Groups > comp.lang.javascript > #20441

Re: Looping holding old copy of array

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Message-ID	<3009252.vL9dYu562Q@PointedEars.de> (permalink)
From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To	Thomas 'PointedEars' Lahn <usenet@PointedEars.de>
Organization	PointedEars Software (PES)
Date	Tue, 25 Jun 2013 23:03:03 +0200
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Subject	Re: Looping holding old copy of array
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Cezary Tomczyk wrote:

> On 2013-06-25 03:06, Thomas 'PointedEars' Lahn wrote:
> [...]
>> Safer and more efficient:
>>
>>    for (var i = 0, len = Aarray.length; i < len; ++i)
>>    {
> 
> By the way of above. According to discussion here
> http://stackoverflow.com/questions/6261953/do-modern-javascript-jiters-need-array-length-caching-in-loops
> in your opinion property "length" still needs to be stored in variable
> before loop? Or this can be omitted because modern browsers caching (?)
> "length" property?

One should never rely on what one cannot know.  You cannot know the runtime 
environments code once written will be exposed to.  There is no good reason 
to assume the value of the ”length” property should be automatically cached 
for a loop in the first place as it could change by statements in the loop.

One *can* know instead that avoiding to access a property repeatedly whose 
value does *not* change, in favor of a local variable that holds this value, 
reduces code complexity.  That has a chance – and it has been showed – to 
increase runtime efficiency, IOW to be faster.  So it is wise to do that.

-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

Thread

Looping holding old copy of array jonas.thornvall@gmail.com - 2013-06-23 22:50 -0700
  Re: Looping holding old copy of array "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2013-06-24 09:44 +0200
    Re: Looping holding old copy of array "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2013-06-24 16:45 -0700
      Re: Looping holding old copy of array Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-06-25 03:06 +0200
        Re: Looping holding old copy of array Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2013-06-25 21:58 +0200
          Re: Looping holding old copy of array Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-06-25 23:03 +0200
  Re: Looping holding old copy of array JJ <duh@nah.meh> - 2013-06-24 15:19 +0700
    Re: Looping holding old copy of array jonas.thornvall@gmail.com - 2013-06-24 03:38 -0700
      Re: Looping holding old copy of array JJ <duh@nah.meh> - 2013-06-25 10:52 +0700

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