Bug 195403

Summary: Customized built-in elements aren't supported
Product: WebKit Reporter: Andreas Deuschlinger <andreas.deuschlinger>
Component: DOMAssignee: Nobody <webkit-unassigned>
Status: RESOLVED DUPLICATE    
Severity: Major CC: arjunyel+webkit.bugzilla, cdumez, incoming-webkitbugs, rniwa
Priority: P2 Keywords: HTML5
Version: WebKit Nightly Build   
Hardware: All   
OS: All   

Description Andreas Deuschlinger 2019-03-07 00:25:42 PST
The HTML Living Standard for Custom Elements specifies support to extend existing built-in elements, by:
- the `is="my-button"` attribute
  https://html.spec.whatwg.org/multipage/custom-elements.html#attr-is
- the `document.createElement('button', { is: 'my-button' })` second argument
  https://dom.spec.whatwg.org/#dom-elementcreationoptions-is

Example:
https://html.spec.whatwg.org/multipage/custom-elements.html#custom-elements-customized-builtin-example

The Webkit Status page gives incorrect information claiming that Custom Elements V1 are supported,
though in fact only "autonomous custom elements" are supported.
https://webkit.org/status/#feature-custom-elements

Caniuse informs about this incomplete implementation correctly:
https://caniuse.com/#feat=custom-elementsv1
Comment 1 arjunyel+webkit.bugzilla 2019-03-08 11:53:01 PST
Previous discussion about this on Github https://github.com/w3c/webcomponents/issues/509#issuecomment-222860736
Comment 2 Ryosuke Niwa 2019-03-09 18:24:45 PST
Our position has been that this feature shouldn't exist in the spec in the first place. I really don't understand how we ended up allowing Google to keep this feature in the HTML5 spec despite of our repeated objections.

*** This bug has been marked as a duplicate of bug 182671 ***
Comment 3 Andreas Deuschlinger 2019-03-12 03:14:19 PDT
Thanks  a lot for your quick feedback:)

Meanwhile i came across element behaviors a the suggested has attributes:
https://www.npmjs.com/package/element-behaviors

Which is what I would really need:) But gies beyond this ticket...