customElements.define("x-component", class extends HTMLElement { constructor() { super(); console.log('constructed!'); } connectedCallback() { console.log('connected!'); } disconnectedCallback() { console.log('disconnected!'); } adoptedCallback() { console.log('adopted!'); } attributeChangedCallback(name, oldValue, newValue) { console.log('attirbuteChanged!', name, oldValue, newValue); } static get observedAttributes() { return ['checked','demo','label']; } });
// "tabs" is not a valid custom element name document.createElement('tabs') instanceof HTMLUnknownElement === true //true // "x-tabs" is a valid custom element name document.createElement('x-tabs') instanceof HTMLElement === true //true
customElements.whenDefined('x-component').then(() => { console.log('x-component defined'); });
<share-buttons> <social-button type="twitter"><a href="...">Twitter</a></social-button> <social-button type="fb"><a href="...">Facebook</a></social-button> <social-button type="plus"><a href="...">G+</a></social-button> </share-buttons> // Fetch all the children of <share-buttons> that are not defined yet. let undefinedButtons = buttons.querySelectorAll(':not(:defined)'); let promises = [...undefinedButtons].map(socialButton => { return customElements.whenDefined(socialButton.localName); )); // Wait for all the social-buttons to be upgraded. Promise.all(promises).then(() => { // All social-button children are ready. });
customeElements.define('x-component',...) let XComponent = customElements.get('x-component'); document.body.appendChild(new XComponent())
const el = document.createElement('x-component'); document.body.appendChild(el); // connectedCallback() called el.remove(); // disconnectedCallback() document.body.appendChild(el); // connectedCallback() called again
const iframe = document.querySelector('iframe'); const iframeImages = iframe.contentDocument.querySelectorAll('img'); const newParent = document.getElementById('images'); iframeImages.forEach(function(imgEl) { newParent.appendChild(document.adoptNode(imgEl)); });
Methods
class XComponent extends HTMLElement { constructor() { super(); } doSomething(){ console.log('doSomething'); } }
let component = document.querySelector('x-component'); component.doSomething();
Attributes & Properties
div.id = 'id-value'; div.hidden = true;
<div id="id-value" hidden>
class XComponent extends HTMLElement { constructor() { super(); } connectedCallback() { this._render(); } get disabled() { return this.hasAttribute('disabled'); } set disabled(val) { // Reflect the value of `disabled` as an attribute. if (val) { this.setAttribute('disabled', ''); } else { this.removeAttribute('disabled'); } this._render(); } _render() { //... } }
attributeChangedCallback(name, oldValue, newValue) { switch (name) { case 'checked': // Note the attributeChangedCallback is only handling the *side effects* // of setting the attribute. this.setAttribute('aria-disabled', !!newValue); break; ... }
attributeChangedCallback(name, oldValue, newValue) { // When the component is disabled, update keyboard/screen reader behavior. if (this.disabled) { this.setAttribute('tabindex', '-1'); this.setAttribute('aria-disabled', 'true'); } else { this.setAttribute('tabindex', '0'); this.setAttribute('aria-disabled', 'false'); } // TODO: also react to the other attribute changing. }
constructor() { super(); this._data = []; } get data() { return _data; } set data(value) { if (this_data === value) return; this._data = value; this._render(); }
Lazy Properties
<x-component [disabled]="model.disabled"></x-component>
let el = document.querySelector('x-component'); el.disabled = true; customElements.define("x-component", class extends HTMLElement { constructor() { super(); } get disabled() { return this.hasAttribute('disabled'); } set disabled(val) { // Reflect the value of `disabled` as an attribute. if (val) { this.setAttribute('disabled', ''); } else { this.removeAttribute('disabled'); } this._render(); } });
let el = document.querySelector('x-component'); el.disabled = true; customElements.define("x-component", class extends HTMLElement { constructor() { super(); } connectedCallback() { this._upgradeProp('disabled'); } get disabled() { return this.hasAttribute('disabled'); } set disabled(val) { // Reflect the value of `disabled` as an attribute. if (val) { this.setAttribute('disabled', ''); } else { this.removeAttribute('disabled'); } this._render(); } _upgradeProp(prop) { if (this.hasOwnProperty(prop)) { let value = this[prop]; delete this[prop]; //delete instance property this[prop] = value; // set prototype property } } });
connectedCallback() { if (!this.hasAttribute('role')) this.setAttribute('role', 'checkbox'); if (!this.hasAttribute('tabindex')) this.setAttribute('tabindex', -1); //element is not reachable via sequential keyboard navigation, but could be focused }