 
 <script src="/js/yomichan.js"></script>
 
diff --git a/ext/sw.js b/ext/sw.js
index bd742f9631..64d8c2b23b 100644
--- a/ext/sw.js
+++ b/ext/sw.js
@@ -20,6 +20,7 @@ self.importScripts(
     '/lib/parse5.js',
     '/lib/wanakana.min.js',
     '/js/core.js',
+    '/js/core/extension-error.js',
     '/js/yomichan.js',
     '/js/accessibility/accessibility-controller.js',
     '/js/background/backend.js',
diff --git a/ext/template-renderer.html b/ext/template-renderer.html
index faf6f73e63..617086a661 100644
--- a/ext/template-renderer.html
+++ b/ext/template-renderer.html
@@ -17,6 +17,8 @@
 <!-- Scripts -->
 <script src="/lib/handlebars.min.js"></script>
 
+<script src="/js/core/extension-error.js"></script>
+
 <script src="/js/data/sandbox/anki-note-data-creator.js"></script>
 <script src="/js/display/sandbox/pronunciation-generator.js"></script>
 <script src="/js/display/sandbox/structured-content-generator.js"></script>
diff --git a/ext/welcome.html b/ext/welcome.html
index f5725f23c6..93060f9c52 100644
--- a/ext/welcome.html
+++ b/ext/welcome.html
@@ -385,6 +385,7 @@ <h2>Basic customization</h2>
 
 <!-- Scripts -->
 <script src="/js/core.js"></script>
+<script src="/js/core/extension-error.js"></script>
 
 <script src="/js/yomichan.js"></script>
 
diff --git a/jsconfig.json b/jsconfig.json
new file mode 100644
index 0000000000..f767584e20
--- /dev/null
+++ b/jsconfig.json
@@ -0,0 +1,35 @@
+{
+    "compilerOptions": {
+        "module": "ES2015",
+        "target": "ES2022",
+        "checkJs": true,
+        "moduleResolution": "node",
+        "strict": true,
+        "strictNullChecks": true,
+        "noImplicitAny": true,
+        "strictPropertyInitialization": true,
+        "suppressImplicitAnyIndexErrors": false,
+        "skipLibCheck": false,
+        "baseUrl": ".",
+        "paths": {
+            "*": ["./types/ext/*"]
+        },
+        "types": [
+            "chrome",
+            "firefox-webext-browser",
+            "handlebars",
+            "jszip",
+            "parse5",
+            "wanakana"
+        ]
+    },
+    "include": [
+        "ext/**/*.js",
+        "types/ext/**/*.ts",
+        "types/other/web-set-timeout.d.ts"
+    ],
+    "exclude": [
+        "node_modules",
+        "ext/lib"
+    ]
+}
\ No newline at end of file
diff --git a/package-lock.json b/package-lock.json
index 1e8901cdf7..b156c4b99e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,23 +11,48 @@
             "license": "GPL-3.0-or-later",
             "devDependencies": {
                 "@playwright/test": "^1.31.2",
+                "@stylistic/eslint-plugin-ts": "^1.4.1",
+                "@types/assert": "^1.5.10",
+                "@types/browserify": "^12.0.40",
+                "@types/chrome": "^0.0.253",
+                "@types/css": "^0.0.37",
+                "@types/events": "^3.0.3",
+                "@types/firefox-webext-browser": "^120.0.0",
+                "@types/handlebars": "^4.1.0",
+                "@types/jsdom": "^21.1.6",
+                "@types/node": "^20.10.0",
+                "@types/wanakana": "^4.0.6",
+                "@typescript-eslint/eslint-plugin": "^6.12.0",
+                "@typescript-eslint/parser": "^6.12.0",
                 "ajv": "^8.11.0",
                 "browserify": "^17.0.0",
                 "css": "^3.0.0",
-                "eslint": "^8.37.0",
+                "eslint": "^8.54.0",
                 "eslint-plugin-header": "^3.1.1",
-                "eslint-plugin-jsdoc": "^39.3.6",
-                "eslint-plugin-jsonc": "^2.8.0",
-                "eslint-plugin-no-unsanitized": "^4.0.1",
+                "eslint-plugin-jsdoc": "^46.9.0",
+                "eslint-plugin-jsonc": "^2.10.0",
+                "eslint-plugin-no-unsanitized": "^4.0.2",
+                "eslint-plugin-unused-imports": "^3.0.0",
                 "fake-indexeddb": "^4.0.0",
                 "html-validate": "^7.6.0",
                 "jsdom": "^20.0.1",
+                "jszip": "^3.10.1",
                 "parse5": "^7.1.2",
                 "stylelint": "^14.14.0",
                 "stylelint-config-recommended": "^9.0.0",
+                "typescript": "^5.2.2",
                 "web-ext": "^7.6.0"
             }
         },
+        "node_modules/@aashutoshrathi/word-wrap": {
+            "version": "1.2.6",
+            "resolved": "https://registry.npmjs.org/@aashutoshrathi/word-wrap/-/word-wrap-1.2.6.tgz",
+            "integrity": "sha512-1Yjs2SvM8TflER/OD3cOjhWWOZb58A2t7wpE2S9XfBYTiIl+XFhQG2bjy4Pu1I+EAlCNUzRDYDdFwFYUKvXcIA==",
+            "dev": true,
+            "engines": {
+                "node": ">=0.10.0"
+            }
+        },
         "node_modules/@babel/code-frame": {
             "version": "7.16.7",
             "resolved": "https://registry.npmjs.org/@babel/code-frame/-/code-frame-7.16.7.tgz",
@@ -203,23 +228,23 @@
             }
         },
         "node_modules/@es-joy/jsdoccomment": {
-            "version": "0.31.0",
-            "resolved": "https://registry.npmjs.org/@es-joy/jsdoccomment/-/jsdoccomment-0.31.0.tgz",
-            "integrity": "sha512-tc1/iuQcnaiSIUVad72PBierDFpsxdUHtEF/OrfqvM1CBAsIoMP51j52jTMb3dXriwhieTo289InzZj72jL3EQ==",
+            "version": "0.41.0",
+            "resolved": "https://registry.npmjs.org/@es-joy/jsdoccomment/-/jsdoccomment-0.41.0.tgz",
+            "integrity": "sha512-aKUhyn1QI5Ksbqcr3fFJj16p99QdjUxXAEuFst1Z47DRyoiMwivIH9MV/ARcJOCXVjPfjITciej8ZD2O/6qUmw==",
             "dev": true,
             "dependencies": {
-                "comment-parser": "1.3.1",
-                "esquery": "^1.4.0",
-                "jsdoc-type-pratt-parser": "~3.1.0"
+                "comment-parser": "1.4.1",
+                "esquery": "^1.5.0",
+                "jsdoc-type-pratt-parser": "~4.0.0"
             },
             "engines": {
-                "node": "^14 || ^16 || ^17 || ^18"
+                "node": ">=16"
             }
         },
         "node_modules/@eslint-community/eslint-utils": {
-            "version": "4.3.0",
-            "resolved": "https://registry.npmjs.org/@eslint-community/eslint-utils/-/eslint-utils-4.3.0.tgz",
-            "integrity": "sha512-v3oplH6FYCULtFuCeqyuTd9D2WKO937Dxdq+GmHOLL72TTRriLxz2VLlNfkZRsvj6PKnOPAtuT6dwrs/pA5DvA==",
+            "version": "4.4.0",
+            "resolved": "https://registry.npmjs.org/@eslint-community/eslint-utils/-/eslint-utils-4.4.0.tgz",
+            "integrity": "sha512-1/sA4dwrzBAyeUoQ6oxahHKmrZvsnLCg4RfxW3ZFGGmQkSNQPFNLV9CUEFQP1x9EYXHTo5p6xdhZM1Ne9p/AfA==",
             "dev": true,
             "dependencies": {
                 "eslint-visitor-keys": "^3.3.0"
@@ -232,23 +257,23 @@
             }
         },
         "node_modules/@eslint-community/regexpp": {
-            "version": "4.4.1",
-            "resolved": "https://registry.npmjs.org/@eslint-community/regexpp/-/regexpp-4.4.1.tgz",
-            "integrity": "sha512-BISJ6ZE4xQsuL/FmsyRaiffpq977bMlsKfGHTQrOGFErfByxIe6iZTxPf/00Zon9b9a7iUykfQwejN3s2ZW/Bw==",
+            "version": "4.6.2",
+            "resolved": "https://registry.npmjs.org/@eslint-community/regexpp/-/regexpp-4.6.2.tgz",
+            "integrity": "sha512-pPTNuaAG3QMH+buKyBIGJs3g/S5y0caxw0ygM3YyE6yJFySwiGGSzA+mM3KJ8QQvzeLh3blwgSonkFjgQdxzMw==",
             "dev": true,
             "engines": {
                 "node": "^12.0.0 || ^14.0.0 || >=16.0.0"
             }
         },
         "node_modules/@eslint/eslintrc": {
-            "version": "2.0.2",
-            "resolved": "https://registry.npmjs.org/@eslint/eslintrc/-/eslintrc-2.0.2.tgz",
-            "integrity": "sha512-3W4f5tDUra+pA+FzgugqL2pRimUTDJWKr7BINqOpkZrC0uYI0NIc0/JFgBROCU07HR6GieA5m3/rsPIhDmCXTQ==",
+            "version": "2.1.3",
+            "resolved": "https://registry.npmjs.org/@eslint/eslintrc/-/eslintrc-2.1.3.tgz",
+            "integrity": "sha512-yZzuIG+jnVu6hNSzFEN07e8BxF3uAzYtQb6uDkaYZLo6oYZDCq454c5kB8zxnzfCYyP4MIuyBn10L0DqwujTmA==",
             "dev": true,
             "dependencies": {
                 "ajv": "^6.12.4",
                 "debug": "^4.3.2",
-                "espree": "^9.5.1",
+                "espree": "^9.6.0",
                 "globals": "^13.19.0",
                 "ignore": "^5.2.0",
                 "import-fresh": "^3.2.1",
@@ -280,9 +305,9 @@
             }
         },
         "node_modules/@eslint/eslintrc/node_modules/eslint-visitor-keys": {
-            "version": "3.4.0",
-            "resolved": "https://registry.npmjs.org/eslint-visitor-keys/-/eslint-visitor-keys-3.4.0.tgz",
-            "integrity": "sha512-HPpKPUBQcAsZOsHAFwTtIKcYlCje62XB7SEAcxjtmW6TD1WVpkS6i6/hOVtTZIl4zGj/mBqpFVGvaDneik+VoQ==",
+            "version": "3.4.2",
+            "resolved": "https://registry.npmjs.org/eslint-visitor-keys/-/eslint-visitor-keys-3.4.2.tgz",
+            "integrity": "sha512-8drBzUEyZ2llkpCA67iYrgEssKDUu68V8ChqqOfFupIaG/LCVPUT+CoGJpT77zJprs4T/W7p07LP7zAIMuweVw==",
             "dev": true,
             "engines": {
                 "node": "^12.22.0 || ^14.17.0 || >=16.0.0"
@@ -292,14 +317,14 @@
             }
         },
         "node_modules/@eslint/eslintrc/node_modules/espree": {
-            "version": "9.5.1",
-            "resolved": "https://registry.npmjs.org/espree/-/espree-9.5.1.tgz",
-            "integrity": "sha512-5yxtHSZXRSW5pvv3hAlXM5+/Oswi1AUFqBmbibKb5s6bp3rGIDkyXU6xCoyuuLhijr4SFwPrXRoZjz0AZDN9tg==",
+            "version": "9.6.1",
+            "resolved": "https://registry.npmjs.org/espree/-/espree-9.6.1.tgz",
+            "integrity": "sha512-oruZaFkjorTpF32kDSI5/75ViwGeZginGGy2NoOSg3Q9bnwlnmDm4HLnkl0RE3n+njDXR037aY1+x58Z/zFdwQ==",
             "dev": true,
             "dependencies": {
-                "acorn": "^8.8.0",
+                "acorn": "^8.9.0",
                 "acorn-jsx": "^5.3.2",
-                "eslint-visitor-keys": "^3.4.0"
+                "eslint-visitor-keys": "^3.4.1"
             },
             "engines": {
                 "node": "^12.22.0 || ^14.17.0 || >=16.0.0"
@@ -315,9 +340,9 @@
             "dev": true
         },
         "node_modules/@eslint/js": {
-            "version": "8.37.0",
-            "resolved": "https://registry.npmjs.org/@eslint/js/-/js-8.37.0.tgz",
-            "integrity": "sha512-x5vzdtOOGgFVDCUs81QRB2+liax8rFg3+7hqM+QhBG0/G3F1ZsoYl97UrqgHgQ9KKT7G6c4V+aTUCgu/n22v1A==",
+            "version": "8.54.0",
+            "resolved": "https://registry.npmjs.org/@eslint/js/-/js-8.54.0.tgz",
+            "integrity": "sha512-ut5V+D+fOoWPgGGNj83GGjnntO39xDy6DWxO0wb7Jp3DcMX0TfIqdzHF85VTQkerdyGmuuMD9AKAo5KiNlf/AQ==",
             "dev": true,
             "engines": {
                 "node": "^12.22.0 || ^14.17.0 || >=16.0.0"
@@ -346,12 +371,12 @@
             }
         },
         "node_modules/@humanwhocodes/config-array": {
-            "version": "0.11.8",
-            "resolved": "https://registry.npmjs.org/@humanwhocodes/config-array/-/config-array-0.11.8.tgz",
-            "integrity": "sha512-UybHIJzJnR5Qc/MsD9Kr+RpO2h+/P1GhOwdiLPXK5TWk5sgTdu88bTD9UP+CKbPPh5Rni1u0GjAdYQLemG8g+g==",
+            "version": "0.11.13",
+            "resolved": "https://registry.npmjs.org/@humanwhocodes/config-array/-/config-array-0.11.13.tgz",
+            "integrity": "sha512-JSBDMiDKSzQVngfRjOdFXgFfklaXI4K9nLF49Auh21lmBWRLIK3+xTErTWD4KU54pb6coM6ESE7Awz/FNU3zgQ==",
             "dev": true,
             "dependencies": {
-                "@humanwhocodes/object-schema": "^1.2.1",
+                "@humanwhocodes/object-schema": "^2.0.1",
                 "debug": "^4.1.1",
                 "minimatch": "^3.0.5"
             },
@@ -373,9 +398,9 @@
             }
         },
         "node_modules/@humanwhocodes/object-schema": {
-            "version": "1.2.1",
-            "resolved": "https://registry.npmjs.org/@humanwhocodes/object-schema/-/object-schema-1.2.1.tgz",
-            "integrity": "sha512-ZnQMnLV4e7hDlUvw8H+U8ASL02SS2Gn6+9Ac3wGGLIe7+je2AeAOxPY+izIPJDfFDb7eDjev0Us8MO1iFRN8hA==",
+            "version": "2.0.1",
+            "resolved": "https://registry.npmjs.org/@humanwhocodes/object-schema/-/object-schema-2.0.1.tgz",
+            "integrity": "sha512-dvuCeX5fC9dXgJn9t+X5atfmgQAzUOWqS1254Gh0m6i8wKd10ebXkfNKiRK+1GWi/yTvvLDHpoxLr0xxxeslWw==",
             "dev": true
         },
         "node_modules/@mdn/browser-compat-data": {
@@ -491,6 +516,71 @@
                 "url": "https://github.com/sindresorhus/is?sponsor=1"
             }
         },
+        "node_modules/@stylistic/eslint-plugin-js": {
+            "version": "1.4.1",
+            "resolved": "https://registry.npmjs.org/@stylistic/eslint-plugin-js/-/eslint-plugin-js-1.4.1.tgz",
+            "integrity": "sha512-WXHPEVw5PB7OML7cLwHJDEcCyLiP7vzKeBbSwmpHLK0oh0JYkoJfTg2hEdFuQT5rQxFy3KzCy9R1mZ0wgLjKrA==",
+            "dev": true,
+            "dependencies": {
+                "acorn": "^8.11.2",
+                "escape-string-regexp": "^4.0.0",
+                "eslint-visitor-keys": "^3.4.3",
+                "espree": "^9.6.1",
+                "graphemer": "^1.4.0"
+            },
+            "engines": {
+                "node": "^16.0.0 || >=18.0.0"
+            },
+            "peerDependencies": {
+                "eslint": ">=8.40.0"
+            }
+        },
+        "node_modules/@stylistic/eslint-plugin-js/node_modules/eslint-visitor-keys": {
+            "version": "3.4.3",
+            "resolved": "https://registry.npmjs.org/eslint-visitor-keys/-/eslint-visitor-keys-3.4.3.tgz",
+            "integrity": "sha512-wpc+LXeiyiisxPlEkUzU6svyS1frIO3Mgxj1fdy7Pm8Ygzguax2N3Fa/D/ag1WqbOprdI+uY6wMUl8/a2G+iag==",
+            "dev": true,
+            "engines": {
+                "node": "^12.22.0 || ^14.17.0 || >=16.0.0"
+            },
+            "funding": {
+                "url": "https://opencollective.com/eslint"
+            }
+        },
+        "node_modules/@stylistic/eslint-plugin-js/node_modules/espree": {
+            "version": "9.6.1",
+            "resolved": "https://registry.npmjs.org/espree/-/espree-9.6.1.tgz",
+            "integrity": "sha512-oruZaFkjorTpF32kDSI5/75ViwGeZginGGy2NoOSg3Q9bnwlnmDm4HLnkl0RE3n+njDXR037aY1+x58Z/zFdwQ==",
+            "dev": true,
+            "dependencies": {
+                "acorn": "^8.9.0",
+                "acorn-jsx": "^5.3.2",
+                "eslint-visitor-keys": "^3.4.1"
+            },
+            "engines": {
+                "node": "^12.22.0 || ^14.17.0 || >=16.0.0"
+            },
+            "funding": {
+                "url": "https://opencollective.com/eslint"
+            }
+        },
+        "node_modules/@stylistic/eslint-plugin-ts": {
+            "version": "1.4.1",
+            "resolved": "https://registry.npmjs.org/@stylistic/eslint-plugin-ts/-/eslint-plugin-ts-1.4.1.tgz",
+            "integrity": "sha512-zuqnxhWoqPhZcxOb7AiYZz1RF/fUCsbJ7xq60IdRWnEY6MPybqYVJAb+SYilJ3PYxqmz8zdZeYkSeVy6f1fNnA==",
+            "dev": true,
+            "dependencies": {
+                "@stylistic/eslint-plugin-js": "1.4.1",
+                "@typescript-eslint/utils": "^6.11.0",
+                "graphemer": "^1.4.0"
+            },
+            "engines": {
+                "node": "^16.0.0 || >=18.0.0"
+            },
+            "peerDependencies": {
+                "eslint": ">=8.40.0"
+            }
+        },
         "node_modules/@szmarczak/http-timer": {
             "version": "5.0.1",
             "resolved": "https://registry.npmjs.org/@szmarczak/http-timer/-/http-timer-5.0.1.tgz",
@@ -512,12 +602,113 @@
                 "node": ">= 10"
             }
         },
+        "node_modules/@types/assert": {
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                 "find-up": {
@@ -11812,6 +12789,13 @@
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         },
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+            "dev": true,
+            "requires": {}
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         "eslint-plugin-header": {
             "version": "3.1.1",
             "resolved": "https://registry.npmjs.org/eslint-plugin-header/-/eslint-plugin-header-3.1.1.tgz",
@@ -11820,27 +12804,41 @@
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+            "version": "46.9.0",
+            "resolved": "https://registry.npmjs.org/eslint-plugin-jsdoc/-/eslint-plugin-jsdoc-46.9.0.tgz",
+            "integrity": "sha512-UQuEtbqLNkPf5Nr/6PPRCtr9xypXY+g8y/Q7gPa0YK7eDhh0y2lWprXRnaYbW7ACgIUvpDKy9X2bZqxtGzBG9Q==",
             "dev": true,
             "requires": {
-                "@es-joy/jsdoccomment": "~0.31.0",
-                "comment-parser": "1.3.1",
+                "@es-joy/jsdoccomment": "~0.41.0",
+                "are-docs-informative": "^0.0.2",
+                "comment-parser": "1.4.1",
                 "debug": "^4.3.4",
                 "escape-string-regexp": "^4.0.0",
-                "esquery": "^1.4.0",
-                "semver": "^7.3.7",
+                "esquery": "^1.5.0",
+                "is-builtin-module": "^3.2.1",
+                "semver": "^7.5.4",
                 "spdx-expression-parse": "^3.0.1"
+            },
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+                    "resolved": "https://registry.npmjs.org/semver/-/semver-7.5.4.tgz",
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+                    "dev": true,
+                    "requires": {
+                        "lru-cache": "^6.0.0"
+                    }
+                }
             }
         },
         "eslint-plugin-jsonc": {
-            "version": "2.8.0",
-            "resolved": "https://registry.npmjs.org/eslint-plugin-jsonc/-/eslint-plugin-jsonc-2.8.0.tgz",
-            "integrity": "sha512-K4VsnztnNwpm+V49CcCu5laq8VjclJpuhfI9LFkOrOyK+BKdQHMzkWo43B4X4rYaVrChm4U9kw/tTU5RHh5Wtg==",
+            "version": "2.10.0",
+            "resolved": "https://registry.npmjs.org/eslint-plugin-jsonc/-/eslint-plugin-jsonc-2.10.0.tgz",
+            "integrity": "sha512-9d//o6Jyh4s1RxC9fNSt1+MMaFN2ruFdXPG9XZcb/mR2KkfjADYiNL/hbU6W0Cyxfg3tS/XSFuhl5LgtMD8hmw==",
             "dev": true,
             "requires": {
                 "@eslint-community/eslint-utils": "^4.2.0",
+                "eslint-compat-utils": "^0.1.2",
                 "jsonc-eslint-parser": "^2.0.4",
                 "natural-compare": "^1.4.0"
             }
@@ -11852,10 +12850,25 @@
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             "requires": {}
         },
+        "eslint-plugin-unused-imports": {
+            "version": "3.0.0",
+            "resolved": "https://registry.npmjs.org/eslint-plugin-unused-imports/-/eslint-plugin-unused-imports-3.0.0.tgz",
+            "integrity": "sha512-sduiswLJfZHeeBJ+MQaG+xYzSWdRXoSw61DpU13mzWumCkR0ufD0HmO4kdNokjrkluMHpj/7PJeN35pgbhW3kw==",
+            "dev": true,
+            "requires": {
+                "eslint-rule-composer": "^0.3.0"
+            }
+        },
+        "eslint-rule-composer": {
+            "version": "0.3.0",
+            "resolved": "https://registry.npmjs.org/eslint-rule-composer/-/eslint-rule-composer-0.3.0.tgz",
+            "integrity": "sha512-bt+Sh8CtDmn2OajxvNO+BX7Wn4CIWMpTRm3MaiKPCQcnnlm0CS2mhui6QaoeQugs+3Kj2ESKEEGJUdVafwhiCg==",
+            "dev": true
+        },
         "eslint-scope": {
-            "version": "7.1.1",
-            "resolved": "https://registry.npmjs.org/eslint-scope/-/eslint-scope-7.1.1.tgz",
-            "integrity": "sha512-QKQM/UXpIiHcLqJ5AOyIW7XZmzjkzQXYE54n1++wb0u9V/abW3l9uQnxX8Z5Xd18xyKIMTUAyQ0k1e8pz6LUrw==",
+            "version": "7.2.2",
+            "resolved": "https://registry.npmjs.org/eslint-scope/-/eslint-scope-7.2.2.tgz",
+            "integrity": "sha512-dOt21O7lTMhDM+X9mB4GX+DZrZtCUJPL/wlcTqxyrx5IvO0IYtILdtrQGQp+8n5S0gwSVmOf9NQrjMOgfQZlIg==",
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@@ -12477,12 +13490,39 @@
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             "dev": true
         },
+        "graphemer": {
+            "version": "1.4.0",
+            "resolved": "https://registry.npmjs.org/graphemer/-/graphemer-1.4.0.tgz",
+            "integrity": "sha512-EtKwoO6kxCL9WO5xipiHTZlSzBm7WLT627TqC/uVRd0HKmq8NXyebnNYxDoBi7wt8eTWrUrKXCOVaFq9x1kgag==",
+            "dev": true
+        },
         "growly": {
             "version": "1.3.0",
             "resolved": "https://registry.npmjs.org/growly/-/growly-1.3.0.tgz",
             "integrity": "sha512-+xGQY0YyAWCnqy7Cd++hc2JqMYzlm0dG30Jd0beaA64sROr8C4nt8Yc9V5Ro3avlSUDTN0ulqP/VBKi1/lLygw==",
             "dev": true
         },
+        "handlebars": {
+            "version": "4.7.8",
+            "resolved": "https://registry.npmjs.org/handlebars/-/handlebars-4.7.8.tgz",
+            "integrity": "sha512-vafaFqs8MZkRrSX7sFVUdo3ap/eNiLnb4IakshzvP56X5Nr1iGKAIqdX6tMlm6HcNRIkr6AxO5jFEoJzzpT8aQ==",
+            "dev": true,
+            "requires": {
+                "minimist": "^1.2.5",
+                "neo-async": "^2.6.2",
+                "source-map": "^0.6.1",
+                "uglify-js": "^3.1.4",
+                "wordwrap": "^1.0.0"
+            },
+            "dependencies": {
+                "source-map": {
+                    "version": "0.6.1",
+                    "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
+                    "integrity": "sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==",
+                    "dev": true
+                }
+            }
+        },
         "har-schema": {
             "version": "2.0.0",
             "resolved": "https://registry.npmjs.org/har-schema/-/har-schema-2.0.0.tgz",
@@ -12783,9 +13823,9 @@
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         "ignore": {
-            "version": "5.2.0",
-            "resolved": "https://registry.npmjs.org/ignore/-/ignore-5.2.0.tgz",
-            "integrity": "sha512-CmxgYGiEPCLhfLnpPp1MoRmifwEIOgjcHXxOBjv7mY96c+eWScsOP9c112ZyLdWHi0FxHjI+4uVhKYp/gcdRmQ==",
+            "version": "5.2.4",
+            "resolved": "https://registry.npmjs.org/ignore/-/ignore-5.2.4.tgz",
+            "integrity": "sha512-MAb38BcSbH0eHNBxn7ql2NH/kX33OkB3lZ1BNdh7ENeRChHTYsTvWrMubiIAMNS2llXEEgZ1MUOBtXChP3kaFQ==",
             "dev": true
         },
         "image-size": {
@@ -12947,6 +13987,15 @@
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             "dev": true
         },
+        "is-builtin-module": {
+            "version": "3.2.1",
+            "resolved": "https://registry.npmjs.org/is-builtin-module/-/is-builtin-module-3.2.1.tgz",
+            "integrity": "sha512-BSLE3HnV2syZ0FK0iMA/yUGplUeMmNz4AW5fnTunbCIqZi4vG3WjJT9FHMy5D69xmAYBHXQhJdALdpwVxV501A==",
+            "dev": true,
+            "requires": {
+                "builtin-modules": "^3.3.0"
+            }
+        },
         "is-callable": {
             "version": "1.2.4",
             "resolved": "https://registry.npmjs.org/is-callable/-/is-callable-1.2.4.tgz",
@@ -13245,9 +14294,9 @@
             "dev": true
         },
         "jsdoc-type-pratt-parser": {
-            "version": "3.1.0",
-            "resolved": "https://registry.npmjs.org/jsdoc-type-pratt-parser/-/jsdoc-type-pratt-parser-3.1.0.tgz",
-            "integrity": "sha512-MgtD0ZiCDk9B+eI73BextfRrVQl0oyzRG8B2BjORts6jbunj4ScKPcyXGTbB6eXL4y9TzxCm6hyeLq/2ASzNdw==",
+            "version": "4.0.0",
+            "resolved": "https://registry.npmjs.org/jsdoc-type-pratt-parser/-/jsdoc-type-pratt-parser-4.0.0.tgz",
+            "integrity": "sha512-YtOli5Cmzy3q4dP26GraSOeAhqecewG04hoO8DY56CH4KJ9Fvv5qKWUCCo3HZob7esJQHCv6/+bnTy72xZZaVQ==",
             "dev": true
         },
         "jsdom": {
@@ -13400,15 +14449,15 @@
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         },
         "jszip": {
-            "version": "3.8.0",
-            "resolved": "https://registry.npmjs.org/jszip/-/jszip-3.8.0.tgz",
-            "integrity": "sha512-cnpQrXvFSLdsR9KR5/x7zdf6c3m8IhZfZzSblFEHSqBaVwD2nvJ4CuCKLyvKvwBgZm08CgfSoiTBQLm5WW9hGw==",
+            "version": "3.10.1",
+            "resolved": "https://registry.npmjs.org/jszip/-/jszip-3.10.1.tgz",
+            "integrity": "sha512-xXDvecyTpGLrqFrvkrUSoxxfJI5AH7U8zxxtVclpsUtMCq4JQ290LY8AW5c7Ggnr/Y/oK+bQMbqK2qmtk3pN4g==",
             "dev": true,
             "requires": {
                 "lie": "~3.3.0",
                 "pako": "~1.0.2",
                 "readable-stream": "~2.3.6",
-                "set-immediate-shim": "~1.0.1"
+                "setimmediate": "^1.0.5"
             }
         },
         "jwa": {
@@ -13940,6 +14989,12 @@
             "dev": true,
             "optional": true
         },
+        "neo-async": {
+            "version": "2.6.2",
+            "resolved": "https://registry.npmjs.org/neo-async/-/neo-async-2.6.2.tgz",
+            "integrity": "sha512-Yd3UES5mWCSqR+qNT93S3UoYUkqAZ9lLg8a7g9rimsWmYGK8cVToA4/sF3RrshdyV3sAGMXVUmpMYOw+dLpOuw==",
+            "dev": true
+        },
         "node-domexception": {
             "version": "1.0.0",
             "resolved": "https://registry.npmjs.org/node-domexception/-/node-domexception-1.0.0.tgz",
@@ -14097,17 +15152,17 @@
             }
         },
         "optionator": {
-            "version": "0.9.1",
-            "resolved": "https://registry.npmjs.org/optionator/-/optionator-0.9.1.tgz",
-            "integrity": "sha512-74RlY5FCnhq4jRxVUPKDaRwrVNXMqsGsiW6AJw4XK8hmtm10wC0ypZBLw5IIp85NZMr91+qd1RvvENwg7jjRFw==",
+            "version": "0.9.3",
+            "resolved": "https://registry.npmjs.org/optionator/-/optionator-0.9.3.tgz",
+            "integrity": "sha512-JjCoypp+jKn1ttEFExxhetCKeJt9zhAgAve5FXHixTvFDW/5aEktX9bufBKLRRMdU7bNtpLfcGu94B3cdEJgjg==",
             "dev": true,
             "requires": {
+                "@aashutoshrathi/word-wrap": "^1.2.3",
                 "deep-is": "^0.1.3",
                 "fast-levenshtein": "^2.0.6",
                 "levn": "^0.4.1",
                 "prelude-ls": "^1.2.1",
-                "type-check": "^0.4.0",
-                "word-wrap": "^1.2.3"
+                "type-check": "^0.4.0"
             }
         },
         "os-browserify": {
@@ -15114,10 +16169,10 @@
                 "semver": "^7.3.5"
             }
         },
-        "set-immediate-shim": {
-            "version": "1.0.1",
-            "resolved": "https://registry.npmjs.org/set-immediate-shim/-/set-immediate-shim-1.0.1.tgz",
-            "integrity": "sha1-SysbJ+uAip+NzEgaWOXlb1mfP2E=",
+        "setimmediate": {
+            "version": "1.0.5",
+            "resolved": "https://registry.npmjs.org/setimmediate/-/setimmediate-1.0.5.tgz",
+            "integrity": "sha512-MATJdZp8sLqDl/68LfQmbP8zKPLQNV6BIZoIgrscFDQ+RsvK/BxeDQOgyxKKoh0y/8h3BqVFnCqQ/gd+reiIXA==",
             "dev": true
         },
         "sha.js": {
@@ -15802,6 +16857,13 @@
             "integrity": "sha512-c1PTsA3tYrIsLGkJkzHF+w9F2EyxfXGo4UyJc4pFL++FMjnq0HJS69T3M7d//gKrFKwy429bouPescbjecU+Zw==",
             "dev": true
         },
+        "ts-api-utils": {
+            "version": "1.0.3",
+            "resolved": "https://registry.npmjs.org/ts-api-utils/-/ts-api-utils-1.0.3.tgz",
+            "integrity": "sha512-wNMeqtMz5NtwpT/UZGY5alT+VoKdSsOOP/kqHFcUW1P/VRhH2wJ48+DN2WwUliNbQ976ETwDL0Ifd2VVvgonvg==",
+            "dev": true,
+            "requires": {}
+        },
         "tty-browserify": {
             "version": "0.0.1",
             "resolved": "https://registry.npmjs.org/tty-browserify/-/tty-browserify-0.0.1.tgz",
@@ -15859,6 +16921,12 @@
                 "is-typedarray": "^1.0.0"
             }
         },
+        "typescript": {
+            "version": "5.2.2",
+            "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.2.2.tgz",
+            "integrity": "sha512-mI4WrpHsbCIcwT9cF4FZvr80QUeKvsUsUvKDoR+X/7XHQH98xYD8YHZg7ANtz2GtZt/CBq2QJ0thkGJMHfqc1w==",
+            "dev": true
+        },
         "typeson": {
             "version": "6.1.0",
             "resolved": "https://registry.npmjs.org/typeson/-/typeson-6.1.0.tgz",
@@ -15910,6 +16978,13 @@
                 }
             }
         },
+        "uglify-js": {
+            "version": "3.17.4",
+            "resolved": "https://registry.npmjs.org/uglify-js/-/uglify-js-3.17.4.tgz",
+            "integrity": "sha512-T9q82TJI9e/C1TAxYvfb16xO120tMVFZrGA3f9/P4424DNu6ypK103y0GPFVa17yotwSyZW5iYXgjYHkGrJW/g==",
+            "dev": true,
+            "optional": true
+        },
         "umd": {
             "version": "3.0.3",
             "resolved": "https://registry.npmjs.org/umd/-/umd-3.0.3.tgz",
@@ -15941,6 +17016,12 @@
                 "xtend": "^4.0.1"
             }
         },
+        "undici-types": {
+            "version": "5.26.5",
+            "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-5.26.5.tgz",
+            "integrity": "sha512-JlCMO+ehdEIKqlFxk6IfVoAUVmgz7cU7zD/h9XZ0qzeosSHmUJVOzSQvvYSYWXkFXC+IfLKSIffhv0sVZup6pA==",
+            "dev": true
+        },
         "unique-string": {
             "version": "3.0.0",
             "resolved": "https://registry.npmjs.org/unique-string/-/unique-string-3.0.0.tgz",
@@ -16355,6 +17436,12 @@
             "integrity": "sha512-Hz/mrNwitNRh/HUAtM/VT/5VH+ygD6DV7mYKZAtHOrbs8U7lvPS6xf7EJKMF0uW1KJCl0H701g3ZGus+muE5vQ==",
             "dev": true
         },
+        "wordwrap": {
+            "version": "1.0.0",
+            "resolved": "https://registry.npmjs.org/wordwrap/-/wordwrap-1.0.0.tgz",
+            "integrity": "sha512-gvVzJFlPycKc5dZN4yPkP8w7Dc37BtP1yczEneOb4uq34pXZcvrtRTmWV8W+Ume+XCxKgbjM+nevkyFPMybd4Q==",
+            "dev": true
+        },
         "wrap-ansi": {
             "version": "8.0.1",
             "resolved": "https://registry.npmjs.org/wrap-ansi/-/wrap-ansi-8.0.1.tgz",
diff --git a/package.json b/package.json
index 22aa9f45d7..ac4f2512f2 100644
--- a/package.json
+++ b/package.json
@@ -8,11 +8,14 @@
     "scripts": {
         "postinstall": "node ./dev/patch-dependencies.js",
         "build": "node ./dev/build.js",
-        "test": "npm run test-lint && npm run test-lint-css && npm run test-lint-html && npm run test-code && npm run test-manifest && npm run test-build",
+        "test": "npm run test-lint && npm run test-ts && npm run test-ts-dev && npm run test-ts-test && npm run test-lint-css && npm run test-lint-html && npm run test-code && npm run test-manifest && npm run test-build",
         "test-lint": "npx eslint . && node ./dev/lint/global-declarations.js && node ./dev/lint/html-scripts.js",
         "test-lint-css": "npx stylelint \"ext/**/*.css\" \"test/**/*.css\" \"dev/**/*.css\"",
         "test-lint-html": "npx html-validate \"ext/**/*.html\" \"test/**/*.html\" \"dev/**/*.html\"",
         "test-lint-web-ext": "npx web-ext lint",
+        "test-ts": "npx tsc --noEmit --project jsconfig.json",
+        "test-ts-dev": "npx tsc --noEmit --project dev/jsconfig.json",
+        "test-ts-test": "npx tsc --noEmit --project test/jsconfig.json",
         "test-code": "node ./test/test-all.js ./test --skip ./test/test-manifest.js",
         "test-manifest": "node ./test/test-manifest.js",
         "test-build": "node ./dev/build.js --dry-run --all"
@@ -37,20 +40,36 @@
     },
     "devDependencies": {
         "@playwright/test": "^1.31.2",
+        "@stylistic/eslint-plugin-ts": "^1.4.1",
+        "@types/assert": "^1.5.10",
+        "@types/browserify": "^12.0.40",
+        "@types/chrome": "^0.0.253",
+        "@types/css": "^0.0.37",
+        "@types/events": "^3.0.3",
+        "@types/firefox-webext-browser": "^120.0.0",
+        "@types/handlebars": "^4.1.0",
+        "@types/jsdom": "^21.1.6",
+        "@types/node": "^20.10.0",
+        "@types/wanakana": "^4.0.6",
+        "@typescript-eslint/eslint-plugin": "^6.12.0",
+        "@typescript-eslint/parser": "^6.12.0",
         "ajv": "^8.11.0",
         "browserify": "^17.0.0",
         "css": "^3.0.0",
-        "eslint": "^8.37.0",
+        "eslint": "^8.54.0",
         "eslint-plugin-header": "^3.1.1",
-        "eslint-plugin-jsdoc": "^39.3.6",
-        "eslint-plugin-jsonc": "^2.8.0",
-        "eslint-plugin-no-unsanitized": "^4.0.1",
+        "eslint-plugin-jsdoc": "^46.9.0",
+        "eslint-plugin-jsonc": "^2.10.0",
+        "eslint-plugin-no-unsanitized": "^4.0.2",
+        "eslint-plugin-unused-imports": "^3.0.0",
         "fake-indexeddb": "^4.0.0",
         "html-validate": "^7.6.0",
         "jsdom": "^20.0.1",
+        "jszip": "^3.10.1",
         "parse5": "^7.1.2",
         "stylelint": "^14.14.0",
         "stylelint-config-recommended": "^9.0.0",
+        "typescript": "^5.2.2",
         "web-ext": "^7.6.0"
     }
 }
diff --git a/test/data/anki-note-builder-test-results.json b/test/data/anki-note-builder-test-results.json
index b752e8788a..49542e39db 100644
--- a/test/data/anki-note-builder-test-results.json
+++ b/test/data/anki-note-builder-test-results.json
@@ -194,7 +194,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 22</li><li>Test Dictionary 2: 28</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: sixteen</li><li>Test Dictionary 2: twenty-two (22)</li><li>Test Dictionary 2: 28</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>つ",
         "furigana-plain": "打[う]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>utsu definition 3</li><li>utsu definition 4</li></ul></div>",
@@ -224,7 +224,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 23</li><li>Test Dictionary 2: 29</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: seventeen</li><li>Test Dictionary 2: twenty-three (23)</li><li>Test Dictionary 2: twenty-nine</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>つ",
         "furigana-plain": "打[ぶ]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>butsu definition 3</li><li>butsu definition 4</li></ul></div>",
@@ -379,7 +379,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 24</li><li>Test Dictionary 2: 30</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: eighteen</li><li>Test Dictionary 2: twenty-four (24)</li><li>Test Dictionary 2: 30</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[う]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>uchikomu definition 3</li><li>uchikomu definition 4</li></ul></div>",
@@ -409,7 +409,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 25</li><li>Test Dictionary 2: 31</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: nineteen</li><li>Test Dictionary 2: twenty-five (25)</li><li>Test Dictionary 2: thirty-one</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[ぶ]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>buchikomu definition 3</li><li>buchikomu definition 4</li></ul></div>",
@@ -499,7 +499,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 22</li><li>Test Dictionary 2: 28</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: sixteen</li><li>Test Dictionary 2: twenty-two (22)</li><li>Test Dictionary 2: 28</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>つ",
         "furigana-plain": "打[う]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>utsu definition 3</li><li>utsu definition 4</li></ul></div>",
@@ -529,7 +529,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 23</li><li>Test Dictionary 2: 29</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: seventeen</li><li>Test Dictionary 2: twenty-three (23)</li><li>Test Dictionary 2: twenty-nine</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>つ",
         "furigana-plain": "打[ぶ]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>butsu definition 3</li><li>butsu definition 4</li></ul></div>",
@@ -759,7 +759,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 22</li><li>Test Dictionary 2: 28</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: sixteen</li><li>Test Dictionary 2: twenty-two (22)</li><li>Test Dictionary 2: 28</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>つ",
         "furigana-plain": "打[う]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>utsu definition 3</li><li>utsu definition 4</li></ul></div>",
@@ -824,7 +824,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 23</li><li>Test Dictionary 2: 29</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: seventeen</li><li>Test Dictionary 2: twenty-three (23)</li><li>Test Dictionary 2: twenty-nine</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>つ",
         "furigana-plain": "打[ぶ]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>butsu definition 3</li><li>butsu definition 4</li></ul></div>",
@@ -889,7 +889,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 24</li><li>Test Dictionary 2: 30</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: eighteen</li><li>Test Dictionary 2: twenty-four (24)</li><li>Test Dictionary 2: 30</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[う]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>uchikomu definition 3</li><li>uchikomu definition 4</li></ul></div>",
@@ -949,7 +949,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 22</li><li>Test Dictionary 2: 28</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: sixteen</li><li>Test Dictionary 2: twenty-two (22)</li><li>Test Dictionary 2: 28</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>つ",
         "furigana-plain": "打[う]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>utsu definition 3</li><li>utsu definition 4</li></ul></div>",
@@ -1014,7 +1014,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 25</li><li>Test Dictionary 2: 31</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: nineteen</li><li>Test Dictionary 2: twenty-five (25)</li><li>Test Dictionary 2: thirty-one</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[ぶ]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>buchikomu definition 3</li><li>buchikomu definition 4</li></ul></div>",
@@ -1074,7 +1074,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 23</li><li>Test Dictionary 2: 29</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: seventeen</li><li>Test Dictionary 2: twenty-three (23)</li><li>Test Dictionary 2: twenty-nine</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>つ",
         "furigana-plain": "打[ぶ]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>butsu definition 3</li><li>butsu definition 4</li></ul></div>",
@@ -1526,7 +1526,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 24</li><li>Test Dictionary 2: 30</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: eighteen</li><li>Test Dictionary 2: twenty-four (24)</li><li>Test Dictionary 2: 30</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[う]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>uchikomu definition 3</li><li>uchikomu definition 4</li></ul></div>",
@@ -1556,7 +1556,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 25</li><li>Test Dictionary 2: 31</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: nineteen</li><li>Test Dictionary 2: twenty-five (25)</li><li>Test Dictionary 2: thirty-one</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[ぶ]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>buchikomu definition 3</li><li>buchikomu definition 4</li></ul></div>",
@@ -1646,7 +1646,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 22</li><li>Test Dictionary 2: 28</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: sixteen</li><li>Test Dictionary 2: twenty-two (22)</li><li>Test Dictionary 2: 28</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>つ",
         "furigana-plain": "打[う]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>utsu definition 3</li><li>utsu definition 4</li></ul></div>",
@@ -1676,7 +1676,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 23</li><li>Test Dictionary 2: 29</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: seventeen</li><li>Test Dictionary 2: twenty-three (23)</li><li>Test Dictionary 2: twenty-nine</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>つ",
         "furigana-plain": "打[ぶ]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>butsu definition 3</li><li>butsu definition 4</li></ul></div>",
@@ -1831,7 +1831,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 24</li><li>Test Dictionary 2: 30</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: eighteen</li><li>Test Dictionary 2: twenty-four (24)</li><li>Test Dictionary 2: 30</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[う]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>uchikomu definition 3</li><li>uchikomu definition 4</li></ul></div>",
@@ -1861,7 +1861,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 25</li><li>Test Dictionary 2: 31</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: nineteen</li><li>Test Dictionary 2: twenty-five (25)</li><li>Test Dictionary 2: thirty-one</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[ぶ]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>buchikomu definition 3</li><li>buchikomu definition 4</li></ul></div>",
@@ -1951,7 +1951,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 22</li><li>Test Dictionary 2: 28</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: sixteen</li><li>Test Dictionary 2: twenty-two (22)</li><li>Test Dictionary 2: 28</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>つ",
         "furigana-plain": "打[う]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>utsu definition 3</li><li>utsu definition 4</li></ul></div>",
@@ -1981,7 +1981,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 23</li><li>Test Dictionary 2: 29</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: seventeen</li><li>Test Dictionary 2: twenty-three (23)</li><li>Test Dictionary 2: twenty-nine</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>つ",
         "furigana-plain": "打[ぶ]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>butsu definition 3</li><li>butsu definition 4</li></ul></div>",
@@ -2136,7 +2136,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 24</li><li>Test Dictionary 2: 30</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 12</li><li>Test Dictionary 2: eighteen</li><li>Test Dictionary 2: twenty-four (24)</li><li>Test Dictionary 2: 30</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[う]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>uchikomu definition 3</li><li>uchikomu definition 4</li></ul></div>",
@@ -2166,7 +2166,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打ち込む",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: 7</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 25</li><li>Test Dictionary 2: 31</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 3</li><li>Test Dictionary 2: seven</li><li>Test Dictionary 2: 13</li><li>Test Dictionary 2: nineteen</li><li>Test Dictionary 2: twenty-five (25)</li><li>Test Dictionary 2: thirty-one</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>ち<ruby>込<rt>こ</rt></ruby>む",
         "furigana-plain": "打[ぶ]ち 込[こ]む",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>buchikomu definition 3</li><li>buchikomu definition 4</li></ul></div>",
@@ -2256,7 +2256,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 22</li><li>Test Dictionary 2: 28</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 10</li><li>Test Dictionary 2: sixteen</li><li>Test Dictionary 2: twenty-two (22)</li><li>Test Dictionary 2: 28</li></ul>",
         "furigana": "<ruby>打<rt>う</rt></ruby>つ",
         "furigana-plain": "打[う]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>utsu definition 3</li><li>utsu definition 4</li></ul></div>",
@@ -2286,7 +2286,7 @@
         "dictionary": "Test Dictionary 2",
         "document-title": "title",
         "expression": "打つ",
-        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: 0</li><li>Test Dictionary 2: 23</li><li>Test Dictionary 2: 29</li></ul>",
+        "frequencies": "<ul style=\"text-align: left;\"><li>Test Dictionary 2: 2</li><li>Test Dictionary 2: 6</li><li>Test Dictionary 2: 11</li><li>Test Dictionary 2: seventeen</li><li>Test Dictionary 2: twenty-three (23)</li><li>Test Dictionary 2: twenty-nine</li></ul>",
         "furigana": "<ruby>打<rt>ぶ</rt></ruby>つ",
         "furigana-plain": "打[ぶ]つ",
         "glossary": "<div style=\"text-align: left;\"><i>(vt, Test Dictionary 2)</i> <ul><li>butsu definition 3</li><li>butsu definition 4</li></ul></div>",
diff --git a/test/data/html/test-document2-script.js b/test/data/html/test-document2-script.js
index 8a1830193d..5a6ad4d19c 100644
--- a/test/data/html/test-document2-script.js
+++ b/test/data/html/test-document2-script.js
@@ -16,40 +16,65 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/**
+ * @param {Element} element
+ */
 function requestFullscreen(element) {
     if (element.requestFullscreen) {
         element.requestFullscreen();
+        // @ts-ignore - Browser compatibility
     } else if (element.mozRequestFullScreen) {
+        // @ts-ignore - Browser compatibility
         element.mozRequestFullScreen();
+        // @ts-ignore - Browser compatibility
     } else if (element.webkitRequestFullscreen) {
+        // @ts-ignore - Browser compatibility
         element.webkitRequestFullscreen();
+        // @ts-ignore - Browser compatibility
     } else if (element.msRequestFullscreen) {
+        // @ts-ignore - Browser compatibility
         element.msRequestFullscreen();
     }
 }
 
