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Feat proposal enable fetching external resources using native fetch API in Node.js version 18 later (#935)
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‎.changeset/young-guests-tap.md

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---
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'wmr': minor
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---
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Add fetching external resources using native fetch API when Node.js version 18 later

‎packages/wmr/src/lib/prerender.js

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@@ -96,11 +96,43 @@ async function workerCode({ cwd, out, publicPath, customRoutes }) {
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let head = { lang: '', title: '', elements: new Set() };
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globalThis.wmr = { ssr: { head } };
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// @ts-ignore
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globalThis.fetch = async url => {
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async function localFetcher(url) {
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const text = () => fs.readFile(`${out}/${String(url).replace(/^\//, '')}`, 'utf-8');
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return { text, json: () => text().then(JSON.parse) };
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};
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}
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const pattern = /^\//;
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if (globalThis.fetch === undefined) {
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// When Node.js version under 17, native fetch API undefined
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// So it will give a warning when the syntax to retrieve the file and the url is passed
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// @ts-ignore
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globalThis.fetch = async url => {
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if (pattern.test(String(url))) {
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return localFetcher(url);
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}
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console.warn(`fetch is not defined in Node.js version under 17, please upgrade to Node.js version 18 later`);
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};
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} else {
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// At that time, implement using reassignment to avoid entering an infinite loop.
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const fetcher = fetch;
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// @ts-ignore
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delete globalThis.fetch;
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// When Node.js version 18 later, native fetch API is defined
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// Override with own implementation if you want to retrieve local files in Node.js 18 later
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// ref https://github.com/preactjs/wmr/pull/935#discussion_r977168334
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// @ts-ignore
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globalThis.fetch = async (url, options) => {
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if (pattern.test(String(url))) {
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return localFetcher(url);
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}
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// When fetching an external resource, it returns the native fetch API
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// though `fetcher` function is an alias created to avoid infinite loops
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return fetcher(url, options);
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};
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}
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// Prevent Rollup from transforming `import()` here.
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const $import = new Function('s', 'return import(s)');

‎packages/wmr/test/fixtures/prerender-external-resource-fetch/index.html

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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="utf8" />
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<title>default title</title>
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</head>
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<body>
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<script src="./index.js" type="module"></script>
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</body>
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</html>

‎packages/wmr/test/fixtures/prerender-external-resource-fetch/index.js

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export async function prerender() {
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const html = await fetch('https://preactjs.com').then(res => res.text());
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return { html, links: ['/'] };
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}

‎packages/wmr/test/fixtures/prerender-resource-fetch/index.js

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@@ -1,4 +1,4 @@
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export async function prerender() {
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const md = await fetch('content.md').then(res => res.text());
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const md = await fetch('/content.md').then(res => res.text());
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return { html: md, links: ['/'] };
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}

‎packages/wmr/test/production.test.js

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@@ -891,6 +891,40 @@ describe('production', () => {
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const index = await fs.readFile(indexHtml, 'utf8');
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expect(index).toMatch(/# hello world/);
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});
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// Whether or not to run the test to fetch external resources depends on whether or not a Node.js version 18 later
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const isNodeVersionUnder18 = Number(process.version.split('.')[0].slice(1)) < 18;
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// Even if you are using Node.js v18 or higher, you will get the error `globalThis.fetch is undefined` here, so get the version from process.version
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// if (globalThis.fetch === undefined)
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if (isNodeVersionUnder18) {
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it.skip('skip should support fetching resources from external links during prerender on Node.js v18 later', () => {});
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it('should not support fetching resources from external links during prerender on Node.js < v18', async () => {
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await loadFixture('prerender-external-resource-fetch', env);
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instance = await runWmr(env.tmp.path, 'build', '--prerender');
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const code = await instance.done;
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await withLog(instance.output, async () => {
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expect(code).toBe(1);
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expect(instance.output.join('\n')).toMatch(
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/fetch is not defined in Node.js version under 17, please upgrade to Node.js version 18 later/
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);
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});
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});
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} else {
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it.skip('skip should not support fetching resources from external links during prerender on Node.js < v18', () => {});
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it('should support fetching resources from external links during prerender on Node.js v18 later', async () => {
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await loadFixture('prerender-external-resource-fetch', env);
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instance = await runWmr(env.tmp.path, 'build', '--prerender');
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const code = await instance.done;
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// when workflow of wmr runtime uses Node.js 18
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// Until then check locally.
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expect(code).toBe(0);
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const indexHtml = path.join(env.tmp.path, 'dist', 'index.html');
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const index = await fs.readFile(indexHtml, 'utf8');
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expect(index).toMatch(/Preact/);
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});
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}
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});
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describe('Code Splitting', () => {

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