JavaScript Closure

Question

I have a simple question about Javascript Closures:

The following function is given:

function outside() {
  var out = 0;
    function inside() {
    out +=1;
    }
  return inside;
} 

var ref = outside();
ref();  
ref();

If I call the function 2 times, out is equal to 2.

Why is out not overwritten by the statement?

var out = 0;

I think the best way to understand it is to experience it. Make a test page (or fiddle) with this code, then go through it, step by step, using your browser's debugger. — Volune, Aug 16 '14 at 22:12

score 1 · Accepted Answer · answered Aug 16 '14 at 22:11

1

The statement var out = 0 is not inside the function returned from outside(). It only runs when you call outside() not when you call ref() (which is the same as inside()).

answered Aug 16 '14 at 22:11

Quentin

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thanks, i totally missed the return statement of outside() – AndyB Aug 16 '14 at 22:20

score 1 · Answer 2 · answered Aug 16 '14 at 22:16

1

outside() returns inside. So ref = inside. When you call ref(), it's like calling inside().

inside has the scope of outside, which contains out. When you call ref(), it increments the out property on the single scope of outside.

answered Aug 16 '14 at 22:16

Tucker Connelly

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JavaScript Closure

2 Answers2