Do local variables inside of a loop get garbage collected?

Question

I'm wondering if it is more efficient to place any vars referenced within a loop, outside of the loop - or can they get garbage collected like vars inside of a function?

var obj = {key:'val'};
for(var i=0; i<10; i++){
    console.log(obj);
}

or

for(var i=0; i<10; i++){
    var obj = {key:'val'};
    console.log(obj);
}

I tried to run some memory test in my browser's profiler but still couldn't tell which method was better.

score 6 · Accepted Answer · edited May 23 '17 at 12:03

6

var is function scoped, not blocked scoped, so it does not matter whether they appear inside the loop or not. What is the scope of variables in JavaScript? explains this distinction.

The next version of JavaScript will have let-scoped variables and the value stored in those would become collectible at the end of a loop body run if declared inside the loop.

edited May 23 '17 at 12:03

Community

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answered Oct 11 '11 at 02:21

Mike Samuel

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Note that stylistically (to avoid confusing readers of your code) it's advisable to always locate `var` statements at the beginning of the function. – intuited Oct 11 '11 at 02:24
@intuited, Good point. I think some tools like JSLint enforce that. – Mike Samuel Oct 11 '11 at 06:02

score 1 · Answer 2 · answered Oct 11 '11 at 02:21

1

Neither will get garbage collected until the variables go out of scope. Scope in Javascript is introduced by functions. A loop construct has no influence on scope whatsoever.

answered Oct 11 '11 at 02:21

deceze

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Thanks for the info. Is either method better than the other for any reason(s)? – George Hess Oct 11 '11 at 02:24
It doesn't really make sense to redeclare the object over and over in the loop, so 1 seems more appropriate. – deceze Oct 11 '11 at 02:26

score 0 · Answer 3 · answered Oct 11 '11 at 02:29

As far as garbage collection, what the other answers say should be true, the browser handles the garbage collection and it doesn't matter if the variable is declared internally, or externally, to a loop.

As for efficiency, your code would be a little more optimized to declare the variable prior to the loop.

Do local variables inside of a loop get garbage collected?

3 Answers3

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