Intent to experiment - Wasm JavaScript Promise Integration

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Francis McCabe

Jan 5, 2024, 12:28:04 PMJan 5
to blink-dev

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Stack Switching denotes a technology that allows programs to suspend and resume computation. This is an active area that is part of the WebAssembly standards track. See and This particular feature refers to the integration between JavaScript Promises and stack switching. This is described in more detail in

Blink component


Search tags

stack switchingPromiseJSPI

TAG review

TAG review status



Interoperability and Compatibility

This spec is backed by a standardization effort. We do not plan to ship the JSPI until it has been standardized by the W3C Wasm WG. However, post standardization, we will depend on all browsers implementing the standard.

Gecko: Positive ( Mozilla have started their own imlementation

WebKit: No signal

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?

Goals for experimentation

Ongoing technical constraints



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


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


Flag name on chrome://flags

Finch feature name


Non-finch justification


Requires code in //chrome?


Tracking bug

Estimated milestones

OriginTrial desktop last130
OriginTrial desktop first122
OriginTrial Android last130
OriginTrial Android first122
OriginTrial webView last130
OriginTrial webView first122

Link to entry on the Chrome Platform Status

Links to previous Intent discussions

Intent to prototype:

This intent message was generated by Chrome Platform Status.

Rick Byers

Jan 10, 2024, 10:11:55 AMJan 10
to Francis McCabe, blink-dev
Hi Francis,
This seems good to experiment with to me. But the key question is who is actually going to test it out in production? You mention "no signals" for web developer interest. There's not much point in doing the overhead of an OT unless we have at least one developer who wants to test out the functionality in a production environment. Can you elaborate?


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Francis McCabe

Jan 10, 2024, 12:43:15 PMJan 10
to blink-dev,, blink-dev, Francis McCabe
In fact, there are several potential partners for evaluating/experimenting with JSPI: the Google Earth team, Figma, Adobe to name a few. It should be emphasized that there are no formal agreements in place here; and that the primary use case for these partners is actually dynamic loading of code (and other) resources on the main thread.

Ken Russell

Jan 10, 2024, 1:55:41 PMJan 10
to Francis McCabe, blink-dev,, Francis McCabe
Google's Meet team also desires to use JSPI to simulate synchronous GPU->CPU readbacks in C++ code on top of the web's asynchronous primitives.

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