webcomponents · bicknellr · Oct 16, 2020 · Oct 12, 2020 · Oct 12, 2020 · Oct 12, 2020
@@ -0,0 +1,50 @@
+<!doctype html>
+<!--
+@license
+Copyright (c) 2020 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+<html>
+<head>
+  <title>Element getAttributeNames</title>
+  <script src="../node_modules/@webcomponents/webcomponentsjs/bundles/webcomponents-pf_dom.js"></script>
+  <script src="./wct-config.js"></script>
+  <script src="../node_modules/wct-browser-legacy/browser.js"></script>
+</head>
+<body>
+  <script>
+    suite('Element getAttributeNames', function() {
+      test('Returns an array of attribute names', () => {
+        const element = document.createElement('div');
+        assert(element.getAttributeNames().length === 0);
+
+        let attributeNames;
+
+        attributeNames = element.getAttributeNames();
+        assert.isArray(attributeNames);
+        assert.deepEqual(attributeNames, []);
+
+        element.setAttribute('name-a', 'value-a');
+        attributeNames = element.getAttributeNames();
+        assert.deepEqual(attributeNames, ['name-a']);
+
+        element.setAttribute('name-b', 'value-b');
+        attributeNames = element.getAttributeNames();
+        assert.deepEqual(attributeNames, ['name-a', 'name-b']);
+
+        element.removeAttribute('name-a');
+        attributeNames = element.getAttributeNames();
+        assert.deepEqual(attributeNames, ['name-b']);
+
+        element.removeAttribute('name-b');
+        attributeNames = element.getAttributeNames();
+        assert.deepEqual(attributeNames, []);
+      });
+    });
+  </script>
+</body>
+</html>
@@ -34,6 +34,7 @@
     'loader-after-load.html',
     'baseuri.html',
     'object-assign.html',
+    'get-attribute-names.html',
     'parent-node/index.html',
     'child-node/index.html',
     'svg-element-class-list.html',

@@ -8,6 +8,8 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+- Polyfill `Element#getAttributeNames`.
+  ([#393](https://github.com/webcomponents/polyfills/pull/393))
 - Add polyfills for ChildNode APIs.
   ([#390](https://github.com/webcomponents/polyfills/pull/390))
 - Add polyfills for select ParentNode APIs.

@@ -10,6 +10,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 
 import '../platform/custom-event.js';
 import '../platform/baseuri.js';
+import '../platform/get-attribute-names.js';
 import '../platform/parent-node/index.js';
 import '../platform/child-node/index.js';
 import '../platform/svg-element-class-list.js';
@@ -0,0 +1,29 @@
+/**
+@license
+Copyright (c) 2020 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at
+http://polymer.github.io/LICENSE.txt The complete set of authors may be found at
+http://polymer.github.io/AUTHORS.txt The complete set of contributors may be
+found at http://polymer.github.io/CONTRIBUTORS.txt Code distributed by Google as
+part of the polymer project is also subject to an additional IP rights grant
+found at http://polymer.github.io/PATENTS.txt
+*/
+
+export {};
+
+const Element_prototype = Element.prototype;
+// In IE11, the `attributes` descriptor is on `Node.prototype`.
+const attributesDescriptor =
+    Object.getOwnPropertyDescriptor(Element_prototype, 'attributes') ??
+    Object.getOwnPropertyDescriptor(Node.prototype, 'attributes');
+// In Safari 9, the `attributes` descriptor's getter is undefined. In Chrome 41,
+// the `attributes` descriptor is a data descriptor on each Element instance.
+const getAttributes = attributesDescriptor?.get ??
+    function(this: Element) { return this.attributes; };
+const map = Array.prototype.map;
+
+if (!Element_prototype.hasOwnProperty('getAttributeNames')) {
+  Element_prototype.getAttributeNames = function getAttributeNames(this: Element): Array<string> {
+    return map.call(getAttributes.call(this), attr => attr.name) as Array<string>;
+  };
+}