+/** */
 function exitFullscreen() {
     if (document.exitFullscreen) {
         document.exitFullscreen();
+        // @ts-ignore - Browser compatibility
     } else if (document.mozCancelFullScreen) {
+        // @ts-ignore - Browser compatibility
         document.mozCancelFullScreen();
+        // @ts-ignore - Browser compatibility
     } else if (document.webkitExitFullscreen) {
+        // @ts-ignore - Browser compatibility
         document.webkitExitFullscreen();
+        // @ts-ignore - Browser compatibility
     } else if (document.msExitFullscreen) {
+        // @ts-ignore - Browser compatibility
         document.msExitFullscreen();
     }
 }
 
+/**
+ * @returns {?Element}
+ */
 function getFullscreenElement() {
     return (
         document.fullscreenElement ||
+        // @ts-ignore - Browser compatibility
         document.msFullscreenElement ||
+        // @ts-ignore - Browser compatibility
         document.mozFullScreenElement ||
+        // @ts-ignore - Browser compatibility
         document.webkitFullscreenElement ||
         null
     );
 }
 
+/**
+ * @param {Element} element
+ */
 function toggleFullscreen(element) {
     if (getFullscreenElement()) {
         exitFullscreen();
@@ -58,6 +83,10 @@ function toggleFullscreen(element) {
     }
 }
 
+/**
+ * @param {HTMLElement|DocumentFragment} container
+ * @param {?Element} [fullscreenElement]
+ */
 function setup(container, fullscreenElement=null) {
     const fullscreenLink = container.querySelector('.fullscreen-link');
     if (fullscreenLink !== null) {
@@ -65,6 +94,7 @@ function setup(container, fullscreenElement=null) {
             fullscreenElement = container.querySelector('.fullscreen-element');
         }
         fullscreenLink.addEventListener('click', (e) => {
+            if (fullscreenElement === null) { return; }
             toggleFullscreen(fullscreenElement);
             e.preventDefault();
             return false;
@@ -74,11 +104,15 @@ function setup(container, fullscreenElement=null) {
     const template = container.querySelector('template');
     const templateContentContainer = container.querySelector('.template-content-container');
     if (template !== null && templateContentContainer !== null) {
-        const mode = container.dataset.shadowMode;
-        const shadow = templateContentContainer.attachShadow({mode});
+        const mode = (container instanceof HTMLElement ? container.dataset.shadowMode : void 0);
+        const shadow = templateContentContainer.attachShadow({
+            mode: (mode === 'open' || mode === 'closed' ? mode : 'open')
+        });
 
         const containerStyles = document.querySelector('#container-styles');
-        shadow.appendChild(containerStyles.cloneNode(true));
+        if (containerStyles !== null) {
+            shadow.appendChild(containerStyles.cloneNode(true));
+        }
 
         const content = document.importNode(template.content, true);
         setup(content);
diff --git a/test/data/translator-test-results-note-data1.json b/test/data/translator-test-results-note-data1.json
index d686563c41..34f7c21ab5 100644
--- a/test/data/translator-test-results-note-data1.json
+++ b/test/data/translator-test-results-note-data1.json
@@ -1659,7 +1659,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "sixteen"
                 },
                 {
                   "index": 4,
@@ -1672,7 +1672,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 22
+                  "frequency": "twenty-two (22)"
                 },
                 {
                   "index": 5,
@@ -1791,7 +1791,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "sixteen"
             },
             {
               "index": 4,
@@ -1804,7 +1804,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 22
+              "frequency": "twenty-two (22)"
             },
             {
               "index": 5,
@@ -1963,7 +1963,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "seventeen"
                 },
                 {
                   "index": 4,
@@ -1976,7 +1976,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 23
+                  "frequency": "twenty-three (23)"
                 },
                 {
                   "index": 5,
@@ -1989,7 +1989,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 29
+                  "frequency": "twenty-nine"
                 }
               ],
               "pitches": [],
@@ -2095,7 +2095,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "seventeen"
             },
             {
               "index": 4,
@@ -2108,7 +2108,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 23
+              "frequency": "twenty-three (23)"
             },
             {
               "index": 5,
@@ -2121,7 +2121,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 29
+              "frequency": "twenty-nine"
             }
           ],
           "pitches": [],
@@ -3651,7 +3651,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -3677,7 +3677,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "eighteen"
                 },
                 {
                   "index": 4,
@@ -3690,7 +3690,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 24
+                  "frequency": "twenty-four (24)"
                 },
                 {
                   "index": 5,
@@ -3813,7 +3813,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -3839,7 +3839,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "eighteen"
             },
             {
               "index": 4,
@@ -3852,7 +3852,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 24
+              "frequency": "twenty-four (24)"
             },
             {
               "index": 5,
@@ -4045,7 +4045,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -4071,7 +4071,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "nineteen"
                 },
                 {
                   "index": 4,
@@ -4084,7 +4084,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 25
+                  "frequency": "twenty-five (25)"
                 },
                 {
                   "index": 5,
@@ -4097,7 +4097,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 31
+                  "frequency": "thirty-one"
                 }
               ],
               "pitches": [
@@ -4207,7 +4207,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -4233,7 +4233,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "nineteen"
             },
             {
               "index": 4,
@@ -4246,7 +4246,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 25
+              "frequency": "twenty-five (25)"
             },
             {
               "index": 5,
@@ -4259,7 +4259,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 31
+              "frequency": "thirty-one"
             }
           ],
           "pitches": [
@@ -5079,7 +5079,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "sixteen"
                 },
                 {
                   "index": 4,
@@ -5092,7 +5092,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 22
+                  "frequency": "twenty-two (22)"
                 },
                 {
                   "index": 5,
@@ -5211,7 +5211,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "sixteen"
             },
             {
               "index": 4,
@@ -5224,7 +5224,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 22
+              "frequency": "twenty-two (22)"
             },
             {
               "index": 5,
@@ -5385,7 +5385,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "seventeen"
                 },
                 {
                   "index": 4,
@@ -5398,7 +5398,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 23
+                  "frequency": "twenty-three (23)"
                 },
                 {
                   "index": 5,
@@ -5411,7 +5411,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 29
+                  "frequency": "twenty-nine"
                 }
               ],
               "pitches": [],
@@ -5517,7 +5517,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "seventeen"
             },
             {
               "index": 4,
@@ -5530,7 +5530,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 23
+              "frequency": "twenty-three (23)"
             },
             {
               "index": 5,
@@ -5543,7 +5543,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 29
+              "frequency": "twenty-nine"
             }
           ],
           "pitches": [],
@@ -7394,7 +7394,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "sixteen"
                 },
                 {
                   "index": 4,
@@ -7407,7 +7407,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 22
+                  "frequency": "twenty-two (22)"
                 },
                 {
                   "index": 5,
@@ -7526,7 +7526,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "sixteen"
             },
             {
               "index": 4,
@@ -7539,7 +7539,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 22
+              "frequency": "twenty-two (22)"
             },
             {
               "index": 5,
@@ -8007,7 +8007,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "seventeen"
                 },
                 {
                   "index": 4,
@@ -8020,7 +8020,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 23
+                  "frequency": "twenty-three (23)"
                 },
                 {
                   "index": 5,
@@ -8033,7 +8033,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 29
+                  "frequency": "twenty-nine"
                 }
               ],
               "pitches": [],
@@ -8139,7 +8139,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "seventeen"
             },
             {
               "index": 4,
@@ -8152,7 +8152,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 23
+              "frequency": "twenty-three (23)"
             },
             {
               "index": 5,
@@ -8165,7 +8165,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 29
+              "frequency": "twenty-nine"
             }
           ],
           "pitches": [],
@@ -8684,7 +8684,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -8710,7 +8710,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "eighteen"
                 },
                 {
                   "index": 4,
@@ -8723,7 +8723,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 24
+                  "frequency": "twenty-four (24)"
                 },
                 {
                   "index": 5,
@@ -8846,7 +8846,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -8872,7 +8872,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "eighteen"
             },
             {
               "index": 4,
@@ -8885,7 +8885,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 24
+              "frequency": "twenty-four (24)"
             },
             {
               "index": 5,
@@ -9412,7 +9412,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "sixteen"
                 },
                 {
                   "index": 4,
@@ -9425,7 +9425,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 22
+                  "frequency": "twenty-two (22)"
                 },
                 {
                   "index": 5,
@@ -9544,7 +9544,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "sixteen"
             },
             {
               "index": 4,
@@ -9557,7 +9557,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 22
+              "frequency": "twenty-two (22)"
             },
             {
               "index": 5,
@@ -10089,7 +10089,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -10115,7 +10115,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "nineteen"
                 },
                 {
                   "index": 4,
@@ -10128,7 +10128,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 25
+                  "frequency": "twenty-five (25)"
                 },
                 {
                   "index": 5,
@@ -10141,7 +10141,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 31
+                  "frequency": "thirty-one"
                 }
               ],
               "pitches": [
@@ -10251,7 +10251,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -10277,7 +10277,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "nineteen"
             },
             {
               "index": 4,
@@ -10290,7 +10290,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 25
+              "frequency": "twenty-five (25)"
             },
             {
               "index": 5,
@@ -10303,7 +10303,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 31
+              "frequency": "thirty-one"
             }
           ],
           "pitches": [
@@ -10817,7 +10817,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "seventeen"
                 },
                 {
                   "index": 4,
@@ -10830,7 +10830,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 23
+                  "frequency": "twenty-three (23)"
                 },
                 {
                   "index": 5,
@@ -10843,7 +10843,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 29
+                  "frequency": "twenty-nine"
                 }
               ],
               "pitches": [],
@@ -10949,7 +10949,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "seventeen"
             },
             {
               "index": 4,
@@ -10962,7 +10962,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 23
+              "frequency": "twenty-three (23)"
             },
             {
               "index": 5,
@@ -10975,7 +10975,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 29
+              "frequency": "twenty-nine"
             }
           ],
           "pitches": [],
@@ -16097,7 +16097,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -16123,7 +16123,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "eighteen"
                 },
                 {
                   "index": 4,
@@ -16136,7 +16136,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 24
+                  "frequency": "twenty-four (24)"
                 },
                 {
                   "index": 5,
@@ -16259,7 +16259,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -16285,7 +16285,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "eighteen"
             },
             {
               "index": 4,
@@ -16298,7 +16298,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 24
+              "frequency": "twenty-four (24)"
             },
             {
               "index": 5,
@@ -16495,7 +16495,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -16521,7 +16521,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "nineteen"
                 },
                 {
                   "index": 4,
@@ -16534,7 +16534,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 25
+                  "frequency": "twenty-five (25)"
                 },
                 {
                   "index": 5,
@@ -16547,7 +16547,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 31
+                  "frequency": "thirty-one"
                 }
               ],
               "pitches": [
@@ -16657,7 +16657,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -16683,7 +16683,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "nineteen"
             },
             {
               "index": 4,
@@ -16696,7 +16696,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 25
+              "frequency": "twenty-five (25)"
             },
             {
               "index": 5,
@@ -16709,7 +16709,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 31
+              "frequency": "thirty-one"
             }
           ],
           "pitches": [
@@ -17529,7 +17529,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "sixteen"
                 },
                 {
                   "index": 4,
@@ -17542,7 +17542,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 22
+                  "frequency": "twenty-two (22)"
                 },
                 {
                   "index": 5,
@@ -17661,7 +17661,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "sixteen"
             },
             {
               "index": 4,
@@ -17674,7 +17674,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 22
+              "frequency": "twenty-two (22)"
             },
             {
               "index": 5,
@@ -17835,7 +17835,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "seventeen"
                 },
                 {
                   "index": 4,
@@ -17848,7 +17848,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 23
+                  "frequency": "twenty-three (23)"
                 },
                 {
                   "index": 5,
@@ -17861,7 +17861,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 29
+                  "frequency": "twenty-nine"
                 }
               ],
               "pitches": [],
@@ -17967,7 +17967,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "seventeen"
             },
             {
               "index": 4,
@@ -17980,7 +17980,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 23
+              "frequency": "twenty-three (23)"
             },
             {
               "index": 5,
@@ -17993,7 +17993,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 29
+              "frequency": "twenty-nine"
             }
           ],
           "pitches": [],
@@ -19523,7 +19523,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -19549,7 +19549,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "eighteen"
                 },
                 {
                   "index": 4,
@@ -19562,7 +19562,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 24
+                  "frequency": "twenty-four (24)"
                 },
                 {
                   "index": 5,
@@ -19685,7 +19685,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -19711,7 +19711,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "eighteen"
             },
             {
               "index": 4,
@@ -19724,7 +19724,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 24
+              "frequency": "twenty-four (24)"
             },
             {
               "index": 5,
@@ -19917,7 +19917,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -19943,7 +19943,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "nineteen"
                 },
                 {
                   "index": 4,
@@ -19956,7 +19956,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 25
+                  "frequency": "twenty-five (25)"
                 },
                 {
                   "index": 5,
@@ -19969,7 +19969,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 31
+                  "frequency": "thirty-one"
                 }
               ],
               "pitches": [
@@ -20079,7 +20079,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -20105,7 +20105,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "nineteen"
             },
             {
               "index": 4,
@@ -20118,7 +20118,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 25
+              "frequency": "twenty-five (25)"
             },
             {
               "index": 5,
@@ -20131,7 +20131,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 31
+              "frequency": "thirty-one"
             }
           ],
           "pitches": [
@@ -20951,7 +20951,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "sixteen"
                 },
                 {
                   "index": 4,
@@ -20964,7 +20964,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 22
+                  "frequency": "twenty-two (22)"
                 },
                 {
                   "index": 5,
@@ -21083,7 +21083,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "sixteen"
             },
             {
               "index": 4,
@@ -21096,7 +21096,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 22
+              "frequency": "twenty-two (22)"
             },
             {
               "index": 5,
@@ -21257,7 +21257,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "seventeen"
                 },
                 {
                   "index": 4,
@@ -21270,7 +21270,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 23
+                  "frequency": "twenty-three (23)"
                 },
                 {
                   "index": 5,
@@ -21283,7 +21283,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 29
+                  "frequency": "twenty-nine"
                 }
               ],
               "pitches": [],
@@ -21389,7 +21389,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "seventeen"
             },
             {
               "index": 4,
@@ -21402,7 +21402,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 23
+              "frequency": "twenty-three (23)"
             },
             {
               "index": 5,
@@ -21415,7 +21415,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 29
+              "frequency": "twenty-nine"
             }
           ],
           "pitches": [],
@@ -22945,7 +22945,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -22971,7 +22971,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "eighteen"
                 },
                 {
                   "index": 4,
@@ -22984,7 +22984,7 @@
                   "expression": "打ち込む",
                   "reading": "うちこむ",
                   "hasReading": true,
-                  "frequency": 24
+                  "frequency": "twenty-four (24)"
                 },
                 {
                   "index": 5,
@@ -23107,7 +23107,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -23133,7 +23133,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "eighteen"
             },
             {
               "index": 4,
@@ -23146,7 +23146,7 @@
               "expression": "打ち込む",
               "reading": "うちこむ",
               "hasReading": true,
-              "frequency": 24
+              "frequency": "twenty-four (24)"
             },
             {
               "index": 5,
@@ -23339,7 +23339,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": false,
-                  "frequency": 7
+                  "frequency": "seven"
                 },
                 {
                   "index": 2,
@@ -23365,7 +23365,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "nineteen"
                 },
                 {
                   "index": 4,
@@ -23378,7 +23378,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 25
+                  "frequency": "twenty-five (25)"
                 },
                 {
                   "index": 5,
@@ -23391,7 +23391,7 @@
                   "expression": "打ち込む",
                   "reading": "ぶちこむ",
                   "hasReading": true,
-                  "frequency": 31
+                  "frequency": "thirty-one"
                 }
               ],
               "pitches": [
@@ -23501,7 +23501,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": false,
-              "frequency": 7
+              "frequency": "seven"
             },
             {
               "index": 2,
@@ -23527,7 +23527,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "nineteen"
             },
             {
               "index": 4,
@@ -23540,7 +23540,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 25
+              "frequency": "twenty-five (25)"
             },
             {
               "index": 5,
@@ -23553,7 +23553,7 @@
               "expression": "打ち込む",
               "reading": "ぶちこむ",
               "hasReading": true,
-              "frequency": 31
+              "frequency": "thirty-one"
             }
           ],
           "pitches": [
@@ -24373,7 +24373,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "sixteen"
                 },
                 {
                   "index": 4,
@@ -24386,7 +24386,7 @@
                   "expression": "打つ",
                   "reading": "うつ",
                   "hasReading": true,
-                  "frequency": 22
+                  "frequency": "twenty-two (22)"
                 },
                 {
                   "index": 5,
@@ -24505,7 +24505,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "sixteen"
             },
             {
               "index": 4,
@@ -24518,7 +24518,7 @@
               "expression": "打つ",
               "reading": "うつ",
               "hasReading": true,
-              "frequency": 22
+              "frequency": "twenty-two (22)"
             },
             {
               "index": 5,
@@ -24679,7 +24679,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 0
+                  "frequency": "seventeen"
                 },
                 {
                   "index": 4,
@@ -24692,7 +24692,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 23
+                  "frequency": "twenty-three (23)"
                 },
                 {
                   "index": 5,
@@ -24705,7 +24705,7 @@
                   "expression": "打つ",
                   "reading": "ぶつ",
                   "hasReading": true,
-                  "frequency": 29
+                  "frequency": "twenty-nine"
                 }
               ],
               "pitches": [],
@@ -24811,7 +24811,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 0
+              "frequency": "seventeen"
             },
             {
               "index": 4,
@@ -24824,7 +24824,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 23
+              "frequency": "twenty-three (23)"
             },
             {
               "index": 5,
@@ -24837,7 +24837,7 @@
               "expression": "打つ",
               "reading": "ぶつ",
               "hasReading": true,
-              "frequency": 29
+              "frequency": "twenty-nine"
             }
           ],
           "pitches": [],
diff --git a/test/data/translator-test-results.json b/test/data/translator-test-results.json
index 98db0ef428..0a7155b885 100644
--- a/test/data/translator-test-results.json
+++ b/test/data/translator-test-results.json
@@ -1101,8 +1101,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "sixteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -1112,8 +1112,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 22,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-two (22)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -1266,8 +1266,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "seventeen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -1277,8 +1277,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 23,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-three (23)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -1288,7 +1288,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 29,
-            "displayValue": null,
+            "displayValue": "twenty-nine",
             "displayValueParsed": false
           }
         ]
@@ -2150,7 +2150,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -2172,8 +2172,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "eighteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -2183,8 +2183,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 24,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-four (24)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -2337,7 +2337,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -2359,8 +2359,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "nineteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -2370,8 +2370,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 25,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-five (25)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -2381,7 +2381,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 31,
-            "displayValue": null,
+            "displayValue": "thirty-one",
             "displayValueParsed": false
           }
         ]
@@ -2860,8 +2860,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "sixteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -2871,8 +2871,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 22,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-two (22)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -3027,8 +3027,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "seventeen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -3038,8 +3038,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 23,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-three (23)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -3049,7 +3049,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 29,
-            "displayValue": null,
+            "displayValue": "twenty-nine",
             "displayValueParsed": false
           }
         ]
@@ -4166,8 +4166,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "sixteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -4177,8 +4177,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 22,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-two (22)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -4502,8 +4502,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "seventeen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -4513,8 +4513,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 23,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-three (23)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -4524,7 +4524,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 29,
-            "displayValue": null,
+            "displayValue": "twenty-nine",
             "displayValueParsed": false
           }
         ]
@@ -4860,7 +4860,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -4882,8 +4882,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "eighteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -4893,8 +4893,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 24,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-four (24)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -5216,8 +5216,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "sixteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -5227,8 +5227,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 22,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-two (22)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -5574,7 +5574,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -5596,8 +5596,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "nineteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -5607,8 +5607,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 25,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-five (25)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -5618,7 +5618,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 31,
-            "displayValue": null,
+            "displayValue": "thirty-one",
             "displayValueParsed": false
           }
         ]
@@ -5930,8 +5930,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "seventeen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -5941,8 +5941,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 23,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-three (23)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -5952,7 +5952,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 29,
-            "displayValue": null,
+            "displayValue": "twenty-nine",
             "displayValueParsed": false
           }
         ]
@@ -9645,7 +9645,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -9667,8 +9667,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "eighteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -9678,8 +9678,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 24,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-four (24)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -9836,7 +9836,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -9858,8 +9858,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "nineteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -9869,8 +9869,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 25,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-five (25)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -9880,7 +9880,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 31,
-            "displayValue": null,
+            "displayValue": "thirty-one",
             "displayValueParsed": false
           }
         ]
@@ -10359,8 +10359,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "sixteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -10370,8 +10370,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 22,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-two (22)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -10526,8 +10526,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "seventeen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -10537,8 +10537,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 23,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-three (23)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -10548,7 +10548,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 29,
-            "displayValue": null,
+            "displayValue": "twenty-nine",
             "displayValueParsed": false
           }
         ]
@@ -11410,7 +11410,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -11432,8 +11432,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "eighteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -11443,8 +11443,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 24,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-four (24)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -11597,7 +11597,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -11619,8 +11619,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "nineteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -11630,8 +11630,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 25,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-five (25)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -11641,7 +11641,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 31,
-            "displayValue": null,
+            "displayValue": "thirty-one",
             "displayValueParsed": false
           }
         ]
@@ -12120,8 +12120,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "sixteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -12131,8 +12131,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 22,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-two (22)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -12287,8 +12287,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "seventeen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -12298,8 +12298,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 23,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-three (23)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -12309,7 +12309,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 29,
-            "displayValue": null,
+            "displayValue": "twenty-nine",
             "displayValueParsed": false
           }
         ]
@@ -13171,7 +13171,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -13193,8 +13193,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "eighteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -13204,8 +13204,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 24,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-four (24)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -13358,7 +13358,7 @@
             "dictionaryPriority": 0,
             "hasReading": false,
             "frequency": 7,
-            "displayValue": null,
+            "displayValue": "seven",
             "displayValueParsed": false
           },
           {
@@ -13380,8 +13380,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "nineteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -13391,8 +13391,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 25,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-five (25)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -13402,7 +13402,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 31,
-            "displayValue": null,
+            "displayValue": "thirty-one",
             "displayValueParsed": false
           }
         ]
@@ -13881,8 +13881,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "sixteen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -13892,8 +13892,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 22,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-two (22)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -14048,8 +14048,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 0,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "seventeen",
+            "displayValueParsed": true
           },
           {
             "index": 4,
@@ -14059,8 +14059,8 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 23,
-            "displayValue": null,
-            "displayValueParsed": false
+            "displayValue": "twenty-three (23)",
+            "displayValueParsed": true
           },
           {
             "index": 5,
@@ -14070,7 +14070,7 @@
             "dictionaryPriority": 0,
             "hasReading": true,
             "frequency": 29,
-            "displayValue": null,
+            "displayValue": "twenty-nine",
             "displayValueParsed": false
           }
         ]
diff --git a/test/jsconfig.json b/test/jsconfig.json
new file mode 100644
index 0000000000..b025918c4c
--- /dev/null
+++ b/test/jsconfig.json
@@ -0,0 +1,39 @@
+{
+    "compilerOptions": {
+        "module": "ES2015",
+        "target": "ES2022",
+        "checkJs": true,
+        "moduleResolution": "node",
+        "strict": true,
+        "strictNullChecks": true,
+        "noImplicitAny": true,
+        "strictPropertyInitialization": true,
+        "suppressImplicitAnyIndexErrors": false,
+        "skipLibCheck": false,
+        "baseUrl": ".",
+        "paths": {
+            "*": ["../types/ext/*"],
+            "dev/*": ["../types/dev/*"],
+            "test/*": ["../types/test/*"]
+        },
+        "types": [
+            "chrome",
+            "firefox-webext-browser",
+            "handlebars",
+            "jszip",
+            "parse5",
+            "wanakana"
+        ]
+    },
+    "include": [
+        "**/*.js",
+        "../ext/**/*.js",
+        "../types/ext/**/*.ts",
+        "../types/dev/**/*.ts",
+        "../types/other/web-set-timeout.d.ts"
+    ],
+    "exclude": [
+        "../node_modules",
+        "../ext/lib"
+    ]
+}
\ No newline at end of file
diff --git a/test/playwright/visual.spec.js b/test/playwright/visual.spec.js
index acb12e97e3..4a4f272742 100644
--- a/test/playwright/visual.spec.js
+++ b/test/playwright/visual.spec.js
@@ -68,10 +68,16 @@ test('visual', async ({context, page, extensionId}) => {
     // take a screenshot of the settings page with jmdict loaded
     await expect.soft(page).toHaveScreenshot('settings-jmdict-loaded.png', {mask: [storage_locator]});
 
+    /**
+     * @param {number} doc_number
+     * @param {number} test_number
+     * @param {import('@playwright/test').ElementHandle<Node>} el
+     * @param {{x: number, y: number}} offset
+     */
     const screenshot = async (doc_number, test_number, el, offset) => {
         const test_name = 'doc' + doc_number + '-test' + test_number;
 
-        const box = await el.boundingBox();
+        const box = (await el.boundingBox()) || {x: 0, y: 0, width: 0, height: 0};
 
         // find the popup frame if it exists
         let popup_frame = page.frames().find((f) => f.url().includes('popup.html'));
@@ -86,7 +92,7 @@ test('visual', async ({context, page, extensionId}) => {
             popup_frame = await frame_attached; // wait for popup to be attached
         }
         try {
-            await (await popup_frame.frameElement()).waitForElementState('visible', {timeout: 500});  // some tests don't have a popup, so don't fail if it's not there; TODO: check if the popup is expected to be there
+            await (await /** @type {import('@playwright/test').Frame} */ (popup_frame).frameElement()).waitForElementState('visible', {timeout: 500});  // some tests don't have a popup, so don't fail if it's not there; TODO: check if the popup is expected to be there
         } catch (error) {
             console.log(test_name + ' has no popup');
         }
@@ -95,7 +101,7 @@ test('visual', async ({context, page, extensionId}) => {
         await expect.soft(page).toHaveScreenshot(test_name + '.png');
 
         await page.mouse.click(0, 0); // click away so popup disappears
-        await (await popup_frame.frameElement()).waitForElementState('hidden'); // wait for popup to disappear
+        await (await /** @type {import('@playwright/test').Frame} */ (popup_frame).frameElement()).waitForElementState('hidden'); // wait for popup to disappear
     };
 
     // Load test-document1.html
diff --git a/test/test-all.js b/test/test-all.js
index d187879ae1..9219d27838 100644
--- a/test/test-all.js
+++ b/test/test-all.js
@@ -22,13 +22,17 @@ const {spawnSync} = require('child_process');
 const {getArgs} = require('../dev/util');
 
 
+/**
+ * @throws {Error}
+ */
 function main() {
-    const args = getArgs(process.argv.slice(2), new Map([
+    const args = getArgs(process.argv.slice(2), new Map(/** @type {[key: string, value: (boolean|null|number|string|string[])][]} */ ([
         ['skip', []],
         [null, []]
-    ]));
-    const directories = args.get(null);
-    const skip = new Set([__filename, ...args.get('skip')].map((value) => path.resolve(value)));
+    ])));
+    const directories = /** @type {string[]} */ (args.get(null));
+    const skipArg = /** @type {string[]} */ (args.get('skip'));
+    const skip = new Set([__filename, ...skipArg].map((value) => path.resolve(value)));
 
     const node = process.execPath;
     const fileNamePattern = /\.js$/i;
diff --git a/test/test-anki-note-builder.js b/test/test-anki-note-builder.js
index ba937302e0..8e0ab9d94c 100644
--- a/test/test-anki-note-builder.js
+++ b/test/test-anki-note-builder.js
@@ -24,10 +24,18 @@ const {testMain} = require('../dev/util');
 const {TranslatorVM} = require('../dev/translator-vm');
 
 
+/**
+ * @template T
+ * @param {T} value
+ * @returns {T}
+ */
 function clone(value) {
     return JSON.parse(JSON.stringify(value));
 }
 
+/**
+ * @returns {Promise<{vm: TranslatorVM, AnkiNoteBuilder: typeof AnkiNoteBuilder2, JapaneseUtil: typeof JapaneseUtil2}>}
+ */
 async function createVM() {
     const dom = new JSDOM();
     const {Node, NodeFilter, document} = dom.window;
@@ -55,10 +63,11 @@ async function createVM() {
         'lib/handlebars.min.js'
     ]);
 
+    /** @type {[typeof JapaneseUtil, typeof AnkiNoteBuilder, typeof AnkiTemplateRenderer]} */
     const [
-        JapaneseUtil,
-        AnkiNoteBuilder,
-        AnkiTemplateRenderer
+        JapaneseUtil2,
+        AnkiNoteBuilder2,
+        AnkiTemplateRenderer2
     ] = vm.get([
         'JapaneseUtil',
         'AnkiNoteBuilder',
@@ -67,20 +76,35 @@ async function createVM() {
 
     class TemplateRendererProxy {
         constructor() {
+            /** @type {?Promise<void>} */
             this._preparePromise = null;
-            this._ankiTemplateRenderer = new AnkiTemplateRenderer();
+            /** @type {AnkiTemplateRenderer} */
+            this._ankiTemplateRenderer = new AnkiTemplateRenderer2();
         }
 
+        /**
+         * @param {string} template
+         * @param {import('template-renderer').PartialOrCompositeRenderData} data
+         * @param {import('anki-templates').RenderMode} type
+         * @returns {Promise<import('template-renderer').RenderResult>}
+         */
         async render(template, data, type) {
             await this._prepare();
             return await this._ankiTemplateRenderer.templateRenderer.render(template, data, type);
         }
 
+        /**
+         * @param {import('template-renderer').RenderMultiItem[]} items
+         * @returns {Promise<import('core').Response<import('template-renderer').RenderResult>[]>}
+         */
         async renderMulti(items) {
             await this._prepare();
-            return await this._serializeMulti(this._ankiTemplateRenderer.templateRenderer.renderMulti(items));
+            return await this._ankiTemplateRenderer.templateRenderer.renderMulti(items);
         }
 
+        /**
+         * @returns {Promise<void>}
+         */
         _prepare() {
             if (this._preparePromise === null) {
                 this._preparePromise = this._prepareInternal();
@@ -88,48 +112,20 @@ async function createVM() {
             return this._preparePromise;
         }
 
+        /** */
         async _prepareInternal() {
             await this._ankiTemplateRenderer.prepare();
         }
-
-        _serializeError(error) {
-            try {
-                if (typeof error === 'object' && error !== null) {
-                    const result = {
-                        name: error.name,
-                        message: error.message,
-                        stack: error.stack
-                    };
-                    if (Object.prototype.hasOwnProperty.call(error, 'data')) {
-                        result.data = error.data;
-                    }
-                    return result;
-                }
-            } catch (e) {
-                // NOP
-            }
-            return {
-                value: error,
-                hasValue: true
-            };
-        }
-
-        _serializeMulti(array) {
-            for (let i = 0, ii = array.length; i < ii; ++i) {
-                const value = array[i];
-                const {error} = value;
-                if (typeof error !== 'undefined') {
-                    value.error = this._serializeError(error);
-                }
-            }
-            return array;
-        }
     }
     vm.set({TemplateRendererProxy});
 
-    return {vm, AnkiNoteBuilder, JapaneseUtil};
+    return {vm, AnkiNoteBuilder: AnkiNoteBuilder2, JapaneseUtil: JapaneseUtil2};
 }
 
+/**
+ * @param {'terms'|'kanji'} type
+ * @returns {string[]}
+ */
 function getFieldMarkers(type) {
     switch (type) {
         case 'terms':
@@ -190,8 +186,19 @@ function getFieldMarkers(type) {
     }
 }
 
+/**
+ * @param {import('dictionary').DictionaryEntry[]} dictionaryEntries
+ * @param {'terms'|'kanji'} type
+ * @param {import('settings').ResultOutputMode} mode
+ * @param {string} template
+ * @param {typeof AnkiNoteBuilder} AnkiNoteBuilder
+ * @param {typeof JapaneseUtil} JapaneseUtil
+ * @param {boolean} write
+ * @returns {Promise<import('anki').NoteFields[]>}
+ */
 async function getRenderResults(dictionaryEntries, type, mode, template, AnkiNoteBuilder, JapaneseUtil, write) {
     const markers = getFieldMarkers(type);
+    /** @type {import('anki-note-builder').Field[]} */
     const fields = [];
     for (const marker of markers) {
         fields.push([marker, `{${marker}}`]);
@@ -224,9 +231,10 @@ async function getRenderResults(dictionaryEntries, type, mode, template, AnkiNot
             query: 'query',
             fullQuery: 'fullQuery'
         };
-        const {note: {fields: noteFields}, errors} = await ankiNoteBuilder.createNote({
+        /** @type {import('anki-note-builder').CreateNoteDetails} */
+        const details = {
             dictionaryEntry,
-            mode: null,
+            mode: 'test',
             context,
             template,
             deckName: 'deckName',
@@ -238,8 +246,11 @@ async function getRenderResults(dictionaryEntries, type, mode, template, AnkiNot
             duplicateScopeCheckAllModels: false,
             resultOutputMode: mode,
             glossaryLayoutMode: 'default',
-            compactTags: false
-        });
+            compactTags: false,
+            requirements: [],
+            mediaOptions: null
+        };
+        const {note: {fields: noteFields}, errors} = await ankiNoteBuilder.createNote(details);
         if (!write) {
             for (const error of errors) {
                 console.error(error);
@@ -253,6 +264,7 @@ async function getRenderResults(dictionaryEntries, type, mode, template, AnkiNot
 }
 
 
+/** */
 async function main() {
     const write = (process.argv[2] === '--write');
 
@@ -274,6 +286,7 @@ async function main() {
             case 'findTerms':
                 {
                     const {name, mode, text} = test;
+                    /** @type {import('translation').FindTermsOptions} */
                     const options = vm.buildOptions(optionsPresets, test.options);
                     const {dictionaryEntries} = clone(await vm.translator.findTerms(mode, text, options));
                     const results = mode !== 'simple' ? clone(await getRenderResults(dictionaryEntries, 'terms', mode, template, AnkiNoteBuilder, JapaneseUtil, write)) : null;
@@ -286,9 +299,10 @@ async function main() {
             case 'findKanji':
                 {
                     const {name, text} = test;
+                    /** @type {import('translation').FindKanjiOptions} */
                     const options = vm.buildOptions(optionsPresets, test.options);
                     const dictionaryEntries = clone(await vm.translator.findKanji(text, options));
-                    const results = clone(await getRenderResults(dictionaryEntries, 'kanji', null, template, AnkiNoteBuilder, JapaneseUtil, write));
+                    const results = clone(await getRenderResults(dictionaryEntries, 'kanji', 'split', template, AnkiNoteBuilder, JapaneseUtil, write));
                     actualResults1.push({name, results});
                     if (!write) {
                         assert.deepStrictEqual(results, expected1.results);
diff --git a/test/test-build-libs.js b/test/test-build-libs.js
index 496f43f8b8..b22db70745 100644
--- a/test/test-build-libs.js
+++ b/test/test-build-libs.js
@@ -20,16 +20,14 @@ const fs = require('fs');
 const assert = require('assert');
 const {getBuildTargets} = require('../dev/build-libs');
 
+/** */
 async function main() {
     try {
         for (const {path: path2, build} of getBuildTargets()) {
-            let expectedContent = await build();
-            if (typeof expectedContent !== 'string') {
-                // Buffer
-                expectedContent = expectedContent.toString('utf8');
-            }
+            const expectedContent = await build();
+            const expectedContentString = typeof expectedContent === 'string' ? expectedContent : expectedContent.toString('utf8');
             const actualContent = fs.readFileSync(path2, {encoding: 'utf8'});
-            assert.strictEqual(actualContent, expectedContent);
+            assert.strictEqual(actualContent, expectedContentString);
         }
     } catch (e) {
         console.error(e);
diff --git a/test/test-cache-map.js b/test/test-cache-map.js
index 863c6acef7..56a31898a9 100644
--- a/test/test-cache-map.js
+++ b/test/test-cache-map.js
@@ -24,20 +24,23 @@ const vm = new VM({console});
 vm.execute([
     'js/general/cache-map.js'
 ]);
-const CacheMap = vm.get('CacheMap');
+/** @type {typeof CacheMap} */
+const CacheMap2 = vm.getSingle('CacheMap');
 
 
+/** */
 function testConstructor() {
-    const data = [
-        [false, () => new CacheMap(0)],
-        [false, () => new CacheMap(1)],
-        [false, () => new CacheMap(Number.MAX_VALUE)],
-        [true,  () => new CacheMap(-1)],
-        [true,  () => new CacheMap(1.5)],
-        [true,  () => new CacheMap(Number.NaN)],
-        [true,  () => new CacheMap(Number.POSITIVE_INFINITY)],
-        [true,  () => new CacheMap('a')]
-    ];
+    const data = /** @type {[throws: boolean, create: () => void][]} */ ([
+        [false, () => new CacheMap2(0)],
+        [false, () => new CacheMap2(1)],
+        [false, () => new CacheMap2(Number.MAX_VALUE)],
+        [true,  () => new CacheMap2(-1)],
+        [true,  () => new CacheMap2(1.5)],
+        [true,  () => new CacheMap2(Number.NaN)],
+        [true,  () => new CacheMap2(Number.POSITIVE_INFINITY)],
+        // @ts-ignore - Ignore because it should throw an error
+        [true,  () => new CacheMap2('a')]
+    ]);
 
     for (const [throws, create] of data) {
         if (throws) {
@@ -48,6 +51,7 @@ function testConstructor() {
     }
 }
 
