Yet more ambiguities in property enumeration

Mark S. Miller erights at google.com
Thu Jun 3 12:37:41 PDT 2010


On Thu, Jun 3, 2010 at 11:54 AM, stay <stay at google.com> wrote:

> On Fri, May 7, 2010 at 1:00 PM, Oliver Hunt <oliver at apple.com> wrote:
> >
> > On May 7, 2010, at 12:56 PM, stay wrote:
> >> Really?  How could sites possibly depend on being able to mark
> >> properties non-enumerable but still have them appear in a for-in loop?
> >
> > Sorry, shadowing with a non-enumerable property is new to ES5, I was
> meaning the behaviour i described is what we need to do to ensure sites
> work.
> >
> > Now days my understanding is the only place where there is confusion over
> behaviour is purely which prototype properties should be enumerated.
> >
> > --Oliver
>
>
> I don't think I ever saw a conclusive answer to the original question:
>
> When a.x is enumerable, b inherits from a, and b.x is marked
> non-enumerable, does x get enumerated in a for-in loop or not?
>
> If not, V8 and WebKit are doing it wrong.  If so, it seems to violate
> the principle that properties on children shadow their parents.
>
> Which is it?
>
> Allen's follow-up messages talked about order of enumeration, which
> I'm not particularly concerned about right now.
>

I thought Allen's answer at <
https://mail.mozilla.org/pipermail/es5-discuss/2010-May/003536.html> was
clear. The property is shadowed and the current WebKit & v8 behaviors are
non-conformant. I have filed bug reports against them at <
https://bugs.webkit.org/show_bug.cgi?id=38970> and <
http://code.google.com/p/v8/issues/detail?id=705>.




> --
> Mike Stay
> stay at google.com
>



-- 
    Cheers,
    --MarkM
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