Is there a performance difference between i++ and ++i in JavaScript? [closed]

Question

I read Is there a performance difference between i++ and ++i in C?:

Is there a performance difference between i++ and ++i if the resulting value is not used?

What's the answer for JavaScript?

For example, which of the following is better?

1. for (var i = 0; i < max; i++) {
     // code
   }
   

2. for (var i = 0; i < max; ++i) {
     // code
   }
   

Penitence

Not enough to matter to you. I tend to prefer the ++i notation unless it's explicitly wrong for the use case. – Overpower

with any decent js engine it should be identical – Janiuszck

i hear there's a jsperf.com but not sure how to use it. – Goon

Pretty sure this is trivial for real performance. – Flashcube

Duplicate of #1547481 – Parkin

Answer 1

Here is an article about this topic: http://jsperf.com/i-vs-i/2

++i seems to be slightly faster (I tested it on firefox) and one reason, according to the article, is:

with i++, before you can increment i under the hood a new copy of i must be created. Using ++i you don't need that extra copy. i++ will return the current value before incrementing i. ++i returns the incremented version i.

Gamekeeper

This is really more of a comment. An answer would explain how that link answers the question. – Offprint

@jasper i was coming to that :) – Gamekeeper

it depends on your browser. ++i is slower in safari but faster in some browsers. – Electrician

"under the hood a new copy of i must be created" - only if you use the result... – Janiuszck

Answer 2

No. There is no difference in execution time. The difference in the two code snippets is when i gets incremented.

for(i = 0; i < max; i++)
{
    console.log(i);
}

This first example will yield the results: 0,1,2,3,...,max-1

for(i = 0; i < max; ++i)
{
    console.log(i);
}

This second example will yield the results: 1,2,3,...,max

i++ increments the value after the operation. ++i increments the value before the operation.

There is no performance difference other than the one less iteration it will make on ++i because the increment is done before the first operation

Polygynist

I'm not sure why the down-vote. The JSPerf linked-to in jidma's answer shows that the two perform the same. – Offprint

Agreed, well within 1% of each other. ++i shows to be 1% slower in Safari 6.x. A good example to explain the difference is var i = 0; alert(++i); vs var i = 0; alert(i++); – Electrician

-1. Both codes print the same thing. – Janiuszck

jsbin.com/oninoy/1/edit – Flashcube

DeveloperKlin: In a loop the assertion that you make about the value if i is invalid, it is however valid when taken in other contexts, like concocting a string. – Offprint

@KarolyHorvath i agree, in order to have different results it should be for(i = 0; i < max; ) console.log(++i) vs for(i = 0; i < max; ) console.log(i++) – Gamekeeper

@Flashcube here is what he meant jsbin.com/oninoy/2/edit – Gamekeeper

I checked out what you guys had said and it appears you are right. Thanks for the clarification. – Polygynist

Yeah, in a loop statement it doesn't make a difference in the output because it gets evaluated after the iteration. You have to use it inside to see the difference like others said. – Flashcube

Is "console.log" slow enough to hide the difference between ++i and i++ ? – Manifestation

@Nateowami: Just wonder if it is meaningful to time a loop with irrelevant function calls that may be too slow than the thing to be measured (i++ or ++i). What if console is a slow serial port or punch card? – Manifestation

@Qi Fan Oh, I see what you were saying. My mistake. Just deleted it. – Adenosine