Re: Array.prototype.splice implementation in 'JS: The Good Parts'

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Message-ID	<1600385.oMNUckLgyt@PointedEars.de> (permalink)
From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To	Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
Organization	PointedEars Software (PES)
Date	Fri, 08 Jun 2012 09:48:25 +0200
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Subject	Re: Array.prototype.splice implementation in 'JS: The Good Parts'
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Jun Woong wrote:

> Thomas 'PointedEars' Lahn <PointedE...@web.de> wrote:
>> Jun Woong wrote:
>> > What does the ECMA standard says about this?
>>
>> <http://ecma-international.org/ecma-262/5.1/#sec-15.4.4>:
>>
>> [...]
>> | b. Let fromPresent be the result of calling the [[HasProperty]]
>> | internal method of O with argument from.
>>
>> var fromPresent = from in O;
>>
>> This is the step in the algorithm where apparently both Crockford and V8
>> are wrong, according to the 5.1 Edition and earlier Editions.  Crockford
>> does not consider `undefined' values for elements, and V8 does not
>> consider uninitialized elements (here: those with indexes 0 and 1).
> 
> Thus, if `a' is intialized as [undefined, undefined, 0] (having all
> elements initialized), the length of the result should be 2, while it
> should be 0 when initialized as [,, 0] (having uninitialized
> elements).

Yes, exactly.  (That 

  var a = [,, 0];

is equivalent to

  var a = [];
  a[2] = 0;

follows from section "11.1.4 Array Initialiser".)

> Thank you very much for the kind explanation and the nice work that
> the link below leads to.
> 
>> ___
>> [1] <http://PointedEars.de/es-matrix>

You are welcome.  (Stay tuned.)


Regards,

PointedEars
-- 
Use any version of Microsoft Frontpage to create your site.
(This won't prevent people from viewing your source, but no one
will want to steal it.)
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Array.splice implementation in 'JS: The Good Parts' Jun Woong <woong@icu.ac.kr> - 2012-06-06 21:17 -0700
  Array.prototype.splice implementation in 'JS: The Good Parts' (was: Array.splice implementation in 'JS: The Good Parts') Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-06-07 20:17 +0200
    Re: Array.prototype.splice implementation in 'JS: The Good Parts' (was: Array.splice implementation in 'JS: The Good Parts') Jun Woong <woong@icu.ac.kr> - 2012-06-07 18:41 -0700
      Re: Array.prototype.splice implementation in 'JS: The Good Parts' Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-06-08 09:48 +0200

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