+/** */
 function testApi() {
     const data = [
         {
@@ -102,16 +106,16 @@ function testApi() {
     ];
 
     for (const {maxSize, expectedSize, calls} of data) {
-        const cache = new CacheMap(maxSize);
+        const cache = new CacheMap2(maxSize);
         assert.strictEqual(cache.maxSize, maxSize);
         for (const call of calls) {
             const {func, args} = call;
             let returnValue;
             switch (func) {
-                case 'get': returnValue = cache.get(...args); break;
-                case 'set': returnValue = cache.set(...args); break;
-                case 'has': returnValue = cache.has(...args); break;
-                case 'clear': returnValue = cache.clear(...args); break;
+                case 'get': returnValue = cache.get(args[0]); break;
+                case 'set': returnValue = cache.set(args[0], args[1]); break;
+                case 'has': returnValue = cache.has(args[0]); break;
+                case 'clear': returnValue = cache.clear(); break;
             }
             if (Object.prototype.hasOwnProperty.call(call, 'returnValue')) {
                 const {returnValue: expectedReturnValue} = call;
@@ -123,6 +127,7 @@ function testApi() {
 }
 
 
+/** */
 function main() {
     testConstructor();
     testApi();
diff --git a/test/test-core.js b/test/test-core.js
index b42f8cf293..2c48ac208b 100644
--- a/test/test-core.js
+++ b/test/test-core.js
@@ -22,18 +22,24 @@ const {VM} = require('../dev/vm');
 
 const vm = new VM();
 vm.execute([
-    'js/core.js'
+    'js/core.js',
+    'js/core/extension-error.js'
 ]);
-const [DynamicProperty, deepEqual] = vm.get(['DynamicProperty', 'deepEqual']);
+const values = vm.get(['DynamicProperty', 'deepEqual']);
+const DynamicProperty2 = /** @type {typeof DynamicProperty} */ (values[0]);
+const deepEqual2 = /** @type {typeof deepEqual} */ (values[1]);
 
 
+/** */
 function testDynamicProperty() {
     const data = [
         {
             initialValue: 0,
+            /** @type {{operation: ?string, expectedDefaultValue: number, expectedValue: number, expectedOverrideCount: number, expeectedEventOccurred: boolean, args: [value: number, priority?: number]}[]} */
             operations: [
                 {
                     operation: null,
+                    args: [0],
                     expectedDefaultValue: 0,
                     expectedValue: 0,
                     expectedOverrideCount: 0,
@@ -132,7 +138,7 @@ function testDynamicProperty() {
     ];
 
     for (const {initialValue, operations} of data) {
-        const property = new DynamicProperty(initialValue);
+        const property = new DynamicProperty2(initialValue);
         const overrideTokens = [];
         let eventOccurred = false;
         const onChange = () => { eventOccurred = true; };
@@ -153,6 +159,7 @@ function testDynamicProperty() {
     }
 }
 
+/** */
 function testDeepEqual() {
     const data = [
         // Simple tests
@@ -272,10 +279,10 @@ function testDeepEqual() {
 
     let index = 0;
     for (const {value1, value2, expected} of data) {
-        const actual1 = deepEqual(value1, value2);
+        const actual1 = deepEqual2(value1, value2);
         assert.strictEqual(actual1, expected, `Failed for test ${index}`);
 
-        const actual2 = deepEqual(value2, value1);
+        const actual2 = deepEqual2(value2, value1);
         assert.strictEqual(actual2, expected, `Failed for test ${index}`);
 
         ++index;
@@ -283,6 +290,7 @@ function testDeepEqual() {
 }
 
 
+/** */
 function main() {
     testDynamicProperty();
     testDeepEqual();
diff --git a/test/test-css-json.js b/test/test-css-json.js
index ddeee6bded..3b4b106b80 100644
--- a/test/test-css-json.js
+++ b/test/test-css-json.js
@@ -23,6 +23,7 @@ const {formatRulesJson, generateRules} = require('../dev/css-to-json-util');
 const {getTargets} = require('../dev/generate-css-json');
 
 
+/** */
 function main() {
     for (const {cssFile, overridesCssFile, outputPath} of getTargets()) {
         const actual = fs.readFileSync(outputPath, {encoding: 'utf8'});
diff --git a/test/test-database.js b/test/test-database.js
index c4cd504ab8..947e369b12 100644
--- a/test/test-database.js
+++ b/test/test-database.js
@@ -25,6 +25,7 @@ const {DatabaseVM, DatabaseVMDictionaryImporterMediaLoader} = require('../dev/da
 const vm = new DatabaseVM();
 vm.execute([
     'js/core.js',
+    'js/core/extension-error.js',
     'js/general/cache-map.js',
     'js/data/json-schema.js',
     'js/media/media-util.js',
@@ -32,19 +33,30 @@ vm.execute([
     'js/data/database.js',
     'js/language/dictionary-database.js'
 ]);
-const DictionaryImporter = vm.get('DictionaryImporter');
-const DictionaryDatabase = vm.get('DictionaryDatabase');
+/** @type {typeof DictionaryImporter} */
+const DictionaryImporter2 = vm.getSingle('DictionaryImporter');
+/** @type {typeof DictionaryDatabase} */
+const DictionaryDatabase2 = vm.getSingle('DictionaryDatabase');
 
 
+/**
+ * @param {string} dictionary
+ * @param {string} [dictionaryName]
+ * @returns {import('jszip')}
+ */
 function createTestDictionaryArchive(dictionary, dictionaryName) {
     const dictionaryDirectory = path.join(__dirname, 'data', 'dictionaries', dictionary);
     return createDictionaryArchive(dictionaryDirectory, dictionaryName);
 }
 
 
+/**
+ * @param {import('dictionary-importer').OnProgressCallback} [onProgress]
+ * @returns {DictionaryImporter}
+ */
 function createDictionaryImporter(onProgress) {
     const dictionaryImporterMediaLoader = new DatabaseVMDictionaryImporterMediaLoader();
-    return new DictionaryImporter(dictionaryImporterMediaLoader, (...args) => {
+    return new DictionaryImporter2(dictionaryImporterMediaLoader, (...args) => {
         const {stepIndex, stepCount, index, count} = args[0];
         assert.ok(stepIndex < stepCount);
         assert.ok(index <= count);
@@ -55,25 +67,58 @@ function createDictionaryImporter(onProgress) {
 }
 
 
+/**
+ * @param {import('dictionary-database').TermEntry[]} dictionaryDatabaseEntries
+ * @param {string} term
+ * @returns {number}
+ */
 function countDictionaryDatabaseEntriesWithTerm(dictionaryDatabaseEntries, term) {
     return dictionaryDatabaseEntries.reduce((i, v) => (i + (v.term === term ? 1 : 0)), 0);
 }
 
+/**
+ * @param {import('dictionary-database').TermEntry[]} dictionaryDatabaseEntries
+ * @param {string} reading
+ * @returns {number}
+ */
 function countDictionaryDatabaseEntriesWithReading(dictionaryDatabaseEntries, reading) {
     return dictionaryDatabaseEntries.reduce((i, v) => (i + (v.reading === reading ? 1 : 0)), 0);
 }
 
+/**
+ * @param {import('dictionary-database').TermMeta[]|import('dictionary-database').KanjiMeta[]} metas
+ * @param {import('dictionary-database').TermMetaType|import('dictionary-database').KanjiMetaType} mode
+ * @returns {number}
+ */
 function countMetasWithMode(metas, mode) {
-    return metas.reduce((i, v) => (i + (v.mode === mode ? 1 : 0)), 0);
+    let i = 0;
+    for (const item of metas) {
+        if (item.mode === mode) { ++i; }
+    }
+    return i;
 }
 
+/**
+ * @param {import('dictionary-database').KanjiEntry[]} kanji
+ * @param {string} character
+ * @returns {number}
+ */
 function countKanjiWithCharacter(kanji, character) {
-    return kanji.reduce((i, v) => (i + (v.character === character ? 1 : 0)), 0);
+    let i = 0;
+    for (const item of kanji) {
+        if (item.character === character) { ++i; }
+    }
+    return i;
 }
 
 
+/**
+ * @param {number} timeout
+ * @returns {Promise<void>}
+ */
 function clearDatabase(timeout) {
     return new Promise((resolve, reject) => {
+        /** @type {?number} */
         let timer = setTimeout(() => {
             timer = null;
             reject(new Error(`clearDatabase failed to resolve after ${timeout}ms`));
@@ -82,11 +127,14 @@ function clearDatabase(timeout) {
         (async () => {
             const indexedDB = vm.indexedDB;
             for (const {name} of await indexedDB.databases()) {
-                await new Promise((resolve2, reject2) => {
+                if (typeof name !== 'string') { continue; }
+                /** @type {Promise<void>} */
+                const promise2 = new Promise((resolve2, reject2) => {
                     const request = indexedDB.deleteDatabase(name);
                     request.onerror = (e) => reject2(e);
                     request.onsuccess = () => resolve2();
                 });
+                await promise2;
             }
             if (timer !== null) {
                 clearTimeout(timer);
@@ -97,6 +145,7 @@ function clearDatabase(timeout) {
 }
 
 
+/** */
 async function testDatabase1() {
     // Load dictionary data
     const testDictionary = createTestDictionaryArchive('valid-dictionary1');
@@ -139,7 +188,7 @@ async function testDatabase1() {
     ];
 
     // Setup database
-    const dictionaryDatabase = new DictionaryDatabase();
+    const dictionaryDatabase = new DictionaryDatabase2();
     await dictionaryDatabase.prepare();
 
     for (const {cleanup} of iterations) {
@@ -203,6 +252,9 @@ async function testDatabase1() {
     await dictionaryDatabase.close();
 }
 
+/**
+ * @param {DictionaryDatabase} database
+ */
 async function testDatabaseEmpty1(database) {
     const info = await database.getDictionaryInfo();
     vm.assert.deepStrictEqual(info, []);
@@ -214,16 +266,21 @@ async function testDatabaseEmpty1(database) {
     });
 }
 
+/**
+ * @param {DictionaryDatabase} database
+ * @param {import('dictionary-database').DictionarySet} titles
+ */
 async function testFindTermsBulkTest1(database, titles) {
+    /** @type {{inputs: {matchType: import('dictionary-database').MatchType, termList: string[]}[], expectedResults: {total: number, terms: [key: string, count: number][], readings: [key: string, count: number][]}}[]} */
     const data = [
         {
             inputs: [
                 {
-                    matchType: null,
+                    matchType: 'exact',
                     termList: ['打', '打つ', '打ち込む']
                 },
                 {
-                    matchType: null,
+                    matchType: 'exact',
                     termList: ['だ', 'ダース', 'うつ', 'ぶつ', 'うちこむ', 'ぶちこむ']
                 },
                 {
@@ -251,7 +308,7 @@ async function testFindTermsBulkTest1(database, titles) {
         {
             inputs: [
                 {
-                    matchType: null,
+                    matchType: 'exact',
                     termList: ['込む']
                 }
             ],
@@ -282,7 +339,7 @@ async function testFindTermsBulkTest1(database, titles) {
         {
             inputs: [
                 {
-                    matchType: null,
+                    matchType: 'exact',
                     termList: []
                 }
             ],
@@ -308,7 +365,12 @@ async function testFindTermsBulkTest1(database, titles) {
     }
 }
 
+/**
+ * @param {DictionaryDatabase} database
+ * @param {import('dictionary-database').DictionarySet} titles
+ */
 async function testTindTermsExactBulk1(database, titles) {
+    /** @type {{inputs: {termList: {term: string, reading: string}[]}[], expectedResults: {total: number, terms: [key: string, count: number][], readings: [key: string, count: number][]}}[]} */
     const data = [
         {
             inputs: [
@@ -412,7 +474,12 @@ async function testTindTermsExactBulk1(database, titles) {
     }
 }
 
+/**
+ * @param {DictionaryDatabase} database
+ * @param {string} mainDictionary
+ */
 async function testFindTermsBySequenceBulk1(database, mainDictionary) {
+    /** @type {{inputs: {sequenceList: number[]}[], expectedResults: {total: number, terms: [key: string, count: number][], readings: [key: string, count: number][]}}[]} */
     const data = [
         {
             inputs: [
@@ -561,7 +628,12 @@ async function testFindTermsBySequenceBulk1(database, mainDictionary) {
     }
 }
 
+/**
+ * @param {DictionaryDatabase} database
+ * @param {import('dictionary-database').DictionarySet} titles
+ */
 async function testFindTermMetaBulk1(database, titles) {
+    /** @type {{inputs: {termList: string[]}[], expectedResults: {total: number, modes: [key: import('dictionary-database').TermMetaType, count: number][]}}[]} */
     const data = [
         {
             inputs: [
@@ -627,7 +699,12 @@ async function testFindTermMetaBulk1(database, titles) {
     }
 }
 
+/**
+ * @param {DictionaryDatabase} database
+ * @param {import('dictionary-database').DictionarySet} titles
+ */
 async function testFindKanjiBulk1(database, titles) {
+    /** @type {{inputs: {kanjiList: string[]}[], expectedResults: {total: number, kanji: [key: string, count: number][]}}[]} */
     const data = [
         {
             inputs: [
@@ -679,7 +756,12 @@ async function testFindKanjiBulk1(database, titles) {
     }
 }
 
+/**
+ * @param {DictionaryDatabase} database
+ * @param {import('dictionary-database').DictionarySet} titles
+ */
 async function testFindKanjiMetaBulk1(database, titles) {
+    /** @type {{inputs: {kanjiList: string[]}[], expectedResults: {total: number, modes: [key: import('dictionary-database').KanjiMetaType, count: number][]}}[]} */
     const data = [
         {
             inputs: [
@@ -731,6 +813,10 @@ async function testFindKanjiMetaBulk1(database, titles) {
     }
 }
 
+/**
+ * @param {DictionaryDatabase} database
+ * @param {string} title
+ */
 async function testFindTagForTitle1(database, title) {
     const data = [
         {
@@ -784,6 +870,7 @@ async function testFindTagForTitle1(database, title) {
 }
 
 
+/** */
 async function testDatabase2() {
     // Load dictionary data
     const testDictionary = createTestDictionaryArchive('valid-dictionary1');
@@ -796,11 +883,13 @@ async function testDatabase2() {
     ]);
 
     // Setup database
-    const dictionaryDatabase = new DictionaryDatabase();
+    const dictionaryDatabase = new DictionaryDatabase2();
+    /** @type {import('dictionary-importer').ImportDetails} */
+    const detaultImportDetails = {prefixWildcardsSupported: false};
 
     // Error: not prepared
-    await assert.rejects(async () => await dictionaryDatabase.deleteDictionary(title, 1000));
-    await assert.rejects(async () => await dictionaryDatabase.findTermsBulk(['?'], titles, null));
+    await assert.rejects(async () => await dictionaryDatabase.deleteDictionary(title, 1000, () => {}));
+    await assert.rejects(async () => await dictionaryDatabase.findTermsBulk(['?'], titles, 'exact'));
     await assert.rejects(async () => await dictionaryDatabase.findTermsExactBulk([{term: '?', reading: '?'}], titles));
     await assert.rejects(async () => await dictionaryDatabase.findTermsBySequenceBulk([{query: 1, dictionary: title}]));
     await assert.rejects(async () => await dictionaryDatabase.findTermMetaBulk(['?'], titles));
@@ -809,23 +898,24 @@ async function testDatabase2() {
     await assert.rejects(async () => await dictionaryDatabase.findKanjiMetaBulk(['?'], titles));
     await assert.rejects(async () => await dictionaryDatabase.findTagForTitle('tag', title));
     await assert.rejects(async () => await dictionaryDatabase.getDictionaryInfo());
-    await assert.rejects(async () => await dictionaryDatabase.getDictionaryCounts(titles, true));
-    await assert.rejects(async () => await createDictionaryImporter().importDictionary(dictionaryDatabase, testDictionarySource, {}));
+    await assert.rejects(async () => await dictionaryDatabase.getDictionaryCounts([...titles.keys()], true));
+    await assert.rejects(async () => await createDictionaryImporter().importDictionary(dictionaryDatabase, testDictionarySource, detaultImportDetails));
 
     await dictionaryDatabase.prepare();
 
     // Error: already prepared
     await assert.rejects(async () => await dictionaryDatabase.prepare());
 
-    await createDictionaryImporter().importDictionary(dictionaryDatabase, testDictionarySource, {});
+    await createDictionaryImporter().importDictionary(dictionaryDatabase, testDictionarySource, detaultImportDetails);
 
     // Error: dictionary already imported
-    await assert.rejects(async () => await createDictionaryImporter().importDictionary(dictionaryDatabase, testDictionarySource, {}));
+    await assert.rejects(async () => await createDictionaryImporter().importDictionary(dictionaryDatabase, testDictionarySource, detaultImportDetails));
 
     await dictionaryDatabase.close();
 }
 
 
+/** */
 async function testDatabase3() {
     const invalidDictionaries = [
         'invalid-dictionary1',
@@ -837,7 +927,9 @@ async function testDatabase3() {
     ];
 
     // Setup database
-    const dictionaryDatabase = new DictionaryDatabase();
+    const dictionaryDatabase = new DictionaryDatabase2();
+    /** @type {import('dictionary-importer').ImportDetails} */
+    const detaultImportDetails = {prefixWildcardsSupported: false};
     await dictionaryDatabase.prepare();
 
     for (const invalidDictionary of invalidDictionaries) {
@@ -846,7 +938,7 @@ async function testDatabase3() {
 
         let error = null;
         try {
-            await createDictionaryImporter().importDictionary(dictionaryDatabase, testDictionarySource, {});
+            await createDictionaryImporter().importDictionary(dictionaryDatabase, testDictionarySource, detaultImportDetails);
         } catch (e) {
             error = e;
         }
@@ -855,9 +947,11 @@ async function testDatabase3() {
             assert.ok(false, `Expected an error while importing ${invalidDictionary}`);
         } else {
             const prefix = 'Dictionary has invalid data';
-            const message = error.message;
+            const message = /** @type {import('core').UnknownObject} */ (error).message;
             assert.ok(typeof message, 'string');
-            assert.ok(message.startsWith(prefix), `Expected error message to start with '${prefix}': ${message}`);
+            if (typeof message === 'string') {
+                assert.ok(message.startsWith(prefix), `Expected error message to start with '${prefix}': ${message}`);
+            }
         }
     }
 
@@ -865,6 +959,7 @@ async function testDatabase3() {
 }
 
 
+/** */
 async function main() {
     const clearTimeout = 5000;
     try {
diff --git a/test/test-deinflector.js b/test/test-deinflector.js
index a20cfc9553..d2b5815234 100644
--- a/test/test-deinflector.js
+++ b/test/test-deinflector.js
@@ -23,8 +23,17 @@ const {testMain} = require('../dev/util');
 const {VM} = require('../dev/vm');
 
 
+/**
+ * @param {typeof Deinflector} Deinflector
+ * @param {Deinflector} deinflector
+ * @param {string} source
+ * @param {string} expectedTerm
+ * @param {string} expectedRule
+ * @param {string[]|undefined} expectedReasons
+ * @returns {{has: false, reasons: null, rules: null}|{has: true, reasons: string[], rules: number}}
+ */
 function hasTermReasons(Deinflector, deinflector, source, expectedTerm, expectedRule, expectedReasons) {
-    for (const {term, reasons, rules} of deinflector.deinflect(source, source)) {
+    for (const {term, reasons, rules} of deinflector.deinflect(source)) {
         if (term !== expectedTerm) { continue; }
         if (typeof expectedRule !== 'undefined') {
             const expectedFlags = Deinflector.rulesToRuleFlags([expectedRule]);
@@ -48,6 +57,7 @@ function hasTermReasons(Deinflector, deinflector, source, expectedTerm, expected
 }
 
 
+/** */
 function testDeinflections() {
     const data = [
         {
@@ -919,14 +929,15 @@ function testDeinflections() {
 
     const vm = new VM();
     vm.execute(['js/language/deinflector.js']);
-    const [Deinflector] = vm.get(['Deinflector']);
+    /** @type {typeof Deinflector} */
+    const Deinflector2 = vm.getSingle('Deinflector');
 
-    const deinflectionReasons = JSON.parse(fs.readFileSync(path.join(__dirname, '..', 'ext', 'data/deinflect.json')));
-    const deinflector = new Deinflector(deinflectionReasons);
+    const deinflectionReasons = JSON.parse(fs.readFileSync(path.join(__dirname, '..', 'ext', 'data/deinflect.json'), {encoding: 'utf8'}));
+    const deinflector = new Deinflector2(deinflectionReasons);
 
     for (const {valid, tests} of data) {
         for (const {source, term, rule, reasons} of tests) {
-            const {has, reasons: actualReasons} = hasTermReasons(Deinflector, deinflector, source, term, rule, reasons);
+            const {has, reasons: actualReasons} = hasTermReasons(Deinflector2, deinflector, source, term, rule, reasons);
             let message = `${source} ${valid ? 'does not have' : 'has'} term candidate ${JSON.stringify(term)}`;
             if (typeof rule !== 'undefined') {
                 message += ` with rule ${JSON.stringify(rule)}`;
@@ -944,6 +955,7 @@ function testDeinflections() {
 }
 
 
+/** */
 function main() {
     testDeinflections();
 }
diff --git a/test/test-dictionary.js b/test/test-dictionary.js
index d4390e19b6..ec48108d2a 100644
--- a/test/test-dictionary.js
+++ b/test/test-dictionary.js
@@ -21,12 +21,18 @@ const {createDictionaryArchive, testMain} = require('../dev/util');
 const dictionaryValidate = require('../dev/dictionary-validate');
 
 
+/**
+ * @param {string} dictionary
+ * @param {string} [dictionaryName]
+ * @returns {import('jszip')}
+ */
 function createTestDictionaryArchive(dictionary, dictionaryName) {
     const dictionaryDirectory = path.join(__dirname, 'data', 'dictionaries', dictionary);
     return createDictionaryArchive(dictionaryDirectory, dictionaryName);
 }
 
 
+/** */
 async function main() {
     const dictionaries = [
         {name: 'valid-dictionary1', valid: true},
diff --git a/test/test-document-util.js b/test/test-document-util.js
index a2458b6182..93ce166954 100644
--- a/test/test-document-util.js
+++ b/test/test-document-util.js
@@ -26,24 +26,48 @@ const {VM} = require('../dev/vm');
 
 // DOMRect class definition
 class DOMRect {
+    /**
+     * @param {number} x
+     * @param {number} y
+     * @param {number} width
+     * @param {number} height
+     */
     constructor(x, y, width, height) {
+        /** @type {number} */
         this._x = x;
+        /** @type {number} */
         this._y = y;
+        /** @type {number} */
         this._width = width;
+        /** @type {number} */
         this._height = height;
     }
 
+    /** @type {number} */
     get x() { return this._x; }
+    /** @type {number} */
     get y() { return this._y; }
+    /** @type {number} */
     get width() { return this._width; }
+    /** @type {number} */
     get height() { return this._height; }
+    /** @type {number} */
     get left() { return this._x + Math.min(0, this._width); }
+    /** @type {number} */
     get right() { return this._x + Math.max(0, this._width); }
+    /** @type {number} */
     get top() { return this._y + Math.min(0, this._height); }
+    /** @type {number} */
     get bottom() { return this._y + Math.max(0, this._height); }
+    /** @returns {string} */
+    toJSON() { return '<not implemented>'; }
 }
 
 
+/**
+ * @param {string} fileName
+ * @returns {JSDOM}
+ */
 function createJSDOM(fileName) {
     const domSource = fs.readFileSync(fileName, {encoding: 'utf8'});
     const dom = new JSDOM(domSource);
@@ -61,10 +85,20 @@ function createJSDOM(fileName) {
     return dom;
 }
 
+/**
+ * @param {Element} element
+ * @param {string|undefined} selector
+ * @returns {?Element}
+ */
 function querySelectorChildOrSelf(element, selector) {
     return selector ? element.querySelector(selector) : element;
 }
 
+/**
+ * @param {JSDOM} dom
+ * @param {?Node} node
+ * @returns {?Text|Node}
+ */
 function getChildTextNodeOrSelf(dom, node) {
     if (node === null) { return null; }
     const Node = dom.window.Node;
@@ -72,6 +106,10 @@ function getChildTextNodeOrSelf(dom, node) {
     return (childNode !== null && childNode.nodeType === Node.TEXT_NODE ? childNode : node);
 }
 
+/**
+ * @param {unknown} value
+ * @returns {unknown}
+ */
 function getPrototypeOfOrNull(value) {
     try {
         return Object.getPrototypeOf(value);
@@ -80,12 +118,17 @@ function getPrototypeOfOrNull(value) {
     }
 }
 
+/**
+ * @param {Document} document
+ * @returns {?Element}
+ */
 function findImposterElement(document) {
     // Finds the imposter element based on it's z-index style
     return document.querySelector('div[style*="2147483646"]>*');
 }
 
 
+/** */
 async function testDocument1() {
     const dom = createJSDOM(path.join(__dirname, 'data', 'html', 'test-document1.html'));
     const window = dom.window;
@@ -101,7 +144,8 @@ async function testDocument1() {
         'js/dom/text-source-element.js',
         'js/dom/document-util.js'
     ]);
-    const [DOMTextScanner, TextSourceRange, TextSourceElement, DocumentUtil] = vm.get([
+    /** @type {[DOMTextScanner: typeof DOMTextScanner, TextSourceRange: typeof TextSourceRange, TextSourceElement: typeof TextSourceElement, DocumentUtil: typeof DocumentUtil]} */
+    const [DOMTextScanner2, TextSourceRange2, TextSourceElement2, DocumentUtil2] = vm.get([
         'DOMTextScanner',
         'TextSourceRange',
         'TextSourceElement',
@@ -109,19 +153,23 @@ async function testDocument1() {
     ]);
 
     try {
-        await testDocumentTextScanningFunctions(dom, {DocumentUtil, TextSourceRange, TextSourceElement});
-        await testTextSourceRangeSeekFunctions(dom, {DOMTextScanner});
+        await testDocumentTextScanningFunctions(dom, {DocumentUtil: DocumentUtil2, TextSourceRange: TextSourceRange2, TextSourceElement: TextSourceElement2});
+        await testTextSourceRangeSeekFunctions(dom, {DOMTextScanner: DOMTextScanner2});
     } finally {
         window.close();
     }
 }
 
+/**
+ * @param {JSDOM} dom
+ * @param {{DocumentUtil: typeof DocumentUtil, TextSourceRange: typeof TextSourceRange, TextSourceElement: typeof TextSourceElement}} details
+ */
 async function testDocumentTextScanningFunctions(dom, {DocumentUtil, TextSourceRange, TextSourceElement}) {
     const document = dom.window.document;
 
-    for (const testElement of document.querySelectorAll('.test[data-test-type=scan]')) {
+    for (const testElement of /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.test[data-test-type=scan]'))) {
         // Get test parameters
-        let {
+        const {
             elementFromPointSelector,
             caretRangeFromPointSelector,
             startNodeSelector,
@@ -140,10 +188,10 @@ async function testDocumentTextScanningFunctions(dom, {DocumentUtil, TextSourceR
         const startNode = getChildTextNodeOrSelf(dom, querySelectorChildOrSelf(testElement, startNodeSelector));
         const endNode = getChildTextNodeOrSelf(dom, querySelectorChildOrSelf(testElement, endNodeSelector));
 
-        startOffset = parseInt(startOffset, 10);
-        endOffset = parseInt(endOffset, 10);
-        sentenceScanExtent = parseInt(sentenceScanExtent, 10);
-        terminateAtNewlines = (terminateAtNewlines !== 'false');
+        const startOffset2 = parseInt(/** @type {string} */ (startOffset), 10);
+        const endOffset2 = parseInt(/** @type {string} */ (endOffset), 10);
+        const sentenceScanExtent2 = parseInt(/** @type {string} */ (sentenceScanExtent), 10);
+        const terminateAtNewlines2 = (terminateAtNewlines !== 'false');
 
         assert.notStrictEqual(elementFromPointValue, null);
         assert.notStrictEqual(caretRangeFromPointValue, null);
@@ -158,11 +206,25 @@ async function testDocumentTextScanningFunctions(dom, {DocumentUtil, TextSourceR
             assert.strictEqual(!!imposter, hasImposter === 'true');
 
             const range = document.createRange();
-            range.setStart(imposter ? imposter : startNode, startOffset);
-            range.setEnd(imposter ? imposter : startNode, endOffset);
+            range.setStart(/** @type {Node} */ (imposter ? imposter : startNode), startOffset2);
+            range.setEnd(/** @type {Node} */ (imposter ? imposter : startNode), endOffset2);
 
             // Override getClientRects to return a rect guaranteed to contain (x, y)
-            range.getClientRects = () => [new DOMRect(x - 1, y - 1, 2, 2)];
+            range.getClientRects = () => {
+                /** @type {import('test/document-types').PseudoDOMRectList} */
+                const domRectList = Object.assign(
+                    [new DOMRect(x - 1, y - 1, 2, 2)],
+                    {
+                        /**
+                         * @this {DOMRect[]}
+                         * @param {number} index
+                         * @returns {DOMRect}
+                         */
+                        item: function item(index) { return this[index]; }
+                    }
+                );
+                return domRectList;
+            };
             return range;
         };
 
@@ -205,8 +267,8 @@ async function testDocumentTextScanningFunctions(dom, {DocumentUtil, TextSourceR
         const sentenceActual = DocumentUtil.extractSentence(
             source,
             false,
-            sentenceScanExtent,
-            terminateAtNewlines,
+            sentenceScanExtent2,
+            terminateAtNewlines2,
             terminatorMap,
             forwardQuoteMap,
             backwardQuoteMap
@@ -218,12 +280,16 @@ async function testDocumentTextScanningFunctions(dom, {DocumentUtil, TextSourceR
     }
 }
 
+/**
+ * @param {JSDOM} dom
+ * @param {{DOMTextScanner: typeof DOMTextScanner}} details
+ */
 async function testTextSourceRangeSeekFunctions(dom, {DOMTextScanner}) {
     const document = dom.window.document;
 
-    for (const testElement of document.querySelectorAll('.test[data-test-type=text-source-range-seek]')) {
+    for (const testElement of /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('.test[data-test-type=text-source-range-seek]'))) {
         // Get test parameters
-        let {
+        const {
             seekNodeSelector,
             seekNodeIsText,
             seekOffset,
@@ -235,33 +301,36 @@ async function testTextSourceRangeSeekFunctions(dom, {DOMTextScanner}) {
             expectedResultContent
         } = testElement.dataset;
 
-        seekOffset = parseInt(seekOffset, 10);
-        seekLength = parseInt(seekLength, 10);
-        expectedResultOffset = parseInt(expectedResultOffset, 10);
+        const seekOffset2 = parseInt(/** @type {string} */ (seekOffset), 10);
+        const seekLength2 = parseInt(/** @type {string} */ (seekLength), 10);
+        const expectedResultOffset2 = parseInt(/** @type {string} */ (expectedResultOffset), 10);
 
-        let seekNode = testElement.querySelector(seekNodeSelector);
-        if (seekNodeIsText === 'true') {
+        /** @type {?Node} */
+        let seekNode = testElement.querySelector(/** @type {string} */ (seekNodeSelector));
+        if (seekNodeIsText === 'true' && seekNode !== null) {
             seekNode = seekNode.firstChild;
         }
 
-        let expectedResultNode = testElement.querySelector(expectedResultNodeSelector);
-        if (expectedResultNodeIsText === 'true') {
+        /** @type {?Node} */
+        let expectedResultNode = testElement.querySelector(/** @type {string} */ (expectedResultNodeSelector));
+        if (expectedResultNodeIsText === 'true' && expectedResultNode !== null) {
             expectedResultNode = expectedResultNode.firstChild;
         }
 
         const {node, offset, content} = (
             seekDirection === 'forward' ?
-            new DOMTextScanner(seekNode, seekOffset, true, false).seek(seekLength) :
-            new DOMTextScanner(seekNode, seekOffset, true, false).seek(-seekLength)
+            new DOMTextScanner(/** @type {Node} */ (seekNode), seekOffset2, true, false).seek(seekLength2) :
+            new DOMTextScanner(/** @type {Node} */ (seekNode), seekOffset2, true, false).seek(-seekLength2)
         );
 
         assert.strictEqual(node, expectedResultNode);
-        assert.strictEqual(offset, expectedResultOffset);
+        assert.strictEqual(offset, expectedResultOffset2);
         assert.strictEqual(content, expectedResultContent);
     }
 }
 
 
+/** */
 async function main() {
     await testDocument1();
 }
diff --git a/test/test-dom-text-scanner.js b/test/test-dom-text-scanner.js
index 37017b0120..6363463fb8 100644
--- a/test/test-dom-text-scanner.js
+++ b/test/test-dom-text-scanner.js
@@ -24,11 +24,20 @@ const {testMain} = require('../dev/util');
 const {VM} = require('../dev/vm');
 
 
+/**
+ * @param {string} fileName
+ * @returns {JSDOM}
+ */
 function createJSDOM(fileName) {
     const domSource = fs.readFileSync(fileName, {encoding: 'utf8'});
     return new JSDOM(domSource);
 }
 
+/**
+ * @param {Element} element
+ * @param {string} selector
+ * @returns {?Node}
+ */
 function querySelectorTextNode(element, selector) {
     let textIndex = -1;
     const match = /::text$|::nth-text\((\d+)\)$/.exec(selector);
@@ -37,13 +46,16 @@ function querySelectorTextNode(element, selector) {
         selector = selector.substring(0, selector.length - match[0].length);
     }
     const result = element.querySelector(selector);
+    if (result === null) {
+        return null;
+    }
     if (textIndex < 0) {
         return result;
     }
     for (let n = result.firstChild; n !== null; n = n.nextSibling) {
-        if (n.nodeType === n.constructor.TEXT_NODE) {
+        if (n.nodeType === /** @type {typeof Node} */ (n.constructor).TEXT_NODE) {
             if (textIndex === 0) {
-                return n;
+                return /** @type {Text} */ (n);
             }
             --textIndex;
         }
@@ -52,10 +64,16 @@ function querySelectorTextNode(element, selector) {
 }
 
 
+/**
+ * @param {import('jsdom').DOMWindow} window
+ * @param {(element: Element) => CSSStyleDeclaration} getComputedStyle
+ * @param {?Node} element
+ * @returns {number}
+ */
 function getComputedFontSizeInPixels(window, getComputedStyle, element) {
     for (; element !== null; element = element.parentNode) {
         if (element.nodeType === window.Node.ELEMENT_NODE) {
-            const fontSize = getComputedStyle(element).fontSize;
+            const fontSize = getComputedStyle(/** @type {Element} */ (element)).fontSize;
             if (fontSize.endsWith('px')) {
                 const value = parseFloat(fontSize.substring(0, fontSize.length - 2));
                 return value;
@@ -66,14 +84,19 @@ function getComputedFontSizeInPixels(window, getComputedStyle, element) {
     return defaultFontSize;
 }
 
+/**
+ * @param {import('jsdom').DOMWindow} window
+ * @returns {(element: Element, pseudoElement?: ?string) => CSSStyleDeclaration}
+ */
 function createAbsoluteGetComputedStyle(window) {
     // Wrapper to convert em units to px units
     const getComputedStyleOld = window.getComputedStyle.bind(window);
+    /** @type {(element: Element, pseudoElement?: ?string) => CSSStyleDeclaration} */
     return (element, ...args) => {
         const style = getComputedStyleOld(element, ...args);
         return new Proxy(style, {
             get: (target, property) => {
-                let result = target[property];
+                let result = /** @type {import('core').SafeAny} */ (target)[property];
                 if (typeof result === 'string') {
                     result = result.replace(/([-+]?\d(?:\.\d)?(?:[eE][-+]?\d+)?)em/g, (g0, g1) => {
                         const fontSize = getComputedFontSizeInPixels(window, getComputedStyleOld, element);
@@ -87,10 +110,14 @@ function createAbsoluteGetComputedStyle(window) {
 }
 
 
+/**
+ * @param {JSDOM} dom
+ * @param {{DOMTextScanner: typeof DOMTextScanner}} details
+ */
 async function testDomTextScanner(dom, {DOMTextScanner}) {
     const document = dom.window.document;
-    for (const testElement of document.querySelectorAll('y-test')) {
-        let testData = JSON.parse(testElement.dataset.testData);
+    for (const testElement of /** @type {NodeListOf<HTMLElement>} */ (document.querySelectorAll('y-test'))) {
+        let testData = JSON.parse(/** @type {string} */ (testElement.dataset.testData));
         if (!Array.isArray(testData)) {
             testData = [testData];
         }
@@ -158,6 +185,7 @@ async function testDomTextScanner(dom, {DOMTextScanner}) {
 }
 
 
+/** */
 async function testDocument1() {
     const dom = createJSDOM(path.join(__dirname, 'data', 'html', 'test-dom-text-scanner.html'));
     const window = dom.window;
@@ -171,15 +199,16 @@ async function testDocument1() {
             'js/data/sandbox/string-util.js',
             'js/dom/dom-text-scanner.js'
         ]);
-        const DOMTextScanner = vm.get('DOMTextScanner');
+        /** @type {typeof DOMTextScanner} */
+        const DOMTextScanner2 = vm.getSingle('DOMTextScanner');
 
-        await testDomTextScanner(dom, {DOMTextScanner});
+        await testDomTextScanner(dom, {DOMTextScanner: DOMTextScanner2});
     } finally {
         window.close();
     }
 }
 
-
+/** */
 async function main() {
     await testDocument1();
 }
diff --git a/test/test-hotkey-util.js b/test/test-hotkey-util.js
index 34f1eb2665..88f5a8d2a6 100644
--- a/test/test-hotkey-util.js
+++ b/test/test-hotkey-util.js
@@ -21,19 +21,30 @@ const {testMain} = require('../dev/util');
 const {VM} = require('../dev/vm');
 
 
+/**
+ * @template T
+ * @param {T} value
+ * @returns {T}
+ */
 function clone(value) {
     return JSON.parse(JSON.stringify(value));
 }
 
+/**
+ * @returns {HotkeyUtil}
+ */
 function createHotkeyUtil() {
     const vm = new VM();
     vm.execute(['js/input/hotkey-util.js']);
-    const [HotkeyUtil] = vm.get(['HotkeyUtil']);
-    return new HotkeyUtil();
+    /** @type {typeof HotkeyUtil} */
+    const HotkeyUtil2 = vm.getSingle('HotkeyUtil');
+    return new HotkeyUtil2();
 }
 
 
+/** */
 function testCommandConversions() {
+    /** @type {{os: import('environment').OperatingSystem, command: string, expectedCommand: string, expectedInput: {key: string, modifiers: import('input').Modifier[]}}[]} */
     const data = [
         {os: 'win', command: 'Alt+F', expectedCommand: 'Alt+F', expectedInput: {key: 'KeyF', modifiers: ['alt']}},
         {os: 'win', command: 'F1',    expectedCommand: 'F1',    expectedInput: {key: 'F1', modifiers: []}},
@@ -61,7 +72,9 @@ function testCommandConversions() {
     }
 }
 
+/** */
 function testDisplayNames() {
+    /** @type {{os: import('environment').OperatingSystem, key: ?string, modifiers: import('input').Modifier[], expected: string}[]} */
     const data = [
         {os: 'win', key: null,   modifiers: [], expected: ''},
         {os: 'win', key: 'KeyF', modifiers: [], expected: 'F'},
@@ -148,7 +161,9 @@ function testDisplayNames() {
     }
 }
 
+/** */
 function testSortModifiers() {
+    /** @type {{modifiers: import('input').Modifier[], expected: import('input').Modifier[]}[]} */
     const data = [
         {modifiers: [], expected: []},
         {modifiers: ['shift', 'alt', 'ctrl', 'mouse4', 'meta', 'mouse1', 'mouse0'], expected: ['meta', 'ctrl', 'alt', 'shift', 'mouse0', 'mouse1', 'mouse4']}
@@ -163,6 +178,7 @@ function testSortModifiers() {
 }
 
 
+/** */
 function main() {
     testCommandConversions();
     testDisplayNames();
diff --git a/test/test-japanese-util.js b/test/test-japanese-util.js
index 4395a11e4f..0a95b85832 100644
--- a/test/test-japanese-util.js
+++ b/test/test-japanese-util.js
@@ -26,11 +26,14 @@ vm.execute([
     'js/language/sandbox/japanese-util.js',
     'js/general/text-source-map.js'
 ]);
-const [JapaneseUtil, TextSourceMap, wanakana] = vm.get(['JapaneseUtil', 'TextSourceMap', 'wanakana']);
-const jp = new JapaneseUtil(wanakana);
+/** @type {[JapaneseUtil: typeof JapaneseUtil, TextSourceMap: typeof TextSourceMap, wanakana: import('wanakana')]} */
+const [JapaneseUtil2, TextSourceMap2, wanakana] = vm.get(['JapaneseUtil', 'TextSourceMap', 'wanakana']);
+const jp = new JapaneseUtil2(wanakana);
 
 
+/** */
 function testIsCodePointKanji() {
+    /** @type {[characters: string, expected: boolean][]} */
     const data = [
         ['力方', true],
         ['\u53f1\u{20b9f}', true],
@@ -40,14 +43,16 @@ function testIsCodePointKanji() {
 
     for (const [characters, expected] of data) {
         for (const character of characters) {
-            const codePoint = character.codePointAt(0);
+            const codePoint = /** @type {number} */ (character.codePointAt(0));
             const actual = jp.isCodePointKanji(codePoint);
             assert.strictEqual(actual, expected, `isCodePointKanji failed for ${character} (\\u{${codePoint.toString(16)}})`);
         }
     }
 }
 
+/** */
 function testIsCodePointKana() {
+    /** @type {[characters: string, expected: boolean][]} */
     const data = [
         ['かたカタ', true],
         ['力方々kata、。？,.?', false],
@@ -56,14 +61,16 @@ function testIsCodePointKana() {
 
     for (const [characters, expected] of data) {
         for (const character of characters) {
-            const codePoint = character.codePointAt(0);
+            const codePoint = /** @type {number} */ (character.codePointAt(0));
             const actual = jp.isCodePointKana(codePoint);
             assert.strictEqual(actual, expected, `isCodePointKana failed for ${character} (\\u{${codePoint.toString(16)}})`);
         }
     }
 }
 
+/** */
 function testIsCodePointJapanese() {
+    /** @type {[characters: string, expected: boolean][]} */
     const data = [
         ['かたカタ力方々、。？', true],
         ['\u53f1\u{20b9f}', true],
@@ -73,14 +80,16 @@ function testIsCodePointJapanese() {
 
     for (const [characters, expected] of data) {
         for (const character of characters) {
-            const codePoint = character.codePointAt(0);
+            const codePoint = /** @type {number} */ (character.codePointAt(0));
             const actual = jp.isCodePointJapanese(codePoint);
             assert.strictEqual(actual, expected, `isCodePointJapanese failed for ${character} (\\u{${codePoint.toString(16)}})`);
         }
     }
 }
 
+/** */
 function testIsStringEntirelyKana() {
+    /** @type {[string: string, expected: boolean][]} */
     const data = [
         ['かたかな', true],
         ['カタカナ', true],
@@ -100,7 +109,9 @@ function testIsStringEntirelyKana() {
     }
 }
 
+/** */
 function testIsStringPartiallyJapanese() {
+    /** @type {[string: string, expected: boolean][]} */
     const data = [
         ['かたかな', true],
         ['カタカナ', true],
@@ -121,7 +132,9 @@ function testIsStringPartiallyJapanese() {
     }
 }
 
+/** */
 function testConvertKatakanaToHiragana() {
+    /** @type {[string: string, expected: string, keepProlongedSoundMarks?: boolean][]} */
     const data = [
         ['かたかな', 'かたかな'],
         ['ひらがな', 'ひらがな'],
@@ -141,7 +154,9 @@ function testConvertKatakanaToHiragana() {
     }
 }
 
