Extended built-ins

[LeaVerou]

Extend built-in elements with custom behavior.

<button is="primary-button">Continue</button>
<script>
	customElements.define("primary-button", PrimaryButton, {extends: "button"});
</script>

MDN URL:

https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/is

Specification URL:

https://html.spec.whatwg.org/multipage/custom-elements.html#attr-is

Any other links?

• https://developer.mozilla.org/en-US/docs/Web/API/CustomElementRegistry/define
• WebKit Standards Position

How stable is this feature?

Controversial (Some implementations that have existed for years, other browsers have declined to implement)

Type of feature

HTML attribute, JS API

What focus area does this feature fall into?

Consuming Web Components, Making Web Components

Details

We could ask about the is attribute and customElementRegistry.define("tagname", Class, {extends}) separately if we want to distinguish consumption from usage.
For now, I’ve included them in the same item.

[colepeters]

May be worth adding this to 'other links', as WebKit is declining to implement this feature: WebKit/standards-positions#97

[LeaVerou]

Done! (though note I had already listed it as "Controversial" because of this)