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Groups > comp.lang.javascript > #29386

Re: Give alert if form checkbox array is empty

From Stefan Weiss <krewecherl@gmail.com>
Newsgroups comp.lang.javascript
Subject Re: Give alert if form checkbox array is empty
Date 2016-01-21 03:17 +0100
Organization albasani.net
Message-ID <n7pf3c$973$1@news.albasani.net> (permalink)
References <d5vt9b95kifj8nb7phn75pl16tpijop14s@4ax.com> <n7njvu$51k$1@news.albasani.net> <mu00ablmp9s6ronvrrejt2npfp5uffhpc5@4ax.com> <1851504.v7CTRd67sv@PointedEars.de>

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On 01/21/2016 00:59, Thomas 'PointedEars' Lahn wrote:
>> for (var i = 0; i < subjectTypes.length; i++) {
> 
>   for (var i = 0, len = subjectTypes.length; i < len; i++) {
> 
> But make sure that you do not modify “len” elsewhere.

Premature optimization is the root of all evil.

> You should familiarize yourself with the Array methods introduced with 
> implementations of ECMAScript Edition 5 at the latest, in order to not write 
> explicit loops where they are not necessary.  Examples have been given.  
> 
> Keep in mind that the built-in implementation of an algorithm is naturally 
> always the most efficient one to use as it is, at best, provided in machine 
> code already.

Had you tested this, you would have discovered that your version - the
one with `[].slice.call(...)` - takes 2 to 17 times longer than the
simple loop, depending on the browser and which checkboxes are checked.

Also, storing `subjectTypes.length` in a variable has almost no benefit:
it makes the loop a tiny bit faster in Firefox (about 5 nanoseconds per
iteration on my laptop), and a tiny bit slower in Chrome (about the same
difference in the other direction). Making assumptions about the
performance of modern JS engines without testing or intimate knowledge
of the internal optimizations is pointless.

Not that speed matters in this case - there are four checkboxes to test,
what kind of performance do you think we need for that? But you were
criticizing posted code for its performance and at the same time
advocating a slower and less readable version, so I thought you'd like
to know.

- stefan

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Thread

Give alert if form checkbox array is empty Bunyip <bunyip@koalanet.com.au> - 2016-01-20 13:28 +1000
  Re: Give alert if form checkbox array is empty JJ <jj4public@vfemail.net> - 2016-01-20 12:30 +0700
    Re: Give alert if form checkbox array is empty Bunyip <bunyip@koalanet.com.au> - 2016-01-20 17:55 +1000
      Re: Give alert if form checkbox array is empty JJ <jj4public@vfemail.net> - 2016-01-20 19:29 +0700
        Re: Give alert if form checkbox array is empty "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2016-01-20 13:46 +0100
  Re: Give alert if form checkbox array is empty Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2016-01-20 08:23 +0000
    Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-20 15:52 +0100
      Re: Give alert if form checkbox array is empty Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2016-01-20 15:43 +0000
        Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-20 17:15 +0100
          Re: Give alert if form checkbox array is empty Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-01-20 17:53 +0000
            Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-20 20:39 +0100
              Re: Give alert if form checkbox array is empty Jon Ribbens <jon+usenet@unequivocal.co.uk> - 2016-01-20 22:46 +0000
          Re: Give alert if form checkbox array is empty Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2016-01-21 07:53 +0000
            Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-21 10:52 +0100
              Re: Give alert if form checkbox array is empty Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2016-01-21 10:26 +0000
                Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-22 00:07 +0100
  Re: Give alert if form checkbox array is empty Stefan Weiss <krewecherl@gmail.com> - 2016-01-20 10:28 +0100
    Re: Give alert if form checkbox array is empty Bunyip <bunyip@koalanet.com.au> - 2016-01-21 08:05 +1000
      Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-21 00:59 +0100
        Re: Give alert if form checkbox array is empty Stefan Weiss <krewecherl@gmail.com> - 2016-01-21 03:17 +0100
          Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-21 08:54 +0100
            Re: Give alert if form checkbox array is empty Stefan Weiss <krewecherl@gmail.com> - 2016-01-21 12:17 +0100
        Re: Give alert if form checkbox array is empty John Harris <niam@jghnorth.org.uk.invalid> - 2016-01-21 14:16 +0000
        Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-21 19:52 -0800
          Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-22 09:48 +0100
            Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-22 10:45 -0800
              Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-23 19:41 +0100
                Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-24 17:51 -0800
                Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-25 19:46 +0100
                Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-27 11:09 -0800
        Re: Give alert if form checkbox array is empty Dr J R Stockton <reply1600@merlyn.demon.co.uk.invalid> - 2016-01-23 22:22 +0000
        Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-27 11:06 -0800
          Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-28 14:46 +0100
            Re: Give alert if form checkbox array is empty Gene Wirchenko <genew@telus.net> - 2016-01-28 10:30 -0800
              Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-28 20:06 +0100
                Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-28 23:32 -0800
                Re: Give alert if form checkbox array is empty "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2016-01-29 09:05 +0100
                Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-29 06:02 -0800
                Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-29 20:54 +0100
                Re: Give alert if form checkbox array is empty John Harris <niam@jghnorth.org.uk.invalid> - 2016-01-29 10:36 +0000
                Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-02-09 04:39 +0100
                Re: Give alert if form checkbox array is empty John Harris <niam@jghnorth.org.uk.invalid> - 2016-02-09 18:07 +0000
                Re: Give alert if form checkbox array is empty Gene Wirchenko <genew@telus.net> - 2016-01-29 09:32 -0800
                Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-29 20:34 +0100
                Re: Give alert if form checkbox array is empty Aleksandro <aleksandro@gmx.com> - 2016-01-29 16:50 -0300
                Re: Give alert if form checkbox array is empty Stefan Weiss <krewecherl@gmail.com> - 2016-01-30 03:31 +0100
                Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-30 04:19 +0100
                Re: Give alert if form checkbox array is empty Stefan Weiss <krewecherl@gmail.com> - 2016-01-30 05:01 +0100
              Re: Give alert if form checkbox array is empty Aleksandro <aleksandro@gmx.com> - 2016-01-28 16:39 -0300
            Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-29 06:04 -0800
              Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-29 20:54 +0100
                Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-29 14:55 -0800
                Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-30 04:55 +0100
                Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-30 15:48 -0800
                Re: Give alert if form checkbox array is empty Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-01-31 21:02 +0100
                Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-01-31 13:08 -0800
                Re: Give alert if form checkbox array is empty Andrew Poulos <ap_prog@hotmail.com> - 2016-02-01 12:28 +1100
                Re: Give alert if form checkbox array is empty Scott Sauyet <scott.sauyet@gmail.com> - 2016-02-01 17:58 -0800
  Re: Give alert if form checkbox array is empty "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2016-01-20 06:25 -0800
  Re: Give alert if form checkbox array is empty Aleksandro <aleksandro@gmx.com> - 2016-01-20 12:54 -0300

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