Le 19/09/2011 09:32, Jason Orendorff a écrit :
On Tue, Sep 6, 2011 at 10:59 AM, Mark S. Miller<erig...@google.com> wrote:
[...] Regarding infinite extensible
objects, the only problem I see off the top of my head is: What would
Object.getOwnPropertyNames return?
Hmm. I wonder if this is a problem even for finite objects.
I'm not sure it's the exact same problem, but it's an interesting question.
js> var x = [];
js> x = Object.getOwnPropertyNames(x);
["length"]
js> x = Object.getOwnPropertyNames(x);
["length", "0"]
js> x = Object.getOwnPropertyNames(x);
["length", "0", "1"]
js> x = Object.getOwnPropertyNames(x);
["length", "0", "1", "2"]
You see where this is going. There's a finite number of array indexes,
and the array .length property is always less than 2^32.
Of course on current machines we will eventually run out of time or
memory, but what is supposed to happen when we cross 2^32?
Object.getOwnPropertyDescriptor creates a native array and, for each own
property, it calls [[DefineOwnProperty]] on this array for an index n
(ES5.1 - 15.2.3.4 step 4.b)
This internal method is special for arrays (ES5.1 - 15.4.5.1). When
crossing 2³², ToString(n) is not an array index anymore, so the property
is added (as per step 5), but the length property gets stuck to its
maximum (2³²).
Since the property is added, continuing results in an infinite loop, the
length property remains at 2³².
David
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