982671 - Promise subclasses throw on construction

Status: RESOLVED INVALID

(Core :: DOM: Core & HTML, defect)

Description

[Jake Archibald [:jakea]]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.146 Safari/537.36

Steps to reproduce:

http://jsbin.com/noloz/2/edit?js,console & press run.


Actual results:

TypeError: Constructor Promise requires 'new'


Expected results:

"It worked!"

Comment 1

[Boris Zbarsky [:bzbarsky]]

Hmm.  So this behavior changed in bug 916644.

Before that, the line "Promise.apply(this, arguments);" created a new Promise and then threw it away.  The return value of the constructor was not in fact a Promise object (and the exception that got thrown was "TypeError: 'then' called on an object that does not implement interface Promise. (line 23)".

Now calling the constructor as a function will throw, at least in non-release builds, instead of doing something totally unexpected.  Note that Chrome has the same behavior.

And the real upshot here is that we don't support ES6 subclassing at all yet; there is no @@create support.  That's bug 838540 (of which this may well be a duplicate).

Comment 2

[Boris Zbarsky [:bzbarsky]]

> at least in non-release builds, 

Er, in release builds too, in this case, starting with Firefox 30.

Comment 3

[Boris Zbarsky [:bzbarsky]]

Marking this invalid; per current ES6 spec this code should not work, afaict.