Add getKey method with tests (#384)

Author: iteriani

index.ts

@@ -17,7 +17,7 @@
 
 export {applyAttr, applyProp, attributes,} from './src/attributes';
 export {close, currentElement, currentPointer, open, patchInner as patch, patchInner, patchOuter, skip, skipNode} from './src/core';
-export {clearCache, importNode} from './src/node_data';
+export {getKey, clearCache, importNode} from './src/node_data';
 export {notifications} from './src/notifications';
 export {symbols} from './src/symbols';
 export {attr, elementClose, elementOpen, elementOpenEnd, elementOpenStart, elementVoid, text, key} from './src/virtual_elements';

src/node_data.ts

@@ -16,6 +16,7 @@
  */
 
 import {Key, NameOrCtorDef} from './types';
+import {assert} from './assertions';
 import {isElement, isText} from './dom_util';
 
 
@@ -88,6 +89,10 @@ function getData(node: Node, key?: Key) {
   return importSingleNode(node, key);
 }
 
+function getKey(node: Node) {
+  assert(node['__incrementalDOMData']);
+  return getData(node).key;
+}
 
 /**
  * Imports single node and its subtree, initializing caches.
@@ -163,6 +168,7 @@ function recordAttributes(node: Element, data: NodeData) {
 /** */
 export {
   getData,
+  getKey,
   initData,
   importNode,
   clearCache,

test/functional/keyed_items.ts

@@ -18,7 +18,7 @@
 // taze: mocha from //third_party/javascript/typings/mocha
 // taze: chai from //third_party/javascript/typings/chai
 
-import {currentElement, elementClose, elementOpen, elementVoid, patch, skip, text, clearCache} from '../../index';
+import {currentElement, currentPointer, elementClose, elementOpen, elementVoid, getKey, patch, skip, text, clearCache} from '../../index';
 import {assertHTMLElement, attachShadow, BROWSER_SUPPORTS_SHADOW_DOM,} from '../util/dom';
 const {expect} = chai;
 
@@ -373,3 +373,28 @@ describe('rendering with keys', () => {
     }
   });
 });
+
+describe('getKey', () => {
+  it('should fail if the element has no node data', () => {
+    const div = document.createElement('div');
+    expect(() => {
+      getKey(div);
+    }).to.throw('Expected value to be defined');
+  });
+
+  it('should return undefined if the element has no key', () => {
+    const div = document.createElement('div');
+    patch(div, () => {
+      elementVoid('div');
+    });
+    expect(getKey(div.firstChild!)).to.be.undefined;
+  });
+
+  it('should return a key if the element has a key', () => {
+    const div = document.createElement('div');
+    patch(div, () => {
+      elementVoid('div', '3');
+    });
+    expect(getKey(div.firstChild!)).to.equal('3')
+  });
+});