+/** */
 function testConvertHiraganaToKatakana() {
+    /** @type {[string: string, expected: string][]} */
     const data = [
         ['かたかな', 'カタカナ'],
         ['ひらがな', 'ヒラガナ'],
@@ -159,7 +174,9 @@ function testConvertHiraganaToKatakana() {
     }
 }
 
+/** */
 function testConvertToRomaji() {
+    /** @type {[string: string, expected: string][]} */
     const data = [
         ['かたかな', 'katakana'],
         ['ひらがな', 'hiragana'],
@@ -177,7 +194,9 @@ function testConvertToRomaji() {
     }
 }
 
+/** */
 function testConvertNumericToFullWidth() {
+    /** @type {[string: string, expected: string][]} */
     const data = [
         ['0123456789', '０１２３４５６７８９'],
         ['abcdefghij', 'abcdefghij'],
@@ -190,7 +209,9 @@ function testConvertNumericToFullWidth() {
     }
 }
 
+/** */
 function testConvertHalfWidthKanaToFullWidth() {
+    /** @type {[string: string, expected: string, expectedSourceMapping?: number[]][]} */
     const data = [
         ['0123456789', '0123456789'],
         ['abcdefghij', 'abcdefghij'],
@@ -203,18 +224,20 @@ function testConvertHalfWidthKanaToFullWidth() {
     ];
 
     for (const [string, expected, expectedSourceMapping] of data) {
-        const sourceMap = new TextSourceMap(string);
+        const sourceMap = new TextSourceMap2(string);
         const actual1 = jp.convertHalfWidthKanaToFullWidth(string, null);
         const actual2 = jp.convertHalfWidthKanaToFullWidth(string, sourceMap);
         assert.strictEqual(actual1, expected);
         assert.strictEqual(actual2, expected);
         if (typeof expectedSourceMapping !== 'undefined') {
-            assert.ok(sourceMap.equals(new TextSourceMap(string, expectedSourceMapping)));
+            assert.ok(sourceMap.equals(new TextSourceMap2(string, expectedSourceMapping)));
         }
     }
 }
 
+/** */
 function testConvertAlphabeticToKana() {
+    /** @type {[string: string, expected: string, expectedSourceMapping?: number[]][]} */
     const data = [
         ['0123456789', '0123456789'],
         ['abcdefghij', 'あbcでfgひj', [1, 1, 1, 2, 1, 1, 2, 1]],
@@ -226,20 +249,22 @@ function testConvertAlphabeticToKana() {
     ];
 
     for (const [string, expected, expectedSourceMapping] of data) {
-        const sourceMap = new TextSourceMap(string);
+        const sourceMap = new TextSourceMap2(string);
         const actual1 = jp.convertAlphabeticToKana(string, null);
         const actual2 = jp.convertAlphabeticToKana(string, sourceMap);
         assert.strictEqual(actual1, expected);
         assert.strictEqual(actual2, expected);
         if (typeof expectedSourceMapping !== 'undefined') {
-            assert.ok(sourceMap.equals(new TextSourceMap(string, expectedSourceMapping)));
+            assert.ok(sourceMap.equals(new TextSourceMap2(string, expectedSourceMapping)));
         }
     }
 }
 
+/** */
 function testDistributeFurigana() {
+    /** @type {[input: [term: string, reading: string], expected: {text: string, reading: string}[]][]} */
     const data = [
-        [
+        ([
             ['有り難う', 'ありがとう'],
             [
                 {text: '有', reading: 'あ'},
@@ -247,7 +272,7 @@ function testDistributeFurigana() {
                 {text: '難', reading: 'がと'},
                 {text: 'う', reading: ''}
             ]
-        ],
+        ]),
         [
             ['方々', 'かたがた'],
             [
@@ -702,7 +727,9 @@ function testDistributeFurigana() {
     }
 }
 
+/** */
 function testDistributeFuriganaInflected() {
+    /** @type {[input: [term: string, reading: string, source: string], expected: {text: string, reading: string}[]][]} */
     const data = [
         [
             ['美味しい', 'おいしい', '美味しかた'],
@@ -751,7 +778,9 @@ function testDistributeFuriganaInflected() {
     }
 }
 
+/** */
 function testCollapseEmphaticSequences() {
+    /** @type {[input: [text: string, fullCollapse: boolean], output: [expected: string, expectedSourceMapping: number[]]][]} */
     const data = [
         [['かこい', false], ['かこい', [1, 1, 1]]],
         [['かこい', true], ['かこい', [1, 1, 1]]],
@@ -793,18 +822,20 @@ function testCollapseEmphaticSequences() {
     ];
 
     for (const [[text, fullCollapse], [expected, expectedSourceMapping]] of data) {
-        const sourceMap = new TextSourceMap(text);
+        const sourceMap = new TextSourceMap2(text);
         const actual1 = jp.collapseEmphaticSequences(text, fullCollapse, null);
         const actual2 = jp.collapseEmphaticSequences(text, fullCollapse, sourceMap);
         assert.strictEqual(actual1, expected);
         assert.strictEqual(actual2, expected);
         if (typeof expectedSourceMapping !== 'undefined') {
-            assert.ok(sourceMap.equals(new TextSourceMap(text, expectedSourceMapping)));
+            assert.ok(sourceMap.equals(new TextSourceMap2(text, expectedSourceMapping)));
         }
     }
 }
 
+/** */
 function testIsMoraPitchHigh() {
+    /** @type {[input: [moraIndex: number, pitchAccentDownstepPosition: number], expected: boolean][]} */
     const data = [
         [[0, 0], false],
         [[1, 0], true],
@@ -838,7 +869,9 @@ function testIsMoraPitchHigh() {
     }
 }
 
+/** */
 function testGetKanaMorae() {
+    /** @type {[text: string, expected: string[]][]} */
     const data = [
         ['かこ', ['か', 'こ']],
         ['かっこ', ['か', 'っ', 'こ']],
@@ -858,6 +891,7 @@ function testGetKanaMorae() {
 }
 
 
+/** */
 function main() {
     testIsCodePointKanji();
     testIsCodePointKana();
diff --git a/test/test-jsdom.js b/test/test-jsdom.js
index 5078c240ea..1ef4978cfc 100644
--- a/test/test-jsdom.js
+++ b/test/test-jsdom.js
@@ -32,13 +32,18 @@ function testJSDOMSelectorBug() {
     const div = document.createElement('div');
     div.innerHTML = '<div class="b"><div class="c"></div></div>';
     const c = div.querySelector('.c');
-    assert.doesNotThrow(() => { c.matches('.a:nth-last-of-type(1) .b .c'); });
+    assert.doesNotThrow(() => {
+        if (c === null) { throw new Error('Element not found'); }
+        c.matches('.a:nth-last-of-type(1) .b .c');
+    });
 }
 
+/** */
 function testJSDOM() {
     testJSDOMSelectorBug();
 }
 
+/** */
 function main() {
     testJSDOM();
 }
diff --git a/test/test-json-schema.js b/test/test-json-schema.js
index 35ecc5e9ca..f9cb023c1b 100644
--- a/test/test-json-schema.js
+++ b/test/test-json-schema.js
@@ -23,30 +23,54 @@ const {VM} = require('../dev/vm');
 const vm = new VM();
 vm.execute([
     'js/core.js',
+    'js/core/extension-error.js',
     'js/general/cache-map.js',
     'js/data/json-schema.js'
 ]);
-const JsonSchema = vm.get('JsonSchema');
+/** @type {typeof JsonSchema} */
+const JsonSchema2 = vm.getSingle('JsonSchema');
 
 
+/**
+ * @param {import('json-schema').Schema} schema
+ * @param {unknown} value
+ * @returns {boolean}
+ */
 function schemaValidate(schema, value) {
-    return new JsonSchema(schema).isValid(value);
+    return new JsonSchema2(schema).isValid(value);
 }
 
+/**
+ * @param {import('json-schema').Schema} schema
+ * @param {unknown} value
+ * @returns {import('json-schema').Value}
+ */
 function getValidValueOrDefault(schema, value) {
-    return new JsonSchema(schema).getValidValueOrDefault(value);
+    return new JsonSchema2(schema).getValidValueOrDefault(value);
 }
 
+/**
+ * @param {import('json-schema').Schema} schema
+ * @param {import('json-schema').Value} value
+ * @returns {import('json-schema').Value}
+ */
 function createProxy(schema, value) {
-    return new JsonSchema(schema).createProxy(value);
+    return new JsonSchema2(schema).createProxy(value);
 }
 
+/**
+ * @template T
+ * @param {T} value
+ * @returns {T}
+ */
 function clone(value) {
     return JSON.parse(JSON.stringify(value));
 }
 
 
+/** */
 function testValidate1() {
+    /** @type {import('json-schema').Schema} */
     const schema = {
         allOf: [
             {
@@ -65,13 +89,19 @@ function testValidate1() {
                 ]
             },
             {
-                not: [
-                    {multipleOf: 20}
-                ]
+                not: {
+                    anyOf: [
+                        {multipleOf: 20}
+                    ]
+                }
             }
         ]
     };
 
+    /**
+     * @param {number} value
+     * @returns {boolean}
+     */
     const jsValidate = (value) => {
         return (
             typeof value === 'number' &&
@@ -93,11 +123,13 @@ function testValidate1() {
     for (let i = -111; i <= 111; i++) {
         const actual = schemaValidate(schema, i);
         const expected = jsValidate(i);
-        assert.strictEqual(actual, expected);
+        assert.strictEqual(actual, expected, `i=${i}; expected=${expected}; actual=${actual}`);
     }
 }
 
+/** */
 function testValidate2() {
+    /** @type {{schema: import('json-schema').Schema, inputs: {expected: boolean, value: unknown}[]}[]} */
     const data = [
         // String tests
         {
@@ -500,7 +532,9 @@ function testValidate2() {
 }
 
 
+/** */
 function testGetValidValueOrDefault1() {
+    /** @type {{schema: import('json-schema').Schema, inputs: [value: unknown, expected: unknown][]}[]} */
     const data = [
         // Test value defaulting on objects with additionalProperties=false
         {
@@ -672,10 +706,10 @@ function testGetValidValueOrDefault1() {
                 type: 'object',
                 required: ['toString'],
                 properties: {
-                    toString: {
+                    toString: /** @type {import('json-schema').SchemaObject} */ ({
                         type: 'string',
                         default: 'default'
-                    }
+                    })
                 }
             },
             inputs: [
@@ -854,7 +888,9 @@ function testGetValidValueOrDefault1() {
 }
 
 
+/** */
 function testProxy1() {
+    /** @type {{schema: import('json-schema').Schema, tests: {error: boolean, value?: import('json-schema').Value, action: (value: import('core').SafeAny) => void}[]}[]} */
     const data = [
         // Object tests
         {
@@ -1000,6 +1036,7 @@ function testProxy1() {
 }
 
 
+/** */
 function main() {
     testValidate1();
     testValidate2();
diff --git a/test/test-manifest.js b/test/test-manifest.js
index b52152de7b..32a498e100 100644
--- a/test/test-manifest.js
+++ b/test/test-manifest.js
@@ -23,11 +23,15 @@ const {testMain} = require('../dev/util');
 const {ManifestUtil} = require('../dev/manifest-util');
 
 
+/**
+ * @returns {string}
+ */
 function loadManifestString() {
     const manifestPath = path.join(__dirname, '..', 'ext', 'manifest.json');
     return fs.readFileSync(manifestPath, {encoding: 'utf8'});
 }
 
+/** */
 function validateManifest() {
     const manifestUtil = new ManifestUtil();
     const manifest1 = loadManifestString();
@@ -36,6 +40,7 @@ function validateManifest() {
 }
 
 
+/** */
 function main() {
     validateManifest();
 }
diff --git a/test/test-object-property-accessor.js b/test/test-object-property-accessor.js
index d225e893d0..8826d6a92e 100644
--- a/test/test-object-property-accessor.js
+++ b/test/test-object-property-accessor.js
@@ -22,9 +22,13 @@ const {VM} = require('../dev/vm');
 
 const vm = new VM({});
 vm.execute('js/general/object-property-accessor.js');
-const ObjectPropertyAccessor = vm.get('ObjectPropertyAccessor');
+/** @type {typeof ObjectPropertyAccessor} */
+const ObjectPropertyAccessor2 = vm.getSingle('ObjectPropertyAccessor');
 
 
+/**
+ * @returns {import('core').UnknownObject}
+ */
 function createTestObject() {
     return {
         0: null,
@@ -42,7 +46,9 @@ function createTestObject() {
 }
 
 
+/** */
 function testGet1() {
+    /** @type {[pathArray: (string|number)[], getExpected: (object: import('core').SafeAny) => unknown][]} */
     const data = [
         [[], (object) => object],
         [['0'], (object) => object['0']],
@@ -58,17 +64,19 @@ function testGet1() {
 
     for (const [pathArray, getExpected] of data) {
         const object = createTestObject();
-        const accessor = new ObjectPropertyAccessor(object);
+        const accessor = new ObjectPropertyAccessor2(object);
         const expected = getExpected(object);
 
         assert.strictEqual(accessor.get(pathArray), expected);
     }
 }
 
+/** */
 function testGet2() {
     const object = createTestObject();
-    const accessor = new ObjectPropertyAccessor(object);
+    const accessor = new ObjectPropertyAccessor2(object);
 
+    /** @type {[pathArray: (string|number)[], message: string][]} */
     const data = [
         [[0], 'Invalid path: [0]'],
         [['0', 'invalid'], 'Invalid path: ["0"].invalid'],
@@ -97,8 +105,10 @@ function testGet2() {
 }
 
 
+/** */
 function testSet1() {
     const testValue = {};
+    /** @type {(string|number)[][]} */
     const data = [
         ['0'],
         ['value1', 'value2'],
@@ -113,18 +123,20 @@ function testSet1() {
 
     for (const pathArray of data) {
         const object = createTestObject();
-        const accessor = new ObjectPropertyAccessor(object);
+        const accessor = new ObjectPropertyAccessor2(object);
 
         accessor.set(pathArray, testValue);
         assert.strictEqual(accessor.get(pathArray), testValue);
     }
 }
 
+/** */
 function testSet2() {
     const object = createTestObject();
-    const accessor = new ObjectPropertyAccessor(object);
+    const accessor = new ObjectPropertyAccessor2(object);
 
     const testValue = {};
+    /** @type {[pathArray: (string|number)[], message: string][]} */
     const data = [
         [[], 'Invalid path'],
         [[0], 'Invalid path: [0]'],
@@ -146,9 +158,16 @@ function testSet2() {
 }
 
 
+/** */
 function testDelete1() {
+    /**
+     * @param {unknown} object
+     * @param {string} property
+     * @returns {boolean}
+     */
     const hasOwn = (object, property) => Object.prototype.hasOwnProperty.call(object, property);
 
+    /** @type {[pathArray: (string|number)[], validate: (object: import('core').SafeAny) => boolean][]} */
     const data = [
         [['0'], (object) => !hasOwn(object, '0')],
         [['value1', 'value2'], (object) => !hasOwn(object.value1, 'value2')],
@@ -160,14 +179,16 @@ function testDelete1() {
 
     for (const [pathArray, validate] of data) {
         const object = createTestObject();
-        const accessor = new ObjectPropertyAccessor(object);
+        const accessor = new ObjectPropertyAccessor2(object);
 
         accessor.delete(pathArray);
         assert.ok(validate(object));
     }
 }
 
+/** */
 function testDelete2() {
+    /** @type {[pathArray: (string|number)[], message: string][]} */
     const data = [
         [[], 'Invalid path'],
         [[0], 'Invalid path: [0]'],
@@ -188,14 +209,16 @@ function testDelete2() {
 
     for (const [pathArray, message] of data) {
         const object = createTestObject();
-        const accessor = new ObjectPropertyAccessor(object);
+        const accessor = new ObjectPropertyAccessor2(object);
 
         assert.throws(() => accessor.delete(pathArray), {message});
     }
 }
 
 
+/** */
 function testSwap1() {
+    /** @type {[pathArray: (string|number)[], compareValues: boolean][]} */
     const data = [
         [['0'], true],
         [['value1', 'value2'], true],
@@ -211,7 +234,7 @@ function testSwap1() {
     for (const [pathArray1, compareValues1] of data) {
         for (const [pathArray2, compareValues2] of data) {
             const object = createTestObject();
-            const accessor = new ObjectPropertyAccessor(object);
+            const accessor = new ObjectPropertyAccessor2(object);
 
             const value1a = accessor.get(pathArray1);
             const value2a = accessor.get(pathArray2);
@@ -229,7 +252,9 @@ function testSwap1() {
     }
 }
 
+/** */
 function testSwap2() {
+    /** @type {[pathArray1: (string|number)[], pathArray2: (string|number)[], checkRevert: boolean, message: string][]} */
     const data = [
         [[], [], false, 'Invalid path 1'],
         [['0'], [], false, 'Invalid path 2'],
@@ -240,7 +265,7 @@ function testSwap2() {
 
     for (const [pathArray1, pathArray2, checkRevert, message] of data) {
         const object = createTestObject();
-        const accessor = new ObjectPropertyAccessor(object);
+        const accessor = new ObjectPropertyAccessor2(object);
 
         let value1a;
         let value2a;
@@ -266,7 +291,9 @@ function testSwap2() {
 }
 
 
+/** */
 function testGetPathString1() {
+    /** @type {[pathArray: (string|number)[], expected: string][]} */
     const data = [
         [[], ''],
         [[0], '[0]'],
@@ -282,23 +309,28 @@ function testGetPathString1() {
     ];
 
     for (const [pathArray, expected] of data) {
-        assert.strictEqual(ObjectPropertyAccessor.getPathString(pathArray), expected);
+        assert.strictEqual(ObjectPropertyAccessor2.getPathString(pathArray), expected);
     }
 }
 
+/** */
 function testGetPathString2() {
+    /** @type {[pathArray: unknown[], message: string][]} */
     const data = [
         [[1.5], 'Invalid index'],
         [[null], 'Invalid type: object']
     ];
 
     for (const [pathArray, message] of data) {
-        assert.throws(() => ObjectPropertyAccessor.getPathString(pathArray), {message});
+        // @ts-ignore - Throwing is expected
+        assert.throws(() => ObjectPropertyAccessor2.getPathString(pathArray), {message});
     }
 }
 
 
+/** */
 function testGetPathArray1() {
+    /** @type {[pathString: string, pathArray: (string|number)[]][]} */
     const data = [
         ['', []],
         ['[0]', [0]],
@@ -318,11 +350,14 @@ function testGetPathArray1() {
     ];
 
     for (const [pathString, expected] of data) {
-        vm.assert.deepStrictEqual(ObjectPropertyAccessor.getPathArray(pathString), expected);
+        // @ts-ignore
+        vm.assert.deepStrictEqual(ObjectPropertyAccessor2.getPathArray(pathString), expected);
     }
 }
 
+/** */
 function testGetPathArray2() {
+    /** @type {[pathString: string, message: string][]} */
     const data = [
         ['?', 'Unexpected character: ?'],
         ['.', 'Unexpected character: .'],
@@ -349,12 +384,14 @@ function testGetPathArray2() {
     ];
 
     for (const [pathString, message] of data) {
-        assert.throws(() => ObjectPropertyAccessor.getPathArray(pathString), {message});
+        assert.throws(() => ObjectPropertyAccessor2.getPathArray(pathString), {message});
     }
 }
 
 
+/** */
 function testHasProperty() {
+    /** @type {[object: unknown, property: unknown, expected: boolean][]} */
     const data = [
         [{}, 'invalid', false],
         [{}, 0, false],
@@ -370,11 +407,14 @@ function testHasProperty() {
     ];
 
     for (const [object, property, expected] of data) {
-        assert.strictEqual(ObjectPropertyAccessor.hasProperty(object, property), expected);
+        // @ts-ignore
+        assert.strictEqual(ObjectPropertyAccessor2.hasProperty(object, property), expected);
     }
 }
 
+/** */
 function testIsValidPropertyType() {
+    /** @type {[object: unknown, property: unknown, expected: boolean][]} */
     const data = [
         [{}, 'invalid', true],
         [{}, 0, false],
@@ -390,11 +430,13 @@ function testIsValidPropertyType() {
     ];
 
     for (const [object, property, expected] of data) {
-        assert.strictEqual(ObjectPropertyAccessor.isValidPropertyType(object, property), expected);
+        // @ts-ignore
+        assert.strictEqual(ObjectPropertyAccessor2.isValidPropertyType(object, property), expected);
     }
 }
 
 
+/** */
 function main() {
     testGet1();
     testGet2();
diff --git a/test/test-options-util.js b/test/test-options-util.js
index 2be6b2f737..b3c45771f9 100644
--- a/test/test-options-util.js
+++ b/test/test-options-util.js
@@ -17,14 +17,19 @@
  */
 
 const fs = require('fs');
-const url = require('url');
+const url = require('node:url');
 const path = require('path');
 const assert = require('assert');
 const {testMain} = require('../dev/util');
 const {VM} = require('../dev/vm');
 
 
+/**
+ * @param {string} extDir
+ * @returns {VM}
+ */
 function createVM(extDir) {
+    /** @type {import('dev/vm').PseudoChrome} */
     const chrome = {
         runtime: {
             getURL(path2) {
@@ -33,6 +38,10 @@ function createVM(extDir) {
         }
     };
 
+    /**
+     * @param {string} url2
+     * @returns {Promise<import('dev/vm').PseudoFetchResponse>}
+     */
     async function fetch(url2) {
         const filePath = url.fileURLToPath(url2);
         await Promise.resolve();
@@ -49,6 +58,7 @@ function createVM(extDir) {
     const vm = new VM({chrome, fetch});
     vm.execute([
         'js/core.js',
+        'js/core/extension-error.js',
         'js/general/cache-map.js',
         'js/data/json-schema.js',
         'js/templates/template-patcher.js',
@@ -59,11 +69,19 @@ function createVM(extDir) {
 }
 
 
+/**
+ * @template T
+ * @param {T} value
+ * @returns {T}
+ */
 function clone(value) {
     return JSON.parse(JSON.stringify(value));
 }
 
 
+/**
+ * @returns {unknown}
+ */
 function createProfileOptionsTestData1() {
     return {
         version: 14,
@@ -164,6 +182,9 @@ function createProfileOptionsTestData1() {
     };
 }
 
+/**
+ * @returns {unknown}
+ */
 function createOptionsTestData1() {
     return {
         profiles: [
@@ -263,6 +284,9 @@ function createOptionsTestData1() {
 }
 
 
+/**
+ * @returns {unknown}
+ */
 function createProfileOptionsUpdatedTestData1() {
     return {
         general: {
@@ -539,6 +563,9 @@ function createProfileOptionsUpdatedTestData1() {
     };
 }
 
+/**
+ * @returns {unknown}
+ */
 function createOptionsUpdatedTestData1() {
     return {
         profiles: [
@@ -632,10 +659,14 @@ function createOptionsUpdatedTestData1() {
 }
 
 
+/**
+ * @param {string} extDir
+ */
 async function testUpdate(extDir) {
     const vm = createVM(extDir);
-    const [OptionsUtil] = vm.get(['OptionsUtil']);
-    const optionsUtil = new OptionsUtil();
+    /** @type {typeof OptionsUtil} */
+    const OptionsUtil2 = vm.getSingle('OptionsUtil');
+    const optionsUtil = new OptionsUtil2();
     await optionsUtil.prepare();
 
     const options = createOptionsTestData1();
@@ -644,7 +675,11 @@ async function testUpdate(extDir) {
     assert.deepStrictEqual(optionsUpdated, optionsExpected);
 }
 
+/**
+ * @param {string} extDir
+ */
 async function testDefault(extDir) {
+    /** @type {((options: import('options-util').IntermediateOptions) => void)[]} */
     const data = [
         (options) => options,
         (options) => {
@@ -656,8 +691,9 @@ async function testDefault(extDir) {
     ];
 
     const vm = createVM(extDir);
-    const [OptionsUtil] = vm.get(['OptionsUtil']);
-    const optionsUtil = new OptionsUtil();
+    /** @type {typeof OptionsUtil} */
+    const OptionsUtil2 = vm.getSingle('OptionsUtil');
+    const optionsUtil = new OptionsUtil2();
     await optionsUtil.prepare();
 
     for (const modify of data) {
@@ -671,13 +707,21 @@ async function testDefault(extDir) {
     }
 }
 
+/**
+ * @param {string} extDir
+ */
 async function testFieldTemplatesUpdate(extDir) {
     const vm = createVM(extDir);
-    const [OptionsUtil, TemplatePatcher] = vm.get(['OptionsUtil', 'TemplatePatcher']);
-    const optionsUtil = new OptionsUtil();
+    /** @type {[OptionsUtil: typeof OptionsUtil, TemplatePatcher: typeof TemplatePatcher]} */
+    const [OptionsUtil2, TemplatePatcher2] = vm.get(['OptionsUtil', 'TemplatePatcher']);
+    const optionsUtil = new OptionsUtil2();
     await optionsUtil.prepare();
 
-    const templatePatcher = new TemplatePatcher();
+    const templatePatcher = new TemplatePatcher2();
+    /**
+     * @param {string} fileName
+     * @returns {string}
+     */
     const loadDataFile = (fileName) => {
         const content = fs.readFileSync(path.join(extDir, fileName), {encoding: 'utf8'});
         return templatePatcher.parsePatch(content).addition;
@@ -691,6 +735,11 @@ async function testFieldTemplatesUpdate(extDir) {
         {version: 12, changes: loadDataFile('data/templates/anki-field-templates-upgrade-v12.handlebars')},
         {version: 13, changes: loadDataFile('data/templates/anki-field-templates-upgrade-v13.handlebars')}
     ];
+    /**
+     * @param {number} startVersion
+     * @param {number} targetVersion
+     * @returns {string}
+     */
     const getUpdateAdditions = (startVersion, targetVersion) => {
         let value = '';
         for (const {version, changes} of updates) {
@@ -1220,7 +1269,7 @@ async function testFieldTemplatesUpdate(extDir) {
 
     const updatesPattern = /<<<UPDATE-ADDITIONS>>>/g;
     for (const {old, expected, oldVersion, newVersion} of data) {
-        const options = createOptionsTestData1();
+        const options = /** @type {import('core').SafeAny} */ (createOptionsTestData1());
         options.profiles[0].options.anki.fieldTemplates = old;
         options.version = oldVersion;
 
@@ -1233,6 +1282,7 @@ async function testFieldTemplatesUpdate(extDir) {
 }
 
 
+/** */
 async function main() {
     const extDir = path.join(__dirname, '..', 'ext');
     await testUpdate(extDir);
diff --git a/test/test-profile-conditions-util.js b/test/test-profile-conditions-util.js
index d51874256c..2e6f751f86 100644
--- a/test/test-profile-conditions-util.js
+++ b/test/test-profile-conditions-util.js
@@ -24,55 +24,61 @@ const {VM} = require('../dev/vm');
 const vm = new VM({});
 vm.execute([
     'js/core.js',
+    'js/core/extension-error.js',
     'js/general/cache-map.js',
     'js/data/json-schema.js',
     'js/background/profile-conditions-util.js'
 ]);
-const [ProfileConditionsUtil] = vm.get(['ProfileConditionsUtil']);
+/** @type {typeof ProfileConditionsUtil} */
+const ProfileConditionsUtil2 = vm.getSingle('ProfileConditionsUtil');
 
 
+/** */
 function testNormalizeContext() {
+    /** @type {{context: import('settings').OptionsContext, expected: import('profile-conditions-util').NormalizedOptionsContext}[]} */
     const data = [
         // Empty
         {
-            context: {},
-            expected: {flags: []}
+            context: {index: 0},
+            expected: {index: 0, flags: []}
         },
 
         // Domain normalization
         {
-            context: {url: ''},
-            expected: {url: '', flags: []}
+            context: {depth: 0, url: ''},
+            expected: {depth: 0, url: '', flags: []}
         },
         {
-            context: {url: 'http://example.com/'},
-            expected: {url: 'http://example.com/', domain: 'example.com', flags: []}
+            context: {depth: 0, url: 'http://example.com/'},
+            expected: {depth: 0, url: 'http://example.com/', domain: 'example.com', flags: []}
         },
         {
-            context: {url: 'http://example.com:1234/'},
-            expected: {url: 'http://example.com:1234/', domain: 'example.com', flags: []}
+            context: {depth: 0, url: 'http://example.com:1234/'},
+            expected: {depth: 0, url: 'http://example.com:1234/', domain: 'example.com', flags: []}
         },
         {
-            context: {url: 'http://user@example.com:1234/'},
-            expected: {url: 'http://user@example.com:1234/', domain: 'example.com', flags: []}
+            context: {depth: 0, url: 'http://user@example.com:1234/'},
+            expected: {depth: 0, url: 'http://user@example.com:1234/', domain: 'example.com', flags: []}
         }
     ];
 
     for (const {context, expected} of data) {
-        const profileConditionsUtil = new ProfileConditionsUtil();
+        const profileConditionsUtil = new ProfileConditionsUtil2();
         const actual = profileConditionsUtil.normalizeContext(context);
         vm.assert.deepStrictEqual(actual, expected);
     }
 }
 
+/** */
 function testSchemas() {
+    /** @type {{conditionGroups: import('settings').ProfileConditionGroup[], expectedSchema?: import('json-schema').Schema, inputs?: {expected: boolean, context: import('settings').OptionsContext}[]}[]} */
     const data = [
         // Empty
         {
             conditionGroups: [],
             expectedSchema: {},
             inputs: [
-                {expected: true, context: {url: 'http://example.com/'}}
+                {expected: true, context: {depth: 0, url: 'http://example.com/'}}
             ]
         },
         {
@@ -81,7 +87,7 @@ function testSchemas() {
             ],
             expectedSchema: {},
             inputs: [
-                {expected: true, context: {url: 'http://example.com/'}}
+                {expected: true, context: {depth: 0, url: 'http://example.com/'}}
             ]
         },
         {
@@ -91,7 +97,7 @@ function testSchemas() {
             ],
             expectedSchema: {},
             inputs: [
-                {expected: true, context: {url: 'http://example.com/'}}
+                {expected: true, context: {depth: 0, url: 'http://example.com/'}}
             ]
         },
 
@@ -133,14 +139,16 @@ function testSchemas() {
                 }
             ],
             expectedSchema: {
-                not: [
-                    {
-                        properties: {
-                            depth: {const: 0}
-                        },
-                        required: ['depth']
-                    }
-                ]
+                not: {
+                    anyOf: [
+                        {
+                            properties: {
+                                depth: {const: 0}
+                            },
+                            required: ['depth']
+                        }
+                    ]
+                }
             },
             inputs: [
                 {expected: false, context: {depth: 0, url: 'http://example.com/'}},
@@ -380,9 +388,9 @@ function testSchemas() {
             },
             inputs: [
                 {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: []}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt']}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift']}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift', 'Ctrl']}}
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt']}},
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift']}},
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift', 'ctrl']}}
             ]
         },
         {
@@ -392,7 +400,7 @@ function testSchemas() {
                         {
                             type: 'modifierKeys',
                             operator: 'are',
-                            value: 'Alt, Shift'
+                            value: 'alt, shift'
                         }
                     ]
                 }
@@ -404,8 +412,8 @@ function testSchemas() {
                         maxItems: 2,
                         minItems: 2,
                         allOf: [
-                            {contains: {const: 'Alt'}},
-                            {contains: {const: 'Shift'}}
+                            {contains: {const: 'alt'}},
+                            {contains: {const: 'shift'}}
                         ]
                     }
                 },
@@ -413,9 +421,9 @@ function testSchemas() {
             },
             inputs: [
                 {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: []}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift']}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift', 'Ctrl']}}
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift']}},
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift', 'ctrl']}}
             ]
         },
         {
@@ -431,24 +439,26 @@ function testSchemas() {
                 }
             ],
             expectedSchema: {
-                not: [
-                    {
-                        properties: {
-                            modifierKeys: {
-                                type: 'array',
-                                maxItems: 0,
-                                minItems: 0
-                            }
-                        },
-                        required: ['modifierKeys']
-                    }
-                ]
+                not: {
+                    anyOf: [
+                        {
+                            properties: {
+                                modifierKeys: {
+                                    type: 'array',
+                                    maxItems: 0,
+                                    minItems: 0
+                                }
+                            },
+                            required: ['modifierKeys']
+                        }
+                    ]
+                }
             },
             inputs: [
                 {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: []}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift', 'Ctrl']}}
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift', 'ctrl']}}
             ]
         },
         {
@@ -458,34 +468,36 @@ function testSchemas() {
                         {
                             type: 'modifierKeys',
                             operator: 'areNot',
-                            value: 'Alt, Shift'
+                            value: 'alt, shift'
                         }
                     ]
                 }
             ],
             expectedSchema: {
-                not: [
-                    {
-                        properties: {
-                            modifierKeys: {
-                                type: 'array',
-                                maxItems: 2,
-                                minItems: 2,
-                                allOf: [
-                                    {contains: {const: 'Alt'}},
-                                    {contains: {const: 'Shift'}}
-                                ]
-                            }
-                        },
-                        required: ['modifierKeys']
-                    }
-                ]
+                not: {
+                    anyOf: [
+                        {
+                            properties: {
+                                modifierKeys: {
+                                    type: 'array',
+                                    maxItems: 2,
+                                    minItems: 2,
+                                    allOf: [
+                                        {contains: {const: 'alt'}},
+                                        {contains: {const: 'shift'}}
+                                    ]
+                                }
+                            },
+                            required: ['modifierKeys']
+                        }
+                    ]
+                }
             },
             inputs: [
                 {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: []}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt']}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift', 'Ctrl']}}
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt']}},
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift', 'ctrl']}}
             ]
         },
         {
@@ -511,9 +523,9 @@ function testSchemas() {
             },
             inputs: [
                 {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: []}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift', 'Ctrl']}}
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift', 'ctrl']}}
             ]
         },
         {
@@ -523,7 +535,7 @@ function testSchemas() {
                         {
                             type: 'modifierKeys',
                             operator: 'include',
-                            value: 'Alt, Shift'
+                            value: 'alt, shift'
                         }
                     ]
                 }
@@ -534,8 +546,8 @@ function testSchemas() {
                         type: 'array',
                         minItems: 2,
                         allOf: [
-                            {contains: {const: 'Alt'}},
-                            {contains: {const: 'Shift'}}
+                            {contains: {const: 'alt'}},
+                            {contains: {const: 'shift'}}
                         ]
                     }
                 },
@@ -543,9 +555,9 @@ function testSchemas() {
             },
             inputs: [
                 {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: []}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift', 'Ctrl']}}
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift', 'ctrl']}}
             ]
         },
         {
@@ -570,9 +582,9 @@ function testSchemas() {
             },
             inputs: [
                 {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: []}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift']}},
-                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift', 'Ctrl']}}
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift']}},
+                {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift', 'ctrl']}}
             ]
         },
         {
@@ -582,7 +594,7 @@ function testSchemas() {
                         {
                             type: 'modifierKeys',
                             operator: 'notInclude',
-                            value: 'Alt, Shift'
+                            value: 'alt, shift'
                         }
                     ]
                 }
@@ -591,19 +603,21 @@ function testSchemas() {
                 properties: {
                     modifierKeys: {
                         type: 'array',
-                        not: [
-                            {contains: {const: 'Alt'}},
-                            {contains: {const: 'Shift'}}
-                        ]
+                        not: {
+                            anyOf: [
+                                {contains: {const: 'alt'}},
+                                {contains: {const: 'shift'}}
+                            ]
+                        }
                     }
                 },
                 required: ['modifierKeys']
             },
             inputs: [
                 {expected: true,  context: {depth: 0, url: 'http://example.com/', modifierKeys: []}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt']}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift']}},
-                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['Alt', 'Shift', 'Ctrl']}}
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt']}},
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift']}},
+                {expected: false, context: {depth: 0, url: 'http://example.com/', modifierKeys: ['alt', 'shift', 'ctrl']}}
             ]
         },
 
@@ -631,11 +645,13 @@ function testSchemas() {
                 }
             },
             inputs: [
-                {expected: true,  context: {}},
-                {expected: true,  context: {flags: []}},
-                {expected: false, context: {flags: ['test1']}},
-                {expected: false, context: {flags: ['test1', 'test2']}},
-                {expected: false, context: {flags: ['test1', 'test2', 'test3']}}
+                {expected: true,  context: {depth: 0, url: ''}},
+                {expected: true,  context: {depth: 0, url: '', flags: []}},
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard', 'test2']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard', 'test2', 'test3']}}
             ]
         },
         {
@@ -645,7 +661,7 @@ function testSchemas() {
                         {
                             type: 'flags',
                             operator: 'are',
-                            value: 'test1, test2'
+                            value: 'clipboard, test2'
                         }
                     ]
                 }
@@ -658,18 +674,20 @@ function testSchemas() {
                         maxItems: 2,
                         minItems: 2,
                         allOf: [
-                            {contains: {const: 'test1'}},
+                            {contains: {const: 'clipboard'}},
                             {contains: {const: 'test2'}}
                         ]
                     }
                 }
             },
             inputs: [
-                {expected: false, context: {}},
-                {expected: false, context: {flags: []}},
-                {expected: false, context: {flags: ['test1']}},
-                {expected: true,  context: {flags: ['test1', 'test2']}},
-                {expected: false, context: {flags: ['test1', 'test2', 'test3']}}
+                {expected: false, context: {depth: 0, url: ''}},
+                {expected: false, context: {depth: 0, url: '', flags: []}},
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard', 'test2', 'test3']}}
             ]
         },
         {
@@ -685,25 +703,29 @@ function testSchemas() {
                 }
             ],
             expectedSchema: {
-                not: [
-                    {
-                        required: ['flags'],
-                        properties: {
-                            flags: {
-                                type: 'array',
-                                maxItems: 0,
-                                minItems: 0
+                not: {
+                    anyOf: [
+                        {
+                            required: ['flags'],
+                            properties: {
+                                flags: {
+                                    type: 'array',
+                                    maxItems: 0,
+                                    minItems: 0
+                                }
                             }
                         }
-                    }
-                ]
+                    ]
+                }
             },
             inputs: [
-                {expected: false, context: {}},
-                {expected: false, context: {flags: []}},
-                {expected: true,  context: {flags: ['test1']}},
-                {expected: true,  context: {flags: ['test1', 'test2']}},
-                {expected: true,  context: {flags: ['test1', 'test2', 'test3']}}
+                {expected: false, context: {depth: 0, url: ''}},
+                {expected: false, context: {depth: 0, url: '', flags: []}},
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2', 'test3']}}
             ]
         },
         {
@@ -713,35 +735,39 @@ function testSchemas() {
                         {
                             type: 'flags',
                             operator: 'areNot',
-                            value: 'test1, test2'
+                            value: 'clipboard, test2'
                         }
                     ]
                 }
             ],
             expectedSchema: {
-                not: [
-                    {
-                        required: ['flags'],
-                        properties: {
-                            flags: {
-                                type: 'array',
-                                maxItems: 2,
-                                minItems: 2,
-                                allOf: [
-                                    {contains: {const: 'test1'}},
-                                    {contains: {const: 'test2'}}
-                                ]
+                not: {
+                    anyOf: [
+                        {
+                            required: ['flags'],
+                            properties: {
+                                flags: {
+                                    type: 'array',
+                                    maxItems: 2,
+                                    minItems: 2,
+                                    allOf: [
+                                        {contains: {const: 'clipboard'}},
+                                        {contains: {const: 'test2'}}
+                                    ]
+                                }
                             }
                         }
-                    }
-                ]
+                    ]
+                }
             },
             inputs: [
-                {expected: true,  context: {}},
-                {expected: true,  context: {flags: []}},
-                {expected: true,  context: {flags: ['test1']}},
-                {expected: false, context: {flags: ['test1', 'test2']}},
-                {expected: true,  context: {flags: ['test1', 'test2', 'test3']}}
+                {expected: true,  context: {depth: 0, url: ''}},
+                {expected: true,  context: {depth: 0, url: '', flags: []}},
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard', 'test2']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2', 'test3']}}
             ]
         },
         {
@@ -766,11 +792,13 @@ function testSchemas() {
                 }
             },
             inputs: [
-                {expected: true,  context: {}},
-                {expected: true,  context: {flags: []}},
-                {expected: true,  context: {flags: ['test1']}},
-                {expected: true,  context: {flags: ['test1', 'test2']}},
-                {expected: true,  context: {flags: ['test1', 'test2', 'test3']}}
+                {expected: true,  context: {depth: 0, url: ''}},
+                {expected: true,  context: {depth: 0, url: '', flags: []}},
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2', 'test3']}}
             ]
         },
         {
@@ -780,7 +808,7 @@ function testSchemas() {
                         {
                             type: 'flags',
                             operator: 'include',
-                            value: 'test1, test2'
+                            value: 'clipboard, test2'
                         }
                     ]
                 }
@@ -792,18 +820,20 @@ function testSchemas() {
                         type: 'array',
                         minItems: 2,
                         allOf: [
-                            {contains: {const: 'test1'}},
+                            {contains: {const: 'clipboard'}},
                             {contains: {const: 'test2'}}
                         ]
                     }
                 }
             },
             inputs: [
-                {expected: false, context: {}},
-                {expected: false, context: {flags: []}},
-                {expected: false, context: {flags: ['test1']}},
-                {expected: true,  context: {flags: ['test1', 'test2']}},
-                {expected: true,  context: {flags: ['test1', 'test2', 'test3']}}
+                {expected: false, context: {depth: 0, url: ''}},
+                {expected: false, context: {depth: 0, url: '', flags: []}},
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2', 'test3']}}
             ]
         },
         {
@@ -827,11 +857,13 @@ function testSchemas() {
                 }
             },
             inputs: [
-                {expected: true,  context: {}},
-                {expected: true,  context: {flags: []}},
-                {expected: true,  context: {flags: ['test1']}},
-                {expected: true,  context: {flags: ['test1', 'test2']}},
-                {expected: true,  context: {flags: ['test1', 'test2', 'test3']}}
+                {expected: true,  context: {depth: 0, url: ''}},
+                {expected: true,  context: {depth: 0, url: '', flags: []}},
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: true,  context: {depth: 0, url: '', flags: ['clipboard', 'test2', 'test3']}}
             ]
         },
         {
@@ -841,7 +873,7 @@ function testSchemas() {
                         {
                             type: 'flags',
                             operator: 'notInclude',
-                            value: 'test1, test2'
+                            value: 'clipboard, test2'
                         }
                     ]
                 }
@@ -851,19 +883,23 @@ function testSchemas() {
                 properties: {
                     flags: {
                         type: 'array',
-                        not: [
-                            {contains: {const: 'test1'}},
-                            {contains: {const: 'test2'}}
-                        ]
+                        not: {
+                            anyOf: [
+                                {contains: {const: 'clipboard'}},
+                                {contains: {const: 'test2'}}
+                            ]
+                        }
                     }
                 }
             },
             inputs: [
-                {expected: true,  context: {}},
-                {expected: true,  context: {flags: []}},
-                {expected: false, context: {flags: ['test1']}},
-                {expected: false, context: {flags: ['test1', 'test2']}},
-                {expected: false, context: {flags: ['test1', 'test2', 'test3']}}
+                {expected: true,  context: {depth: 0, url: ''}},
+                {expected: true,  context: {depth: 0, url: '', flags: []}},
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard', 'test2']}},
+                // @ts-ignore - Ignore type for string flag for testing purposes
+                {expected: false, context: {depth: 0, url: '', flags: ['clipboard', 'test2', 'test3']}}
             ]
         },
 
