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The customElements read-only property of the Window interface returns a reference to the CustomElementRegistry object, which can be used to register new custom elements and get information about previously registered custom elements.


let customElementRegistry = window.customElements;

Return value

A CustomElementRegistry object instance representing the custom element registry for the current window.


The most common example you'll see of this property being used is to get access to the CustomElementRegistry.define() method to define and register a new custom element, e.g.:

let customElementRegistry = window.customElements;
customElementRegistry.define('my-custom-element', MyCustomElement);

However, it is usually shortened to something like the following:

  class extends HTMLElement {
    constructor() {
      const template = document
      const shadowRoot = this.attachShadow({mode: 'open'})

See our web-components-examples repo for more usage examples.


Specification Status Comment
HTML Living Standard
The definition of 'window.customElements' in that specification.
Living Standard Initial definition.

Browser compatibility

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help!

Feature Firefox (Gecko) Chrome Edge Internet Explorer Opera Safari
window.customElements No support (Yes) No support ? ? ?
Feature Firefox Mobile (Gecko) Chrome for Android IE Mobile Opera Mobile Safari Mobile
window.customElements ? ? ? ? ?

Document Tags and Contributors

 Contributors to this page: chrisdavidmills, Jedipedia, BrodaNoel, bunnybooboo, arthurevans
 Last updated by: chrisdavidmills,