What is happening in this closure?

Question

function makeMultiplier(x){
        return function(y) {
            return x * y;
    }
}

var by10 = makeMultiplier(10);
console.log(by10(7));

How is it possible to pass in two parameters when make multiplier only accepts one? I'm unsure as to how this syntax is working.

@Pointy: I assume he's talking about how you can call the result of `makeMultiplier()`. — Matt, Jul 07 '14 at 14:54
This question has absolutely nothing to do with [tag:jquery]!!! — Bergi, Jul 07 '14 at 14:57
possible duplicate of [Can someone explain this Javascript closure example](http://stackoverflow.com/q/23915510/1048572) or [Returning functions in javascript, understanding scope & closures](http://stackoverflow.com/q/8487768/1048572)? — Bergi, Jul 07 '14 at 15:00

score 5 · Accepted Answer · edited May 23 '17 at 10:26

How is it possible to pass in two parameters when make multiplier only accepts one?

Because makeMultiplier() returns a function.

function makeMultiplier(x){
    return function(y) {
        return x * y;
    }
}

var by10 = makeMultiplier(10); // by10 is now function (y) { return x * y }, with x bound to 10.
console.log(by10(7)); // So now we can call it like a function.

I've coincidentally answered this question as well today about functions returning functions. It might help.

What is happening in this closure?

1 Answers1