@@ -1074,7 +1110,7 @@ function testSchemas() {
     ];
 
     for (const {conditionGroups, expectedSchema, inputs} of data) {
-        const profileConditionsUtil = new ProfileConditionsUtil();
+        const profileConditionsUtil = new ProfileConditionsUtil2();
         const schema = profileConditionsUtil.createSchema(conditionGroups);
         if (typeof expectedSchema !== 'undefined') {
             vm.assert.deepStrictEqual(schema.schema, expectedSchema);
@@ -1090,6 +1126,7 @@ function testSchemas() {
 }
 
 
+/** */
 function main() {
     testNormalizeContext();
     testSchemas();
diff --git a/test/test-text-source-map.js b/test/test-text-source-map.js
index dd8d3bbd32..834a3d0713 100644
--- a/test/test-text-source-map.js
+++ b/test/test-text-source-map.js
@@ -22,9 +22,11 @@ const {VM} = require('../dev/vm');
 
 const vm = new VM();
 vm.execute(['js/general/text-source-map.js']);
-const TextSourceMap = vm.get('TextSourceMap');
+/** @type {typeof TextSourceMap} */
+const TextSourceMap2 = vm.getSingle('TextSourceMap');
 
 
+/** */
 function testSource() {
     const data = [
         ['source1'],
@@ -33,12 +35,14 @@ function testSource() {
     ];
 
     for (const [source] of data) {
-        const sourceMap = new TextSourceMap(source);
+        const sourceMap = new TextSourceMap2(source);
         assert.strictEqual(source, sourceMap.source);
     }
 }
 
+/** */
 function testEquals() {
+    /** @type {[args1: [source1: string, mapping1: ?(number[])], args2: [source2: string, mapping2: ?(number[])], expectedEquals: boolean][]} */
     const data = [
         [['source1', null], ['source1', null], true],
         [['source2', null], ['source2', null], true],
@@ -70,15 +74,17 @@ function testEquals() {
     ];
 
     for (const [[source1, mapping1], [source2, mapping2], expectedEquals] of data) {
-        const sourceMap1 = new TextSourceMap(source1, mapping1);
-        const sourceMap2 = new TextSourceMap(source2, mapping2);
+        const sourceMap1 = new TextSourceMap2(source1, mapping1);
+        const sourceMap2 = new TextSourceMap2(source2, mapping2);
         assert.ok(sourceMap1.equals(sourceMap1));
         assert.ok(sourceMap2.equals(sourceMap2));
         assert.strictEqual(sourceMap1.equals(sourceMap2), expectedEquals);
     }
 }
 
+/** */
 function testGetSourceLength() {
+    /** @type {[args: [source: string, mapping: number[]], finalLength: number, expectedValue: number][]} */
     const data = [
         [['source', [1, 1, 1, 1, 1, 1]], 1, 1],
         [['source', [1, 1, 1, 1, 1, 1]], 2, 2],
@@ -98,12 +104,14 @@ function testGetSourceLength() {
     ];
 
     for (const [[source, mapping], finalLength, expectedValue] of data) {
-        const sourceMap = new TextSourceMap(source, mapping);
+        const sourceMap = new TextSourceMap2(source, mapping);
         assert.strictEqual(sourceMap.getSourceLength(finalLength), expectedValue);
     }
 }
 
+/** */
 function testCombineInsert() {
+    /** @type {[args: [source: string, mapping: ?(number[])], expectedArgs: [expectedSource: string, expectedMapping: ?(number[])], operations: [operation: string, arg1: number, arg2: number][]][]} */
     const data = [
         // No operations
         [
@@ -207,8 +215,8 @@ function testCombineInsert() {
     ];
 
     for (const [[source, mapping], [expectedSource, expectedMapping], operations] of data) {
-        const sourceMap = new TextSourceMap(source, mapping);
-        const expectedSourceMap = new TextSourceMap(expectedSource, expectedMapping);
+        const sourceMap = new TextSourceMap2(source, mapping);
+        const expectedSourceMap = new TextSourceMap2(expectedSource, expectedMapping);
         for (const [operation, ...args] of operations) {
             switch (operation) {
                 case 'combine':
@@ -224,6 +232,7 @@ function testCombineInsert() {
 }
 
 
+/** */
 function main() {
     testSource();
     testEquals();
diff --git a/test/test-translator.js b/test/test-translator.js
index 485eb665e0..0c84e0be2b 100644
--- a/test/test-translator.js
+++ b/test/test-translator.js
@@ -23,11 +23,17 @@ const {testMain} = require('../dev/util');
 const {TranslatorVM} = require('../dev/translator-vm');
 
 
+/**
+ * @template T
+ * @param {T} value
+ * @returns {T}
+ */
 function clone(value) {
     return JSON.parse(JSON.stringify(value));
 }
 
 
+/** */
 async function main() {
     const write = (process.argv[2] === '--write');
 
@@ -54,6 +60,7 @@ async function main() {
             case 'findTerms':
                 {
                     const {name, mode, text} = test;
+                    /** @type {import('translation').FindTermsOptions} */
                     const options = translatorVM.buildOptions(optionsPresets, test.options);
                     const {dictionaryEntries, originalTextLength} = clone(await translatorVM.translator.findTerms(mode, text, options));
                     const noteDataList = mode !== 'simple' ? clone(dictionaryEntries.map((dictionaryEntry) => translatorVM.createTestAnkiNoteData(clone(dictionaryEntry), mode))) : null;
@@ -69,9 +76,10 @@ async function main() {
             case 'findKanji':
                 {
                     const {name, text} = test;
+                    /** @type {import('translation').FindKanjiOptions} */
                     const options = translatorVM.buildOptions(optionsPresets, test.options);
                     const dictionaryEntries = clone(await translatorVM.translator.findKanji(text, options));
-                    const noteDataList = clone(dictionaryEntries.map((dictionaryEntry) => translatorVM.createTestAnkiNoteData(clone(dictionaryEntry), null)));
+                    const noteDataList = clone(dictionaryEntries.map((dictionaryEntry) => translatorVM.createTestAnkiNoteData(clone(dictionaryEntry), 'split')));
                     actualResults1.push({name, dictionaryEntries});
                     actualResults2.push({name, noteDataList});
                     if (!write) {
diff --git a/test/test-workers.js b/test/test-workers.js
index b4ec4d7d3b..3de7ac4806 100644
--- a/test/test-workers.js
+++ b/test/test-workers.js
@@ -24,21 +24,33 @@ const assert = require('assert');
 
 
 class StubClass {
+    /** */
     prepare() {
         // NOP
     }
 }
 
 
+/**
+ * @returns {import('core').SafeAny}
+ */
 function loadEslint() {
     return JSON.parse(fs.readFileSync(path.join(__dirname, '..', '.eslintrc.json'), {encoding: 'utf8'}));
 }
 
+/**
+ * @param {string[]} scriptPaths
+ * @returns {string[]}
+ */
 function filterScriptPaths(scriptPaths) {
     const extDirName = 'ext';
     return scriptPaths.filter((src) => !src.startsWith('/lib/')).map((src) => `${extDirName}${src}`);
 }
 
+/**
+ * @param {string} fileName
+ * @returns {string[]}
+ */
 function getAllHtmlScriptPaths(fileName) {
     const domSource = fs.readFileSync(fileName, {encoding: 'utf8'});
     const dom = new JSDOM(domSource);
@@ -52,6 +64,9 @@ function getAllHtmlScriptPaths(fileName) {
     }
 }
 
+/**
+ * @param {string[]} scripts
+ */
 function convertBackgroundScriptsToServiceWorkerScripts(scripts) {
     // Use parse5-based SimpleDOMParser
     scripts.splice(0, 0, '/lib/parse5.js');
@@ -60,9 +75,18 @@ function convertBackgroundScriptsToServiceWorkerScripts(scripts) {
     scripts[index] = '/js/dom/simple-dom-parser.js';
 }
 
+/**
+ * @param {string} scriptPath
+ * @param {import('core').UnknownObject} fields
+ * @returns {string[]}
+ */
 function getImportedScripts(scriptPath, fields) {
+    /** @type {string[]} */
     const importedScripts = [];
 
+    /**
+     * @param {...string} scripts
+     */
     const importScripts = (...scripts) => {
         importedScripts.push(...scripts);
     };
@@ -74,6 +98,7 @@ function getImportedScripts(scriptPath, fields) {
     return importedScripts;
 }
 
+/** */
 function testServiceWorker() {
     // Verify that sw.js scripts match background.html scripts
     const extDir = path.join(__dirname, '..', 'ext');
@@ -85,7 +110,7 @@ function testServiceWorker() {
     // Verify that eslint config lists files correctly
     const expectedSwRulesFiles = filterScriptPaths(scripts);
     const eslintConfig = loadEslint();
-    const swRules = eslintConfig.overrides.find((item) => (
+    const swRules = /** @type {import('core').SafeAny[]} */ (eslintConfig.overrides).find((item) => (
         typeof item.env === 'object' &&
         item.env !== null &&
         item.env.serviceworker === true
@@ -95,6 +120,7 @@ function testServiceWorker() {
     assert.deepStrictEqual(swRules.files, expectedSwRulesFiles);
 }
 
+/** */
 function testWorkers() {
     testWorker(
         'js/language/dictionary-worker-main.js',
@@ -102,6 +128,10 @@ function testWorkers() {
     );
 }
 
+/**
+ * @param {string} scriptPath
+ * @param {import('core').UnknownObject} fields
+ */
 function testWorker(scriptPath, fields) {
     // Get script paths
     const scripts = getImportedScripts(scriptPath, fields);
@@ -110,17 +140,18 @@ function testWorker(scriptPath, fields) {
     const expectedRulesFiles = filterScriptPaths(scripts);
     const expectedRulesFilesSet = new Set(expectedRulesFiles);
     const eslintConfig = loadEslint();
-    const rules = eslintConfig.overrides.find((item) => (
+    const rules = /** @type {import('core').SafeAny[]} */ (eslintConfig.overrides).find((item) => (
         typeof item.env === 'object' &&
         item.env !== null &&
         item.env.worker === true
     ));
     assert.ok(typeof rules !== 'undefined');
     assert.ok(Array.isArray(rules.files));
-    assert.deepStrictEqual(rules.files.filter((v) => expectedRulesFilesSet.has(v)), expectedRulesFiles);
+    assert.deepStrictEqual(/** @type {import('core').SafeAny[]} */ (rules.files).filter((v) => expectedRulesFilesSet.has(v)), expectedRulesFiles);
 }
 
