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The define() method of the CustomElementRegistry interface defines a new custom element.

There are two types of custom elements you can create:

  • Autonomous custom element: Standalone elements; they don't inherit from built-in HTML elements.
  • Customized built-in element: These elements inherit from — and extend — built-in HTML elements.

Syntax

customElements.define(name, constructor, options);

Parameters

name
Name for the new custom element. Note that custom element names must contain a hyphen.
constructor
Constructor for the new custom element.
options Optional
Object that controls how the element is defined. One option is currently supported:
  • extends: String specifying the name of a built-in element to extend. Used to create a customized built-in element.

Return value

Void.

Exceptions

Exception Description
NotSupportedError The CustomElementRegistry already contains an entry with the same name or the same constructor (or is otherwise already defined), or extends is specified and it is a valid custom element name, or extends is specified but the element it is trying to extend is an unknown element.
SyntaxError The provided name is not a valid custom element name.
TypeError The referenced constructor is not a constructor.

Note: You'll often get NotSupportedErrors thrown that seem like define() is failing, but in actual fact it is a problem with Element.attachShadow(). Check that page too if you are coming up against problems.

Examples

Autonomous custom element

The following code is taken from our popup-info-box-web-component example (see it live also).

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

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

    // Create spans
    var wrapper = document.createElement('span');
    wrapper.setAttribute('class','wrapper');
    var icon = document.createElement('span');
    icon.setAttribute('class','icon');
    icon.setAttribute('tabindex', 0);
    var info = document.createElement('span');
    info.setAttribute('class','info');

    // Take attribute content and put it inside the info span
    var text = this.getAttribute('text');
    info.textContent = text;

    // Insert icon
    var imgUrl;
    if(this.hasAttribute('img')) {
      imgUrl = this.getAttribute('img');
    } else {
      imgUrl = 'img/default.png';
    }
    var img = document.createElement('img');
    img.src = imgUrl;
    icon.appendChild(img);

    // Create some CSS to apply to the shadow dom
    var style = document.createElement('style');

    style.textContent = '.wrapper {' +
                           'position: relative;' +
                        '}' +

                         '.info {' +
                            'font-size: 0.8rem;' +
                            'width: 200px;' +
                            'display: inline-block;' +
                            'border: 1px solid black;' +
                            'padding: 10px;' +
                            'background: white;' +
                            'border-radius: 10px;' +
                            'opacity: 0;' +
                            'transition: 0.6s all;' +
                            'position: absolute;' +
                            'bottom: 20px;' +
                            'left: 10px;' +
                            'z-index: 3;' +
                          '}' +

                          'img {' +
                            'width: 1.2rem' +
                          '}' +

                          '.icon:hover + .info, .icon:focus + .info {' +
                            'opacity: 1;' +
                          '}';

    // attach the created elements to the shadow dom

    shadow.appendChild(style);
    shadow.appendChild(wrapper);
    wrapper.appendChild(icon);
    wrapper.appendChild(info);
  }
}

// Define the new element
customElements.define('popup-info', PopUpInfo);
<popup-info img="img/alt.png" text="Your card validation code (CVC) is an extra
                                    security feature — it is the last 3 or 4 
                                    numbers on the back of your card.">

Note: Constructors for autonomous custom elements must extend HTMLElement.

Customized built-in element

The following code is taken from our word-count-web-component example (see it live also).

// 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' });
<p is="word-count"></p>

Specifications

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

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic support
Experimental
Chrome Full support 66
Notes
Full support 66
Notes
Notes Support for 'Customized built-in elements' as well.
Full support 54
Notes
Notes Support for 'Autonomous custom elements' only.
Edge No support No
Notes
No support No
Notes
Notes Under consideration
Firefox Full support 63
Full support 63
Full support 59
Disabled
Disabled From version 59: this feature is behind the dom.webcomponents.customelements.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
No support ? — 59
Disabled
Disabled Until version 59 (exclusive): this feature is behind the dom.webcomponents.enabled preference (needs to be set to true) and the dom.webcomponents.customelements.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera Full support 53
Notes
Full support 53
Notes
Notes Support for 'Customized built-in elements' as well.
Full support 41
Notes
Notes Support for 'Autonomous custom elements' only.
Safari Full support 10.1
Notes
Full support 10.1
Notes
Notes Supports 'Autonomous custom elements' but not 'Customized built-in elements'
WebView Android Full support 66
Notes
Full support 66
Notes
Notes Support for 'Customized built-in elements' as well.
Full support 54
Notes
Notes Support for 'Autonomous custom elements' only.
Chrome Android Full support 66
Notes
Full support 66
Notes
Notes Support for 'Customized built-in elements' as well.
Full support 54
Notes
Notes Support for 'Autonomous custom elements' only.
Edge Mobile No support No
Notes
No support No
Notes
Notes Under consideration
Firefox Android Full support 63
Full support 63
Full support 59
Disabled
Disabled From version 59: this feature is behind the dom.webcomponents.customelements.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
No support ? — 59
Disabled
Disabled Until version 59 (exclusive): this feature is behind the dom.webcomponents.enabled preference (needs to be set to true) and the dom.webcomponents.customelements.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Opera Android Full support 53
Notes
Full support 53
Notes
Notes Support for 'Customized built-in elements' as well.
Full support 41
Notes
Notes Support for 'Autonomous custom elements' only.
Safari iOS Full support 10.1
Notes
Full support 10.1
Notes
Notes Supports 'Autonomous custom elements' but not 'Customized built-in elements'
Samsung Internet Android Full support 6.0
Notes
Full support 6.0
Notes
Notes Support for 'Autonomous custom elements' only.

Legend

Full support  
Full support
No support  
No support
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.

Etiquetas y colaboradores del documento

Última actualización por: jpmedley,