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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: JS Array problem
Date: Tue, 21 Oct 2014 19:02:34 +0200
Organization: PointedEars Software (PES)
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Mel Smith wrote:

> "danca" <cyberdanny@tiscalinet.it> wrote […]:
>> Il 20/10/2014 23:11, Mel Smith ha scritto:
>> Maybe something like this?
>>
>> var a,b,c,d ;
>> var abcd = ["a","b","c","d"] ;
>> for (var i= 0; i<abcd.length; i++) {
>>      eval(abcd[i]+"="+i);
>> }
> 
> […]
>     Yes, That's what I was looking for.

Hardly, as it is harder to debug and more error-prone.  It will not work in 
strict mode (the scope chain of eval code is empty then), which you should 
be using in order to avoid common programming errors.

Also,

  for (var i = 0, len = abcd.length; i < len; ++i)

is more efficient when “abcd.length” does not change;

  for (var i = abcd.length; i--;)

is even more efficient if the array is not sparse and order does not matter.  

If the array-like object is sparse, the most efficient way, where order 
matters and non-index own properties are not expected, is probably

  var indexes = Object.keys(abcd);
  for (var i = 0, len = indexes.length; i < len; ++i)
  {
    var index = indexes[i];
    abcd[index] = …;
  }

(Array indexes are names of own enumerable properties.  If non-index own 
properties are expected, an additional test of the property name is 
required.)

-- 
PointedEars
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