Array lengthening methods applied to maximally long arrays

[Allen Wirfs-Brock]

Here's what I observed:

Opera 9.63  - conforms to ES3/ES5 spec.
Range error on a.push(1) after creating a non-array index property named "4294967295" and leaving length as 4294967295
Chrome 1.0.154.65 conforms to ES3/ES5 spec.
Range error on a.push(1) after creating a non-array index property named "4294967295" and leaving length as 4294967295

Firefox 3.0.8 - does not conform
No range error on a.push(1) returns 0, creates a non-array index property named "4294967295" and sets length to 0
Safari 3.1.2 - does not conform
No range error on a.push(1) returns 0, creates a non-array index property named "4294967295" and sets length to 0

IE8 - does not conform
No range error on a.push(1) returns 0, creates a non-array index property named "-1" and sets length to 0

It's possible that developmental builds of the above produce different results.  As there is significant variance I don't see a strong reason to change the spec. to reflect the FF behavior.

It might be arguably better if pop threw the range error before creating any new properties.  This would be easy to specify (and detect in implementations) for pop but for consistency that approach should probably also be applied to all the Array.prototype functions and it might be considerably harder to specify/implement such pre-flight checking for some of the more complex algorithms particularly in the presences of accessor properties with side-effects.

In an earlier draft I tried to say that final state of the array was unspecified if any exception was thrown but there was considerable negative reaction to that proposal.

Allen



>-----Original Message-----
>From: es-discuss-bounces at mozilla.org [mailto:es-discuss-
>bounces at mozilla.org] On Behalf Of James Graham
>Sent: Wednesday, May 13, 2009 2:15 AM
>To: es-discuss at mozilla.org
>Subject: Array lengthening methods applied to maximally long arrays
>
>As far as I can tell, the ES5-specified behavior of
>
>a = new Array()
>a.length = Math.pow(2,32)-1
>a.push(1)
>
>is to create a non-array-index property of the array with name
>4294967296 (i.e. 2^32) and value 1 before throwing a RangeError hen
>trying to update the length. However this property isn't created in the
>majority of implementations (at least it doesn't happen in my builds of
>Spidermonkey, V8 and Squirrelfish) and since it is rather surprising
>that the operation would, in some sense, succeed before throwing an
>error, it seems like it might be nice to change this part of the spec to
>reflect the implementations.
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