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Node-API-JSC: napi_typeof reports napi_object for JSObjectMakeConstructor constructors #194
Description
Follow-up from the native fetch() polyfill review (#188).
napi_typeof in js_native_api_javascriptcore.cc decides function-ness solely via JSObjectIsFunction, which returns false for constructors created with JSObjectMakeConstructor on some JSC builds (e.g. libjavascriptcoregtk). As a result it reports napi_object where V8 returns napi_function, so Napi IsFunction() incorrectly rejects otherwise-valid constructors (e.g. the Blob polyfill).
Both the Fetch polyfill (#188) and the File polyfill currently carry an identical IsUndefined()/IsNull() workaround to detect the constructor without IsFunction().
A fix in napi_typeof (also consulting JSObjectIsConstructor in addition to JSObjectIsFunction) would let both polyfills drop the workaround rather than spreading per-polyfill copies.
Activity
Address review: fix napi_typeof for JSC constructors (BabylonJS#194) …
bkaradzic-microsoft commentedon Aug 18, 2026
Fixed by #207 (merged 2026-07-28).
That PR changed
napi_typeofinCore/Node-API/Source/js_native_api_javascriptcore.ccto consultJSObjectIsConstructorin addition toJSObjectIsFunction, so constructors created viaJSObjectMakeConstructor(i.e. node-addon-apiDefineClassconstructors) now reportnapi_functionon JSC builds such as libjavascriptcoregtk, matching V8.With that in place the
IsUndefined()/IsNull()workarounds carried by the Fetch (#188) and File polyfills were removed in the same PR.Closing as completed.