Intent to prototype: WebAssembly JS-Promise-Integration

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Ryan Hunt

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May 4, 2026, 2:30:54 PM (2 days ago) May 4
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Summary:

WebAssembly JS-Promise-Integration (JS-PI) allows sync WebAssembly code to
use async Web API's.

This is achieved by suspending the synchronous WebAssembly execution stack and
yielding a new promise which awaits the results of the Web API's promise. When
the Web API's promise resolves, the wasm execution is resumed with the results
of the Web API.

This feature has been developed behind a pref. I intend to enable it as
Nightly-only in Fx152. If there are no major regressions we'd like to let it
ride the trains to release in Fx152 or Fx153 (I'll send a separate
intent-to-ship).

Bug:

Specification:

This is a Phase 4 WebAssembly Proposal that is finished but just hasn't been
merged into the official spec document yet.

Standards Body:
W3C (WebAssembly CG & WG)

Platform Coverage:
all.

DevTools Bug:

Extensions Bug:
N/A

Use Counter:
N/A

Standards-Positions Discussion:

Other Browsers:

Preference:
javascript.options.wasm_js_promise_integration

web-platform-tests:



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