On Sun, Apr 10, 2011 at 11:21 PM, David Herman <[email protected]> wrote:
> I wondered if someone was going to make this point.
>
> > That should be
> >
> > while (!{}.hasOwnProperty.call(obj, key))
> >
> > which works even if obj has an own property named 'hasOwnProperty'.
>
> Not if someone mutates Object.prototype.hasOwnProperty or
> Function.prototype.call. I don't think we need to polish a proof of concept.
>
First, I agree that for the original purpose of this thread, this polishing
is irrelevant, so I have changed the subject. But your counter-examples do
help to highlight something I've been thinking about. Because of such
pervasive mutability, we really haven't had a clear notion of "correctness"
for JavaScript. For normal JavaScript programs, if run after some other code
has already mutated that environment's primordials arbitrarily, there's so
little they can count on that very few programs could be written "correctly"
under these onerous assumptions[1]. For the notion of "correctness" in
JavaScript to be useful, I think we must allow JavaScript programs to rely
on the primordial at least continuing to obey their original contract.
However, the use of objects as maps from strings to values is pervasive,
e.g., in JSON unserialization, so we should not allow general purpose
JavaScript programs to rely on, for example, 'hasOwnProperty' not being
overridden.
Retrofitting a reasonable theory of correctness after the fact is a tricky
exercise. The above theory represents a practical compromise between the
assumption that common programs make (primordials obey their original
contracts) vs. the assumptions that common programs break (hasOwnProperty is
not overridden). Thus, I claim that the original program should not be
considered "correct", while the modified program should, despite the
problematic cases raised by your counter-example.
[1] SES initialization freezes the primordials, so SES programs can safely
assume they are frozen. But the point I'm making here are not specific to
SES.
>
> Dave
>
>
--
Cheers,
--MarkM
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