An extensible class to define hyperHTML based Custom Elements.
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Andrea Giammarchi
Andrea Giammarchi 3.1.0
Latest commit 8069cd5 Sep 13, 2018


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An extensible class to define hyperHTML based Custom Elements.

npm install hyperhtml-element

hyperHTML included

This class attaches all hyperHTML methods to itself, with the only exception of the define method, used in here to define Custom Elements instead.

To have same define functionality, please use HyperHTMLElement.intent(...) which provides exact same API.


You can find more info about this helper in hyperHTML documentation page.

The Class

const HyperHTMLElement = require('hyperhtml-element');

class MyElement extends HyperHTMLElement {

  // observed attributes are automatically defined as accessors
  static get observedAttributes() { return ['key']; }

  // boolean attributes are automatically defined as accessors
  // and will set or remove the passed value
  static get booleanAttributes() { return ['active']; }

  // invoked once the component has been fully upgraded
  // suitable to perform any sort of setup
  // granted to be invoked right before either
  // connectedCallback or attributeChangedCallback
  created() {
    // triggers automatically attributeChangedCallback
    this.key = 'value';

  attributeChangedCallback(name, prev, curr) {
    // when invoked, attributes will be already reflected
    // through their accessor
    this.key === curr; // true, and curr === "value"
    this.getAttribute('key') === this.key; // always true

  render() {
    // lazily defined, this.html property points to an hyperHTML bound context
    // which could be the element shadowRoot or the element itself.
    // All events can be handled directly by the context, thanks to handleEvent
    return this.html`
    Hello <strong onclick=${this}>HyperHTMLElement</strong>
    ( ${this.state.clicks} )`;

  // using the inherited handleEvent,
  // events can be easily defined as methods with `on` prefix.
  onclick(e) {
    // `this` refers to the current custom element
    console.log(this, 'click',;
    // state handling, updates the view
    this.setState({clicks: this.state.clicks + 1});

  // alternatively, you can specify a `data-call`
  // attribute with the name of the method to invoke
  // this.html`<i data-call=onAnyEvent onclick=${this}>try</i>`;
  onAnyEvent(e) {
    // `this` still refers to the current custom element
    console.log(this, e.type, e.currentTarget,;

  // you can also use Preact-like events handling
  // this is less efficient, but migration friendly.
  // The method is bound once per instance so that
  // this.handleClick === this.handleClick is always true
  // this.html`<i onclick=${this.handleClick}>try</i>`;
  handleClick(e) {
    // `this` still refers to the current custom element
    console.log(this, e.type, e.currentTarget,;

  // define a default state to use whenever this.state is accessed
  // it can create states from observed properties too
  get defaultState() {
    return {clicks: 0, key: this.key};

  // this method is Preact friendly, once invoked
  // as this.setState({new: 'value'});
  // it will shallow copy properties over
  // and it will invoke this.render() right after

  // all other native Custom Elements method works as usual
  // connectedCallback() { ... }
  // adoptedCallback() { ... }

// classes must be defined through their public static method
// this is the moment the class will be fully setup once
// and registered to the customElements Registry.

New in v1.8

You can now define custom elements builtins too:

class MyLink extends HyperHTMLElement {
  created() { this.render(); }
  render() {
    return this.html`hello there!`;
MyLink.define('my-link', {extends: 'a'});


HyperHTMLElement is compatible with every mobile browser and IE11 or greater.

There is a native live test page also transpiled for ES5 browsers.