Intent to Ship: Scoped Custom Element Registry

[Chromestatus]

Contact emails

mason...@google.com, jayso...@microsoft.com, leo...@microsoft.com

Explainer

https://github.com/WICG/webcomponents/blob/gh-pages/proposals/Scoped-Custom-Element-Registries.md
https://github.com/whatwg/html/issues/10854

Specification

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

Summary

This feature allows for multiple custom element definitions for a single tag name to exist within a page to prevent custom element name conflicts when a web app uses libraries from multiple sources. This is achieved by allowing user code to create multiple custom element registries and associate them with tree scopes and elements that function as scoping object for custom element creation/definition/upgrade.

Blink component

Blink>HTML>CustomElements

Web Feature ID

scoped-custom-element-registries

TAG review

https://github.com/w3ctag/design-reviews/issues/1070

TAG review status

Issues addressed

Risks

Interoperability and Compatibility

None

Gecko: Positive (https://github.com/mozilla/standards-positions/issues/424)

WebKit: Shipped/Shipping (https://developer.apple.com/documentation/safari-release-notes/safari-26-release-notes)

Web developers: Positive Scoped custom element registry has been a long-awaited feature from the Web Components Community Group, and the current polyfill that didn't solve the entire problem has 24k+ downloads per week.

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

None

Debuggability

None

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

Yes
https://wpt.fyi/results/custom-elements/registries?label=master&label=experimental&aligned

Flag name on about://flags

None

Finch feature name

ScopedCustomElementRegistry

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/40826514

Estimated milestones

Shipping on desktop	143
Shipping on Android	143
Shipping on WebView	143

Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).

None

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5090435261792256?gate=6499099686207488

Links to previous Intent discussions

Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAFqEGhaAi0t1ffJoE8Du9bB2Wwxt6CewJjxz2Y_m9qWuoAa-Ug%40mail.gmail.com

This intent message was generated by Chrome Platform Status.

[Rick Byers]

I'm very happy to see this, looks great! We're slowly getting the web to a place where we have real component modularity :-)

I have one question about debuggability below, but since that bit has already been approved in Chromestatus it's not blocking. LGTM1

Are you sure? If I'm trying to debug a web page and trying to understand the behavior of <my-foo> elements, might I now get confused due to the multiple definitions for the same element name? I played with this a little and I guess I can always just rely on commands like $0.constructor to find the relevant source. But Firefox has a UI badge and hover action for this:

Perhaps the scoped custom element registry makes a UI feature like this go from nice-to-have to essential? @Danil Somsikov for his thoughts since he reviewed and approved the Debuggability bit for this feature. 

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[Rick Byers]

Sorry one more question. I see the feature is still in status=test mode and so the WPTs are still all failing on the experimental bot. Can you share the current WPT results please?

If, for whatever reason, you don't end up going right to status=stable on this feature now, please update the feature to status=experimental to get test results visible. 

[Jayson Chen]

I believe we are going right to status=stable when we ship the feature. Currently with ScopedCustomElementRegistry feature flag on, it is passing all WPTs for custom elements, including the ones created specifically for scoped registry work. It's being tested under this virtual test suite: third_party/blink/web_tests/virtual/scoped-custom-element-registry/

Debuggability wise, I agree that it's something valuable and worth exploring given that we can have different constructors under the same element name now.

[Rick Byers]

Oh sounds good, thanks Jayson. 

Rick

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[Mike Taylor]

LGTM2

To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAFUtAY9UARAHnScc3YrrxYpWgCLJp4jDkHB2QFWTk%3DgrpoHCtg%40mail.gmail.com.

[Vladimir Levin]

LGTM3

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