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/Web APIs

CustomElementRegistry

The CustomElementRegistry interface provides methods for registering custom elements and querying registered elements. To get an instance of it, use the window.customElements property.

Methods

CustomElementRegistry.define()

Defines a new custom element.

CustomElementRegistry.get()

Returns the constructor for the named custom element, or undefined if the custom element is not defined.

CustomElementRegistry.upgrade()

Upgrades a custom element directly, even before it is connected to its shadow root.

CustomElementRegistry.whenDefined()

Returns an empty promise that resolves when a custom element becomes defined with the given name. If such a custom element is already defined, the returned promise is immediately fulfilled.

Examples

The following code is taken from our word-count-web-component example (see it live also). Note how we use the CustomElementRegistry.define() method to define the custom element after creating its class.

// Create a class for the element
class WordCount extends HTMLParagraphElement {
  constructor() {
    // Always call super first in constructor
    super();

    // count words in element's parent element
    var wcParent = this.parentNode;

    function countWords(node){
      var text = node.innerText || node.textContent
      return text.split(/\s+/g).length;
    }

    var count = 'Words: ' + countWords(wcParent);

    // Create a shadow root
    var shadow = this.attachShadow({mode: 'open'});

    // Create text node and add word count to it
    var text = document.createElement('span');
    text.textContent = count;

    // Append it to the shadow root
    shadow.appendChild(text);

    // Update count when element content changes
    setInterval(function() {
      var count = 'Words: ' + countWords(wcParent);
      text.textContent = count;
    }, 200)

  }
}

// Define the new element
customElements.define('word-count', WordCount, { extends: 'p' });

Note: The CustomElementRegistry is available through the Window.customElements property.

Specifications

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
CustomElementRegistry
54
79
63
No
41
10.1
54
54
63
41
10.3
6.0
builtin
67
79
63
No
54
No
67
67
63
48
No
9.0
define
67
Support for 'Customized built-in elements' as well.
54
Support for 'Autonomous custom elements' only.
79
Support for 'Customized built-in elements' as well.
79
Support for 'Autonomous custom elements' only.
63
No
54
Support for 'Customized built-in elements' as well.
41
Support for 'Autonomous custom elements' only.
10.1
Supports 'Autonomous custom elements' but not 'Customized built-in elements'
67
Support for 'Customized built-in elements' as well.
54
Support for 'Autonomous custom elements' only.
67
Support for 'Customized built-in elements' as well.
54
Support for 'Autonomous custom elements' only.
63
48
Support for 'Customized built-in elements' as well.
41
Support for 'Autonomous custom elements' only.
10.3
Supports 'Autonomous custom elements' but not 'Customized built-in elements'
9.0
Support for 'Customized built-in elements' as well.
6.0
Support for 'Autonomous custom elements' only.
get
67
Support for 'Customized built-in elements' as well.
54
Support for 'Autonomous custom elements' only.
79
Support for 'Customized built-in elements' as well.
79
Support for 'Autonomous custom elements' only.
63
No
54
Support for 'Customized built-in elements' as well.
41
Support for 'Autonomous custom elements' only.
10.1
Supports 'Autonomous custom elements' but not 'Customized built-in elements'
67
Support for 'Customized built-in elements' as well.
54
Support for 'Autonomous custom elements' only.
67
Support for 'Customized built-in elements' as well.
54
Support for 'Autonomous custom elements' only.
63
48
Support for 'Customized built-in elements' as well.
41
Support for 'Autonomous custom elements' only.
10.3
Supports 'Autonomous custom elements' but not 'Customized built-in elements'
9.0
Support for 'Customized built-in elements' as well.
6.0
Support for 'Autonomous custom elements' only.
upgrade
68
79
63
No
55
12.1
68
68
63
48
12.2
10.0
whenDefined
67
Support for 'Customized built-in elements' as well.
54
Support for 'Autonomous custom elements' only.
79
Support for 'Customized built-in elements' as well.
79
Support for 'Autonomous custom elements' only.
63
No
54
Support for 'Customized built-in elements' as well.
41
Support for 'Autonomous custom elements' only.
10.1
Supports 'Autonomous custom elements' but not 'Customized built-in elements'
67
Support for 'Customized built-in elements' as well.
54
Support for 'Autonomous custom elements' only.
67
Support for 'Customized built-in elements' as well.
54
Support for 'Autonomous custom elements' only.
63
48
Support for 'Customized built-in elements' as well.
41
Support for 'Autonomous custom elements' only.
10.3
Supports 'Autonomous custom elements' but not 'Customized built-in elements'
9.0
Support for 'Customized built-in elements' as well.
6.0
Support for 'Autonomous custom elements' only.

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/CustomElementRegistry