Returning Value From JS Closures

I am currently trying to understand closures but there is something which I don’t seem to get no matter how many videos or forum posts I check.

As an example, here is a simple closure with a parentFunction and a childFunction:

function parentFunction(a, b) {
    function childFunction() {
        return a + b;
    }
    return childFunction;
}

What I don’t understand is why is it necessary to assign the parentFunction to a variable and call it if I want the value returned from the childFunction:

let test = parentFunction(1, 2)

console.log(test());

If I called the parent function directly, shouldn’t it have the same outcome? For example:

console.log(parentFunction(1, 2));

Isn’t it the same as assigning it to the variable first but with an extra step? Is it just because of the syntax being that way and that’s it?

>Solution :

When you put it into a variable first, you’re also invoking it when logging the result.

let test = parentFunction(1, 2)
console.log(test());
//              ^^

Substituting in parentFunction(1, 2) and removing the test variable entirely would be equivalent

console.log(test                ()); // before
console.log(parentFunction(1, 2)()); // after

But your second version lacks the () at the end, which is why it’s not the same.

console.log(parentFunction(1, 2)()); // after
//                              ^^ your second version lacks this

parentFunction returns a function. You must call the function to get the resulting number from it, otherwise you have just the function.