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.
Instance 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.getName()
-
Returns the name for the already-defined custom element, or
null
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.
js
// 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
const wcParent = this.parentNode;
function countWords(node) {
const text = node.innerText || node.textContent;
return text
.trim()
.split(/\s+/g)
.filter((a) => a.trim().length > 0).length;
}
const count = `Words: ${countWords(wcParent)}`;
// Create a shadow root
const shadow = this.attachShadow({ mode: "open" });
// Create text node and add word count to it
const text = document.createElement("span");
text.textContent = count;
// Append it to the shadow root
shadow.appendChild(text);
// Update count when element content changes
setInterval(() => {
const 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
BCD tables only load in the browser