 
+/** */
 function main() {
     try {
         testServiceWorker();
diff --git a/types/dev/dictionary-validate.d.ts b/types/dev/dictionary-validate.d.ts
new file mode 100644
index 0000000000..c39f4335c2
--- /dev/null
+++ b/types/dev/dictionary-validate.d.ts
@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as SchemaValidate from './schema-validate';
+
+export type Schema = SchemaValidate.Schema;
+
+export type Schemas = {
+    index: Schema;
+    kanjiBankV1: Schema;
+    kanjiBankV3: Schema;
+    kanjiMetaBankV3: Schema;
+    tagBankV3: Schema;
+    termBankV1: Schema;
+    termBankV3: Schema;
+    termMetaBankV3: Schema;
+};
diff --git a/types/dev/manifest.d.ts b/types/dev/manifest.d.ts
new file mode 100644
index 0000000000..4fdf3b14b6
--- /dev/null
+++ b/types/dev/manifest.d.ts
@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type Manifest = {
+    manifest: chrome.runtime.Manifest;
+    defaultVariant: string;
+    variants: ManifestVariant[];
+};
+
+export type ManifestVariant = {
+    name: string;
+    buildable?: boolean;
+    inherit?: string;
+    fileName?: string;
+    fileCopies?: string[];
+    excludeFiles?: string[];
+    modifications: Modification[];
+};
+
+export type Modification = (
+    ModificationReplace |
+    ModificationDelete |
+    ModificationSet |
+    ModificationAdd |
+    ModificationRemove |
+    ModificationSplice |
+    ModificationCopy |
+    ModificationMove
+);
+
+export type ModificationReplace = {
+    action: 'replace';
+    path: PropertyPath;
+    pattern: string;
+    patternFlags: string;
+    replacement: string;
+};
+
+export type ModificationDelete = {
+    action: 'delete';
+    path: PropertyPath;
+};
+
+export type ModificationSet = {
+    action: 'set';
+    path: PropertyPath;
+    value: unknown;
+    before?: string;
+    after?: string;
+    index?: number;
+    command?: Command;
+};
+
+export type ModificationAdd = {
+    action: 'add';
+    path: PropertyPath;
+    items: unknown[];
+};
+
+export type ModificationRemove = {
+    action: 'remove';
+    path: PropertyPath;
+    item: unknown;
+};
+
+export type ModificationSplice = {
+    action: 'splice';
+    path: PropertyPath;
+    start: number;
+    deleteCount: number;
+    items: unknown[];
+};
+
+export type ModificationCopy = {
+    action: 'copy';
+    path: PropertyPath;
+    newPath: PropertyPath;
+    before?: string;
+    after?: string;
+    index?: number;
+};
+
+export type ModificationMove = {
+    action: 'move';
+    path: PropertyPath;
+    newPath: PropertyPath;
+    before?: string;
+    after?: string;
+    index?: number;
+};
+
+export type PropertyPath = (string | number)[];
+
+export type Command = {
+    command: string;
+    args: string[];
+    trim: boolean;
+};
diff --git a/types/dev/schema-validate.d.ts b/types/dev/schema-validate.d.ts
new file mode 100644
index 0000000000..b30c8a04d1
--- /dev/null
+++ b/types/dev/schema-validate.d.ts
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as AjvModule from 'ajv';
+
+export type ValidateMode = 'ajv' | null;
+
+export type Schema = unknown;
+
+export type Ajv = typeof AjvModule.default;
diff --git a/types/dev/vm.d.ts b/types/dev/vm.d.ts
new file mode 100644
index 0000000000..f103de97a5
--- /dev/null
+++ b/types/dev/vm.d.ts
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Translation from '../ext/translation';
+
+export type PseudoURL = {
+    hash: string;
+    host: string;
+    hostname: string;
+    href: string;
+    toString(): string;
+    origin: string;
+    password: string;
+    pathname: string;
+    port: string;
+    protocol: string;
+    search: string;
+    searchParams: URLSearchParams;
+    username: string;
+    toJSON(): string;
+};
+
+export type VMAssert = {
+    deepStrictEqual: (actual: unknown, expected: unknown) => void;
+};
+
+export type PseudoChrome = {
+    runtime: {
+        getURL(path: string): string;
+    };
+};
+
+export type PseudoFetchResponse = {
+    ok: boolean;
+    status: number;
+    statusText: string;
+    text(): Promise<string>;
+    json(): Promise<unknown>;
+};
+
+export type OptionsPresetObject = {
+    [key: string]: OptionsPreset;
+};
+
+export type OptionsPreset = Partial<Translation.FindTermsOptions>;
diff --git a/types/ext/anki-controller.d.ts b/types/ext/anki-controller.d.ts
new file mode 100644
index 0000000000..f9a3d6460d
--- /dev/null
+++ b/types/ext/anki-controller.d.ts
@@ -0,0 +1,27 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type AnkiData = {
+    deckNames: string[];
+    modelNames: string[];
+};
+
+export type FieldEntry = {
+    fieldName: string;
+    inputField: HTMLInputElement;
+    fieldNameContainerNode: HTMLElement;
+};
diff --git a/types/ext/anki-note-builder.d.ts b/types/ext/anki-note-builder.d.ts
new file mode 100644
index 0000000000..fbcb932833
--- /dev/null
+++ b/types/ext/anki-note-builder.d.ts
@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Anki from './anki';
+import type * as AnkiTemplates from './anki-templates';
+import type * as AnkiTemplatesInternal from './anki-templates-internal';
+import type * as Audio from './audio';
+import type * as Dictionary from './dictionary';
+import type * as Extension from './extension';
+import type * as Settings from './settings';
+import type * as TemplateRenderer from './template-renderer';
+
+export type CreateNoteDetails = {
+    dictionaryEntry: Dictionary.DictionaryEntry;
+    mode: AnkiTemplatesInternal.CreateMode;
+    context: AnkiTemplatesInternal.Context;
+    template: string;
+    deckName: string;
+    modelName: string;
+    fields: Field[];
+    tags: string[];
+    requirements: Requirement[];
+    checkForDuplicates: boolean;
+    duplicateScope: Settings.AnkiDuplicateScope;
+    duplicateScopeCheckAllModels: boolean;
+    resultOutputMode: Settings.ResultOutputMode;
+    glossaryLayoutMode: Settings.GlossaryLayoutMode;
+    compactTags: boolean;
+    mediaOptions: MediaOptions | null;
+};
+
+export type Field = [
+    name: string,
+    value: string,
+];
+
+export type CreateNoteResult = {
+    note: Anki.Note;
+    errors: Error[];
+    requirements: Requirement[];
+};
+
+export type GetRenderingDataDetails = {
+    dictionaryEntry: Dictionary.DictionaryEntry;
+    mode: AnkiTemplatesInternal.CreateMode;
+    context: AnkiTemplatesInternal.Context;
+    resultOutputMode?: Settings.ResultOutputMode;
+    glossaryLayoutMode?: Settings.GlossaryLayoutMode;
+    compactTags?: boolean;
+    marker: string;
+};
+
+export type CommonData = AnkiTemplatesInternal.CreateDetails;
+
+export type RequirementGeneric = {
+    type: 'audio' | 'screenshot' | 'clipboardImage' | 'clipboardText' | 'selectionText';
+};
+
+export type RequirementTextFurigana = {
+    type: 'textFurigana';
+    text: string;
+    readingMode: AnkiTemplates.TextFuriganaReadingMode;
+};
+
+export type RequirementDictionaryMedia = {
+    type: 'dictionaryMedia';
+    dictionary: string;
+    path: string;
+};
+
+export type Requirement = RequirementGeneric | RequirementTextFurigana | RequirementDictionaryMedia;
+
+export type AudioMediaOptions = {
+    sources: Audio.AudioSourceInfo[];
+    preferredAudioIndex: number | null;
+    idleTimeout: number | null;
+};
+
+export type MediaOptions = {
+    audio: AudioMediaOptions | null;
+    screenshot: {
+        format: Settings.AnkiScreenshotFormat;
+        quality: number;
+        contentOrigin: Extension.ContentOrigin;
+    };
+    textParsing: {
+        optionsContext: Settings.OptionsContext;
+        scanLength: number;
+    };
+};
+
+export type TextFuriganaDetails = {
+    text: string;
+    readingMode: AnkiTemplates.TextFuriganaReadingMode;
+};
+
+export type BatchedRequestGroup = {
+    template: string;
+    commonDataRequestsMap: Map<CommonData, BatchedRequestData[]>;
+};
+
+export type BatchedRequestData = {
+    resolve: (result: TemplateRenderer.RenderResult) => void;
+    reject: (reason?: unknown) => void;
+    marker: string;
+};
diff --git a/types/ext/anki-template-renderer-content-manager.d.ts b/types/ext/anki-template-renderer-content-manager.d.ts
new file mode 100644
index 0000000000..d7667ae2f9
--- /dev/null
+++ b/types/ext/anki-template-renderer-content-manager.d.ts
@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** A callback used when a media file has been loaded. */
+export type OnLoadCallback = (
+    /** The URL of the media that was loaded. */
+    url: string,
+) => void;
+
+/** A callback used when a media file should be unloaded. */
+export type OnUnloadCallback = (
+    /** Whether or not the media was fully loaded. */
+    fullyLoaded: boolean,
+) => void;
diff --git a/types/ext/anki-templates-internal.d.ts b/types/ext/anki-templates-internal.d.ts
new file mode 100644
index 0000000000..4cb500501e
--- /dev/null
+++ b/types/ext/anki-templates-internal.d.ts
@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as AnkiTemplates from './anki-templates';
+import type * as Dictionary from './dictionary';
+import type * as Settings from './settings';
+
+export type Context = {
+    url: string;
+    documentTitle: string;
+    query: string;
+    fullQuery: string;
+    sentence: ContextSentence;
+};
+
+export type ContextSentence = {
+    text?: string;
+    offset?: number;
+};
+
+export type CreateModeNoTest = 'kanji' | 'term-kanji' | 'term-kana';
+
+export type CreateMode = CreateModeNoTest | 'test';
+
+export type CreateDetails = {
+    /** The dictionary entry. */
+    dictionaryEntry: Dictionary.DictionaryEntry;
+    /** The result output mode. */
+    resultOutputMode: Settings.ResultOutputMode;
+    /** The mode being used to generate the Anki data. */
+    mode: CreateMode;
+    /** The glossary layout mode. */
+    glossaryLayoutMode: Settings.GlossaryLayoutMode;
+    /** Whether or not compact tags mode is enabled. */
+    compactTags: boolean;
+    /** Contextual information about the source of the dictionary entry. */
+    context: Context;
+    /** Media data. */
+    media?: AnkiTemplates.Media;
+};
+
+export type CachedValue<T> = {
+    getter: () => T;
+    hasValue: boolean;
+    value: T | undefined;
+};
diff --git a/types/ext/anki-templates.d.ts b/types/ext/anki-templates.d.ts
new file mode 100644
index 0000000000..c7e49905db
--- /dev/null
+++ b/types/ext/anki-templates.d.ts
@@ -0,0 +1,276 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Dictionary from './dictionary';
+import type * as DictionaryData from './dictionary-data';
+import type * as DictionaryDataUtil from './dictionary-data-util';
+
+export type RenderMode = 'ankiNote';
+
+export type Context = {
+    query: string;
+    fullQuery: string;
+    document: {title: string};
+};
+
+export type Media = {
+    audio?: MediaObject;
+    screenshot?: MediaObject;
+    clipboardImage?: MediaObject;
+    clipboardText?: MediaObject;
+    selectionText?: MediaObject;
+    textFurigana?: TextFuriganaSegment[];
+    dictionaryMedia?: DictionaryMedia;
+};
+
+export type MediaObject = {value: string};
+
+export type MediaSimpleType = (
+    'audio' |
+    'screenshot' |
+    'clipboardImage' |
+    'clipboardText' |
+    'selectionText'
+);
+
+export type MediaType = (
+    MediaSimpleType |
+    'textFurigana' |
+    'dictionaryMedia'
+);
+
+export type TextFuriganaSegment = {
+    text: string;
+    readingMode: TextFuriganaReadingMode;
+    details: MediaObject;
+};
+
+export type TextFuriganaReadingMode = 'hiragana' | 'katakana' | null;
+
+export type DictionaryMedia = {
+    [dictionary: string]: {
+        [path: string]: MediaObject;
+    };
+};
+
+export type NoteData = {
+    marker: string;
+    readonly definition: DictionaryEntry;
+    glossaryLayoutMode: string;
+    compactTags: boolean;
+    group: boolean;
+    merge: boolean;
+    modeTermKanji: boolean;
+    modeTermKana: boolean;
+    modeKanji: boolean;
+    compactGlossaries: boolean;
+    readonly uniqueExpressions: string[];
+    readonly uniqueReadings: string[];
+    readonly pitches: PitchGroup[];
+    readonly pitchCount: number;
+    readonly context: Context;
+    media: Media;
+    readonly dictionaryEntry: Dictionary.DictionaryEntry;
+};
+
+export type PitchGroup = {
+    dictionary: string;
+    pitches: Pitch[];
+};
+
+export type Pitch = {
+    expressions: string[];
+    reading: string;
+    position: number;
+    nasalPositions: number[];
+    devoicePositions: number[];
+    tags: PitchTag[];
+    exclusiveExpressions: string[];
+    exclusiveReadings: string[];
+};
+
+/**
+ * For legacy reasons, {@link Pitch} has a custom tag type that resembles {@link Dictionary.Tag}.
+ */
+export type PitchTag = {
+    name: string;
+    category: string;
+    order: number;
+    score: number;
+    content: string[];
+    dictionaries: string[];
+    redundant: boolean;
+};
+
+export type KanjiDictionaryEntry = {
+    type: 'kanji';
+    character: string;
+    dictionary: string;
+    onyomi: string[];
+    kunyomi: string[];
+    glossary: string[];
+    readonly tags: Tag[];
+    readonly stats: KanjiStatGroups;
+    readonly frequencies: KanjiFrequency[];
+    url: string;
+    readonly cloze: Cloze;
+};
+
+export type KanjiStatGroups = {
+    [propName: string]: KanjiStat[];
+};
+
+export type KanjiStat = {
+    name: string;
+    category: string;
+    notes: string;
+    order: number;
+    score: number;
+    dictionary: string;
+    value: number | string;
+};
+
+export type KanjiFrequency = {
+    index: number;
+    dictionary: string;
+    dictionaryOrder: {
+        index: number;
+        priority: number;
+    };
+    character: string;
+    frequency: number | string;
+};
+
+export type TermDictionaryEntryType = 'term' | 'termGrouped' | 'termMerged';
+
+export type TermDictionaryEntry = {
+    type: TermDictionaryEntryType;
+    id?: number;
+    source: string | null;
+    rawSource: string | null;
+    sourceTerm?: string | null;
+    reasons: string[];
+    score: number;
+    isPrimary?: boolean;
+    readonly sequence: number;
+    readonly dictionary: string;
+    dictionaryOrder: {
+        index: number;
+        priority: number;
+    };
+    readonly dictionaryNames: string[];
+    readonly expression: string | string[];
+    readonly reading: string | string[];
+    readonly expressions: TermHeadword[];
+    readonly glossary?: DictionaryData.TermGlossary[];
+    readonly definitionTags?: Tag[];
+    readonly termTags?: Tag[];
+    readonly definitions?: TermDefinition[];
+    readonly frequencies: TermFrequency[];
+    readonly pitches: TermPronunciation[];
+    sourceTermExactMatchCount: number;
+    url: string;
+    readonly cloze: Cloze;
+    readonly furiganaSegments?: FuriganaSegment[];
+};
+
+export type TermDictionaryEntryCommonInfo = {
+    uniqueTerms: string[];
+    uniqueReadings: string[];
+    definitionTags: Tag[];
+    definitions?: TermDefinition[];
+};
+
+export type UnknownDictionaryEntry = Record<string, never>;
+
+export type DictionaryEntry = KanjiDictionaryEntry | TermDictionaryEntry | UnknownDictionaryEntry;
+
+export type Tag = {
+    name: string;
+    category: string;
+    order: number;
+    score: number;
+    notes: string;
+    dictionary: string;
+    redundant: boolean;
+};
+
+export type TermDefinition = {
+    sequence: number;
+    dictionary: string;
+    glossary: DictionaryData.TermGlossary[];
+    definitionTags: Tag[];
+    only?: string[];
+};
+
+export type TermFrequency = {
+    index: number;
+    expressionIndex: number;
+    dictionary: string;
+    dictionaryOrder: {
+        index: number;
+        priority: number;
+    };
+    expression: string;
+    reading: string;
+    hasReading: boolean;
+    frequency: number | string;
+};
+
+export type TermPronunciation = {
+    index: number;
+    expressionIndex: number;
+    dictionary: string;
+    dictionaryOrder: {
+        index: number;
+        priority: number;
+    };
+    expression: string;
+    reading: string;
+    readonly pitches: TermPitch[];
+};
+
+export type TermPitch = {
+    position: number;
+    tags: Tag[];
+};
+
+export type TermFrequencyType = DictionaryDataUtil.TermFrequencyType;
+
+export type TermHeadword = {
+    sourceTerm: string;
+    expression: string;
+    reading: string;
+    readonly termTags: Tag[];
+    readonly frequencies: TermFrequency[];
+    readonly pitches: TermPronunciation[];
+    readonly furiganaSegments: FuriganaSegment[];
+    readonly termFrequency: TermFrequencyType;
+    wordClasses: string[];
+};
+
+export type FuriganaSegment = {
+    text: string;
+    furigana: string;
+};
+
+export type Cloze = {
+    sentence: string;
+    prefix: string;
+    body: string;
+    suffix: string;
+};
diff --git a/types/ext/anki.d.ts b/types/ext/anki.d.ts
new file mode 100644
index 0000000000..051cd3e93f
--- /dev/null
+++ b/types/ext/anki.d.ts
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Core from './core';
+import type * as Settings from './settings';
+
+export type NoteId = number;
+
+export type CardId = number;
+
+export type Note = {
+    fields: NoteFields;
+    tags: string[];
+    deckName: string;
+    modelName: string;
+    options: {
+        allowDuplicate: boolean;
+        duplicateScope: Settings.AnkiDuplicateScope;
+        duplicateScopeOptions: {
+            deckName: string | null;
+            checkChildren: boolean;
+            checkAllModels: boolean;
+        };
+    };
+};
+
+export type NoteFields = {
+    [field: string]: string;
+};
+
+export type NoteInfoWrapper = {
+    canAdd: boolean;
+    valid: boolean;
+    noteIds: NoteId[] | null;
+    noteInfos?: (NoteInfo | null)[];
+};
+
+export type NoteInfo = {
+    noteId: NoteId;
+    tags: string[];
+    fields: {[key: string]: NoteFieldInfo};
+    modelName: string;
+    cards: CardId[];
+};
+
+export type NoteFieldInfo = {
+    value: string;
+    order: number;
+};
+
+export type ApiReflectResult = {
+    scopes: string[];
+    actions: string[];
+};
+
+export type MessageBody = {
+    action: string;
+    params: Core.SerializableObject;
+    version: number;
+    key?: string;
+};
diff --git a/types/ext/api.d.ts b/types/ext/api.d.ts
new file mode 100644
index 0000000000..19a62c1c54
--- /dev/null
+++ b/types/ext/api.d.ts
@@ -0,0 +1,460 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Anki from './anki';
+import type * as AnkiNoteBuilder from './anki-note-builder';
+import type * as Audio from './audio';
+import type * as AudioDownloader from './audio-downloader';
+import type * as Backend from './backend';
+import type * as Core from './core';
+import type * as Dictionary from './dictionary';
+import type * as DictionaryDatabase from './dictionary-database';
+import type * as DictionaryImporter from './dictionary-importer';
+import type * as Environment from './environment';
+import type * as Extension from './extension';
+import type * as Log from './log';
+import type * as Settings from './settings';
+import type * as SettingsModifications from './settings-modifications';
+import type * as Translation from './translation';
+import type * as Translator from './translator';
+
+// Generic
+
+export type Handler<TDetails, TResult, THasSender extends boolean = false> = (
+    details: TDetails,
+    sender: (THasSender extends true ? chrome.runtime.MessageSender : void)
+) => (TResult | Promise<TResult>);
+
+// optionsGet
+
+export type OptionsGetDetails = {
+    optionsContext: Settings.OptionsContext;
+};
+
+export type OptionsGetResult = Settings.ProfileOptions;
+
+// optionsGetFull
+
+export type OptionsGetFullDetails = Record<string, never>;
+
+export type OptionsGetFullResult = Settings.Options;
+
+// termsFind
+
+export type FindTermsDetails = {
+    matchType?: Translation.FindTermsMatchType;
+    deinflect?: boolean;
+};
+
+export type TermsFindDetails = {
+    text: string;
+    details: FindTermsDetails;
+    optionsContext: Settings.OptionsContext;
+};
+
+export type TermsFindResult = {
+    dictionaryEntries: Dictionary.TermDictionaryEntry[];
+    originalTextLength: number;
+};
+
+// parseText
+
+export type ParseTextDetails = {
+    text: string;
+    optionsContext: Settings.OptionsContext;
+    scanLength: number;
+    useInternalParser: boolean;
+    useMecabParser: boolean;
+};
+
+export type ParseTextResult = ParseTextResultItem[];
+
+export type ParseTextResultItem = {
+    id: string;
+    source: 'scanning-parser' | 'mecab';
+    dictionary: null | string;
+    content: ParseTextLine[];
+};
+
+export type ParseTextSegment = {
+    text: string;
+    reading: string;
+};
+
+export type ParseTextLine = ParseTextSegment[];
+
+// kanjiFind
+
+export type KanjiFindDetails = {
+    text: string;
+    optionsContext: Settings.OptionsContext;
+};
+
+export type KanjiFindResult = Dictionary.KanjiDictionaryEntry[];
+
+// isAnkiConnected
+
+export type IsAnkiConnectedDetails = Record<string, never>;
+
+export type IsAnkiConnectedResult = boolean;
+
+// getAnkiConnectVersion
+
+export type GetAnkiConnectVersionDetails = Record<string, never>;
+
+export type GetAnkiConnectVersionResult = number | null;
+
+// addAnkiNote
+
+export type AddAnkiNoteDetails = {
+    note: Anki.Note;
+};
+
+export type AddAnkiNoteResult = Anki.NoteId | null;
+
+// getAnkiNoteInfo
+
+export type GetAnkiNoteInfoDetails = {
+    notes: Anki.Note[];
+    fetchAdditionalInfo: boolean;
+};
+
+export type GetAnkiNoteInfoResult = Anki.NoteInfoWrapper[];
+
+// injectAnkiNoteMedia
+
+export type InjectAnkiNoteMediaDetails = {
+    timestamp: number;
+    definitionDetails: InjectAnkiNoteMediaDefinitionDetails;
+    audioDetails: InjectAnkiNoteMediaAudioDetails | null;
+    screenshotDetails: InjectAnkiNoteMediaScreenshotDetails | null;
+    clipboardDetails: InjectAnkiNoteMediaClipboardDetails | null;
+    dictionaryMediaDetails: InjectAnkiNoteMediaDictionaryMediaDetails[];
+};
+
+export type InjectAnkiNoteMediaTermDefinitionDetails = {
+    type: 'term';
+    term: string;
+    reading: string;
+};
+
+export type InjectAnkiNoteMediaKanjiDefinitionDetails = {
+    type: 'kanji';
+    character: string;
+};
+
+export type InjectAnkiNoteMediaDefinitionDetails = InjectAnkiNoteMediaTermDefinitionDetails | InjectAnkiNoteMediaKanjiDefinitionDetails;
+
+export type InjectAnkiNoteMediaAudioDetails = AnkiNoteBuilder.AudioMediaOptions;
+
+export type InjectAnkiNoteMediaScreenshotDetails = {
+    tabId: number;
+    frameId: number;
+    format: Settings.AnkiScreenshotFormat;
+    quality: number;
+};
+
+export type InjectAnkiNoteMediaClipboardDetails = {
+    image: boolean;
+    text: boolean;
+};
+
+export type InjectAnkiNoteMediaDictionaryMediaDetails = {
+    dictionary: string;
+    path: string;
+};
+
+export type InjectAnkiNoteMediaResult = {
+    screenshotFileName: string | null;
+    clipboardImageFileName: string | null;
+    clipboardText: string | null;
+    audioFileName: string | null;
+    dictionaryMedia: InjectAnkiNoteDictionaryMediaResult[];
+    errors: Core.SerializedError[];
+};
+
+export type InjectAnkiNoteDictionaryMediaResult = {
+    dictionary: string;
+    path: string;
+    fileName: string | null;
+};
+
+// noteView
+
+export type NoteViewDetails = {
+    noteId: Anki.NoteId;
+    mode: Settings.AnkiNoteGuiMode;
+    allowFallback: boolean;
+};
+
+export type NoteViewResult = Settings.AnkiNoteGuiMode;
+
+// suspendAnkiCardsForNote
+
+export type SuspendAnkiCardsForNoteDetails = {
+    noteId: Anki.NoteId;
+};
+
+export type SuspendAnkiCardsForNoteResult = number;
+
+// getTermAudioInfoList
+
+export type GetTermAudioInfoListDetails = {
+    source: Audio.AudioSourceInfo;
+    term: string;
+    reading: string;
+};
+
+export type GetTermAudioInfoListResult = AudioDownloader.Info[];
+
+// commandExec
+
+export type CommandExecDetails = {
+    command: string;
+    params?: Core.SerializableObject;
+};
+
+export type CommandExecResult = boolean;
+
+// sendMessageToFrame
+
+export type SendMessageToFrameDetails = {
+    frameId: number;
+    action: string;
+    params?: Core.SerializableObject;
+};
+
+export type SendMessageToFrameResult = boolean;
+
+// broadcastTab
+
+export type BroadcastTabDetails = {
+    action: string;
+    params?: Core.SerializableObject;
+};
+
+export type BroadcastTabResult = boolean;
+
+// frameInformationGet
+
+export type FrameInformationGetDetails = Record<string, never>;
+
+export type FrameInformationGetResult = Extension.ContentOrigin;
+
+// injectStylesheet
+
+export type InjectStylesheetDetails = {
+    type: 'file' | 'code';
+    value: string;
+};
+
+export type InjectStylesheetResult = void;
+
+// getStylesheetContent
+
+export type GetStylesheetContentDetails = {
+    url: string;
+};
+
+export type GetStylesheetContentResult = string;
+
+// getEnvironmentInfo
+
+export type GetEnvironmentInfoDetails = Record<string, never>;
+
+export type GetEnvironmentInfoResult = Environment.Info;
+
+// clipboardGet
+
+export type ClipboardGetDetails = Record<string, never>;
+
+export type ClipboardGetResult = string;
+
+// getDisplayTemplatesHtml
+
+export type GetDisplayTemplatesHtmlDetails = Record<string, never>;
+
+export type GetDisplayTemplatesHtmlResult = string;
+
+// getZoom
+
+export type GetZoomDetails = Record<string, never>;
+
+export type GetZoomResult = {
+    zoomFactor: number;
+};
+
+// getDefaultAnkiFieldTemplates
+
+export type GetDefaultAnkiFieldTemplatesDetails = Record<string, never>;
+
+export type GetDefaultAnkiFieldTemplatesResult = string;
+
+// getDictionaryInfo
+
+export type GetDictionaryInfoDetails = Record<string, never>;
+
+export type GetDictionaryInfoResult = DictionaryImporter.Summary[];
+
+// purgeDatabase
+
+export type PurgeDatabaseDetails = Record<string, never>;
+
+export type PurgeDatabaseResult = void;
+
+// getMedia
+
+export type GetMediaDetails = {
+    targets: GetMediaDetailsTarget[];
+};
+
+export type GetMediaDetailsTarget = {
+    path: string;
+    dictionary: string;
+};
+
+export type GetMediaResult = DictionaryDatabase.MediaDataStringContent[];
+
+// log
+
+export type LogDetails = {
+    error: Core.SerializedError;
+    level: Log.LogLevel;
+    context: Log.LogContext | undefined;
+};
+
+export type LogResult = void;
+
+// logIndicatorClear
+
+export type LogIndicatorClearDetails = Record<string, never>;
+
+export type LogIndicatorClearResult = void;
+
+// modifySettings
+
+export type ModifySettingsDetails = {
+    targets: SettingsModifications.ScopedModification[];
+    source: string;
+};
+
+export type ModifySettingsResult = Core.Response<SettingsModifications.ModificationResult>[];
+
+// getSettings
+
+export type GetSettingsDetails = {
+    targets: SettingsModifications.ScopedRead[];
+};
+
+export type GetSettingsResult = Core.Response<SettingsModifications.ModificationResult>[];
+
+// setAllSettings
+
+export type SetAllSettingsDetails = {
+    value: Settings.Options;
+    source: string;
+};
+
+export type SetAllSettingsResult = void;
+
+// getOrCreateSearchPopup
+
+export type GetOrCreateSearchPopupDetails = {
+    focus?: boolean | 'ifCreated';
+    text?: string;
+};
+
+export type GetOrCreateSearchPopupResult = {
+    tabId: number | null;
+    windowId: number;
+};
+
+// isTabSearchPopup
+
+export type IsTabSearchPopupDetails = {
+    tabId: number;
+};
+
+export type IsTabSearchPopupResult = boolean;
+
+// triggerDatabaseUpdated
+
+export type TriggerDatabaseUpdatedDetails = {
+    type: Backend.DatabaseUpdateType;
+    cause: Backend.DatabaseUpdateCause;
+};
+
+export type TriggerDatabaseUpdatedResult = void;
+
+// testMecab
+
+export type TestMecabDetails = Record<string, never>;
+
+export type TestMecabResult = true;
+
+// textHasJapaneseCharacters
+
+export type TextHasJapaneseCharactersDetails = {
+    text: string;
+};
+
+export type TextHasJapaneseCharactersResult = boolean;
+
+// getTermFrequencies
+
+export type GetTermFrequenciesDetails = {
+    termReadingList: GetTermFrequenciesDetailsTermReadingListItem[];
+    dictionaries: string[];
+};
+
+export type GetTermFrequenciesDetailsTermReadingListItem = {
+    term: string;
+    reading: string | null;
+};
+
+export type GetTermFrequenciesResult = Translator.TermFrequencySimple[];
+
+// findAnkiNotes
+
+export type FindAnkiNotesDetails = {
+    query: string;
+};
+
+export type FindAnkiNotesResult = Anki.NoteId[];
+
+// loadExtensionScripts
+
+export type LoadExtensionScriptsDetails = {
+    files: string[];
+};
+
+export type LoadExtensionScriptsResult = void;
+
+// requestBackendReadySignal
+
+export type RequestBackendReadySignalDetails = Record<string, never>;
+
+export type RequestBackendReadySignalResult = boolean;
+
+// createActionPort
+
+export type CreateActionPortDetails = Record<string, never>;
+
+export type CreateActionPortResult = {
+    name: string;
+    id: string;
+};
diff --git a/types/ext/audio-controller.d.ts b/types/ext/audio-controller.d.ts
new file mode 100644
index 0000000000..e8317aaf94
--- /dev/null
+++ b/types/ext/audio-controller.d.ts
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type EventType = 'voicesUpdated';
+
+export type VoiceInfo = {
+    voice: SpeechSynthesisVoice;
+    isJapanese: boolean;
+    index: number;
+};
diff --git a/types/ext/audio-downloader.d.ts b/types/ext/audio-downloader.d.ts
new file mode 100644
index 0000000000..b8e812f8d6
--- /dev/null
+++ b/types/ext/audio-downloader.d.ts
@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Audio from './audio';
+
+export type GetInfoHandler = (
+    term: string,
+    reading: string,
+    details?: Audio.AudioSourceInfo,
+) => Promise<Info[]>;
+
+export type Info = Info1 | Info2;
+
+export type Info1 = {
+    type: 'url';
+    url: string;
+    name?: string;
+};
+
+export type Info2 = {
+    type: 'tts';
+    text: string;
+    voice: string;
+    name?: undefined;
+};
+
+export type AudioBinaryBase64 = {
+    data: string;
+    contentType: string | null;
+};
diff --git a/types/ext/audio-system.d.ts b/types/ext/audio-system.d.ts
new file mode 100644
index 0000000000..e9766ed1e7
--- /dev/null
+++ b/types/ext/audio-system.d.ts
@@ -0,0 +1,18 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type EventType = 'voiceschanged';
diff --git a/types/ext/audio.d.ts b/types/ext/audio.d.ts
new file mode 100644
index 0000000000..4bf952c634
--- /dev/null
+++ b/types/ext/audio.d.ts
@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as DisplayAudio from './display-audio';
+
+export type AudioSourceInfo = DisplayAudio.AudioSourceShort;
diff --git a/types/ext/backend.d.ts b/types/ext/backend.d.ts
new file mode 100644
index 0000000000..5f1bd83d9d
--- /dev/null
+++ b/types/ext/backend.d.ts
@@ -0,0 +1,123 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Api from './api';
+import type * as Core from './core';
+
+export type MessageHandlerDetails = {
+    async: boolean;
+    contentScript: boolean;
+    handler: (params: Core.SerializableObject | undefined, sender: chrome.runtime.MessageSender) => unknown;
+};
+export type MessageHandlerMap = Map<string, MessageHandlerDetails>;
+export type MessageHandlerMapInit = [key: string, handlerDetails: MessageHandlerDetails][];
+
+export type MessageHandlerWithProgressDetails = {
+    async: boolean;
+    contentScript: boolean;
+    handler: (params: Core.SerializableObject | undefined, sender: chrome.runtime.MessageSender, onProgress: (...data: unknown[]) => void) => (Promise<unknown> | unknown);
+};
+export type MessageHandlerWithProgressMap = Map<string, MessageHandlerWithProgressDetails>;
+export type MessageHandlerWithProgressMapInit = [key: string, handlerDetails: MessageHandlerWithProgressDetails][];
+
+export type DatabaseUpdateType = 'dictionary';
+export type DatabaseUpdateCause = 'purge' | 'delete' | 'import';
+
+export type MecabParseResults = [
+    dictionary: string,
+    content: Api.ParseTextLine[],
+][];
+
+export type TabInfo = {
+    tab: chrome.tabs.Tab;
+    url: string | null;
+};
+
+export type SettingModification = SettingModificationSet | SettingModificationDelete | SettingModificationSwap | SettingModificationSplice | SettingModificationPush;
+
+export type SettingModificationSet = {
+    action: 'set';
+    path: string;
+    value: unknown;
+};
+
+export type SettingModificationDelete = {
+    action: 'delete';
+    path: string;
+};
+
+export type SettingModificationSwap = {
+    action: 'swap';
+    path1: string;
+    path2: string;
+};
+
+export type SettingModificationSplice = {
+    action: 'splice';
+    path: string;
+    start: number;
+    deleteCount: number;
+    items: unknown[];
+};
+
+export type SettingModificationPush = {
+    action: 'push';
+    path: string;
+    items: unknown[];
+};
+
+export type FindTabsPredicate = (tabInfo: TabInfo) => boolean | Promise<boolean>;
+
+export type InvokeWithProgressRequestMessage = (
+    InvokeWithProgressRequestFragmentMessage |
+    InvokeWithProgressRequestInvokeMessage
+);
+
+export type InvokeWithProgressRequestFragmentMessage = {
+    action: 'fragment';
+    data: string;
+};
+
+export type InvokeWithProgressRequestInvokeMessage = {
+    action: 'invoke';
+};
+
+export type InvokeWithProgressResponseMessage<TReturn = unknown> = (
+    InvokeWithProgressResponseProgressMessage |
+    InvokeWithProgressResponseCompleteMessage<TReturn> |
+    InvokeWithProgressResponseErrorMessage |
+    InvokeWithProgressResponseAcknowledgeMessage
+);
+
+export type InvokeWithProgressResponseProgressMessage = {
+    type: 'progress';
+    data: unknown[];
+};
+
+export type InvokeWithProgressResponseCompleteMessage<TReturn = unknown> = {
+    type: 'complete';
+    data: TReturn;
+};
+
+export type InvokeWithProgressResponseErrorMessage = {
+    type: 'error';
+    data: Core.SerializedError;
+};
+
+export type InvokeWithProgressResponseAcknowledgeMessage = {
+    type: 'ack';
+};
diff --git a/types/ext/backup-controller.d.ts b/types/ext/backup-controller.d.ts
new file mode 100644
index 0000000000..d494ceb9c4
--- /dev/null
+++ b/types/ext/backup-controller.d.ts
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Environment from './environment';
+import type * as Settings from './settings';
+
+export type BackupData = {
+    version: number;
+    date: string;
+    url: string;
+    manifest: chrome.runtime.Manifest;
+    environment: Environment.Info;
+    userAgent: string;
+    permissions: chrome.permissions.Permissions;
+    options: Settings.Options;
+};
+
+export type ShowSettingsImportWarningsResult = {
+    result: boolean;
+    sanitize?: boolean;
+};
diff --git a/types/ext/cache-map.d.ts b/types/ext/cache-map.d.ts
new file mode 100644
index 0000000000..a4b8bb1a86
--- /dev/null
+++ b/types/ext/cache-map.d.ts
@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export interface Node<K, V> {
+    key: K | null;
+    value: V | null;
+    previous: Node<K, V> | null;
+    next: Node<K, V> | null;
+}
diff --git a/types/ext/clipboard-monitor.d.ts b/types/ext/clipboard-monitor.d.ts
new file mode 100644
index 0000000000..f8cf7d029c
--- /dev/null
+++ b/types/ext/clipboard-monitor.d.ts
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type EventType = 'change';
+
+export type ChangeEvent = {
+    text: string;
+};
+
+export type ClipboardReaderLike = {
+    getText: (useRichText: boolean) => Promise<string>;
+};
diff --git a/types/ext/core.d.ts b/types/ext/core.d.ts
new file mode 100644
index 0000000000..ce3a09f0b5
--- /dev/null
+++ b/types/ext/core.d.ts
@@ -0,0 +1,102 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type TypeofResult = 'string' | 'number' | 'bigint' | 'boolean' | 'symbol' | 'undefined' | 'object' | 'function';
+
+/** This type is used as an explicit way of permitting the `any` type. */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export type SafeAny = any;
+
+/** This type is used as an explicit way of permitting the `Function` type. */
+// eslint-disable-next-line @typescript-eslint/ban-types
+export type SafeFunction = Function;
+
+/** This type is used as an explicit way of permitting the `any` type. */
+export type RejectionReason = SafeAny;
+
+/** This type is used as an explicit way of permitting the `object` type. */
+export type SerializableObject = {[key: string]: unknown};
+
+/** This type is used as an explicit way of permitting the `object` type. */
+export type SerializableObjectAny = {[key: string]: SafeAny};
+
+/** This type is used as an explicit way of permitting the `object` type. */
+export type UnknownObject = {[key: string | symbol]: unknown};
+
+export type TokenString = string;
+
+export type TokenObject = Record<string, never>;
+
+export type DeferredPromiseDetails<T> = {
+    promise: Promise<T>;
+    resolve: (value: T) => void;
+    reject: (reason?: RejectionReason) => void;
+};
+
+export type SerializedError1 = {
+    name: string;
+    message: string;
+    stack: string;
+    data?: unknown;
+    hasValue?: undefined;
+};
+
+export type SerializedError2 = {
+    value: unknown;
+    hasValue: true;
+};
+
+export type SerializedError = SerializedError1 | SerializedError2;
+
+export type ResponseSuccess<T = unknown> = {
+    result: T;
+    error?: undefined;
+};
+
+export type ResponseError = {
+    error: SerializedError;
+    result?: undefined;
+};
+
+export type Response<T = unknown> = ResponseSuccess<T> | ResponseError;
+
+export type MessageHandler = (params: SafeAny, ...extraArgs: SafeAny[]) => (
+    SafeAny |
+    Promise<SafeAny> |
+    MessageHandlerAsyncResult
+);
+
+export type MessageHandlerAsyncResult = {
+    async: boolean;
+    result: SafeAny | Promise<SafeAny>;
+};
+
+export type MessageHandlerDetails = {
+    /**
+     * Whether or not the handler is async or not. Values include `false`, `true`, or `'dynamic'`.
+     * When the value is `'dynamic'`, the handler should return an object of the format `{async: boolean, result: any}`.
+     */
+    async: boolean | 'dynamic';
+    /**
+     * A handler function which is passed `params` and `...extraArgs` as arguments.
+     */
+    handler: MessageHandler;
+};
+
+export type MessageHandlerMap = Map<string, MessageHandlerDetails>;
+
+export type MessageHandlerArray = [key: string, handlerDetails: MessageHandlerDetails][];
diff --git a/types/ext/cross-frame-api.d.ts b/types/ext/cross-frame-api.d.ts
new file mode 100644
index 0000000000..5cedbec94f
--- /dev/null
+++ b/types/ext/cross-frame-api.d.ts
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Core from './core';
+
+export type CrossFrameAPIPortEventType = 'disconnect';
+
+export type AcknowledgeMessage = {
+    type: 'ack';
+    id: number;
+};
+
+export type ResultMessage = {
+    type: 'result';
+    id: number;
+    data: Core.Response<unknown>;
+};
+
+export type InvokeMessage = {
+    type: 'invoke';
+    id: number;
+    data: InvocationData;
+};
+
+export type InvocationData = {
+    action: string;
+    params: Core.SerializableObject;
+};
+
+export type Message = AcknowledgeMessage | ResultMessage | InvokeMessage;
+
+export type Invocation = {
+    id: number;
+    resolve: (value: Core.SafeAny) => void;
+    reject: (reason?: unknown) => void;
+    responseTimeout: number;
+    action: string;
+    ack: boolean;
+    timer: number | null;
+};
diff --git a/types/ext/css-style-applier.d.ts b/types/ext/css-style-applier.d.ts
new file mode 100644
index 0000000000..d4db2da69d
--- /dev/null
+++ b/types/ext/css-style-applier.d.ts
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type RawStyleData = {
+    selectors: string[];
+    styles: RawStyleDataStyleArray;
+}[];
+
+export type RawStyleDataStyleArray = [
+    property: string,
+    value: string,
+][];
+
+/**
+ * A CSS rule.
+ */
+export type CssRule = {
+    /** A CSS selector string representing one or more selectors. */
+    selectors: string;
+    /** A list of CSS property and value pairs. */
+    styles: CssDeclaration[];
+};
+
+/**
+ * A single CSS property declaration.
+ */
+export type CssDeclaration = {
+    /** A CSS property's name, using kebab-case. */
+    property: string;
+    /** The property's value. */
+    value: string;
+};
diff --git a/types/ext/database.d.ts b/types/ext/database.d.ts
new file mode 100644
index 0000000000..e4a58e6011
--- /dev/null
+++ b/types/ext/database.d.ts
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type StructureDefinition<TObjectStoreName extends string> = {
+    version: number;
+    stores: {[name in TObjectStoreName]: StoreDefinition};
+};
+
+export type StoreDefinition = {
+    primaryKey: IDBObjectStoreParameters;
+    indices: string[];
+};
+
+export type UpdateFunction = (
+    db: IDBDatabase,
+    transaction: IDBTransaction,
+    oldVersion: number,
+    newVersion: number | null,
+) => void;
+
+export type CountTarget = [
+    objectStoreOrIndex: IDBObjectStore | IDBIndex,
+    query: IDBValidKey | IDBKeyRange | undefined,
+];
diff --git a/types/ext/deinflector.d.ts b/types/ext/deinflector.d.ts
new file mode 100644
index 0000000000..e6fc203ea6
--- /dev/null
+++ b/types/ext/deinflector.d.ts
@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as TranslationInternal from './translation-internal';
+
+export type ReasonTypeRaw = 'v1' | 'v5' | 'vs' | 'vk' | 'vz' | 'adj-i' | 'iru';
+
+export type ReasonsRaw = {
+    [reason: string]: {
+        kanaIn: string;
+        kanaOut: string;
+        rulesIn: ReasonTypeRaw[];
+        rulesOut: ReasonTypeRaw[];
+    }[];
+};
+
+export type ReasonVariant = [
+    kanaIn: string,
+    kanaOut: string,
+    rulesIn: TranslationInternal.DeinflectionRuleFlags,
+    rulesOut: TranslationInternal.DeinflectionRuleFlags,
+];
+
+export type Reason = [
+    reason: string,
+    variants: ReasonVariant[],
+];
diff --git a/types/ext/dictionary-data-util.d.ts b/types/ext/dictionary-data-util.d.ts
new file mode 100644
index 0000000000..751283680d
--- /dev/null
+++ b/types/ext/dictionary-data-util.d.ts
@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Dictionary from './dictionary';
+
+export type FrequencyData = {
+    frequency: number;
+    displayValue: string | null;
+};
+
+export type KanjiFrequenciesMap3 = Map<string, FrequencyData>;
+
+export type TermFrequenciesMap1 = Map<string, TermFrequenciesMap2>;
+
+export type TermFrequenciesMap2 = Map<string, TermFrequenciesMap2Data>;
+
+export type TermFrequenciesMap2Data = {
+    term: string;
+    reading: string | null;
+    values: TermFrequenciesMap3;
+};
+
+export type KanjiFrequenciesMap1 = Map<string, KanjiFrequenciesMap2>;
+
+export type KanjiFrequenciesMap2 = Map<string, KanjiFrequenciesMap2Data>;
+
+export type KanjiFrequenciesMap2Data = {
+    character: string;
+    values: KanjiFrequenciesMap3;
+};
+
+export type TermFrequenciesMap3 = Map<string, FrequencyData>;
+
+export type DictionaryFrequency<T> = {
+    dictionary: string;
+    frequencies: T[];
+};
+
+export type TermFrequency = {
+    term: string;
+    reading: string | null;
+    values: FrequencyData[];
+};
+
+export type KanjiFrequency = {
+    character: string;
+    values: FrequencyData[];
+};
+
+export type TermFrequencyType = 'popular' | 'rare' | 'normal';
+
+export type GroupedPronunciationInternal = {
+    terms: Set<string>;
+    reading: string;
+    position: number;
+    nasalPositions: number[];
+    devoicePositions: number[];
+    tags: Dictionary.Tag[];
+};
+
+export type GroupedPronunciation = {
+    terms: string[];
+    reading: string;
+    position: number;
+    nasalPositions: number[];
+    devoicePositions: number[];
+    tags: Dictionary.Tag[];
+    exclusiveTerms: string[];
+    exclusiveReadings: string[];
+};
+
+export type DictionaryGroupedPronunciations = {
+    dictionary: string;
+    pronunciations: GroupedPronunciation[];
+};
+
+export type TagGroup = {
+    tag: Dictionary.Tag;
+    headwordIndices: number[];
+};
diff --git a/types/ext/dictionary-data.d.ts b/types/ext/dictionary-data.d.ts
new file mode 100644
index 0000000000..f594f913d0
--- /dev/null
+++ b/types/ext/dictionary-data.d.ts
@@ -0,0 +1,147 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as StructuredContent from './structured-content';
+
+export type IndexVersion = 1 | 2 | 3;
+
+export type Index = {
+    format?: IndexVersion;
+    version?: IndexVersion;
+    title: string;
+    revision: string;
+    sequenced?: boolean;
+    author?: string;
+    url?: string;
+    description?: string;
+    attribution?: string;
+    frequencyMode?: 'occurrence-based' | 'rank-based';
+    tagMeta?: IndexTagMeta;
+};
+
+export type IndexTagMeta = {
+    [name: string]: IndexTag;
+};
+
+export type IndexTag = {
+    category: string;
+    order: number;
+    notes: string;
+    score: number;
+};
+
+export type TermV1 = [
+    expression: string,
+    reading: string,
+    definitionTags: string | null,
+    rules: string,
+    score: number,
+    ...glossary: string[],
+];
+
+export type TermV3 = [
+    expression: string,
+    reading: string,
+    definitionTags: string | null,
+    rules: string,
+    score: number,
+    glossary: TermGlossary[],
+    sequence: number,
+    termTags: string,
+];
+
+export type KanjiV1 = [
+    character: string,
+    onyomi: string,
+    kunyomi: string,
+    tags: string,
+    ...meanings: string[],
+];
+
+export type KanjiV3 = [
+    character: string,
+    onyomi: string,
+    kunyomi: string,
+    tags: string,
+    meanings: string[],
+    stats: {[name: string]: string},
+];
+
+export type TermGlossary = (
+    TermGlossaryString |
+    TermGlossaryText |
+    TermGlossaryImage |
+    TermGlossaryStructuredContent
+);
+
+export type TermGlossaryString = string;
+export type TermGlossaryText = {type: 'text', text: string};
+export type TermGlossaryImage = {type: 'image'} & TermImage;
+export type TermGlossaryStructuredContent = {type: 'structured-content', content: StructuredContent.Content};
+
+export type TermImage = StructuredContent.ImageElementBase;
+
+export type Tag = [
+    name: string,
+    category: string,
+    order: number,
+    notes: string,
+    score: number,
+];
+
+export type GenericFrequencyData = string | number | {
+    value: number;
+    displayValue?: string;
+    reading?: undefined; // Used for type disambiguation, field does not actually exist
+};
+
+export type TermMeta = TermMetaFrequency | TermMetaPitch;
+
+export type TermMetaFrequencyDataWithReading = {
+    reading: string;
+    frequency: GenericFrequencyData;
+};
+
+export type TermMetaFrequency = [
+    expression: string,
+    mode: 'freq',
+    data: GenericFrequencyData | TermMetaFrequencyDataWithReading,
+];
+
+export type TermMetaPitchData = {
+    reading: string;
+    pitches: {
+        position: number;
+        nasal?: number | number[];
+        devoice?: number | number[];
+        tags?: string[];
+    }[];
+};
+
+export type TermMetaPitch = [
+    expression: string,
+    mode: 'pitch',
+    data: TermMetaPitchData,
+];
+
+export type KanjiMeta = KanjiMetaFrequency;
+
+export type KanjiMetaFrequency = [
+    character: string,
+    mode: 'freq',
+    data: GenericFrequencyData,
+];
diff --git a/types/ext/dictionary-database.d.ts b/types/ext/dictionary-database.d.ts
new file mode 100644
index 0000000000..2e0f854b73
--- /dev/null
+++ b/types/ext/dictionary-database.d.ts
@@ -0,0 +1,240 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Dictionary from './dictionary';
+import type * as DictionaryData from './dictionary-data';
+import type * as DictionaryImporter from './dictionary-importer';
+
+export type DatabaseId = {
+    id: number; // Automatic database primary key
+};
+
+export interface MediaDataBase<TContentType = unknown> {
+    dictionary: string;
+    path: string;
+    mediaType: string;
+    width: number;
+    height: number;
+    content: TContentType;
+}
+
+export interface MediaDataArrayBufferContent extends MediaDataBase<ArrayBuffer> {}
+export interface MediaDataStringContent extends MediaDataBase<string> {}
+
+export type Media = {index: number} & MediaDataBase<ArrayBuffer>;
+
+export type DatabaseTermEntry = {
+    expression: string;
+    reading: string;
+    expressionReverse?: string;
+    readingReverse?: string;
+    definitionTags: string | null;
+    /** Legacy alias for the `definitionTags` field. */
+    tags?: string;
+    rules: string;
+    score: number;
+    glossary: DictionaryData.TermGlossary[];
+    sequence?: number;
+    termTags?: string;
+    dictionary: string;
+};
+
+export type DatabaseTermEntryWithId = DatabaseTermEntry & DatabaseId;
+
+export type TermEntry = {
+    index: number;
+    matchType: MatchType;
+    matchSource: MatchSource;
+    term: string;
+    reading: string;
+    definitionTags: string[];
+    termTags: string[];
+    rules: string[];
+    definitions: DictionaryData.TermGlossary[];
+    score: number;
+    dictionary: string;
+    id: number;
+    sequence: number;
+};
+
+export type DatabaseKanjiEntry = {
+    character: string;
+    onyomi: string;
+    kunyomi: string;
+    tags: string;
+    meanings: string[];
+    dictionary: string;
+    stats?: {[name: string]: string};
+};
+
+export type KanjiEntry = {
+    index: number;
+    character: string;
+    onyomi: string[];
+    kunyomi: string[];
+    tags: string[];
+    definitions: string[];
+    stats: {[name: string]: string};
+    dictionary: string;
+};
+
+export type Tag = {
+    name: string;
+    category: string;
+    order: number;
+    notes: string;
+    score: number;
+    dictionary: string;
+};
+
+export type DatabaseTermMeta = DatabaseTermMetaFrequency | DatabaseTermMetaPitch;
+
+export type DatabaseTermMetaFrequency = {
+    expression: string;
+    mode: 'freq';
+    data: DictionaryData.GenericFrequencyData | DictionaryData.TermMetaFrequencyDataWithReading;
+    dictionary: string;
+};
+
+export type DatabaseTermMetaPitch = {
+    expression: string;
+    mode: 'pitch';
+    data: DictionaryData.TermMetaPitchData;
+    dictionary: string;
+};
+
+export type TermMetaFrequencyDataWithReading = {
+    reading: string;
+    frequency: DictionaryData.GenericFrequencyData;
+};
+
+export type TermMeta = TermMetaFrequency | TermMetaPitch;
+
+export type TermMetaType = TermMeta['mode'];
+
+export type TermMetaFrequency = {
+    index: number;
+    term: string;
+    mode: 'freq';
+    data: DictionaryData.GenericFrequencyData | DictionaryData.TermMetaFrequencyDataWithReading;
+    dictionary: string;
+};
+
+export type TermMetaPitch = {
+    index: number;
+    term: string;
+    mode: 'pitch';
+    data: DictionaryData.TermMetaPitchData;
+    dictionary: string;
+};
+
+export type DatabaseKanjiMeta = DatabaseKanjiMetaFrequency;
+
+export type DatabaseKanjiMetaFrequency = {
+    character: string;
+    mode: 'freq';
+    data: DictionaryData.GenericFrequencyData;
+    dictionary: string;
+};
+
+export type KanjiMeta = KanjiMetaFrequency;
+
+export type KanjiMetaType = KanjiMeta['mode'];
+
+export type KanjiMetaFrequency = {
+    index: number;
+    character: string;
+    mode: 'freq';
+    data: DictionaryData.GenericFrequencyData;
+    dictionary: string;
+};
+
+export type DictionaryCounts = {
+    total: DictionaryCountGroup | null;
+    counts: DictionaryCountGroup[];
+};
+
+export type DictionaryCountGroup = {
+    [key: string]: number;
+};
+
+export type ObjectStoreName = (
+    'dictionaries' |
+    'terms' |
+    'termMeta' |
+    'kanji' |
+    'kanjiMeta' |
+    'tagMeta' |
+    'media'
+);
+
+/* eslint-disable @stylistic/ts/indent */
+export type ObjectStoreData<T extends ObjectStoreName> = (
+    T extends 'dictionaries' ? DictionaryImporter.Summary :
+    T extends 'terms' ? DatabaseTermEntry :
+    T extends 'termMeta' ? DatabaseTermMeta :
+    T extends 'kanji' ? DatabaseKanjiEntry :
+    T extends 'kanjiMeta' ? DatabaseKanjiMeta :
+    T extends 'tagMeta' ? Tag :
+    T extends 'media' ? MediaDataArrayBufferContent :
+    never
+);
+/* eslint-enable @stylistic/ts/indent */
+
+export type DeleteDictionaryProgressData = {
+    count: number;
+    processed: number;
+    storeCount: number;
+    storesProcesed: number;
+};
+
+export type DeleteDictionaryProgressCallback = (data: DeleteDictionaryProgressData) => void;
+
