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A Custom Element radio group which demonstrates roving tabindex
<!--
Copyright 2016 Google Inc. 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.
-->
<style>
.demo {
margin-left: 80px;
}
radio-button {
position: relative;
display: block;
font-size: 18px;
}
radio-button:focus {
outline: none;
}
radio-button::before {
content: '';
display: block;
width: 10px;
height: 10px;
border: 1px solid black;
position: absolute;
left: -18px;
top: 7px;
border-radius: 50%;
}
radio-button:focus::before {
box-shadow: 0 0 3px 3px #83BEFF;
}
radio-button[aria-checked="true"]::before {
content: '';
display: block;
width: 10px;
height: 10px;
background: red;
position: absolute;
left: -18px;
top: 7px;
border-radius: 50%;
}
</style>
<div class="demo">
<radio-group>
<radio-button>Water</radio-button>
<radio-button>Coffee</radio-button>
<radio-button>Tea</radio-button>
<radio-button>Cola</radio-button>
<radio-button>Ginger Ale</radio-button>
</radio-group>
</div>
<script src="https://cdn.rawgit.com/webcomponents/custom-elements/master/custom-elements.min.js"></script>
<script>
class RadioButton extends HTMLElement {
constructor() {
super();
}
connectedCallback() {
this.setAttribute('role', 'radio');
this.setAttribute('tabindex', -1);
this.setAttribute('aria-checked', false);
}
}
window.customElements.define('radio-button', RadioButton);
// Define values for keycodes
const VK_LEFT = 37;
const VK_UP = 38;
const VK_RIGHT = 39;
const VK_DOWN = 40;
class RadioGroup extends HTMLElement {
constructor() {
super();
}
connectedCallback() {
this.setAttribute('role', 'radiogroup');
this.radios = Array.from(this.querySelectorAll('radio-button'));
// Setup initial state
if (this.hasAttribute('selected')) {
let selected = this.getAttribute('selected');
this._selected = selected;
this.radios[selected].setAttribute('tabindex', 0);
this.radios[selected].setAttribute('aria-checked', true);
} else {
this._selected = 0;
this.radios[0].setAttribute('tabindex', 0);
}
this.addEventListener('keydown', this.handleKeyDown.bind(this));
this.addEventListener('click', this.handleClick.bind(this));
}
handleKeyDown(e) {
switch(e.keyCode) {
case VK_UP:
case VK_LEFT: {
e.preventDefault();
if (this.selected === 0) {
this.selected = this.radios.length - 1;
} else {
this.selected--;
}
break;
}
case VK_DOWN:
case VK_RIGHT: {
e.preventDefault();
if (this.selected === this.radios.length - 1) {
this.selected = 0;
} else {
this.selected++;
}
break;
}
}
}
handleClick(e) {
const idx = this.radios.indexOf(e.target);
if (idx === -1) {
return;
}
this.selected = idx;
}
set selected(idx) {
if (isFinite(this.selected)) {
// Set the old button to tabindex -1
let previousSelected = this.radios[this.selected];
previousSelected.tabIndex = -1;
previousSelected.removeAttribute('aria-checked', false);
}
// Set the new button to tabindex 0 and focus it
let newSelected = this.radios[idx];
newSelected.tabIndex = 0;
newSelected.focus();
newSelected.setAttribute('aria-checked', true);
this.setAttribute('selected', idx);
this._selected = idx;
}
get selected() {
return this._selected;
}
}
window.customElements.define('radio-group', RadioGroup);
</script>
@alexgwolff
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alexgwolff commented Nov 5, 2021

Hey, this code can have memory leaks

Change constructor to:

constructor() {
     super();
     this.handleKeyDown =  this.handleKeyDown.bind(this);
     this.handleClick = this.handleClick.bind(this);
}

Fix line 111 to:

 this.addEventListener('keydown', this.handleKeyDown);
 this.addEventListener('click', this.handleClick);

and add

disconnectedCallback() { 
 this.removeEventListener('keydown', this.handleKeyDown);
 this.removeEventListener('click', this.handleClick);
}

Explanation:
this.fn.bind(this) and () => fn always create a new function (a new ref) and without removeEventListener this node always be alive in memory

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