Decrementing While Loop ordering Javascript

Question

this is actually my first post about javascript. Would like to know, the performance of the following code as it is a "Decrementing while loop" inside that while loop has an Incrementing variable.

var i = data.d.length;
var i_counter=0;


while (i--)
{
   console.log(i_counter++)
}

My reason for adding i_counter++ is for sorting purposes. Would it slightly affect the loops performance for thousand of records? Would this code below much better than aboves performance?

for (var i = 0; i < data.d.length; i++) {
   console.log(i)
}

I have seen an online loop stress test online and this shows that decrementing while is the best. Is it true? http://jsperf.com/fastest-array-loops-in-javascript/32 Please give me a fiddle to stress test the code. Thank you. Suggestions are well accepted.

There is no "performance" issue. For all practical purposes they take the same amount of work: use the form that is most clear. — user2864740, Aug 12 '14 at 06:59
Hi, suggestion well appreciated, can you provide me a sample fiddle about stress testing about my code? Thanks, — user3932204, Aug 12 '14 at 07:02
The only slow operation we can see is the console.log. *That* is costly. Decrementing or incrementing isn't. — Denys Séguret, Aug 12 '14 at 07:03
So my code provided above is still much more faster than this code?for (var i = 0; i < data.d.length; i++) {} — user3932204, Aug 12 '14 at 07:05
@user3932204 No. It is "about the same speed" for all practical purposes, even with two additional property lookups. Create a microbenchmark if you like: http://jsperf.com — user2864740, Aug 12 '14 at 07:08
No : it takes about the same time. The standard `for` loop in the increment direction is optimized. You could try to profile that using [jsperf](http://jsperf.com) but you'd mostly see measuring artifacts, it's not worth the pain. — Denys Séguret, Aug 12 '14 at 07:08
You're on the wrong path. That's *not* where your program needs optimization. You should really **profile** to find the hot spots before even trying to do this kind of optimizations. — Denys Séguret, Aug 12 '14 at 07:10
I've been struggling to find what is the best and fastest loop over the internet most I see was using decrementing while loop. Now you are pointing out the standard for loop as the optimized and fastest? I am confused now, just a newbie :(.. learning coding standards. — user3932204, Aug 12 '14 at 07:12

score 1 · Answer 1 · edited May 23 '17 at 10:33

In both cases the runtime is by magnitudes dominated by console.log, which performs potentially blocking IO (log functions are in general not cheap, in particular when they produce visible console/UI output).

Assuming console.log a no-op, the first code should have a slight advantage since d.length is not re-evaluated every iteration (which is two dictionary lookups in the unoptimized case). A very intelligent JS runtime may be able to avoid this out even for the second case, though.

The best advice is, to optimize last and only after profiling which parts of your code are actual bottlenecks. FF and Chrome have profiling tools built-in for this purpose.

For the perfect JS loop iteration, have a look at this related SO question. Doing an extra increment on every iteration should not dramatically affect things.

Thank you but, sorry, please disregard the console.log. – user3932204 Aug 12 '14 at 07:13 — user3932204, Aug 12 '14 at 07:13

Decrementing While Loop ordering Javascript

1 Answers1