Le 20/12/2012 11:09, Tom Van Cutsem a écrit :
(...)
The right fix (at least, it feels like the obvious right fix to me),
is not to test whether O === Receiver, but rather just let the
algorithm explicitly test whether the Receiver object already defines
an own property with key P, to decide between update vs. addition:
replace step 5.b with:
5.b Let existingDesc be the result of calling the [[GetOwnProperty]]
internal method of Receiver with argument P.
5.c If existingDesc is not undefined, then
... // same steps as before
Now, for normal objects, this test is redundant since existingDesc and
ownDesc will denote the same property. But that redundancy is
harmless, just as in ES5 [[Put]] it was redundant to call both
[[GetProperty]] and [[GetOwnProperty]] on the same object. In the fast
path, engines will not follow this algorithm anyway. If Receiver is a
proxy, then the difference matters and the proxy will be able to
intercept the call to [[GetOwnProperty]] (which is what makes this
revised algorithm work in the presence of proxies).
A note in the spec to explain this would probably be a good idea,
because it's a very subtle difference.
David
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