Function inside function vs function returns function in JavaScript

Question

I am studying JavaScript and I can't understand this.

function Out1()
{
    function In1()
        {
            console.log("text inside function In1");
        }
    return In1();
}


function Out2()
{
    return function In2()
        {
            console.log("text inside function In2");
        };
}

Out1();    // text inside function In1
Out2();    //

Out2(); outputs nothing in console. What I am doing wrong?

Out2 returns an anonymous function which needs execution to produce your expected output. Out2()() would do that. — Linus Kleen
– Linus Kleen, Commented Mar 5, 2015 at 15:03

T.J. Crowder · Accepted Answer · 2015-03-05 15:06:10Z

1

Out2(); outputs nothing in console. What I am doing wrong?

Out2 returns a reference to the function it created. It doesn't call that function. You could call it by using () on the returned reference:

//  vv-------- These call `Out2`   
Out2()();
//    ^^------ These call the function referenced returned by `Out2`

E.g.:

var f = Out2(); // `f` is now a reference to the `In2` function
f();            // This calls `In2`

answered Mar 5, 2015 at 15:06

T.J. Crowder

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1 Comment

Jonas Over a year ago

Thanks T.J Crowder. In fact, you answered 2 questions at once. First one was the title one, and the second one (I hope I am not wrong) the need of the () after the variable that makes a closure to obtain the return.

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