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

The global registry is used for registering custom elements by default, but a shadow root can choose to use a scoped custom element registry in order to avoid potential clashes in defined element names.

Value

A CustomElementRegistry.

Examples

Basic usage

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.

For example:

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

Note that the custom element class is commonly defined directly inside the define() call, as shown:

customElements.define(
  "element-details",
  class extends HTMLElement {
    constructor() {
      super();
      const template = document.getElementById("element-details-template");
      const shadowRoot = this.attachShadow({ mode: "open" }).appendChild(
        document.importNode(template.content, true),
      );
    }
  },
);

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

Specifications

Browser compatibility