Bug 149477 – PromiseSubclass.resolve does not "cast" correctly

• Status: RESOLVED
• Resolution: DUPLICATE
• Component: JavaScriptCore

[Stefan Penner]

http://www.ecma-international.org/ecma-262/6.0/#sec-promise.resolve

the following lines of the spec text:

25.4.4.5.a 
25.4.4.5.c

Indicate

class PromiseSubclass extends Promise { }
PromiseSubclass.resolve(Promise.resolve()).constructor === PromiseSubclass;

Unfortunately, today the following is true:

PromiseSubclass.resolve(Promise.resolve()).constructor === Promise;

Related patch to V8 -> https://codereview.chromium.org/1362773002

[Yusuke Suzuki]

This is because the current Promise cannot be subclassible.
We can fix this by using newTarget in C++ Promise constructor as a workaround.
But ideally, this should be fixed by moving Promise to JS implemented constructor.

[Alexey Shvayka]

Promise subclassing was implemented in https://trac.webkit.org/changeset/191276.
Tests:
  JSTests/es6/Promise_is_subclassable_*.js
  JSTests/stress/derived-promise-constructor-*.js

*** This bug has been marked as a duplicate of bug 149380 ***