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
Specification |
---|
HTML Standard # custom-elements-api |
Browser compatibility
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