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Re: 'pushing' vs direct array assignment ?

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On 2013-06-03 22:39, Scott Sauyet wrote:
> Mel Smith wrote:
> 
>>     I build an array in JS that can be from 9 elements thru to nearly 1500
>> elements [ ... ]
>>
>>       // to add this object to this (possibly very big) array should I use
>> the 'push' method :
>>       anames.push(nuobj) ;
>>
>>       // or should I use direct array assignment
>>       anames[anames.length] = nuobj ;
>>
>>     or, is there another preferred way to do this quickly ?

The first question I would ask is: are you going to populate your array
once or many times? If it's only once, then just forget about
optimization, it will run too fast to notice with either method.

That was the pragmatic answer ... and now for the fun part :)

> One micro-benchmark can be found here:
> 
>     <http://jsperf.com/array-index-push/3>
> 
> In all the more recent browsers except IE9, `push` is faster.
> Unfortunately, in IE8 and IE9, it's quite a bit slower.  And since
> that's already the slowest environment, you'll have to make a decision
> with that in mind.

That's unexpected. Looking more closely at your test case, there is one
optimization that has a very measurable impact here, at least in Chrome:

For the index insertion test, instead of

   var a = [];           // and append 1000 elements

initialize the array to the proper size first:

   var a = Array(1000);  // and set 1000 elements

Obviously, that doesn't work for the two other tests, but there's a
definite improvement in Chrome for "index insertion":

With a = []:

   UA          | ops/sec
  -------------+------------------------------
   Chrome[1]   |  57,773  for index insertion
   Firefox[2]  |  63,650  for index insertion

With a = Array(1000):

   UA          | ops/sec
  -------------+------------------------------
   Chrome[1]   | 230,493  for index insertion
   Firefox[2]  |  65,300  for index insertion


No significant change in FF.
In Chromium, with the Array() optimization, the index insertion test is
roughly 50% faster than push(); and ~4x faster than with 'a = []';
I'm almost out of RAM, so I can't start a VM and test other browsers.
Stupid old laptops and their 4GB limit...

[1] Chromium 25.0.1364.160
[2] Firefox 21
both running on Ubuntu 12.4 64bit


> But regardless of speed, `push` is certainly cleaner.  And in my mind,
> that counts for a fair bit.

I agree.
Premature micro-optimization is a waste of time (but oh so much fun).

Things were different 6-7 years ago. I remember making exactly this
optimization and getting a very noticable reduction in UI lag. But that
was for an HTML/JS spreadsheet app, so we had a _lot_ of array copy
operations.


- stefan

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Thread

'pushing' vs direct array assignment ? "Mel Smith" <med_cutout_syntel@aol.com> - 2013-06-03 13:59 -0600
  Re: 'pushing' vs direct array assignment ? Scott Sauyet <scott.sauyet@gmail.com> - 2013-06-03 13:39 -0700
    Re: 'pushing' vs direct array assignment ? "Mel Smith" <med_cutout_syntel@aol.com> - 2013-06-03 14:46 -0600
    Re: 'pushing' vs direct array assignment ? Stefan Weiss <krewecherl@gmail.com> - 2013-06-04 02:07 +0200
      Re: 'pushing' vs direct array assignment ? "Mel Smith" <med_cutout_syntel@aol.com> - 2013-06-03 18:40 -0600
        Re: 'pushing' vs direct array assignment ? "Mel Smith" <med_cutout_syntel@aol.com> - 2013-06-03 20:38 -0600
        Re: 'pushing' vs direct array assignment ? Martin Leese <please@see.Web.for.e-mail.INVALID> - 2013-06-04 09:11 -0600
          Re: 'pushing' vs direct array assignment ? "Mel Smith" <med_cutout_syntel@aol.com> - 2013-06-04 12:47 -0600
            Re: 'pushing' vs direct array assignment ? Stefan Weiss <krewecherl@gmail.com> - 2013-06-04 22:44 +0200
              Re: 'pushing' vs direct array assignment ? "Mel Smith" <med_cutout_syntel@aol.com> - 2013-06-04 16:02 -0600
            Re: 'pushing' vs direct array assignment ? Martin Leese <please@see.Web.for.e-mail.INVALID> - 2013-06-04 20:24 -0600
              Re: 'pushing' vs direct array assignment ? Gregor Kofler <usenet@gregorkofler.com> - 2013-06-05 14:50 +0200
                Re: 'pushing' vs direct array assignment ? Martin Leese <please@see.Web.for.e-mail.INVALID> - 2013-06-05 22:38 -0600
              Re: 'pushing' vs direct array assignment ? Tim Slattery <Slattery_T@bls.gov> - 2013-06-05 08:51 -0400
                OT: Accept-Encoding (was: 'pushing' vs direct array assignment ?) Christoph Becker <cmbecker69@gmx.de> - 2013-06-05 15:23 +0200
  Re: 'pushing' vs direct array assignment ? RobG <rgqld@iinet.net.au> - 2013-06-05 18:12 -0700
    Re: 'pushing' vs direct array assignment ? "Mel Smith" <med_cutout_syntel@aol.com> - 2013-06-06 08:54 -0600

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