Web Compatibility of Scoped Custom Element Registries

[annevk]

What is the issue with the HTML Standard?

I stumbled across https://issues.chromium.org/issues/325035505 and the carmax.com issue reproduces in WebKit so unfortunately the new API design still has this problem. Quirking/outreach might be one solution, but maybe more such examples will come up?

cc @karlcow @rniwa @schenney-chromium

[rniwa]

Given this is an issue with Polymer's polyfill which is used on many production sites, I don't think we can quirk it. We should probably rename customElements to something else. Maybe customElementsRegistry.

[annevk]

Sigh. This is why we can't have nice things. I think we should drop the s with the new suffix, i.e., customElementRegistry. If we're going to solve this polyfill nonsense with a rename some more people should probably be in the loop.

cc @smaug---- @domenic @mfreed7 @justinfagnani

[annevk]

For reference: https://github.com/search?q=if+%28%21ShadowRoot.prototype.createElement%29&type=code

[annevk]

We have prototyped a solution that seems to work and preserves the API pretty much as-is (still unfortunate though; please stop polyfilling and deploying polyfills):

• Denote ShadowRoot's customElements with [Replaceable] in Web IDL
• Change the type of ShadowRootInit's customElements member to any and ignore all non-CustomElementRegistry values.

[trusktr]

customElementRegistry

Just in case, if that doesn't work out and a rename has to be done, I'd say elementRegistry is nice. It is very obvious that new elements are "custom", so imo no need to keep the "custom" adjective.

[annevk]

I updated whatwg/dom#1341 to account for this. I'm happy with this resolution so removing agenda+.

[rniwa]

Hm... looks like there is another polyfill written by Google that's incompatible with enabling this version of the scoped custom element registries.

[rniwa]

We need to rename ShadowRoot.prototype.customElements after all because some versions of scoped custom element registries polyfill written by Google is incompatible with having this property. For now I'm renaming it to customElementRegistry in WebKit/WebKit#41910 but we can bikeshed the name.