I might have missed it, but how is this new feature going to be used by
web developers? Do you have custom C compiler for the experiment? And do
you need to do something in C to enable it? Or whatever language people
prefer.
/Daniel
On 2025-08-13 20:04, Thomas Lively wrote:
Yes, apologies. The explainer link should be the same as the
specification link:
https://github.com/WebAssembly/custom-descriptors/blob/main/proposals/custom-descriptors/Overview.md
On Wed, Aug 13, 2025 at 7:58 AM Daniel Bratell <bratel...@gmail.com>
wrote:
The explainer link is dead, but maybe it was meant to be the same
as the Specification link?
/Daniel
On 2025-08-12 00:50, 'Thomas Lively' via blink-dev wrote:
Contact emails
tliv...@google.com, ecmzieg...@chromium.org, jkumme...@chromium.org
Explainer
https://github.com/WebAssembly/custom-descriptors/blob/main/proposals/custom-rtts/Overview.md
<https://github.com/WebAssembly/custom-rtts/blob/main/proposals/custom-rtts/Overview.md>
Specification
https://github.com/WebAssembly/custom-descriptors/blob/main/proposals/custom-descriptors/Overview.md
Summary
Allows WebAssembly to store data associated with source-level
types more efficiently in new "custom descriptor" objects. These
custom descriptors can be configured with prototypes for the
WebAssembly objects of that source-level type. This allows
methods to be installed on a WebAssembly object's prototype chain
and called directly from JS using normal method call syntax. The
prototypes and methods can be configured declaratively using an
imported builtin function.
Blink component
Blink>JavaScript>WebAssembly
<https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3EJavaScript%3EWebAssembly%22>
TAG review
None
TAG review status
Pending
Origin Trial documentation link
https://github.com/WebAssembly/custom-descriptors/blob/main/proposals/custom-descriptors/Overview.md
Risks
Interoperability and Compatibility
None
/Gecko/: No signal
/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?
None
Goals for experimentation
Initially we are looking to measure real-world performance, heap
usage, and OOM rate impact of just the core Wasm part of the
proposal. We want to verify that heap usage and OOM rates will
decrease as expected and that the performance impact is
negligible. If we do measure a performance impact, that will
inform additional optimization work we would need to do in the
implementation. Notably, the JS interop features of the proposal
are out of scope for this initial experimentation. They will
likely be evaluated in follow-on experiments.
Ongoing technical constraints
None.
Debuggability
None
Will this feature be supported on all six Blink platforms
(Windows, Mac, Linux, ChromeOS, Android, and Android
WebView)?
No
Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?
No
Flag name on about://flags
None
Finch feature name
None
Non-finch justification
None
Requires code in //chrome?
False
Estimated milestones
Origin trial desktop first 141
Origin trial desktop last 147
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/6024844719947776?gate=5062088692858880
This intent message was generated by Chrome Platform Status
<https://chromestatus.com/>.
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