Wasm js-types proposal - missing

What type of issue is this?

Missing compatibility data

What information was incorrect, unhelpful, or incomplete?

Please add compatibility data for these implemented js-types features:

• WebAssembly.Memory.prototype.type().
• WebAssembly.Table.prototype.type().
• WebAssembly.Global.prototype.type().
• The minimum descriptor option for WebAssembly.Memory().
• The minimum descriptor option for WebAssembly.Table().
• WebAssembly.Function, its constructor, and WebAssembly.Function.prototype.type().
• The type property on descriptors returned by WebAssembly.Module.imports().
• The type property on descriptors returned by WebAssembly.Module.exports().

All of these have implementations exposed in Firefox Nightly; they are not merely unimplemented proposal text. See Firefox’s implementation and Nightly-only build configuration.

Also include two constructor descriptor values omitted from the earlier list:

• element: "funcref" for WebAssembly.Table().
• value: "funcref" for WebAssembly.Global().

The proposal makes "anyfunc" an alias of "funcref". Both spellings are accepted by WebKit’s Table constructor and Global constructor. See the proposal change introducing the alias.

Record constructor options and accepted values separately under the corresponding constructor entries. Passing an existing { value, mutable } descriptor to WebAssembly.Global() does not itself constitute a new overload.

What browsers does this problem apply to, if applicable?

Firefox

What did you expect to see?

Firefox Nightly: The three instance methods, both minimum options, WebAssembly.Function and its method, and both module descriptor extensions are implemented behind ENABLE_WASM_TYPE_REFLECTIONS. Firefox’s build configuration enables this for Nightly by default, not release builds. Implementation, configuration.

Safari/WebKit: There is implementation evidence for the constructor additions and reflection methods, but availability must distinguish release versions from development builds. A WebKit change dated July 17, 2026 moved the previously unconditionally installed type() methods behind useWasmJSTypes, which defaults to false.

Did you test this? If so, how?

Verification consisted of reviewing browser implementation code, build configuration, and implementation-change records.

Can you link to any release notes, bugs, pull requests, or MDN pages related to this?

• JavaScript type reflection proposal.
• Firefox implementer confirmation of Nightly-only support.
• Firefox bug concerning "funcref" reflection and constructor input.
• MDN documentation PR.
• Related MDN documentation issue

Do you have anything more you want to share?

Investigation done by Codex

MDN URL

No response

MDN metadata

No response

Start by reviewing the existing WebAssembly compatibility entries and the JavaScript type reflection proposal cited in the issue. Add separate compatibility data for the listed methods, constructor options, accepted values, and module descriptor properties, distinguishing Firefox Nightly and WebKit development support where applicable. Verify that any aliases and omitted constructor values are represented separately as requested.