[Bug 29421] Should getters on a global without an explicit 'this' really throw TypeError?

https://www.w3.org/Bugs/Public/show_bug.cgi?id=29421

--- Comment #3 from Christophe Dumez <dchris@gmail.com> ---
(In reply to Christophe Dumez from comment #2)
> (In reply to Boris Zbarsky from comment #1)
> > So the big web compat constraint here is that this should do the right thing:
> > 
> >   var perf = performance;
> > 
> > needs to work.  I believe in spec terms this ends up in
> > http://www.ecma-international.org/ecma-262/6.0/#sec-object-environment-
> > records-getbindingvalue-n-s which lands in
> > http://www.ecma-international.org/ecma-262/6.0/#sec-get-o-p which will use
> > the object associated with the object enviroment record (in this case the
> > global) as "this".  So for this part to work, no effort is needed on the
> > part of IDL.
> > 
> > You're correct that the current Firefox behavior makes this also work:
> > 
> >   Object.getOwnPropertyDescriptor(window, "performance").get.call()
> > 
> > I tried this in a few other browsers, with the following results:
> > 
> > 1) Chrome.  Seems to not actually have accessor properties on the window
> > yet.  Presumably they're still updating to Web IDL for the window...  In any
> > case, Object.getOwnPropertyDescriptor(window, "performance") returns a value
> > descriptor.
> > 
> > 2) Safari.  Has some bizarre setup where descriptors on the global have
> > undefined get and no value, but stuff somehow still works.  Basically,
> > totally violates the ES spec.
> 
> Yes, I work on WebKit and am currently fixing this issue. This is also why I
> wanted the behavior of implicit 'this' for the global Window Object to be
> clarified.
> 
> On WebKit nightly, it does return getters/setters now but the following:
> $ Object.getOwnPropertyDescriptor(window.__proto__, "performance").get.call()
> throws a "TypeError: The DOMWindow.performance getter can only be used on
> instances of DOMWindow" for now.
> 
> > 
> > 3) IE11.  This seems to put the properties on window.__proto__, not window. 
> > Subject to that constraint,
> > Object.getOwnPropertyDescriptor(window.__proto__, "performance").get.call()
> > works.
> > 
> > 4) Edge.  Object.getOwnPropertyDescriptor(window, "performance").get.call()
> > works.
> > 
> > Speccing the Firefox/Edge behavior makes some sense to me, especially
> > because the only reason the bareword works otherwise is because it takes a
> > weird path to the getter.
> 
> Also, I think we should be clear about which window we should fall back to
> when 'this' is null/undefined, in the case of subframes. E.g.
> 
> otherWin = open("about:blank");
> locationGetter = Object.getOwnPropertyDescriptor(otherWin, "location").get;
> locationGetter.call()
> 
> should this be identical to:
> locationGetter.call(otherWin)
> or
> locationGetter.call(window)
> ?

FYI, in this case, I would expect locationGetter.call() to behave the same way
as locationGetter.call(window) as I think this is how it works in EcmaScript.

However, Firefox seems to do locationGetter.call(otherWin) in this case.

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Received on Friday, 5 February 2016 19:50:11 UTC