CODEWITHSUNDEEP
javascriptclosures
SkinnyG33k
SkinnyG33k

Reputation: 1731

Why does this closure return function?

While watching Learning to Love JavaScript, I got hung up on why this 2nd version wouldn't work. It just returns 'function'. Is a closure not allowed to have a variable directly assigned to it? 

function getCtr() {
    var i = 0;
    return function() {
        console.log(++i);
    }
}
var ctr = getCtr();
ctr();
ctr();
ctr();
/* console
1
2
3
*/
/*--------------------------------------
 *   This doesn't work
 */
var ctr = function() {
    var i = 0;
    return function() {
        console.log(++i);
    }
}
ctr();
ctr();
ctr();
/*   console
 *   => [Function]
 */

Video Link http://youtu.be/seX7jYI96GE?t=11m12s

Upvotes: 0

Views: 81

Answers (2)

Pointy
Pointy

Reputation: 413712

It prints that because the function does return a function.

Try

ctr()();

The two forms of function declaration you used have almost exactly the same effect. Both simply create a function and bind it to a symbol. All you really changed in the second version is the name involved ("ctr" instead of "getCtr").

That is, if your test had been like the first setup:

var actualCtr = ctr();

actualCtr();
actualCtr();
actualCtr();

you'll see that it really is the same.

Upvotes: 4

Ned Batchelder
Ned Batchelder

Reputation: 375564

In your first version, you define a function getCtr. Then you invoke getCtr, keeping the result as ctr. Then you invoke ctr repeatedly. You are calling the result of calling a function.

In the second version, you define ctr as your first function, then you invoke it repeatedly. You aren't invoking the result of invoking the function.

Here's a version of your second code that works:

var ctr = (function() {
        var i = 0;
        return function() {
            console.log(++i);
        }
    })();
ctr();
ctr();
ctr();

Upvotes: 1

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