Comments on: Optimizing JavaScript (part 1)

By: Shamasis Bhattacharya

Shamasis Bhattacharya — Tue, 26 May 2009 19:31:38 +0000

“===” may not be a desirable operator for every situation. In case of switch statement, the switching variable is compared for existence only once. Whereas, in case of if-else block, both sides of the “==” operator is checked for existence and that, to some extent, adds up to the execution time.

Now, with an if-else block with “===” operator, the above logic theoretically appears to have been overcome. But, apparently it is not! I did run a test of 100000 iterations with 20 cases and if-else per loop and the result still shows that switch-case is faster and that “==” or “===” has almost no difference in execution time. (View Testing Script)

And ah! The link you mentioned is really worthwhile. It really has some extensive validation of the above points.

By: nico

nico — Tue, 26 May 2009 12:30:56 +0000

In your “if, else if” block, you compare the value with operator == which converts type of data. Lots of web sites advise the use of ===.
I think a switch statement is performing a comparison same way than ==. So are you sure it would be quicker than the “if, else is” block with operator === ?
For a great benchmark on the loops performance, there is :
http://blogs.sun.com/greimer/entry/best_way_to_code_a
which shows how bad is the “for (var i in array)” !!

By: Shamasis Bhattacharya

Shamasis Bhattacharya — Fri, 01 May 2009 07:37:13 +0000

Well... I think that using a language profiler to track execution times is another alternative. For JavaScript, a good profiler is FireBug. Other than that, there is JS Profiler 2.o. Using a profiler is a more robust and technically sound way to track memory leak and performance of your applications. I will soon write a section enunciating the benefits of using a profiler.

By: Rahul B.

Rahul B. — Fri, 01 May 2009 06:01:38 +0000

One way how you can check your execution time on javascript is using date tag, see the example below:

<script type="text/javascript">
function check_processing_time(){
  var start_time,end_time;
    start_time = new Date().getTime();
    FunctionName();
    end_time=new Date().getTime();
alert('Elapsed time: '+((endTime-startTime)/1000)+' seconds.');
}
</script>

By: Shamasis Bhattacharya

Shamasis Bhattacharya — Wed, 29 Apr 2009 20:07:08 +0000

Oops! Typo there! i- should be i−−! (You see, Windows Live Writer automatically converted -- to a longer dash!) My statement : for(var i = 10000; i; i−−) is equivalent to for(var i = 10000; i==0; i−−)

By: Dhruva

Dhruva — Wed, 29 Apr 2009 19:01:41 +0000

(var i = 10000; i>0; i––)
is what you mean to say, right?

By: Andy L

Andy L — Sat, 25 Apr 2009 20:54:59 +0000

Damn! I could never believe that counting down in a loop works… and guess what you actually made me write a test code to try it out.

It worked in FF and Chrome but very little difference in IE. Even then… it works.