+export type MatchType = Dictionary.TermSourceMatchType;
+
+export type MatchSource = Dictionary.TermSourceMatchSource;
+
+export type DictionaryAndQueryRequest = {
+    query: string | number;
+    dictionary: string;
+};
+
+export type TermExactRequest = {
+    term: string;
+    reading: string;
+};
+
+export type MediaRequest = {
+    path: string;
+    dictionary: string;
+};
+
+export type FindMultiBulkData<TItem = unknown> = {
+    item: TItem;
+    itemIndex: number;
+    indexIndex: number;
+};
+
+export type CreateQuery<TItem> = (item: TItem) => (IDBValidKey | IDBKeyRange | null);
+
+export type FindPredicate<TItem, TRow> = (row: TRow, item: TItem) => boolean;
+
+export type CreateResult<TItem, TRow, TResult> = (row: TRow, data: FindMultiBulkData<TItem>) => TResult;
+
+export type DictionarySet = {
+    has(value: string): boolean;
+};
diff --git a/types/ext/dictionary-importer-media-loader.d.ts b/types/ext/dictionary-importer-media-loader.d.ts
new file mode 100644
index 0000000000..afbb1902bb
--- /dev/null
+++ b/types/ext/dictionary-importer-media-loader.d.ts
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Attempts to load an image using an ArrayBuffer and a media type to return details about it.
+ * @param content The binary content for the image, encoded as an ArrayBuffer.
+ * @param mediaType The media type for the image content.
+ * @param transfer An optional array of data that should be transferred in `postMessage` calls.
+ *   When the resulting promise resolves, this array will contain the `content` object.
+ * @returns Details about the requested image content.
+ * @throws {Error} An error can be thrown if the image fails to load.
+ */
+export type GetImageDetailsFunction = (
+    content: ArrayBuffer,
+    mediaType: string,
+    transfer?: Transferable[]
+) => Promise<{content: ArrayBuffer, width: number, height: number}>;
+
+
+export type GenericMediaLoader = {
+    getImageDetails: GetImageDetailsFunction;
+};
diff --git a/types/ext/dictionary-importer.d.ts b/types/ext/dictionary-importer.d.ts
new file mode 100644
index 0000000000..16ce66ce18
--- /dev/null
+++ b/types/ext/dictionary-importer.d.ts
@@ -0,0 +1,95 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as DictionaryData from './dictionary-data';
+import type * as DictionaryDatabase from './dictionary-database';
+import type * as StructuredContent from './structured-content';
+
+export type OnProgressCallback = (data: ProgressData) => void;
+
+export type ProgressData = {
+    stepIndex: number;
+    stepCount: number;
+    index: number;
+    count: number;
+};
+
+export type ImportResult = {
+    result: Summary;
+    errors: Error[];
+};
+
+export type ImportDetails = {
+    prefixWildcardsSupported: boolean;
+};
+
+export type Summary = {
+    title: string;
+    revision: string;
+    sequenced: boolean;
+    version: number;
+    importDate: number;
+    prefixWildcardsSupported: boolean;
+    counts: SummaryCounts;
+    author?: string;
+    url?: string;
+    description?: string;
+    attribution?: string;
+    frequencyMode?: 'occurrence-based' | 'rank-based';
+};
+
+export type SummaryCounts = {
+    terms: SummaryItemCount;
+    termMeta: SummaryMetaCount;
+    kanji: SummaryItemCount;
+    kanjiMeta: SummaryMetaCount;
+    tagMeta: SummaryItemCount;
+    media: SummaryItemCount;
+};
+
+export type SummaryItemCount = {
+    total: number;
+};
+
+export type SummaryMetaCount = {
+    total: number;
+    [key: string]: number;
+};
+
+export type ImportRequirement = (
+    ImageImportRequirement |
+    StructuredContentImageImportRequirement
+);
+
+export type ImageImportRequirement = {
+    type: 'image';
+    target: DictionaryData.TermGlossaryImage;
+    source: DictionaryData.TermGlossaryImage;
+    entry: DictionaryDatabase.DatabaseTermEntry;
+};
+
+export type StructuredContentImageImportRequirement = {
+    type: 'structured-content-image';
+    target: StructuredContent.ImageElement;
+    source: StructuredContent.ImageElement;
+    entry: DictionaryDatabase.DatabaseTermEntry;
+};
+
+export type ImportRequirementContext = {
+    archive: import('jszip');
+    media: Map<string, DictionaryDatabase.MediaDataArrayBufferContent>;
+};
diff --git a/types/ext/dictionary-worker-handler.d.ts b/types/ext/dictionary-worker-handler.d.ts
new file mode 100644
index 0000000000..ddd6134c3a
--- /dev/null
+++ b/types/ext/dictionary-worker-handler.d.ts
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as DictionaryImporter from './dictionary-importer';
+import type * as DictionaryWorkerMediaLoader from './dictionary-worker-media-loader';
+
+export type OnProgressCallback = (...args: unknown[]) => void;
+
+export type Message = (
+    ImportDictionaryMessage |
+    DeleteDictionaryMessage |
+    GetDictionaryCountsMessage |
+    GetImageDetailsResponseMessage
+);
+
+export type ImportDictionaryMessage = {
+    action: 'importDictionary';
+    params: ImportDictionaryMessageParams;
+};
+
+export type ImportDictionaryMessageParams = {
+    details: DictionaryImporter.ImportDetails;
+    archiveContent: ArrayBuffer;
+};
+
+export type DeleteDictionaryMessage = {
+    action: 'deleteDictionary';
+    params: DeleteDictionaryMessageParams;
+};
+
+export type DeleteDictionaryMessageParams = {
+    dictionaryTitle: string;
+};
+
+export type GetDictionaryCountsMessage = {
+    action: 'getDictionaryCounts';
+    params: GetDictionaryCountsMessageParams;
+};
+
+export type GetDictionaryCountsMessageParams = {
+    dictionaryNames: string[];
+    getTotal: boolean;
+};
+
+export type GetImageDetailsResponseMessage = {
+    action: 'getImageDetails.response';
+    params: DictionaryWorkerMediaLoader.HandleMessageParams;
+};
diff --git a/types/ext/dictionary-worker-media-loader.d.ts b/types/ext/dictionary-worker-media-loader.d.ts
new file mode 100644
index 0000000000..fab012834c
--- /dev/null
+++ b/types/ext/dictionary-worker-media-loader.d.ts
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Core from './core';
+
+export type ImageDetails = {
+    content: ArrayBuffer;
+    width: number;
+    height: number;
+};
+
+export type HandleMessageParams = {id: string} & Core.Response<ImageDetails>;
diff --git a/types/ext/dictionary-worker.d.ts b/types/ext/dictionary-worker.d.ts
new file mode 100644
index 0000000000..570d37cd9e
--- /dev/null
+++ b/types/ext/dictionary-worker.d.ts
@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Core from './core';
+import type * as DictionaryImporter from './dictionary-importer';
+import type * as DictionaryDatabase from './dictionary-database';
+
+export type InvokeDetails<TResponseRaw = unknown, TResponse = unknown> = {
+    complete: boolean;
+    worker: Worker | null;
+    resolve: ((result: TResponse) => void) | null;
+    reject: ((reason?: Core.RejectionReason) => void) | null;
+    onMessage: ((event: MessageEvent<MessageData<TResponseRaw>>) => void) | null;
+    onProgress: ((...args: unknown[]) => void) | null;
+    formatResult: ((result: TResponseRaw) => TResponse) | null;
+};
+
+export type MessageCompleteData<TResponseRaw> = {
+    action: 'complete';
+    params: MessageCompleteParams<TResponseRaw>;
+};
+
+export type MessageProgressData = {
+    action: 'progress';
+    params: MessageProgressParams;
+};
+
+export type MessageGetImageDetailsData = {
+    action: 'getImageDetails';
+    params: MessageGetImageDetailsParams;
+};
+
+export type MessageCompleteParams<TResponseRaw> = Core.Response<TResponseRaw>;
+
+export type MessageProgressParams = {
+    args: unknown[];
+};
+
+export type MessageGetImageDetailsParams = {
+    id: string;
+    content: ArrayBuffer;
+    mediaType: string;
+};
+
+export type MessageData<TResponseRaw> = MessageCompleteData<TResponseRaw> | MessageProgressData | MessageGetImageDetailsData;
+
+export type MessageCompleteResultSerialized = {
+    result: DictionaryImporter.Summary;
+    errors: Core.SerializedError[];
+};
+
+export type MessageCompleteResult = {
+    result: DictionaryImporter.Summary;
+    errors: Error[];
+};
+
+export type ImportProgressCallback = (details: DictionaryImporter.ProgressData) => void;
+
+export type DeleteProgressCallback = (details: DictionaryDatabase.DeleteDictionaryProgressData) => void;
diff --git a/types/ext/dictionary.d.ts b/types/ext/dictionary.d.ts
new file mode 100644
index 0000000000..3e90dec0e1
--- /dev/null
+++ b/types/ext/dictionary.d.ts
@@ -0,0 +1,477 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ * Copyright (C) 2021-2022  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as DictionaryData from './dictionary-data';
+
+// Common
+
+/**
+ * A generic dictionary entry which is used as the base interface.
+ */
+export type DictionaryEntry = KanjiDictionaryEntry | TermDictionaryEntry;
+
+export type DictionaryEntryType = DictionaryEntry['type'];
+
+/**
+ * A tag represents some brief information about part of a dictionary entry.
+ */
+export type Tag = {
+    /**
+     * The name of the tag.
+     */
+    name: string;
+    /**
+     * The category of the tag.
+     */
+    category: string;
+    /**
+     * A number indicating the sorting order of the tag.
+     */
+    order: number;
+    /**
+     * A score value for the tag.
+     */
+    score: number;
+    /**
+     * An array of descriptions for the tag. * If there are multiple entries,
+     * the values will typically have originated from different dictionaries.
+     * However, there is no correlation between the length of this array and
+     * the length of the `dictionaries` field, as duplicates are removed.
+     */
+    content: string[];
+    /**
+     * An array of dictionary names that contained a tag with this name and category.
+     */
+    dictionaries: string[];
+    /**
+     * Whether or not this tag is redundant with previous tags.
+     */
+    redundant: boolean;
+};
+
+// Kanji
+
+/**
+ * A dictionary entry for a kanji character.
+ */
+export type KanjiDictionaryEntry = {
+    /**
+     * The type of the entry.
+     */
+    type: 'kanji';
+    /**
+     * The kanji character that was looked up.
+     */
+    character: string;
+    /**
+     * The name of the dictionary that the information originated from.
+     */
+    dictionary: string;
+    /**
+     * Onyomi readings for the kanji character.
+     */
+    onyomi: string[];
+    /**
+     * Kunyomi readings for the kanji character.
+     */
+    kunyomi: string[];
+    /**
+     * Tags for the kanji character.
+     */
+    tags: Tag[];
+    /**
+     * An object containing stats about the kanji character.
+     */
+    stats: KanjiStatGroups;
+    /**
+     * Definitions for the kanji character.
+     */
+    definitions: string[];
+    /**
+     * Frequency information for the kanji character.
+     */
+    frequencies: KanjiFrequency[];
+};
+
+/**
+ * An object with groups of stats about a kanji character.
+ */
+export type KanjiStatGroups = {
+    /**
+     * A group of stats.
+     * @param propName The name of the group.
+     */
+    [propName: string]: KanjiStat[];
+};
+
+/**
+ * A stat represents a generic piece of information about a kanji character.
+ */
+export type KanjiStat = {
+    /**
+     * The name of the stat.
+     */
+    name: string;
+    /**
+     * The category of the stat.
+     */
+    category: string;
+    /**
+     * A description of the stat.
+     */
+    content: string;
+    /**
+     * A number indicating the sorting order of the stat.
+     */
+    order: number;
+    /**
+     * A score value for the stat.
+     */
+    score: number;
+    /**
+     * The name of the dictionary that the stat originated from.
+     */
+    dictionary: string;
+    /**
+     * A value for the stat.
+     */
+    value: number | string;
+};
+
+/**
+ * Frequency information corresponds to how frequently a character appears in a corpus,
+ * which can be a number of occurrences or an overall rank.
+ */
+export type KanjiFrequency = {
+    /**
+     * The original order of the frequency, which is usually used for sorting.
+     */
+    index: number;
+    /**
+     * The name of the dictionary that the frequency information originated from.
+     */
+    dictionary: string;
+    /**
+     * The index of the dictionary in the original list of dictionaries used for the lookup.
+     */
+    dictionaryIndex: number;
+    /**
+     * The priority of the dictionary.
+     */
+    dictionaryPriority: number;
+    /**
+     * The kanji character for the frequency.
+     */
+    character: string;
+    /**
+     * The frequency for the character, as a number of occurrences or an overall rank.
+     */
+    frequency: number;
+    /**
+     * A display value to show to the user.
+     */
+    displayValue: string | null;
+    /**
+     * Whether or not the displayValue string was parsed to determine the frequency value.
+     */
+    displayValueParsed: boolean;
+};
+
+// Terms
+
+/**
+ * A dictionary entry for a term or group of terms.
+ */
+export type TermDictionaryEntry = {
+    /**
+     * The type of the entry.
+     */
+    type: 'term';
+    /**
+     * Whether or not any of the sources is a primary source. Primary sources are derived from the
+     * original search text, while non-primary sources originate from related terms.
+     */
+    isPrimary: boolean;
+    /**
+     * A list of inflections that was applied to get the term.
+     */
+    inflections: string[];
+    /**
+     * A score for the dictionary entry.
+     */
+    score: number;
+    /**
+     * The sorting value based on the determined term frequency.
+     */
+    frequencyOrder: number;
+    /**
+     * The index of the dictionary in the original list of dictionaries used for the lookup.
+     */
+    dictionaryIndex: number;
+    /**
+     * The priority of the dictionary.
+     */
+    dictionaryPriority: number;
+    /**
+     * The number of primary sources that had an exact text match for the term.
+     */
+    sourceTermExactMatchCount: number;
+    /**
+     * The maximum length of the transformed text for all primary sources.
+     */
+    maxTransformedTextLength: number;
+    /**
+     * Headwords for the entry.
+     */
+    headwords: TermHeadword[];
+    /**
+     * Definitions for the entry.
+     */
+    definitions: TermDefinition[];
+    /**
+     * Pronunciations for the entry.
+     */
+    pronunciations: TermPronunciation[];
+    /**
+     * Frequencies for the entry.
+     */
+    frequencies: TermFrequency[];
+};
+
+/**
+ * A term headword is a combination of a term, reading, and auxiliary information.
+ */
+export type TermHeadword = {
+    /**
+     * The original order of the headword, which is usually used for sorting.
+     */
+    index: number;
+    /**
+     * The text for the term.
+     */
+    term: string;
+    /**
+     * The reading of the term.
+     */
+    reading: string;
+    /**
+     * The sources of the term.
+     */
+    sources: TermSource[];
+    /**
+     * Tags for the headword.
+     */
+    tags: Tag[];
+    /**
+     * List of word classes (part of speech) for the headword.
+     */
+    wordClasses: string[];
+};
+
+/**
+ * A definition contains a list of entries and information about what what terms it corresponds to.
+ */
+export type TermDefinition = {
+    /**
+     * The original order of the definition, which is usually used for sorting.
+     */
+    index: number;
+    /**
+     * A list of headwords that this definition corresponds to.
+     */
+    headwordIndices: number[];
+    /**
+     * The name of the dictionary that the definition information originated from.
+     */
+    dictionary: string;
+    /**
+     * The index of the dictionary in the original list of dictionaries used for the lookup.
+     */
+    dictionaryIndex: number;
+    /**
+     * The priority of the dictionary.
+     */
+    dictionaryPriority: number;
+    /**
+     * Database ID for the definition.
+     */
+    id: number;
+    /**
+     * A score for the definition.
+     */
+    score: number;
+    /**
+     * The sorting value based on the determined term frequency.
+     */
+    frequencyOrder: number;
+    /**
+     * A list of database sequence numbers for the term. A value of `-1` corresponds to no sequence.
+     * The list can have multiple values if multiple definitions with different sequences have been merged.
+     * The list should always have at least one item.
+     */
+    sequences: number[];
+    /**
+     * Whether or not any of the sources is a primary source. Primary sources are derived from the
+     * original search text, while non-primary sources originate from related terms.
+     */
+    isPrimary: boolean;
+    /**
+     * Tags for the definition.
+     */
+    tags: Tag[];
+    /**
+     * The definition entries.
+     */
+    entries: DictionaryData.TermGlossary[];
+};
+
+/**
+ * A term pronunciation represents different ways to pronounce one of the headwords.
+ */
+export type TermPronunciation = {
+    /**
+     * The original order of the pronunciation, which is usually used for sorting.
+     */
+    index: number;
+    /**
+     * Which headword this pronunciation corresponds to.
+     */
+    headwordIndex: number;
+    /**
+     * The name of the dictionary that the proununciation information originated from.
+     */
+    dictionary: string;
+    /**
+     * The index of the dictionary in the original list of dictionaries used for the lookup.
+     */
+    dictionaryIndex: number;
+    /**
+     * The priority of the dictionary.
+     */
+    dictionaryPriority: number;
+    /**
+     * The pitch accent representations for the term.
+     */
+    pitches: TermPitch[];
+};
+
+/**
+ * Pitch accent information for a term, represented as the position of the downstep.
+ */
+export type TermPitch = {
+    /**
+     * Position of the downstep, as a number of mora.
+     */
+    position: number;
+    /**
+     * Positions of morae with a nasal sound.
+     */
+    nasalPositions: number[];
+    /**
+     * Positions of morae with a devoiced sound.
+     */
+    devoicePositions: number[];
+    /**
+     * Tags for the pitch accent.
+     */
+    tags: Tag[];
+};
+
+/**
+ * Frequency information corresponds to how frequently a term appears in a corpus,
+ * which can be a number of occurrences or an overall rank.
+ */
+export type TermFrequency = {
+    /**
+     * The original order of the frequency, which is usually used for sorting.
+     */
+    index: number;
+    /**
+     * Which headword this frequency corresponds to.
+     */
+    headwordIndex: number;
+    /**
+     * The name of the dictionary that the frequency information originated from.
+     */
+    dictionary: string;
+    /**
+     * The index of the dictionary in the original list of dictionaries used for the lookup.
+     */
+    dictionaryIndex: number;
+    /**
+     * The priority of the dictionary.
+     */
+    dictionaryPriority: number;
+    /**
+     * Whether or not the frequency had an explicit reading specified.
+     */
+    hasReading: boolean;
+    /**
+     * The frequency for the term, as a number of occurrences or an overall rank.
+     */
+    frequency: number;
+    /**
+     * A display value to show to the user.
+     */
+    displayValue: string | null;
+    /**
+     * Whether or not the displayValue string was parsed to determine the frequency value.
+     */
+    displayValueParsed: boolean;
+};
+
+/**
+ * Enum representing how the search term relates to the final term.
+ */
+export type TermSourceMatchType = 'exact' | 'prefix' | 'suffix';
+
+/**
+ * Enum representing what database field was used to match the source term.
+ */
+export type TermSourceMatchSource = 'term' | 'reading' | 'sequence';
+
+/**
+ * Source information represents how the original text was transformed to get to the final term.
+ */
+export type TermSource = {
+    /**
+     * The original text that was searched.
+     */
+    originalText: string;
+    /**
+     * The original text after being transformed, but before applying deinflections.
+     */
+    transformedText: string;
+    /**
+     * The final text after applying deinflections.
+     */
+    deinflectedText: string;
+    /**
+     * How the deinflected text matches the value from the database.
+     */
+    matchType: TermSourceMatchType;
+    /**
+     * Which field was used to match the database entry.
+     */
+    matchSource: TermSourceMatchSource;
+    /**
+     * Whether or not this source is a primary source. Primary sources are derived from the
+     * original search text, while non-primary sources originate from related terms.
+     */
+    isPrimary: boolean;
+};
diff --git a/types/ext/display-anki.d.ts b/types/ext/display-anki.d.ts
new file mode 100644
index 0000000000..cc59a5c35b
--- /dev/null
+++ b/types/ext/display-anki.d.ts
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Anki from './anki';
+import type * as AnkiNoteBuilder from './anki-note-builder';
+import type * as AnkiTemplates from './anki-templates';
+import type * as AnkiTemplatesInternal from './anki-templates-internal';
+
+export type CreateMode = AnkiTemplatesInternal.CreateModeNoTest;
+
+export type LogData = {
+    ankiNoteData: AnkiTemplates.NoteData | undefined;
+    ankiNoteDataException: Error | undefined;
+    ankiNotes: AnkiNoteLogData[];
+};
+
+export type AnkiNoteLogData = {
+    mode: CreateMode;
+    note: Anki.Note | undefined;
+    errors?: Error[];
+    requirements?: AnkiNoteBuilder.Requirement[];
+};
+
+export type DictionaryEntryDetails = {
+    modeMap: Map<CreateMode, DictionaryEntryModeDetails>;
+};
+
+export type DictionaryEntryModeDetails = {
+    mode: CreateMode;
+    note: Anki.Note;
+    errors: Error[];
+    requirements: AnkiNoteBuilder.Requirement[];
+    canAdd: boolean;
+    valid: boolean;
+    noteIds: Anki.NoteId[] | null;
+    noteInfos?: (Anki.NoteInfo | null)[];
+    ankiError: Error | null;
+};
+
+export type CreateNoteResult = {
+    note: Anki.Note;
+    errors: Error[];
+    requirements: AnkiNoteBuilder.Requirement[];
+};
diff --git a/types/ext/display-audio.d.ts b/types/ext/display-audio.d.ts
new file mode 100644
index 0000000000..2ef252b127
--- /dev/null
+++ b/types/ext/display-audio.d.ts
@@ -0,0 +1,99 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Audio from './audio';
+import type * as Settings from './settings';
+import type * as AudioDownloader from './audio-downloader';
+
+export type CacheItem = {
+    sourceMap: Map<number, CachedInfoList>;
+    primaryCardAudio: PrimaryCardAudio | null;
+};
+
+export type CachedInfoList = {
+    infoListPromise: Promise<AudioInfoList>;
+    infoList: AudioInfoList | null;
+};
+
+export type AudioInfoList = AudioInfoListItem[];
+
+export type AudioInfoListItem = {
+    info: AudioDownloader.Info;
+    audioPromise: Promise<GenericAudio> | null;
+    audioResolved: boolean;
+    audio: GenericAudio | null;
+};
+
+export type PrimaryCardAudio = {
+    index: number;
+    subIndex: number | null;
+};
+
+export type SourceInfo = {
+    source: AudioSource | null;
+    subIndex: number | null;
+};
+
+export type AudioSource = {
+    index: number;
+    type: Settings.AudioSourceType;
+    url: string;
+    voice: string;
+    isInOptions: boolean;
+    downloadable: boolean;
+    name: string;
+    nameIndex: number;
+    nameUnique: boolean;
+};
+
+export type AudioSourceShort = {
+    type: Settings.AudioSourceType;
+    url: string;
+    voice: string;
+};
+
+export type AudioMediaOptions = {
+    sources: Audio.AudioSourceInfo[];
+    preferredAudioIndex: number | null;
+};
+
+export type PlayAudioResult = {
+    audio: GenericAudio | null;
+    source: AudioSource | null;
+    subIndex: number;
+    valid: boolean;
+};
+
+export type TermAudio = {
+    audio: GenericAudio;
+    source: AudioSource;
+    subIndex: number;
+};
+
+export type CreateAudioResult = {
+    audio: GenericAudio | null;
+    index: number;
+    cacheUpdated: boolean;
+};
+
+export type GenericAudio = HTMLAudioElement | TextToSpeechAudio;
+
+export type MenuItemEntry = {
+    valid: boolean | null;
+    index: number | null;
+    name: string | null;
+};
diff --git a/types/ext/display-content-manager.d.ts b/types/ext/display-content-manager.d.ts
new file mode 100644
index 0000000000..dc2269cf46
--- /dev/null
+++ b/types/ext/display-content-manager.d.ts
@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as DictionaryDatabase from './dictionary-database';
+
+/** A callback used when a media file has been loaded. */
+export type OnLoadCallback = (
+    /** The URL of the media that was loaded. */
+    url: string,
+) => void;
+
+/** A callback used when a media file should be unloaded. */
+export type OnUnloadCallback = (
+    /** Whether or not the media was fully loaded. */
+    fullyLoaded: boolean,
+) => void;
+
+export type CachedMediaDataLoaded = {
+    data: DictionaryDatabase.MediaDataStringContent;
+    url: string;
+};
+
+export type LoadMediaDataInfo = {
+    onUnload: OnUnloadCallback;
+    loaded: boolean;
+};
\ No newline at end of file
diff --git a/types/ext/display-history.d.ts b/types/ext/display-history.d.ts
new file mode 100644
index 0000000000..2ba5006b6b
--- /dev/null
+++ b/types/ext/display-history.d.ts
@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Display from './display';
+
+export type Entry = {
+    id: string;
+    url: string;
+    next: Entry | null;
+    previous: Entry | null;
+    state: EntryState | null;
+    content: EntryContent | null;
+};
+
+export type EntryState = Display.HistoryState;
+
+export type EntryContent = Display.HistoryContent;
+
+export type EventType = 'stateChanged';
+
+export type StateChangedEvent = {
+    synthetic: boolean;
+};
diff --git a/types/ext/display.d.ts b/types/ext/display.d.ts
new file mode 100644
index 0000000000..feb049fb1a
--- /dev/null
+++ b/types/ext/display.d.ts
@@ -0,0 +1,202 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Core from './core';
+import type * as Dictionary from './dictionary';
+import type * as Extension from './extension';
+import type * as Settings from './settings';
+import type * as TextScanner from './text-scanner';
+import type * as TextSource from './text-source';
+
+export type HistoryMode = 'clear' | 'overwrite' | 'new';
+
+export type DisplayPageType = 'search' | 'popup';
+
+export type PageType = 'terms' | 'kanji' | 'unloaded' | 'clear';
+
+/**
+ * Information about how popup content should be shown, specifically related to the inner popup content.
+ */
+export type ContentDetails = {
+    /** Whether or not the frame should be `focus()`'d. */
+    focus: boolean;
+    /** An object containing key-value pairs representing the URL search params. */
+    params: HistoryParams;
+    /** The semi-persistent state assigned to the navigation entry. */
+    state: HistoryState | null;
+    /** The non-persistent content assigned to the navigation entry. */
+    content: HistoryContent | null;
+    /** How the navigation history should be modified. */
+    historyMode: HistoryMode;
+};
+
+/**
+ * An object containing key-value pairs representing the URL search params.
+ */
+export type HistoryParams = {
+    /** The type of content that is being shown. */
+    type?: PageType;
+    /** The search query. */
+    query?: string;
+    /** Whether or not wildcards can be used for the search query. */
+    wildcards?: 'on' | 'off';
+    /** The start position of the `query` string as an index into the `full` query string. */
+    offset?: string;
+    /** The full search text. If absent, `query` is the full search text. */
+    full?: string;
+    /** Whether or not the full search query should be forced to be visible. */
+    ['full-visible']?: 'true' | 'false';
+    /** Whether or not the query should be looked up. If it is not looked up, the content should be provided. */
+    lookup?: 'true' | 'false';
+    /** Other values; only used for assignment. */
+    [otherKey: string]: unknown;
+};
+
+/**
+ * The semi-persistent state assigned to the navigation entry.
+ */
+export type HistoryState = {
+    /** What was the cause of the navigation. */
+    cause?: 'queryParser';
+    /** The sentence context. */
+    sentence?: HistoryStateSentence;
+    /** The index of the dictionary entry to focus. */
+    focusEntry?: number;
+    /** The horizontal scroll position. */
+    scrollX?: number;
+    /** The vertical scroll position. */
+    scrollY?: number;
+    /** The options context which should be used for lookups. */
+    optionsContext?: Settings.OptionsContext;
+    /** The originating URL of the content. */
+    url?: string;
+    /** The originating document title of the content. */
+    documentTitle?: string;
+};
+
+/**
+ * The sentence context.
+ */
+export type HistoryStateSentence = {
+    /** The full string. */
+    text: string;
+    /** The offset from the start of `text` to the full search query. */
+    offset: number;
+};
+
+/**
+ * The non-persistent content assigned to the navigation entry.
+ */
+export type HistoryContent = {
+    /** Whether or not any CSS animations should occur. */
+    animate?: boolean;
+    /** An array of dictionary entries to display as content. */
+    dictionaryEntries?: Dictionary.DictionaryEntry[];
+    /** The identifying information for the frame the content originated from. */
+    contentOrigin?: Extension.ContentOrigin;
+};
+
+export type SearchPersistentStateControllerEventType = 'modeChange';
+
+export type SearchMode = null | 'popup' | 'action-popup';
+
+export type GetSearchContextCallback = TextScanner.GetSearchContextCallbackSync;
+
+export type QueryParserConstructorDetails = {
+    getSearchContext: GetSearchContextCallback;
+    japaneseUtil: JapaneseUtil;
+};
+
+export type QueryParserOptions = {
+    selectedParser: string | null;
+    termSpacing: boolean;
+    readingMode: Settings.ParsingReadingMode;
+    useInternalParser: boolean;
+    useMecabParser: boolean;
+    scanning: TextScanner.Options;
+};
+
+export type QueryParserEventType = 'searched';
+
+export type QueryParserSearchedEvent = {
+    textScanner: TextScanner;
+    type: PageType;
+    dictionaryEntries: Dictionary.DictionaryEntry[];
+    sentence: HistoryStateSentence;
+    inputInfo: TextScanner.InputInfo;
+    textSource: TextSource.TextSource;
+    optionsContext: Settings.OptionsContext;
+    sentenceOffset: number | null;
+};
+
+export type DisplayEventType = (
+    'optionsUpdated' |
+    'frameVisibilityChange' |
+    'logDictionaryEntryData' |
+    'contentClear' |
+    'contentUpdateStart' |
+    'contentUpdateEntry' |
+    'contentUpdateComplete'
+);
+
+export type OptionsUpdatedEvent = {
+    options: Settings.ProfileOptions;
+};
+
+export type FrameVisibilityChangeEvent = {
+    value: boolean;
+};
+
+export type LogDictionaryEntryDataEvent = {
+    dictionaryEntry: Dictionary.DictionaryEntry;
+    promises: Promise<unknown>[];
+};
+
+export type ContentUpdateStartEvent = {
+    type: PageType;
+    query: string;
+};
+
+export type ContentUpdateEntryEvent = {
+    dictionaryEntry: Dictionary.DictionaryEntry;
+    element: Element;
+    index: number;
+};
+
+export type ContentUpdateCompleteEvent = {
+    type: PageType;
+};
+
+export type ConfigureMessageDetails = {
+    depth: number;
+    parentPopupId: string;
+    parentFrameId: number;
+    childrenSupported: boolean;
+    scale: number;
+    optionsContext: Settings.OptionsContext;
+};
+
+export type MessageDetails = {
+    action: string;
+    params: Core.SerializableObject;
+};
+
+export type DisplayGeneratorConstructorDetails = {
+    japaneseUtil: JapaneseUtil;
+    contentManager: DisplayContentManager;
+    hotkeyHelpController?: HotkeyHelpController | null;
+};
diff --git a/types/ext/document-util.d.ts b/types/ext/document-util.d.ts
new file mode 100644
index 0000000000..28dfe8990f
--- /dev/null
+++ b/types/ext/document-util.d.ts
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type NormalizedWritingMode = 'horizontal-tb' | 'vertical-rl' | 'vertical-lr' | 'sideways-rl' | 'sideways-lr';
+
+/**
+ * Options to configure how element detection is performed.
+ */
+export type GetRangeFromPointOptions = {
+    /**
+     * Whether or deep content scanning should be performed. When deep content scanning is enabled,
+     * some transparent overlay elements will be ignored when looking for the element at the input position.
+     */
+    deepContentScan: boolean;
+    /**
+     * Whether or not zoom coordinates should be normalized.
+     */
+    normalizeCssZoom: boolean;
+};
+
+/**
+ * Scans the document for text or elements with text information at the given coordinate.
+ * Coordinates are provided in [client space](https://developer.mozilla.org/en-US/docs/Web/CSS/CSSOM_View/Coordinate_systems).
+ * @returns A range for the hovered text or element, or `null` if no applicable content was found.
+ */
+export type GetRangeFromPointHandler = (
+    /** The x coordinate to search at. */
+    x: number,
+    /** The y coordinate to search at. */
+    y: number,
+    /** Options to configure how element detection is performed. */
+    options: GetRangeFromPointOptions,
+) => (TextSourceRange | TextSourceElement | null);
+
+export type ToNumberConstraints = {
+    min?: string | number;
+    max?: string | number;
+    step?: string | number;
+};
diff --git a/types/ext/dom-data-binder.d.ts b/types/ext/dom-data-binder.d.ts
new file mode 100644
index 0000000000..ca0036c3e6
--- /dev/null
+++ b/types/ext/dom-data-binder.d.ts
@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as TaskAccumulator from './task-accumulator';
+
+export type CreateElementMetadataCallback<T> = (element: Element) => T | undefined;
+
+export type CompareElementMetadataCallback<T> = (metadata1: T, metadata2: T) => boolean;
+
+export type GetValuesCallback<T> = (args: GetValuesDetails<T>[]) => Promise<TaskResult[]>;
+
+export type SetValuesCallback<T> = (args: SetValuesDetails<T>[]) => Promise<TaskResult[]>;
+
+export type GetValuesDetails<T> = {
+    element: Element;
+    metadata: T;
+};
+
+export type SetValuesDetails<T> = {
+    element: Element;
+    metadata: T;
+    value: ValueType;
+};
+
+export type OnErrorCallback<T> = (error: Error, stale: boolean, element: Element, metadata: T) => void;
+
+export type ConstructorDetails<T> = {
+    selector: string;
+    createElementMetadata: CreateElementMetadataCallback<T>;
+    compareElementMetadata: CompareElementMetadataCallback<T>;
+    getValues: GetValuesCallback<T>;
+    setValues: SetValuesCallback<T>;
+    onError?: OnErrorCallback<T> | null;
+};
+
+export type ElementObserver<T> = {
+    element: Element;
+    type: NormalizedElementType;
+    value: unknown;
+    hasValue: boolean;
+    onChange: null | (() => void);
+    metadata: T;
+};
+
+export type SettingChangedEventData = {
+    value: boolean | string | number;
+};
+
+export type SettingChangedEvent = CustomEvent<SettingChangedEventData>;
+
+export type NormalizedElementType = 'textarea' | 'select' | 'text' | 'checkbox' | 'number' | null;
+
+export type UpdateTaskValue = {all: boolean};
+
+export type AssignTaskValue = {value: ValueType};
+
+export type ValueType = boolean | string | number | null;
+
+export type UpdateTask<T> = [
+    key: ElementObserver<T> | null,
+    task: TaskAccumulator.Task<UpdateTaskValue>,
+];
+
+export type AssignTask<T> = [
+    key: ElementObserver<T> | null,
+    task: TaskAccumulator.Task<AssignTaskValue>,
+];
+
+export type ApplyTarget<T> = [
+    observer: ElementObserver<T>,
+    task: TaskAccumulator.Task<UpdateTaskValue> | TaskAccumulator.Task<AssignTaskValue> | null,
+];
+
+export type TaskResultError = {
+    error: Error;
+    result?: undefined;
+};
+
+export type TaskResultSuccess<T = unknown> = {
+    error?: undefined;
+    result: T;
+};
+
+export type TaskResult<T = unknown> = TaskResultError | TaskResultSuccess<T>;
diff --git a/types/ext/dynamic-loader.d.ts b/types/ext/dynamic-loader.d.ts
new file mode 100644
index 0000000000..39b9113a3e
--- /dev/null
+++ b/types/ext/dynamic-loader.d.ts
@@ -0,0 +1,20 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type DynamicLoaderSentinelDetails = {
+    script: HTMLScriptElement | null;
+};
diff --git a/types/ext/dynamic-property.d.ts b/types/ext/dynamic-property.d.ts
new file mode 100644
index 0000000000..5ec886d27c
--- /dev/null
+++ b/types/ext/dynamic-property.d.ts
@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type EventType = 'change';
+
+export type ChangeEventDetails<T> = {
+    value: T;
+};
diff --git a/types/ext/environment.d.ts b/types/ext/environment.d.ts
new file mode 100644
index 0000000000..9c0f5bf64f
--- /dev/null
+++ b/types/ext/environment.d.ts
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type Info = {
+    browser: Browser;
+    platform: {os: OperatingSystem};
+};
+
+export type Browser = 'chrome' | 'firefox' | 'firefox-mobile' | 'edge' | 'edge-legacy' | 'safari';
+
+export type OperatingSystem = chrome.runtime.PlatformOs | 'unknown';
diff --git a/types/ext/event-listener-collection.d.ts b/types/ext/event-listener-collection.d.ts
new file mode 100644
index 0000000000..daeeecabcd
--- /dev/null
+++ b/types/ext/event-listener-collection.d.ts
@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Core from './core';
+
+export type EventListenerFunction = (...args: Core.SafeAny[]) => unknown;
+
+export type EventTarget = {
+    addEventListener(
+        type: string,
+        listener: EventListener | EventListenerObject | EventListenerFunction,
+        options?: AddEventListenerOptions | boolean,
+    ): void;
+    removeEventListener(
+        type: string,
+        listener: EventListener | EventListenerObject | EventListenerFunction,
+        options?: EventListenerOptions | boolean,
+    ): void;
+};
+
+export type ExtensionEvent<TCallback = EventListenerFunction, TArgs = unknown> = {
+    addListener(callback: TCallback, ...args: TArgs[]): void;
+    removeListener(callback: TCallback, ...args: TArgs[]): void;
+};
+
+export type EventTargetDetails = {
+    type: 'removeEventListener';
+    target: EventTarget;
+    eventName: string;
+    listener: EventListener | EventListenerObject | EventListenerFunction;
+    options: EventListenerOptions | boolean | undefined;
+};
+
+export type ExtensionEventDetails = {
+    type: 'removeListener';
+    target: ExtensionEvent;
+    callback: EventListenerFunction;
+    args: unknown[];
+};
+
+export type EventDispatcherDetails = {
+    type: 'off';
+    target: EventDispatcher<string>;
+    eventName: string;
+    callback: EventListenerFunction;
+};
+
+export type EventListenerDetails = EventTargetDetails | ExtensionEventDetails | EventDispatcherDetails;
+
+export type AddEventListenerArgs = [
+    target: EventTarget,
+    type: string,
+    listener: EventListener | EventListenerObject | EventListenerFunction,
+    options?: AddEventListenerOptions | boolean,
+];
+
+export type AddListenerArgs<TCallback = EventListenerFunction, TArgs = unknown> = [
+    target: ExtensionEvent<TCallback, TArgs>,
+    callback: TCallback,
+    ...args: TArgs[],
+];
+
+export type OnArgs = [
+    target: EventDispatcher<string>,
+    eventName: string,
+    callback: (details: Core.SafeAny) => void,
+];
diff --git a/types/ext/extension.d.ts b/types/ext/extension.d.ts
new file mode 100644
index 0000000000..1c86a4ca84
--- /dev/null
+++ b/types/ext/extension.d.ts
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Core from './core';
+
+export type ChromeRuntimeSendMessageArgs1 = [
+    message: Core.SafeAny,
+];
+
+export type ChromeRuntimeSendMessageArgs2 = [
+    message: Core.SafeAny,
+    responseCallback: (response: Core.SafeAny) => void,
+];
+
+export type ChromeRuntimeSendMessageArgs3 = [
+    message: Core.SafeAny,
+    options: chrome.runtime.MessageOptions,
+    responseCallback: (response: Core.SafeAny) => void,
+];
+
+export type ChromeRuntimeSendMessageArgs4 = [
+    extensionId: string | undefined | null,
+    message: Core.SafeAny,
+    responseCallback: (response: Core.SafeAny) => void,
+];
+
+export type ChromeRuntimeSendMessageArgs5 = [
+    extensionId: string | undefined | null,
+    message: Core.SafeAny,
+    options: chrome.runtime.MessageOptions,
+    responseCallback: (response: Core.SafeAny) => void,
+];
+
+export type ChromeRuntimeSendMessageArgs = ChromeRuntimeSendMessageArgs1 | ChromeRuntimeSendMessageArgs2 | ChromeRuntimeSendMessageArgs3 | ChromeRuntimeSendMessageArgs4 | ChromeRuntimeSendMessageArgs5;
+
+export type ExtensionEventType = 'extensionUnloaded' | 'optionsUpdated' | 'databaseUpdated' | 'zoomChanged' | 'closePopups' | 'dynamicLoaderSentinel' | 'storageChanged';
+
+export type HtmlElementWithContentWindow = HTMLIFrameElement | HTMLFrameElement | HTMLObjectElement;
+
+export type ContentOrigin = {
+    tabId?: number;
+    frameId?: number;
+};
+
+export type ChromeRuntimeMessage = {
+    action: string;
+    params?: Core.SerializableObject;
+};
+
+export type ChromeRuntimeMessageWithFrameId = ChromeRuntimeMessage & {
+    frameId?: number;
+};
+
+export type ChromeRuntimeOnMessageCallback<TMessage = ChromeRuntimeMessage> = (
+    message: TMessage,
+    sender: chrome.runtime.MessageSender,
+    sendResponse: ChromeRuntimeMessageSendResponseFunction,
+) => boolean | void;
+
+export type ChromeRuntimeMessageSendResponseFunction = (response?: unknown) => void;
diff --git a/types/ext/frame-ancestry-handler.d.ts b/types/ext/frame-ancestry-handler.d.ts
new file mode 100644
index 0000000000..3c9e32bfdb
--- /dev/null
+++ b/types/ext/frame-ancestry-handler.d.ts
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type RequestFrameInfoResponseParams = {
+    frameId: number;
+    nonce: string;
+    more: boolean;
+};
+
+export type RequestFrameInfoResponseReturn = {
+    nonce: string;
+};
diff --git a/types/ext/frame-client.d.ts b/types/ext/frame-client.d.ts
new file mode 100644
index 0000000000..54d0d88091
--- /dev/null
+++ b/types/ext/frame-client.d.ts
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Extension from './extension';
+
+export type Message<T = unknown> = {
+    token: string;
+    secret: string;
+    data: T;
+};
+
+export type SetupFrameFunction = (frame: Extension.HtmlElementWithContentWindow) => void;
+
+export type FrameEndpointReadyDetails = {
+    secret: string;
+};
+
+export type FrameEndpointConnectedDetails = {
+    secret: string;
+    token: string;
+};
diff --git a/types/ext/frame-offset-forwarder.d.ts b/types/ext/frame-offset-forwarder.d.ts
new file mode 100644
index 0000000000..6cc0aef28f
--- /dev/null
+++ b/types/ext/frame-offset-forwarder.d.ts
@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type ChildFrameRect = {
+    x: number;
+    y: number;
+    width: number;
+    height: number;
+};
diff --git a/types/ext/frontend.d.ts b/types/ext/frontend.d.ts
new file mode 100644
index 0000000000..3acafe0a9d
--- /dev/null
+++ b/types/ext/frontend.d.ts
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** Details about how to set up the instance. */
+export type ConstructorDetails = {
+    /** The type of page, one of 'web', 'popup', or 'search'. */
+    pageType: PageType;
+    /** A PopupFactory instance to use for generating popups. */
+    popupFactory: PopupFactory;
+    /** The nesting depth value of the popup. */
+    depth: number;
+    /** The tab ID of the host tab. */
+    tabId: number | undefined;
+    /** The frame ID of the host frame. */
+    frameId: number;
+    /** The popup ID of the parent popup if one exists, otherwise null. */
+    parentPopupId: string | null;
+    /** The frame ID of the parent popup if one exists, otherwise null. */
+    parentFrameId: number | null;
+    /** Whether or not proxy popups should be used. */
+    useProxyPopup: boolean;
+    /** Whether or not window popups can be used. */
+    canUseWindowPopup?: boolean;
+    /** Whether or not popups can be hosted in the root frame. */
+    allowRootFramePopupProxy: boolean;
+    /** Whether popups can create child popups or not. */
+    childrenSupported?: boolean;
+    /** A HotkeyHandler instance. */
+    hotkeyHandler: HotkeyHandler;
+};
+
+export type PageType = 'web' | 'popup' | 'search';
+
+export type FrontendRequestReadyBroadcastParams = {
+    frameId: number;
+};
+
+export type GetPopupInfoResult = {
+    popupId: string | null;
+};
+
+export type FrontendReadyDetails = {
+    frameId: number;
+};
diff --git a/types/ext/generic-setting-controller.d.ts b/types/ext/generic-setting-controller.d.ts
new file mode 100644
index 0000000000..5e3435c524
--- /dev/null
+++ b/types/ext/generic-setting-controller.d.ts
@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as SettingsModifications from './settings-modifications';
+import type * as DocumentUtil from './document-util';
+
+export type TransformType = TransformData['type'];
+
+export type ElementMetadata = {
+    path: string;
+    scope: SettingsModifications.OptionsScopeType | undefined;
+    transforms: TransformData[];
+    transformRaw: string | undefined;
+};
+
+export type TransformFunction = (
+    value: unknown,
+    data: TransformData,
+    element: Element,
+) => unknown;
+
+export type TransformStep = 'pre' | 'post';
+
+export type TransformData = (
+    SetAttributeTransformData |
+    SetVisibilityTransformData |
+    SplitTagsTransformData |
+    JoinTagsTransformData |
+    ToNumberConstraintsTransformData |
+    ToBooleanTransformData |
+    ToStringTransformData |
+    ConditionalConvertTransformData
+);
+
+export type TransformDataBase = {
+    step?: TransformStep;
+};
+
+export type SetAttributeTransformData = TransformDataBase & {
+    type: 'setAttribute';
+    ancestorDistance?: number;
+    selector?: string;
+    attribute: string;
+};
+
+export type SetVisibilityTransformData = TransformDataBase & {
+    type: 'setVisibility';
+    ancestorDistance?: number;
+    selector?: string;
+    condition: OperationData;
+};
+
+export type SplitTagsTransformData = TransformDataBase & {
+    type: 'splitTags';
+};
+
+export type JoinTagsTransformData = TransformDataBase & {
+    type: 'joinTags';
+};
+
+export type ToNumberConstraintsTransformData = TransformDataBase & {
+    type: 'toNumber';
+    constraints?: DocumentUtil.ToNumberConstraints;
+};
+
+export type ToBooleanTransformData = TransformDataBase & {
+    type: 'toBoolean';
+};
+
+export type ToStringTransformData = TransformDataBase & {
+    type: 'toString';
+};
+
+export type ConditionalConvertTransformData = TransformDataBase & {
+    type: 'conditionalConvert';
+    cases?: ConditionalConvertCase[];
+};
+
+export type ConditionalConvertCase = {
+    default?: boolean;
+    result: unknown;
+} & OperationData;
+
+export type OperationData = {
+    op: string;
+    value: unknown;
+};
diff --git a/types/ext/hotkey-handler.d.ts b/types/ext/hotkey-handler.d.ts
new file mode 100644
index 0000000000..7b2b4cb3c9
--- /dev/null
+++ b/types/ext/hotkey-handler.d.ts
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Input from './input';
+
+export type EventType = 'keydownNonHotkey';
+
+export type HotkeyInfo = {
+    modifiers: Set<Input.ModifierKey>;
+    action: string;
+    argument: unknown;
+};
+
+export type HotkeyHandlers = {
+    handlers: HotkeyInfo[];
+};
diff --git a/types/ext/input.d.ts b/types/ext/input.d.ts
new file mode 100644
index 0000000000..fbcb4df36f
--- /dev/null
+++ b/types/ext/input.d.ts
@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type ModifierKey = 'alt' | 'ctrl' | 'meta' | 'shift';
+export type ModifierMouseButton = 'mouse0' | 'mouse1' | 'mouse2' | 'mouse3' | 'mouse4' | 'mouse5';
+export type Modifier = ModifierKey | ModifierMouseButton;
+export type ModifierType = 'key' | 'mouse';
diff --git a/types/ext/japanese-util.d.ts b/types/ext/japanese-util.d.ts
new file mode 100644
index 0000000000..c2d2c41114
--- /dev/null
+++ b/types/ext/japanese-util.d.ts
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type CodepointRange = [
+    minInclusive: number,
+    maxInclusive: number,
+];
+
+export type FuriganaGroup = {
+    isKana: boolean;
+    text: string;
+    textNormalized: string | null;
+};
+
+export type FuriganaSegment = {
+    text: string;
+    reading: string;
+};
+
+export type PitchCategory = (
+    'heiban' |
+    'kifuku' |
+    'atamadaka' |
+    'odaka' |
+    'nakadaka'
+);
+
+export type DiacriticType = 'dakuten' | 'handakuten';
diff --git a/types/ext/json-schema.d.ts b/types/ext/json-schema.d.ts
new file mode 100644
index 0000000000..c959628ba2
--- /dev/null
+++ b/types/ext/json-schema.d.ts
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type ValueObject = {[key: string]: Value};
+
+export type Value = string | number | boolean | null | Value[] | ValueObject;
+
+export type ValueObjectOrArray = ValueObject | Value[];
+
+export type Type = 'string' | 'number' | 'integer' | 'object' | 'array' | 'boolean' | 'null';
+
+export type SchemaObject = {
+    type?: Type | Type[];
+    required?: string[];
+
+    default?: Value;
+    enum?: Value[];
+    const?: Value;
+    minimum?: number;
+    maximum?: number;
+    exclusiveMinimum?: number;
+    exclusiveMaximum?: number;
+    multipleOf?: number;
+    minLength?: number;
+    maxLength?: number;
+    pattern?: string;
+    patternFlags?: string;
+    minItems?: number;
+    maxItems?: number;
+    minProperties?: number;
+    maxProperties?: number;
+    definitions?: {[key: string]: Schema};
+
+    $ref?: string;
+
+    properties?: {[key: string]: Schema};
+    additionalProperties?: Schema;
+    not?: Schema;
+    oneOf?: Schema[];
+    allOf?: Schema[];
+    anyOf?: Schema[];
+    contains?: Schema;
+    prefixItems?: Schema[];
+    items?: Schema | Schema[]; // Legacy schema format for the array
+    additionalItems?: Schema;
+    if?: Schema;
+    then?: Schema;
+    else?: Schema;
+};
+
+export type Schema = SchemaObject | true | false;
+
+export type SchemaStackItem = {
+    schema: Schema | Schema[];
+    path: string | number | null;
+};
+
+export type ValueStackItem = {
+    value: unknown;
+    path: string | number | null;
+};
diff --git a/types/ext/keyboard-mouse-input-field.d.ts b/types/ext/keyboard-mouse-input-field.d.ts
new file mode 100644
index 0000000000..321e49cc69
--- /dev/null
+++ b/types/ext/keyboard-mouse-input-field.d.ts
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Input from './input';
+
+export type EventType = 'change';
+
+export type ChangeEvent = {
+    key: string | null;
+    modifiers: Input.Modifier[];
+};
diff --git a/types/ext/keyboard-shortcut-controller.d.ts b/types/ext/keyboard-shortcut-controller.d.ts
new file mode 100644
index 0000000000..0f276ce941
--- /dev/null
+++ b/types/ext/keyboard-shortcut-controller.d.ts
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Settings from './settings';
+
+export type ActionDetails = {
+    scopes: Set<Settings.InputsHotkeyScope>;
+    argument?: {
+        template: string;
+        default: string;
+    };
+};
diff --git a/types/ext/log.d.ts b/types/ext/log.d.ts
new file mode 100644
index 0000000000..ac2f606bcd
--- /dev/null
+++ b/types/ext/log.d.ts
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type LogLevel = 'log' | 'info' | 'debug' | 'warn' | 'error';
+
+export type LoggerEventType = 'log';
+
+export type LogContext = {
+    url: string;
+};
diff --git a/types/ext/mecab.d.ts b/types/ext/mecab.d.ts
new file mode 100644
index 0000000000..bcbd476f41
--- /dev/null
+++ b/types/ext/mecab.d.ts
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type ParseResultRaw = {
+    [key: string]: ParseResultLineRaw[];
+};
+
+export type ParseResultLineRaw = ParseResultTermRaw[];
+
+export type ParseResultTermRaw = {
+    expression?: string;
+    reading?: string;
+    source?: string;
+};
+
+/** The resulting data from an invocation of `parseText`. */
+export type ParseResult = {
+    /** The dictionary name for the parsed result. */
+    name: string;
+    /** The resulting parsed terms. */
+    lines: ParseFragment[][];
+};
+
+/** A fragment of the parsed text. */
