Finiteness of object properties set

[David Bruant]

Le 19/09/2011 09:32, Jason Orendorff a écrit :
> On Tue, Sep 6, 2011 at 10:59 AM, Mark S. Miller<erights at 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