Intent to Prototype and Ship: Expose CSSStyleValue hierarchy to Worker contexts

[Javier Fernandez]

Contact emails

jfern...@igalia.com

Specification

https://www.w3.org/TR/css-typed-om-1/#stylevalue-subclasses

Summary

The CSS Typed OM spec exposes the CSSStyleValue hierarchy to worker global scopes ([Exposed=(Window, Worker, PaintWorklet, LayoutWorklet)]), but Blink only exposed CSSStyleValue, CSSKeywordValue, CSSNumericValue, CSSUnitValue and CSSUnparsedValue to Window and the worklets. As a result these constructors were undefined in Workers, unlike in Firefox and Safari.

Blink component

Blink>CSS

Web Feature ID

css-typed-om

Motivation

Aligns Chrome with the spec's [Exposed] set and removes a cross‑thread inconsistency (these constructors are currently undefined in workers); enables off‑main‑thread CSS value manipulation

Initial public proposal

No information provided

TAG review

No information provided

TAG review status

Not applicable

Goals for experimentation

None

Risks

Interoperability and Compatibility

This feature is already shipped by Firefox and Safari and it's purely additive worker‑scope exposure; zero change to existing Window behavior; matches the spec. Only theoretical risk: content that feature‑detects these globals inside a worker

Gecko: Shipped/Shipping

WebKit: Shipped/Shipping

Web developers: No signals

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?

No information provided

Debuggability

No special tooling; interfaces work in the worker DevTools console like any other worker‑exposed API

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
css/css-typed-om/stylevalue-subclasses/*.any.js (global=window,worker): cssKeywordValue, cssKeywordValue-value, cssUnparsedValue-empty, numeric-objects/cssUnitValue-to; and (full‑scope) the converted create-a-type, cssMathInvert-type, cssMathNegate-type, add-two-types, cssnumericvalue-multiply-two-types, arithmetic, to .any.js. (The CSSMath* ones require the full‑scope exposure.) https://wpt.fyi/results/css/css-typed-om/stylevalue-subclasses?label=experimental&label=master&aligned

Flag name on about://flags

No information provided

Finch feature name

No information provided

Non-finch justification

This is just a minor CSS change to allow some CSS javascript bindings to be run in Worker context, but that were already exposed to the Web via Window context.

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/issues/534781956

Estimated milestones

Shipping on desktop	153
Shipping on Android	153
Shipping on WebView	153

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).

https://github.com/w3c/csswg-drafts/issues/14229

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5114591051907072?gate=6116938171416576

This intent message was generated by Chrome Platform Status.