+export type ParseFragment = {
+    /** The term. */
+    term: string;
+    /** The reading of the term. */
+    reading: string;
+    /** The source text. */
+    source: string;
+};
diff --git a/types/ext/options-util.d.ts b/types/ext/options-util.d.ts
new file mode 100644
index 0000000000..e03e4be282
--- /dev/null
+++ b/types/ext/options-util.d.ts
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Core from './core';
+
+export type LegacyOptions = Core.SafeAny;
+
+export type IntermediateOptions = Core.SafeAny;
+
+export type LegacyUpdateFunction = (options: LegacyOptions) => void;
+
+export type ModernUpdateFunction = ModernUpdateFunctionSync | ModernUpdateFunctionAsync;
+
+export type ModernUpdateFunctionSync = (options: IntermediateOptions) => IntermediateOptions;
+
+export type ModernUpdateFunctionAsync = (options: IntermediateOptions) => Promise<IntermediateOptions>;
+
+export type ModernUpdate = {
+    async: boolean;
+    update: ModernUpdateFunction;
+};
diff --git a/types/ext/panel-element.d.ts b/types/ext/panel-element.d.ts
new file mode 100644
index 0000000000..d267b836b2
--- /dev/null
+++ b/types/ext/panel-element.d.ts
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type EventType = 'visibilityChanged' | 'closeCompleted';
+
+export type VisibilityChangedEvent = {
+    visible: boolean;
+};
+
+export type CloseCompletedEvent = {
+    reopening: boolean;
+};
+
+/* eslint-disable @stylistic/ts/indent */
+export type Event<T extends EventType> = (
+    T extends 'visibilityChanged' ? VisibilityChangedEvent :
+    T extends 'closeCompleted' ? CloseCompletedEvent :
+    never
+);
+/* eslint-enable @stylistic/ts/indent */
+
+export type ConstructorDetails = {
+    node: HTMLElement;
+    closingAnimationDuration: number;
+};
diff --git a/types/ext/popup-factory.d.ts b/types/ext/popup-factory.d.ts
new file mode 100644
index 0000000000..a167a6f7d7
--- /dev/null
+++ b/types/ext/popup-factory.d.ts
@@ -0,0 +1,32 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/** Details about how to acquire the popup. */
+export type GetOrCreatePopupDetails = {
+    /** The ID of the frame that should host the popup. */
+    frameId?: number | null;
+    /** A specific ID used to find an existing popup, or to assign to the new popup. */
+    id?: string | null;
+    /** The ID of the parent popup. */
+    parentPopupId?: string | null;
+    /** A specific depth value to assign to the popup. */
+    depth?: number | null;
+    /** Whether or not a separate popup window should be used, rather than an iframe. */
+    popupWindow?: boolean;
+    /** Whether or not the popup is able to show child popups. */
+    childrenSupported?: boolean;
+};
diff --git a/types/ext/popup-menu.d.ts b/types/ext/popup-menu.d.ts
new file mode 100644
index 0000000000..c20ebf69c8
--- /dev/null
+++ b/types/ext/popup-menu.d.ts
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type EventType = 'close';
+
+export type CloseReason = 'close' | 'outside' | 'item' | 'resize';
+
+export type MenuOpenEventDetails = {
+    menu: PopupMenu;
+};
+
+export type MenuCloseEventDetails = {
+    menu: PopupMenu;
+    item: HTMLElement | null;
+    action: string | null;
+    cause: CloseReason;
+    altKey: boolean;
+    ctrlKey: boolean;
+    metaKey: boolean;
+    shiftKey: boolean;
+};
+
+export type MenuOpenEvent = CustomEvent<MenuOpenEventDetails>;
+
+export type MenuCloseEvent = CustomEvent<MenuCloseEventDetails>;
diff --git a/types/ext/popup.d.ts b/types/ext/popup.d.ts
new file mode 100644
index 0000000000..bcbc86621e
--- /dev/null
+++ b/types/ext/popup.d.ts
@@ -0,0 +1,132 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as DocumentUtil from './document-util';
+import type * as Settings from './settings';
+
+export type PopupAny = Popup | PopupWindow | PopupProxy;
+
+/**
+ * Information about how popup content should be shown, specifically related to the outer popup frame.
+ */
+export type ContentDetails = {
+    /** The options context for the content to show. */
+    optionsContext: Settings.OptionsContext | null;
+    /** The rectangles of the source content. */
+    sourceRects: Rect[];
+    /** The normalized CSS writing-mode value of the source content. */
+    writingMode: DocumentUtil.NormalizedWritingMode;
+};
+
+/**
+ * A rectangle representing a DOM region, similar to DOMRect.
+ */
+export type Rect = {
+    /** The left position of the rectangle. */
+    left: number;
+    /** The top position of the rectangle. */
+    top: number;
+    /** The right position of the rectangle. */
+    right: number;
+    /** The bottom position of the rectangle. */
+    bottom: number;
+};
+
+/**
+ * A rectangle representing a DOM region, similar to DOMRect but with a `valid` property.
+ */
+export type ValidRect = {
+    /** The left position of the rectangle. */
+    left: number;
+    /** The top position of the rectangle. */
+    top: number;
+    /** The right position of the rectangle. */
+    right: number;
+    /** The bottom position of the rectangle. */
+    bottom: number;
+    /** Whether or not the rectangle is valid. */
+    valid: boolean;
+};
+
+/**
+ * A rectangle representing a DOM region for placing the popup frame.
+ */
+export type SizeRect = {
+    /** The left position of the rectangle. */
+    left: number;
+    /** The top position of the rectangle. */
+    top: number;
+    /** The width of the rectangle. */
+    width: number;
+    /** The height of the rectangle. */
+    height: number;
+    /** Whether or not the rectangle is positioned to the right of the source rectangle. */
+    after: boolean;
+    /** Whether or not the rectangle is positioned below the source rectangle. */
+    below: boolean;
+};
+
+export type ValidSize = {
+    width: number;
+    height: number;
+    valid: boolean;
+};
+
+export type CustomOuterCssChangedEvent = {
+    node: HTMLStyleElement | HTMLLinkElement | null;
+    useWebExtensionApi: boolean;
+    inShadow: boolean;
+};
+
+export type PopupAnyEventType = PopupEventType | PopupProxyEventType | PopupWindowEventType;
+
+export type PopupEventType = 'customOuterCssChanged' | 'framePointerOver' | 'framePointerOut' | 'offsetNotFound';
+
+export type PopupProxyEventType = 'offsetNotFound';
+
+export type PopupWindowEventType = never;
+
+export type PopupConstructorDetails = {
+    /** The ID of the popup. */
+    id: string;
+    /** The depth of the popup. */
+    depth: number;
+    /** The ID of the host frame. */
+    frameId: number;
+    /** Whether or not the popup is able to show child popups. */
+    childrenSupported: boolean;
+};
+
+export type PopupWindowConstructorDetails = {
+    /** The ID of the popup. */
+    id: string;
+    /** The depth of the popup. */
+    depth: number;
+    /** The ID of the host frame. */
+    frameId: number;
+};
+
+export type PopupProxyConstructorDetails = {
+    /** The ID of the popup. */
+    id: string;
+    /** The depth of the popup. */
+    depth: number;
+    /** The ID of the host frame. */
+    frameId: number;
+    /** A `FrameOffsetForwarder` instance which is used to determine frame positioning. */
+    frameOffsetForwarder: FrameOffsetForwarder | null;
+};
diff --git a/types/ext/profile-conditions-ui.d.ts b/types/ext/profile-conditions-ui.d.ts
new file mode 100644
index 0000000000..7aa22e938e
--- /dev/null
+++ b/types/ext/profile-conditions-ui.d.ts
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Settings from './settings';
+
+export type EventType = 'conditionGroupCountChanged';
+
+export type DescriptorType = Settings.ProfileConditionType;
+
+export type Descriptor = {
+    displayName: string;
+    defaultOperator: string;
+    operators: Map<string, OperatorInternal>;
+};
+
+export type ValidateFunction = (value: string) => boolean;
+
+export type NormalizeFunction = (value: unknown) => string;
+
+export type OperatorInternal = {
+    displayName: string;
+    type: string;
+    defaultValue: string;
+    resetDefaultOnChange?: boolean;
+    validate?: ValidateFunction;
+    normalize?: NormalizeFunction;
+};
+
+export type Operator = {
+    displayName: string;
+    type: string;
+    defaultValue: string;
+    resetDefaultOnChange: boolean | null;
+    validate: ValidateFunction | null;
+    normalize: NormalizeFunction | null;
+};
+
+export type ConditionGroupCountChangedEvent = {
+    count: number;
+    profileIndex: number;
+};
+
+export type DescriptorInfo = {
+    name: DescriptorType;
+    displayName: string;
+};
+
+export type OperatorInfo = {
+    name: string;
+    displayName: string;
+};
+
+export type InputData = {
+    validate: ValidateFunction | null;
+    normalize: NormalizeFunction | null;
+};
diff --git a/types/ext/profile-conditions-util.d.ts b/types/ext/profile-conditions-util.d.ts
new file mode 100644
index 0000000000..1590441042
--- /dev/null
+++ b/types/ext/profile-conditions-util.d.ts
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as JsonSchema from './json-schema';
+import type * as Settings from './settings';
+
+export type OperatorMapArray = [
+    key: string,
+    function: CreateSchemaFunction,
+][];
+
+export type CreateSchemaFunction = (
+    value: unknown,
+) => JsonSchema.Schema;
+
+export type NormalizedOptionsContext1 = Settings.OptionsContext1 & {
+    domain?: string;
+};
+
+export type NormalizedOptionsContext2 = Settings.OptionsContext2;
+
+export type NormalizedOptionsContext3 = Settings.OptionsContext2;
+
+export type NormalizedOptionsContext = NormalizedOptionsContext1 | NormalizedOptionsContext2 | NormalizedOptionsContext3;
diff --git a/types/ext/request-builder.d.ts b/types/ext/request-builder.d.ts
new file mode 100644
index 0000000000..0acf5ede95
--- /dev/null
+++ b/types/ext/request-builder.d.ts
@@ -0,0 +1,21 @@
+/*
+* Copyright (C) 2023  Yomitan Authors
+*
+* This program is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation, either version 3 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+export type FetchEventListeners = {
+    onBeforeSendHeaders: ((details: chrome.webRequest.WebRequestHeadersDetails) => (chrome.webRequest.BlockingResponse | void)) | null;
+    onErrorOccurred: ((details: chrome.webRequest.WebResponseErrorDetails) => void) | null;
+};
diff --git a/types/ext/script-manager.d.ts b/types/ext/script-manager.d.ts
new file mode 100644
index 0000000000..8933715285
--- /dev/null
+++ b/types/ext/script-manager.d.ts
@@ -0,0 +1,56 @@
+/*
+* Copyright (C) 2023  Yomitan Authors
+*
+* This program is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation, either version 3 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+export type RunAt = 'document_start' | 'document_end' | 'document_idle';
+
+/** The script registration details. */
+export type RegistrationDetails = {
+    /** Same as `matches` in the `content_scripts` manifest key. */
+    matches: string[];
+
+    /** Regex match pattern to use as a fallback when native content script registration isn't supported. */
+    /** Should be equivalent to `matches`. */
+    urlMatches: string;
+
+    /** Same as `run_at` in the `content_scripts` manifest key. */
+    runAt: RunAt;
+
+    /** Same as `exclude_matches` in the `content_scripts` manifest key. */
+    excludeMatches?: string[];
+
+    /** Same as `match_about_blank` in the `content_scripts` manifest key. */
+    matchAboutBlank: boolean;
+
+    /** Same as `all_frames` in the `content_scripts` manifest key. */
+    allFrames: boolean;
+
+    /** List of CSS paths. */
+    css?: string[];
+
+    /** List of script paths. */
+    js?: string[];
+};
+
+export type ContentScriptInjectionDetails = {
+    allFrames: boolean;
+    matchAboutBlank: boolean;
+    runAt: RunAt;
+    css?: string[];
+    js?: string[];
+    urlRegex: RegExp | null;
+};
+
diff --git a/types/ext/selector-observer.d.ts b/types/ext/selector-observer.d.ts
new file mode 100644
index 0000000000..a84b2addd8
--- /dev/null
+++ b/types/ext/selector-observer.d.ts
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type OnAddedCallback<T> = (element: Element) => T | undefined;
+
+export type OnRemovedCallback<T> = (element: Element, data: T) => void;
+
+export type OnChildrenUpdatedCallback<T> = (element: Element, data: T) => void;
+
+export type IsStaleCallback<T> = (element: Element, data: T) => boolean;
+
+export type ConstructorDetails<T> = {
+    /** A string CSS selector used to find elements. */
+    selector: string;
+    /** A string CSS selector used to filter elements, or `null` for no filtering. */
+    ignoreSelector?: string | null;
+    /** A function which is invoked for each element that is added that matches the selector. */
+    onAdded?: OnAddedCallback<T> | null;
+    /** A function which is invoked for each element that is removed, or `null`. */
+    onRemoved?: OnRemovedCallback<T> | null;
+    /** A function which is invoked for each element which has its children updated, or `null`. */
+    onChildrenUpdated?: OnChildrenUpdatedCallback<T> | null;
+    /**
+     * A function which checks if the data is stale for a given element, or `null`.
+     * If the element is stale, it will be removed and potentially re-added.
+     */
+    isStale?: IsStaleCallback<T> | null;
+};
+
+export type MutationRecordLike = {
+    type: string;
+    addedNodes: Node[];
+    removedNodes: Node[];
+    target: Node;
+};
+
+export type Observer<T> = {
+    element: Element;
+    ancestors: Node[];
+    data: T;
+};
diff --git a/types/ext/settings-controller.d.ts b/types/ext/settings-controller.d.ts
new file mode 100644
index 0000000000..4a5bef3d54
--- /dev/null
+++ b/types/ext/settings-controller.d.ts
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Settings from './settings';
+import type * as SettingsModifications from './settings-modifications';
+import type * as Core from './core';
+
+export type PageExitPrevention = {
+    end: () => void;
+};
+
+export type EventType = 'optionsChanged' | 'optionsContextChanged' | 'permissionsChanged' | 'dictionarySettingsReordered' | 'scanInputsChanged';
+
+export type OptionsChangedEvent = {
+    options: Settings.ProfileOptions;
+    optionsContext: Settings.OptionsContext;
+};
+
+export type PermissionsChangedEvent = {
+    permissions: chrome.permissions.Permissions;
+};
+
+export type DictionarySettingsReorderedEvent = {
+    source: DictionaryController;
+};
+
+export type ScanInputsChangedEvent = {
+    source: ScanInputsController | ScanInputsSimpleController;
+};
+
+export type SettingsRead<THasScope extends boolean> = THasScope extends true ? SettingsModifications.ScopedRead : SettingsModifications.Read;
+
+export type SettingsModification<THasScope extends boolean> = THasScope extends true ? SettingsModifications.ScopedModification : SettingsModifications.Modification;
+
+export type SettingsExtraFields<THasScope extends boolean> = THasScope extends true ? null : SettingsModifications.OptionsScope;
+
+export type ModifyResult = Core.Response<SettingsModifications.ModificationResult>;
diff --git a/types/ext/settings-modifications.d.ts b/types/ext/settings-modifications.d.ts
new file mode 100644
index 0000000000..5541383afe
--- /dev/null
+++ b/types/ext/settings-modifications.d.ts
@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Settings from './settings';
+
+export type OptionsScope = {
+    scope: OptionsScopeType;
+    optionsContext: Settings.OptionsContext | null;
+};
+
+export type OptionsScopeType = 'profile' | 'global';
+
+export type Read = {
+    path: string;
+};
+
+export type ModificationSet = {
+    action: 'set';
+    path: string;
+    value: unknown;
+};
+
+export type ModificationDelete = {
+    action: 'delete';
+    path: string;
+};
+
+export type ModificationSwap = {
+    action: 'swap';
+    path1: string;
+    path2: string;
+};
+
+export type ModificationSplice = {
+    action: 'splice';
+    path: string;
+    start: number;
+    deleteCount: number;
+    items: unknown[];
+};
+
+export type ModificationPush = {
+    action: 'push';
+    path: string;
+    items: unknown[];
+};
+
+export type Modification = (
+    ModificationSet |
+    ModificationDelete |
+    ModificationSwap |
+    ModificationSplice |
+    ModificationPush
+);
+
+export type ScopedRead = Read & OptionsScope;
+export type ScopedModificationSet = ModificationSet & OptionsScope;
+export type ScopedModificationDelete = ModificationDelete & OptionsScope;
+export type ScopedModificationSwap = ModificationSwap & OptionsScope;
+export type ScopedModificationSplice = ModificationSplice & OptionsScope;
+export type ScopedModificationPush = ModificationPush & OptionsScope;
+
+export type ScopedModification = (
+    ScopedModificationSet |
+    ScopedModificationDelete |
+    ScopedModificationSwap |
+    ScopedModificationSplice |
+    ScopedModificationPush
+);
+
+export type ModificationSetResult = unknown;
+export type ModificationDeleteResult = true;
+export type ModificationSwapResult = true;
+export type ModificationSpliceResult = unknown[];
+export type ModificationPushResult = number;
+
+export type ModificationResult = (
+    ModificationSetResult |
+    ModificationDeleteResult |
+    ModificationSwapResult |
+    ModificationSpliceResult |
+    ModificationPushResult
+);
diff --git a/types/ext/settings.d.ts b/types/ext/settings.d.ts
new file mode 100644
index 0000000000..19c4aa1f54
--- /dev/null
+++ b/types/ext/settings.d.ts
@@ -0,0 +1,382 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Input from './input';
+
+export type OptionsContextFlag = 'clipboard';
+
+export type OptionsContext1 = {
+    url: string;
+    depth: number;
+    index?: undefined;
+    current?: undefined;
+    flags?: OptionsContextFlag[];
+    modifiers?: Input.Modifier[];
+    modifierKeys?: Input.ModifierKey[];
+};
+
+export type OptionsContext2 = {
+    index: number;
+    url?: undefined;
+    depth?: undefined;
+    current?: undefined;
+    flags?: OptionsContextFlag[];
+    modifiers?: Input.Modifier[];
+    modifierKeys?: Input.ModifierKey[];
+};
+
+export type OptionsContext3 = {
+    current: true;
+    url?: undefined;
+    depth?: undefined;
+    index?: undefined;
+    flags?: OptionsContextFlag[];
+    modifiers?: Input.Modifier[];
+    modifierKeys?: Input.ModifierKey[];
+};
+
+export type OptionsContext = OptionsContext1 | OptionsContext2 | OptionsContext3;
+
+export type Options = {
+    version: number;
+    profiles: Profile[];
+    profileCurrent: number;
+    global: GlobalOptions;
+};
+
+export type GlobalOptions = {
+    database: GlobalDatabaseOptions;
+};
+
+export type GlobalDatabaseOptions = {
+    prefixWildcardsSupported: boolean;
+};
+
+export type Profile = {
+    name: string;
+    conditionGroups: ProfileConditionGroup[];
+    options: ProfileOptions;
+};
+
+export type ProfileConditionGroup = {
+    conditions: ProfileCondition[];
+};
+
+export type ProfileConditionType = 'popupLevel' | 'url' | 'modifierKeys' | 'flags';
+
+export type ProfileCondition = {
+    type: ProfileConditionType;
+    operator: string;
+    value: string;
+};
+
+export type ProfileOptions = {
+    general: GeneralOptions;
+    popupWindow: PopupWindowOptions;
+    audio: AudioOptions;
+    scanning: ScanningOptions;
+    translation: TranslationOptions;
+    dictionaries: DictionariesOptions;
+    parsing: ParsingOptions;
+    anki: AnkiOptions;
+    sentenceParsing: SentenceParsingOptions;
+    inputs: InputsOptions;
+    clipboard: ClipboardOptions;
+    accessibility: AccessibilityOptions;
+};
+
+export type GeneralOptions = {
+    enable: boolean;
+    resultOutputMode: ResultOutputMode;
+    debugInfo: boolean;
+    maxResults: number;
+    showAdvanced: boolean;
+    popupDisplayMode: PopupDisplayMode;
+    popupWidth: number;
+    popupHeight: number;
+    popupHorizontalOffset: number;
+    popupVerticalOffset: number;
+    popupHorizontalOffset2: number;
+    popupVerticalOffset2: number;
+    popupHorizontalTextPosition: PopupHorizontalTextPosition;
+    popupVerticalTextPosition: PopupVerticalTextPosition;
+    popupScalingFactor: number;
+    popupScaleRelativeToPageZoom: boolean;
+    popupScaleRelativeToVisualViewport: boolean;
+    showGuide: boolean;
+    compactTags: boolean;
+    glossaryLayoutMode: GlossaryLayoutMode;
+    mainDictionary: string;
+    popupTheme: PopupTheme;
+    popupOuterTheme: PopupOuterTheme;
+    customPopupCss: string;
+    customPopupOuterCss: string;
+    enableWanakana: boolean;
+    showPitchAccentDownstepNotation: boolean;
+    showPitchAccentPositionNotation: boolean;
+    showPitchAccentGraph: boolean;
+    showIframePopupsInRootFrame: boolean;
+    useSecurePopupFrameUrl: boolean;
+    usePopupShadowDom: boolean;
+    usePopupWindow: boolean;
+    popupCurrentIndicatorMode: PopupCurrentIndicatorMode;
+    popupActionBarVisibility: PopupActionBarVisibility;
+    popupActionBarLocation: PopupActionBarLocation;
+    frequencyDisplayMode: FrequencyDisplayMode;
+    termDisplayMode: TermDisplayMode;
+    sortFrequencyDictionary: string | null;
+    sortFrequencyDictionaryOrder: SortFrequencyDictionaryOrder;
+};
+
+export type PopupWindowOptions = {
+    width: number;
+    height: number;
+    left: number;
+    top: number;
+    useLeft: boolean;
+    useTop: boolean;
+    windowType: PopupWindowType;
+    windowState: PopupWindowState;
+};
+
+export type AudioOptions = {
+    enabled: boolean;
+    volume: number;
+    autoPlay: boolean;
+    sources: AudioSourceOptions[];
+};
+
+export type AudioSourceOptions = {
+    type: AudioSourceType;
+    url: string;
+    voice: string;
+};
+
+export type ScanningOptions = {
+    inputs: ScanningInput[];
+    preventMiddleMouse: ScanningPreventMiddleMouseOptions;
+    touchInputEnabled: boolean;
+    pointerEventsEnabled: boolean;
+    selectText: boolean;
+    alphanumeric: boolean;
+    autoHideResults: boolean;
+    delay: number;
+    hideDelay: number;
+    length: number;
+    deepDomScan: boolean;
+    popupNestingMaxDepth: number;
+    enablePopupSearch: boolean;
+    enableOnPopupExpressions: boolean;
+    enableOnSearchPage: boolean;
+    enableSearchTags: boolean;
+    layoutAwareScan: boolean;
+    matchTypePrefix: boolean;
+    hidePopupOnCursorExit: boolean;
+    hidePopupOnCursorExitDelay: number;
+    normalizeCssZoom: boolean;
+};
+
+export type ScanningInput = {
+    include: string;
+    exclude: string;
+    types: ScanningInputTypes;
+    options: ScanningInputOptions;
+};
+
+export type ScanningInputTypes = {
+    mouse: boolean;
+    touch: boolean;
+    pen: boolean;
+};
+
+export type ScanningInputOptions = {
+    showAdvanced: boolean;
+    searchTerms: boolean;
+    searchKanji: boolean;
+    scanOnTouchMove: boolean;
+    scanOnTouchPress: boolean;
+    scanOnTouchRelease: boolean;
+    scanOnPenMove: boolean;
+    scanOnPenHover: boolean;
+    scanOnPenReleaseHover: boolean;
+    scanOnPenPress: boolean;
+    scanOnPenRelease: boolean;
+    preventTouchScrolling: boolean;
+    preventPenScrolling: boolean;
+};
+
+export type ScanningPreventMiddleMouseOptions = {
+    onWebPages: boolean;
+    onPopupPages: boolean;
+    onSearchPages: boolean;
+    onSearchQuery: boolean;
+};
+
+export type TranslationOptions = {
+    convertHalfWidthCharacters: TranslationConvertType;
+    convertNumericCharacters: TranslationConvertType;
+    convertAlphabeticCharacters: TranslationConvertType;
+    convertHiraganaToKatakana: TranslationConvertType;
+    convertKatakanaToHiragana: TranslationConvertType;
+    collapseEmphaticSequences: TranslationCollapseEmphaticSequences;
+    textReplacements: TranslationTextReplacementOptions;
+};
+
+export type TranslationTextReplacementOptions = {
+    searchOriginal: boolean;
+    groups: TranslationTextReplacementGroup[][];
+};
+
+export type TranslationTextReplacementGroup = {
+    pattern: string;
+    ignoreCase: boolean;
+    replacement: string;
+};
+
+export type DictionariesOptions = DictionaryOptions[];
+
+export type DictionaryOptions = {
+    name: string;
+    priority: number;
+    enabled: boolean;
+    allowSecondarySearches: boolean;
+    definitionsCollapsible: DictionaryDefinitionsCollapsible;
+};
+
+export type ParsingOptions = {
+    enableScanningParser: boolean;
+    enableMecabParser: boolean;
+    selectedParser: string | null;
+    termSpacing: boolean;
+    readingMode: ParsingReadingMode;
+};
+
+export type AnkiOptions = {
+    enable: boolean;
+    server: string;
+    tags: string[];
+    screenshot: AnkiScreenshotOptions;
+    terms: AnkiNoteOptions;
+    kanji: AnkiNoteOptions;
+    duplicateScope: AnkiDuplicateScope;
+    duplicateScopeCheckAllModels: boolean;
+    checkForDuplicates: boolean;
+    fieldTemplates: string | null;
+    suspendNewCards: boolean;
+    displayTags: AnkiDisplayTags;
+    noteGuiMode: AnkiNoteGuiMode;
+    apiKey: string;
+    downloadTimeout: number;
+};
+
+export type AnkiCardType = 'terms' | 'kanji';
+
+export type AnkiScreenshotOptions = {
+    format: AnkiScreenshotFormat;
+    quality: number;
+};
+
+export type AnkiNoteOptions = {
+    deck: string;
+    model: string;
+    fields: AnkiNoteFields;
+};
+
+export type AnkiNoteFields = {
+    [key: string]: string;
+};
+
+export type SentenceParsingOptions = {
+    scanExtent: number;
+    terminationCharacterMode: SentenceTerminationCharacterMode;
+    terminationCharacters: SentenceParsingTerminationCharacterOption[];
+};
+
+export type SentenceParsingTerminationCharacterOption = {
+    enabled: boolean;
+    character1: string;
+    character2: string | null;
+    includeCharacterAtStart: boolean;
+    includeCharacterAtEnd: boolean;
+};
+
+export type InputsOptions = {
+    hotkeys: InputsHotkeyOptions[];
+};
+
+export type InputsHotkeyOptions = {
+    action: string;
+    argument: string;
+    key: string | null;
+    modifiers: InputsHotkeyModifier[];
+    scopes: InputsHotkeyScope[];
+    enabled: boolean;
+};
+
+export type ClipboardOptions = {
+    enableBackgroundMonitor: boolean;
+    enableSearchPageMonitor: boolean;
+    autoSearchContent: boolean;
+    maximumSearchLength: number;
+};
+
+export type AccessibilityOptions = {
+    forceGoogleDocsHtmlRendering: boolean;
+};
+
+export type PreventMiddleMouseOptions = {
+    onWebPages: boolean;
+    onPopupPages: boolean;
+    onSearchPages: boolean;
+    onSearchQuery: boolean;
+};
+
+export type ResultOutputMode = 'group' | 'merge' | 'split';
+export type PopupDisplayMode = 'default' | 'full-width';
+export type PopupHorizontalTextPosition = 'below' | 'above';
+export type PopupVerticalTextPosition = 'default' | 'before' | 'after' | 'left' | 'right';
+export type GlossaryLayoutMode = 'default' | 'compact';
+export type PopupTheme = 'light' | 'dark' | 'browser';
+export type PopupOuterTheme = 'light' | 'dark' | 'browser' | 'site';
+export type PopupCurrentIndicatorMode = 'none' | 'asterisk' | 'triangle' | 'bar-left' | 'bar-right' | 'dot-left' | 'dot-right';
+export type PopupActionBarVisibility = 'auto' | 'always';
+export type PopupActionBarLocation = 'left' | 'right' | 'top' | 'bottom';
+export type FrequencyDisplayMode = 'tags' | 'tags-grouped' | 'split-tags' | 'split-tags-grouped' | 'inline-list' | 'list';
+export type TermDisplayMode = 'ruby' | 'ruby-and-reading' | 'term-and-reading';
+export type SortFrequencyDictionaryOrder = 'ascending' | 'descending';
+
+export type PopupWindowType = 'normal' | 'popup';
+export type PopupWindowState = 'normal' | 'maximized' | 'fullscreen';
+
+export type AudioSourceType = 'jpod101' | 'jpod101-alternate' | 'jisho' | 'text-to-speech' | 'text-to-speech-reading' | 'custom' | 'custom-json';
+
+export type TranslationConvertType = 'false' | 'true' | 'variant';
+export type TranslationCollapseEmphaticSequences = 'false' | 'true' | 'full';
+
+export type DictionaryDefinitionsCollapsible = 'not-collapsible' | 'expanded' | 'collapsed' | 'force-collapsed' | 'force-expanded';
+
+export type ParsingReadingMode = 'hiragana' | 'katakana' | 'romaji' | 'dictionary-reading' | 'none';
+
+export type AnkiScreenshotFormat = 'png' | 'jpeg';
+export type AnkiDuplicateScope = 'collection' | 'deck' | 'deck-root';
+export type AnkiDisplayTags = 'never' | 'always' | 'non-standard';
+export type AnkiNoteGuiMode = 'browse' | 'edit';
+
+export type SentenceTerminationCharacterMode = 'custom' | 'custom-no-newlines' | 'newlines' | 'none';
+
+export type InputsHotkeyModifier = 'alt' | 'ctrl' | 'shift' | 'meta';
+export type InputsHotkeyScope = 'popup' | 'search' | 'web';
diff --git a/types/ext/simple-dom-parser.d.ts b/types/ext/simple-dom-parser.d.ts
new file mode 100644
index 0000000000..5fefe69d6a
--- /dev/null
+++ b/types/ext/simple-dom-parser.d.ts
@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type {
+    Document as Parse5Document,
+    Element as Parse5Element,
+    ChildNode as Parse5ChildNode,
+} from 'parse5/dist/tree-adapters/default';
+
+/**
+ * This type is used as a generic reference to an element object from a generic DOM API.
+ */
+// eslint-disable-next-line @typescript-eslint/ban-types
+export type Element = object;
+
+export type ISimpleDomParser = {
+    getElementById(id: string, root?: Element): Element | null;
+    getElementByTagName(tagName: string, root?: Element): Element | null;
+    getElementsByTagName(tagName: string, root?: Element): Element[];
+    getElementsByClassName(className: string, root?: Element): Element[];
+    getAttribute(element: Element, attribute: string): string | null;
+    getTextContent(element: Element): string;
+};
diff --git a/types/ext/structured-content.d.ts b/types/ext/structured-content.d.ts
new file mode 100644
index 0000000000..09755c882c
--- /dev/null
+++ b/types/ext/structured-content.d.ts
@@ -0,0 +1,205 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as DictionaryData from './dictionary-data';
+
+export type VerticalAlign = 'baseline' | 'sub' | 'super' | 'text-top' | 'text-bottom' | 'middle' | 'top' | 'bottom';
+
+export type TextDecorationLine = 'underline' | 'overline' | 'line-through';
+
+export type TextDecorationLineOrNone = 'none' | TextDecorationLine;
+
+export type FontStyle = 'normal' | 'italic';
+
+export type FontWeight = 'normal' | 'bold';
+
+export type TextAlign = 'start' | 'end' | 'left' | 'right' | 'center' | 'justify' | 'justify-all' | 'match-parent';
+
+export type SizeUnits = 'px' | 'em';
+
+export type ImageRendering = 'auto' | 'pixelated' | 'crisp-edges';
+
+export type ImageAppearance = 'auto' | 'monochrome';
+
+export type Image = DictionaryData.TermImage & {
+    verticalAlign: VerticalAlign;
+    sizeUnits: SizeUnits;
+};
+
+export type Data = {
+    [key: string]: string;
+};
+
+export type StructuredContentStyle = {
+    fontStyle?: FontStyle;
+    fontWeight?: FontWeight;
+    fontSize?: string;
+    textDecorationLine?: TextDecorationLineOrNone | TextDecorationLine[];
+    verticalAlign?: VerticalAlign;
+    textAlign?: TextAlign;
+    marginTop?: number;
+    marginLeft?: number;
+    marginRight?: number;
+    marginBottom?: number;
+    listStyleType?: string;
+};
+
+export type LineBreak = {
+    tag: 'br';
+    data?: Data;
+    /**
+     * This element doesn't support children.
+     */
+    content?: undefined;
+    /**
+     * This element doesn't support language.
+     */
+    lang?: undefined;
+};
+
+export type UnstyledElement = {
+    tag: 'ruby' | 'rt' | 'rp' | 'table' | 'thead' | 'tbody' | 'tfoot' | 'tr';
+    content?: Content;
+    data?: Data;
+    /**
+     * Defines the language of an element in the format defined by RFC 5646.
+     */
+    lang?: string;
+};
+
+export type TableElement = {
+    tag: 'td' | 'th';
+    content?: Content;
+    data?: Data;
+    colSpan?: number;
+    rowSpan?: number;
+    style?: StructuredContentStyle;
+    /**
+     * Defines the language of an element in the format defined by RFC 5646.
+     */
+    lang?: string;
+};
+
+export type StyledElement = {
+    tag: 'span' | 'div' | 'ol' | 'ul' | 'li';
+    content?: Content;
+    data?: Data;
+    style?: StructuredContentStyle;
+    /**
+     * Defines the language of an element in the format defined by RFC 5646.
+     */
+    lang?: string;
+};
+
+export type ImageElementBase = {
+    data?: Data;
+    /**
+     * Path to the image file in the archive.
+     */
+    path: string;
+    /**
+     * Preferred width of the image.
+     */
+    width?: number;
+    /**
+     * Preferred width of the image.
+     */
+    height?: number;
+    /**
+     * Preferred width of the image.
+     * This is only used in the internal database.
+     */
+    preferredWidth?: number;
+    /**
+     * Preferred width of the image.
+     * This is only used in the internal database.
+     */
+    preferredHeight?: number;
+    /**
+     * Hover text for the image.
+     */
+    title?: string;
+    /**
+     * Description of the image.
+     */
+    description?: string;
+    /**
+     * Whether or not the image should appear pixelated at sizes larger than the image's native resolution.
+     */
+    pixelated?: boolean;
+    /**
+     * Controls how the image is rendered. The value of this field supersedes the pixelated field.
+     */
+    imageRendering?: ImageRendering;
+    /**
+     * Controls the appearance of the image. The 'monochrome' value will mask the opaque parts of the image using the current text color.
+     */
+    appearance?: ImageAppearance;
+    /**
+     * Whether or not a background color is displayed behind the image.
+     */
+    background?: boolean;
+    /**
+     * Whether or not the image is collapsed by default.
+     */
+    collapsed?: boolean;
+    /**
+     * Whether or not the image can be collapsed.
+     */
+    collapsible?: boolean;
+    /**
+     * This property is not defined on the base class.
+     */
+    verticalAlign?: undefined;
+    /**
+     * This property is not defined on the base class.
+     */
+    sizeUnits?: undefined;
+};
+
+export type ImageElement = ImageElementBase & {
+    tag: 'img';
+    /**
+     * This element doesn't support children.
+     */
+    content?: undefined;
+    /**
+     * The vertical alignment of the image.
+     */
+    verticalAlign?: VerticalAlign;
+    /**
+     * The units for the width and height.
+     */
+    sizeUnits?: SizeUnits;
+};
+
+export type LinkElement = {
+    tag: 'a';
+    content?: Content;
+    /**
+     * The URL for the link. URLs starting with a ? are treated as internal links to other dictionary content.
+     */
+    href: string;
+    /**
+     * Defines the language of an element in the format defined by RFC 5646.
+     */
+    lang?: string;
+};
+
+export type Element = LineBreak | UnstyledElement | TableElement | StyledElement | ImageElement | LinkElement;
+
+export type Content = string | Element | Content[];
diff --git a/types/ext/task-accumulator.d.ts b/types/ext/task-accumulator.d.ts
new file mode 100644
index 0000000000..772949f6de
--- /dev/null
+++ b/types/ext/task-accumulator.d.ts
@@ -0,0 +1,21 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export interface Task<V> {
+    data: V;
+    stale: boolean;
+}
diff --git a/types/ext/template-patcher.d.ts b/types/ext/template-patcher.d.ts
new file mode 100644
index 0000000000..852d3768ab
--- /dev/null
+++ b/types/ext/template-patcher.d.ts
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type Patch = {
+    addition: string;
+    modifications: {
+        current: string;
+        replacement: string;
+    }[];
+};
diff --git a/types/ext/template-renderer-frame-api.d.ts b/types/ext/template-renderer-frame-api.d.ts
new file mode 100644
index 0000000000..e00a0711d8
--- /dev/null
+++ b/types/ext/template-renderer-frame-api.d.ts
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Core from './core';
+
+export type MessageData = {
+    action: string;
+    params: Core.SerializableObject;
+    id: string;
+};
diff --git a/types/ext/template-renderer.d.ts b/types/ext/template-renderer.d.ts
new file mode 100644
index 0000000000..169fee7814
--- /dev/null
+++ b/types/ext/template-renderer.d.ts
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as AnkiNoteBuilder from './anki-note-builder';
+import type * as AnkiTemplates from './anki-templates';
+import type * as Core from './core';
+
+export type RenderResult = {
+    result: string;
+    requirements: AnkiNoteBuilder.Requirement[];
+};
+
+export type RenderMultiItem = {
+    template: string;
+    templateItems: RenderMultiTemplateItem[];
+};
+
+export type RenderMultiTemplateItem = {
+    type: AnkiTemplates.RenderMode;
+    commonData: AnkiNoteBuilder.CommonData;
+    datas: PartialOrCompositeRenderData[];
+};
+
+export type PartialRenderData = {
+    marker: string;
+    commonData?: undefined;
+};
+
+export type CompositeRenderData = {
+    marker: string;
+    commonData: AnkiNoteBuilder.CommonData;
+};
+
+export type PartialOrCompositeRenderData = PartialRenderData | CompositeRenderData;
+
+export type DataType = {
+    modifier: (data: CompositeRenderData) => AnkiTemplates.NoteData;
+    composeData: (data: PartialOrCompositeRenderData, commonData: AnkiNoteBuilder.CommonData) => CompositeRenderData;
+};
+
+export type HelperOptionsFunction<TResult = unknown> = (context: unknown) => TResult;
+
+export type HelperOptions = {
+    fn: HelperOptionsFunction;
+    inverse: HelperOptionsFunction;
+    hash: Core.SafeAny;
+    data?: Core.SafeAny;
+};
+
+export type HelperFunction<TReturn = unknown> = (args: unknown[], context: unknown, options: HelperOptions) => TReturn;
+
+export type HelperFunctionsDescriptor = [
+    name: string,
+    helper: HelperFunction<unknown>,
+][];
+
+export type SetupCallbackResult = {
+    requirements: AnkiNoteBuilder.Requirement[];
+};
+
+export type CleanupCallbackResult = void;
diff --git a/types/ext/text-scanner.d.ts b/types/ext/text-scanner.d.ts
new file mode 100644
index 0000000000..494c1a52ec
--- /dev/null
+++ b/types/ext/text-scanner.d.ts
@@ -0,0 +1,185 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Dictionary from './dictionary';
+import type * as Display from './display';
+import type * as Input from './input';
+import type * as Settings from './settings';
+import type * as TextSource from './text-source';
+
+export type SearchResultDetail = {
+    documentTitle: string;
+};
+
+export type Options = {
+    inputs?: InputOptionsOuter[];
+    deepContentScan?: boolean;
+    normalizeCssZoom?: boolean;
+    selectText?: boolean;
+    delay?: number;
+    touchInputEnabled?: boolean;
+    pointerEventsEnabled?: boolean;
+    scanLength?: number;
+    layoutAwareScan?: boolean;
+    preventMiddleMouse?: boolean;
+    matchTypePrefix?: boolean;
+    sentenceParsingOptions?: SentenceParsingOptions;
+};
+
+export type InputOptionsOuter = {
+    include: string;
+    exclude: string;
+    types: {
+        mouse: boolean;
+        touch: boolean;
+        pen: boolean;
+    };
+    options: InputOptions;
+};
+
+export type InputOptions = {
+    searchTerms: boolean;
+    searchKanji: boolean;
+    scanOnTouchMove: boolean;
+    scanOnTouchPress: boolean;
+    scanOnTouchRelease: boolean;
+    scanOnPenMove: boolean;
+    scanOnPenHover: boolean;
+    scanOnPenReleaseHover: boolean;
+    scanOnPenPress: boolean;
+    scanOnPenRelease: boolean;
+    preventTouchScrolling: boolean;
+    preventPenScrolling: boolean;
+};
+
+export type SentenceParsingOptions = {
+    scanExtent: number;
+    terminationCharacterMode: Settings.SentenceTerminationCharacterMode;
+    terminationCharacters: Settings.SentenceParsingTerminationCharacterOption[];
+};
+
+export type InputConfig = {
+    include: string[];
+    exclude: string[];
+    types: Set<PointerType>;
+    searchTerms: boolean;
+    searchKanji: boolean;
+    scanOnTouchMove: boolean;
+    scanOnTouchPress: boolean;
+    scanOnTouchRelease: boolean;
+    scanOnPenMove: boolean;
+    scanOnPenHover: boolean;
+    scanOnPenReleaseHover: boolean;
+    scanOnPenPress: boolean;
+    scanOnPenRelease: boolean;
+    preventTouchScrolling: boolean;
+    preventPenScrolling: boolean;
+};
+
+export type SearchedEventDetails = {
+    textScanner: TextScanner;
+    type: Display.PageType | null;
+    dictionaryEntries: Dictionary.DictionaryEntry[] | null;
+    sentence: Display.HistoryStateSentence | null;
+    inputInfo: InputInfo;
+    textSource: TextSource.TextSource;
+    optionsContext: Settings.OptionsContext | null;
+    detail: SearchResultDetail | null;
+    error: Error | null;
+};
+
+export type InputInfo = {
+    input: InputConfig | null;
+    pointerType: PointerType;
+    eventType: PointerEventType;
+    passive: boolean;
+    modifiers: Input.Modifier[];
+    modifierKeys: Input.ModifierKey[];
+    detail: InputInfoDetail | undefined;
+};
+
+export type InputInfoDetail = {
+    focus: boolean;
+    restoreSelection: boolean;
+};
+
+export type EventType = 'searched' | 'clear';
+
+export type GetSearchContextCallback = GetSearchContextCallbackSync | GetSearchContextCallbackAsync;
+
+export type GetSearchContextCallbackSync = () => SearchContext;
+
+export type GetSearchContextCallbackAsync = () => Promise<SearchContext>;
+
+export type ConstructorDetails = {
+    node: HTMLElement | Window;
+    getSearchContext: GetSearchContextCallback;
+    ignoreElements?: (() => Element[]) | null;
+    ignorePoint?: ((x: number, y: number) => Promise<boolean>) | null;
+    searchTerms?: boolean;
+    searchKanji?: boolean;
+    searchOnClick?: boolean;
+    searchOnClickOnly?: boolean;
+};
+
+export type SearchContext = {
+    optionsContext: Settings.OptionsContext;
+    detail?: SearchResultDetail;
+};
+
+export type SelectionRestoreInfo = {
+    ranges: Range[];
+};
+
+export type TermSearchResults = {
+    type: 'terms';
+    dictionaryEntries: Dictionary.TermDictionaryEntry[];
+    sentence: Sentence;
+};
+
+export type KanjiSearchResults = {
+    type: 'kanji';
+    dictionaryEntries: Dictionary.KanjiDictionaryEntry[];
+    sentence: Sentence;
+};
+
+export type SearchResults = TermSearchResults | KanjiSearchResults;
+
+export type Sentence = {
+    text: string;
+    offset: number;
+};
+
+export type PointerType = (
+    'pen' |
+    'mouse' |
+    'touch' |
+    'script'
+);
+
+export type PointerEventType = (
+    'mouseMove' |
+    'pointerOver' |
+    'pointerDown' |
+    'pointerMove' |
+    'pointerUp' |
+    'touchStart' |
+    'touchEnd' |
+    'touchMove' |
+    'click' |
+    'script'
+);
diff --git a/types/ext/text-source.d.ts b/types/ext/text-source.d.ts
new file mode 100644
index 0000000000..37c65bd929
--- /dev/null
+++ b/types/ext/text-source.d.ts
@@ -0,0 +1,18 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type TextSource = TextSourceRange | TextSourceElement;
diff --git a/types/ext/translation-internal.d.ts b/types/ext/translation-internal.d.ts
new file mode 100644
index 0000000000..00f51b05c7
--- /dev/null
+++ b/types/ext/translation-internal.d.ts
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Translation from './translation';
+import type * as DictionaryDatabase from './dictionary-database';
+
+export type TextDeinflectionOptions = [
+    textReplacements: Translation.FindTermsTextReplacement[] | null,
+    halfWidth: boolean,
+    numeric: boolean,
+    alphabetic: boolean,
+    katakana: boolean,
+    hiragana: boolean,
+    emphatic: [collapseEmphatic: boolean, collapseEmphaticFull: boolean],
+];
+
+export type TextDeinflectionOptionsArrays = [
+    textReplacements: (Translation.FindTermsTextReplacement[] | null)[],
+    halfWidth: boolean[],
+    numeric: boolean[],
+    alphabetic: boolean[],
+    katakana: boolean[],
+    hiragana: boolean[],
+    emphatic: [collapseEmphatic: boolean, collapseEmphaticFull: boolean][],
+];
+
+export enum DeinflectionRuleFlags {
+    None = 0x0,
+    VerbIchidan = 0b00000001, // Verb ichidan
+    VerbGodan = 0b00000010, // Verb godan
+    VerbSuru = 0b00000100, // Verb suru
+    VerbKuru = 0b00001000, // Verb kuru
+    VerbZuru = 0b00010000, // Verb zuru
+    AdjectiveI = 0b00100000, // Adjective i
+    IruEndingIntermediate = 0b01000000, // Intermediate -iru endings for progressive or perfect tense
+}
+
+export type Deinflection = {
+    term: string;
+    rules: DeinflectionRuleFlags;
+    reasons: string[];
+};
+
+export type DatabaseDeinflection = {
+    originalText: string;
+    transformedText: string;
+    deinflectedText: string;
+    rules: DeinflectionRuleFlags;
+    reasons: string[];
+    databaseEntries: DictionaryDatabase.TermEntry[];
+};
diff --git a/types/ext/translation.d.ts b/types/ext/translation.d.ts
new file mode 100644
index 0000000000..3c41c9f367
--- /dev/null
+++ b/types/ext/translation.d.ts
@@ -0,0 +1,171 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ * Copyright (C) 2022  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Dictionary from './dictionary';
+
+// Kanji
+
+/**
+ * An options object for use with `Translator.findKanji`.
+ */
+export type FindKanjiOptions = {
+    /**
+     * The mapping of dictionaries to search for kanji in.
+     * The key is the dictionary name.
+     */
+    enabledDictionaryMap: Map<string, FindKanjiDictionary>;
+};
+
+/**
+ * Details about a dictionary.
+ */
+export type FindKanjiDictionary = {
+    /**
+     * The index of the dictionary
+     */
+    index: number;
+    /**
+     * The priority of the dictionary
+     */
+    priority: number;
+};
+
+// Terms
+
+/**
+ * An options object for use with `Translator.findTerms`.
+ */
+export type FindTermsOptions = {
+    /**
+     * The matching type for looking up terms.
+     */
+    matchType: FindTermsMatchType;
+    /**
+     * Whether or not deinflection should be performed.
+     */
+    deinflect: boolean;
+    /**
+     * The name of the primary dictionary to search.
+     */
+    mainDictionary: string;
+    /**
+     * The name of the frequency dictionary used for sorting
+     */
+    sortFrequencyDictionary: string | null;
+    /**
+     * The order used when using a sorting dictionary.
+     */
+    sortFrequencyDictionaryOrder: FindTermsSortOrder;
+    /**
+     * Whether or not non-Japanese characters should be searched.
+     */
+    removeNonJapaneseCharacters: boolean;
+    /**
+     * Whether or not half-width characters should be converted to full-width characters.
+     */
+    convertHalfWidthCharacters: FindTermsVariantMode;
+    /**
+     * Whether or not ASCII numeric characters should be converted to full-width numeric characters.
+     */
+    convertNumericCharacters: FindTermsVariantMode;
+    /**
+     * Whether or not alphabetic characters should be converted to kana.
+     */
+    convertAlphabeticCharacters: FindTermsVariantMode;
+    /**
+     * Whether or not hiragana characters should be converted to katakana.
+     */
+    convertHiraganaToKatakana: FindTermsVariantMode;
+    /**
+     * Whether or not katakana characters should be converted to hiragana.
+     */
+    convertKatakanaToHiragana: FindTermsVariantMode;
+    /**
+     * How emphatic character sequences should be collapsed.
+     */
+    collapseEmphaticSequences: FindTermsEmphaticSequencesMode;
+    /**
+     * An iterable sequence of text replacements to be applied during the term lookup process.
+     */
+    textReplacements: (FindTermsTextReplacement[] | null)[];
+    /**
+     * The mapping of dictionaries to search for terms in.
+     * The key is the dictionary name.
+     */
+    enabledDictionaryMap: TermEnabledDictionaryMap;
+    /**
+     * A set of dictionary names which should have definitions removed.
+     */
+    excludeDictionaryDefinitions: Set<string> | null;
+};
+
+/**
+ * The matching type for looking up terms.
+ */
+export type FindTermsMatchType = Dictionary.TermSourceMatchType;
+
+/**
+ * A sorting order to use when finding terms.
+ */
+export type FindTermsSortOrder = 'ascending' | 'descending';
+
+/**
+ * Mode describing how to handle variations.
+ */
+export type FindTermsVariantMode = 'false' | 'true' | 'variant';
+
+/**
+ * Mode describing how to handle emphatic sequence variations.
+ */
+export type FindTermsEmphaticSequencesMode = 'false' | 'true' | 'full';
+
+/**
+ * Information about how text should be replaced when looking up terms.
+ */
+export type FindTermsTextReplacement = {
+    /**
+     * The pattern to replace.
+     */
+    pattern: RegExp;
+    /**
+     * The replacement string. This can contain special sequences, such as `$&`.
+     */
+    replacement: string;
+};
+
+/**
+ * Details about a dictionary.
+ */
+export type FindTermDictionary = {
+    /**
+     * The index of the dictionary
+     */
+    index: number;
+    /**
+     * The priority of the dictionary
+     */
+    priority: number;
+    /**
+     * Whether or not secondary term searches are allowed for this dictionary.
+     */
+    allowSecondarySearches: boolean;
+};
+
+export type TermEnabledDictionaryMap = Map<string, FindTermDictionary>;
+
+export type KanjiEnabledDictionaryMap = Map<string, FindKanjiDictionary>;
diff --git a/types/ext/translator.d.ts b/types/ext/translator.d.ts
new file mode 100644
index 0000000000..f17b3bf612
--- /dev/null
+++ b/types/ext/translator.d.ts
@@ -0,0 +1,83 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import type * as Dictionary from './dictionary';
+import type * as DictionaryDatabase from './dictionary-database';
+
+export type ConstructorDetails = {
+    /** An instance of JapaneseUtil. */
+    japaneseUtil: JapaneseUtil;
+    /** An instance of DictionaryDatabase. */
+    database: DictionaryDatabase;
+};
+
+/**
+ * Information about how popup content should be shown, specifically related to the outer popup frame.
+ */
+export type TermFrequencySimple = {
+    /** The term. */
+    term: string;
+    /** The reading of the term. */
+    reading: string | null;
+    /** The name of the dictionary that the term frequency originates from. */
+    dictionary: string;
+    /** Whether or not a reading was specified. */
+    hasReading: boolean;
+    /** The frequency value for the term. */
+    frequency: number;
+    /** The display value for the frequency, or `null` if none is specified. */
+    displayValue: string | null;
+    /** Whether or not the `frequency` field is derived from a parsed string. */
+    displayValueParsed: boolean;
+};
+
+export type TagGroup = {
+    dictionary: string;
+    tagNames: string[];
+};
+
+export type TagExpansionTarget = {
+    tags: Dictionary.Tag[];
+    tagGroups: TagGroup[];
+};
+
+export type DictionaryTagCache = Map<string, TagCache>;
+
+export type TagCache = Map<string, DictionaryDatabase.Tag | null>;
+
+export type TagTargetMap = Map<string, Map<string, TagTargetItem>>;
+
+export type TagTargetItem = {
+    query: string;
+    dictionary: string;
+    tagName: string;
+    cache: TagCache | null;
+    databaseTag: DictionaryDatabase.Tag | null;
+    targets: Dictionary.Tag[][];
+};
+
+export type DictionaryEntryGroup = {
+    ids: Set<number>;
+    dictionaryEntries: Dictionary.TermDictionaryEntry[];
+};
+
+export type SequenceQuery = {
+    query: number;
+    dictionary: string;
+};
+
+export type FindTermsMode = 'simple' | 'group' | 'merge' | 'split';
diff --git a/types/other/web-set-timeout.d.ts b/types/other/web-set-timeout.d.ts
new file mode 100644
index 0000000000..98e40daba2
--- /dev/null
+++ b/types/other/web-set-timeout.d.ts
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+declare module 'web-set-timeout' {
+    global {
+        // These types are used to ensure that setTimeout returns a number
+        function setTimeout<TArgs extends unknown[]>(callback: (...args: TArgs) => void, ms?: number, ...args: TArgs): number;
+        function setTimeout(callback: (args: void) => void, ms?: number): number;
+    }
+}
diff --git a/types/test/document-types.d.ts b/types/test/document-types.d.ts
new file mode 100644
index 0000000000..44831397f0
--- /dev/null
+++ b/types/test/document-types.d.ts
@@ -0,0 +1,18 @@
+/*
+ * Copyright (C) 2023  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+export type PseudoDOMRectList = DOMRect[] & {item: (index: number) => DOMRect};