Bug 292727 – Error.isError() should also support DOMException

• Status: NEW
• Component: DOM

[Tetsuharu Ohzeki [UTC+9]]

`Error.isError(new DOMException)` should be `true`, but it's not on https://github.com/WebKit/WebKit/tree/b6e7f29ea5831ff7f0c67baf36d5820969181eba

[Tetsuharu Ohzeki [UTC+9]]

Pull request: https://github.com/WebKit/WebKit/pull/45113

[Tetsuharu Ohzeki [UTC+9]]

By the spec, `Error.isError(new DOMException)` should be `true`:

1. Error.isError see whether the given object has `[[ErrorData]]` internal slot. https://tc39.es/proposal-is-error/#sec-abstract-operations-for-error-objects
2. DOMException would also has `[[ErrorData]]` internal slot. https://webidl.spec.whatwg.org/#js-DOMException-specialness

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Our implementations of Error.isError uses `JSC::JSObject::isErrorInstance()` internally and checks whether the `JSCell::type()` is `JSC::JSType::ErrorInstanceType`.

But `WebCore::JSDOMException::createStructure()` passes `JSC::TypeInfo(JSC::ObjectType, StructureFlags)` for the `typeInfo` 3rd arguments of `JSC::Structure::create()`.  This causes `Error.isError(new DOMException) === false`.

[Radar WebKit Bug Importer]

<rdar://problem/151390471>