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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