Comments on: Extreme JavaScript optimization

By: Por uma Web mais rápida: 26 técnicas de otimização de Sites « Cândido Sales Blog

Mon, 12 Sep 2011 18:32:57 +0000

[...] a performance. Usar iframes em excesso então é um quase um crime. E há também as práticas de otimização de código e lógica JavaScript, como quebrar longas tarefas em pedaços menores com WebWorkers ou setTimeout, evitando bloqueio da [...]

By: Garth Henson

Garth Henson — Thu, 02 Sep 2010 18:26:32 +0000

Ugh. Code above should be (hopefully works this time): var i = 1, j = 1; alert([i, i++, i].join(',')); alert([j, ++j, j].join(','));

By: Garth Henson

Garth Henson — Thu, 02 Sep 2010 18:22:14 +0000

Ara, great work, as usual. Appreciate the simplistic yet profitable approach to optimization. I have been playing with the recommended process and benchmarking to see just how much things can speed up, and when combined, there is up to a 15-20% performance increase when you get up into the millions of iterations.

@Florent, you also have to be careful about simply switching the increment and decrement order dependent upon what you want your code to do. If you want the value to be evaluated BEFORE the increment/decrement is performed, you need to keep it after the variable name. Consider the following for an example:

var i = 1, j = 1;
alert([i, i++, i].join(‘,’));
alert([j, ++j, j].join(‘,’));

In this sample, the first will output 1,1,2 while the second will produce 1,2,2. Changing the order of the operator will change the evaluation order of the value as well. Switching this in code can very quickly become a hazard unless you are certain what the intended outcome is.

By: Mahesh

Mahesh — Thu, 26 Aug 2010 14:23:50 +0000

Thanks for simplified instruction for JavaScript optimization. I am now more enthused to devote time and learn these techniques.

By: Huang Xinhao

Huang Xinhao — Thu, 13 May 2010 06:37:35 +0000

Are these impove necessary for a normal website?

By: Brian

Brian — Sun, 21 Mar 2010 19:20:09 +0000

I’ve done some messing about with this concept of the loop using a for loop and found that regardless of whether I define i (i.e. var i =0;) with the var keyword or not it still creates an i global variable that is also manipulated with the for loop. This was surprising to see and it contradicts everything I read about it being made a local variable in this case. I checked it over many times to make sure I didn’t a mistake but this is the case. This means that the interpreter goes outside of the loop every time it has to change the value of i. How do you handle this?

By: Wynand

Wynand — Mon, 22 Feb 2010 20:50:00 +0000

Great post!

By: AlvaroG

AlvaroG — Wed, 13 Jan 2010 16:12:32 +0000

it doesn’t matter the dummy example, just use it if you’ve a loop with hard data manipulation inside, i use this extreme optimization with an average of 400 object instances and it works perfectly reducing the exec time from 10secs to 1 second or less time, remember it’s “extreme optimization” not “extreme optimization for dummies”, don’t feed the troll.

If you want to reduce the script time execution (with hard to read code) use this, it’s a optimization for execution not for reading.

Good posts!

By: Philip Tellis

Philip Tellis — Thu, 31 Dec 2009 09:20:31 +0000

@Florent: profile your code before deciding whether to use --i or i--. This is true even in C. Modern compilers are pretty smart.

By: Florent Vaucelle

Florent Vaucelle — Mon, 28 Dec 2009 10:27:11 +0000

@jsq, thanks for the answer!
I try hard not to forget semicolons, but sometimes some escape…