Add toArray utility function to convert array-like objects to arrays.

src/dom.js

@@ -16,6 +16,7 @@
 
 import {dashToCamelCase} from './string';
 import {dev} from './log';
+import {toArray} from './types';
 
 /**
  * Waits until the child element is constructed. Once the child is found, the
@@ -328,13 +329,7 @@ export function childElementsByAttr(parent, attr) {
     scopeSelectorSupported = isScopeSelectorSupported(parent);
   }
   if (scopeSelectorSupported) {
-    const nodeList = parent.querySelectorAll(':scope > [' + attr + ']');
-    // Convert NodeList into Array.<Element>.
-    const children = [];
-    for (let i = 0; i < nodeList.length; i++) {
-      children.push(nodeList[i]);
-    }
-    return children;
+    return toArray(parent.querySelectorAll(':scope > [' + attr + ']'));
   }
   return childElements(parent, el => {
     return el.hasAttribute(attr);

src/types.js

@@ -35,6 +35,24 @@ export function isArray(value) {
   return Array.isArray(value);
 }
 
+/**
+ * Converts an array-like object to an array.
+ * @param {?IArrayLike<T>|string} arrayLike
+ * @return {!Array<T>}
+ * @template T
+ */
+export function toArray(arrayLike) {
+  if (!arrayLike) {
+    return [];
+  }
+  const length = arrayLike.length;
+  const array = new Array(length);
+  for (let i = 0; i < array.length; i++) {
+    array[i] = arrayLike[i];
+  }
+  return array;
+}
+
 /**
  * Determines if value is actually an Object.
  * @param {*} value

test/functional/test-types.js

@@ -0,0 +1,62 @@
+/**
+ * Copyright 2016 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as types from '../../src/types';
+
+describe('Types', () => {
+  describe('toArray', () => {
+
+    it('should return empty array if null is passed', () => {
+      expect(types.toArray(null).length).to.equal(0);
+      expect(types.toArray(undefined).length).to.equal(0);
+    });
+
+    it('should convert NodeList to array', () => {
+      const parent = document.createElement('div');
+      parent.appendChild(document.createElement('p'));
+      parent.appendChild(document.createElement('span'));
+      parent.appendChild(document.createElement('div'));
+      const arr = types.toArray(parent.childNodes);
+      expect(arr[0]).to.equal(parent.childNodes[0]);
+      expect(arr.length).to.equal(3);
+      expect(Array.isArray(arr)).to.be.true;
+    });
+
+    it('should convert HTMLCollection to array', () => {
+      const parent = document.createElement('div');
+      parent.appendChild(document.createElement('form'));
+      parent.appendChild(document.createElement('form'));
+      document.body.appendChild(parent);
+      const arr = types.toArray(document.forms);
+      expect(arr[0]).to.equal(document.forms[0]);
+      expect(arr.length).to.equal(2);
+      expect(Array.isArray(arr)).to.be.true;
+      document.body.removeChild(parent);
+    });
+
+    it('should convert HTMLOptionsCollection to array', () => {
+      const parent = document.createElement('select');
+      parent.appendChild(document.createElement('option'));
+      parent.appendChild(document.createElement('option'));
+      parent.appendChild(document.createElement('option'));
+      parent.appendChild(document.createElement('option'));
+      const arr = types.toArray(parent.options);
+      expect(arr[0]).to.equal(parent.options[0]);
+      expect(arr.length).to.equal(4);
+      expect(Array.isArray(arr)).to.be.true;
+    });
+  });
+});