Nested functions in closure not being called properly in Javascript

Question

I am new to Javascript and learning about closures and nested scope.

The prompt asks for this: Write a function that has three nested functions, each taking one number as an argument. The inner-most function should return the sum of all three numbers.

This is what I have come up:

var outMost = function (num1) {
var x = num1;
var innerMost = function (num2) {
    var y = num2;
    var innerInnerMost = function (num3) {
        console.log(x + y + num3);
    }
    return innerInnerMost;
}
return innerMost;
}

var firstNum = outMost(1);
firstNum(2);
firstNum((3));

Please help me understand what I am doing wrong -- I have gone on numerous website to learn about closures and scope but nothing seems to explain it well. Thank you for the help.

Notice that the x and y variables are not necessary, the num1 and num2 named parameters are variables in the same scopes that you could simply use directly for the sum. — Bergi
– Bergi, Commented Sep 21, 2014 at 19:27

Harry Pehkonen · Accepted Answer · 2014-09-21 19:24:10Z

1

When you call firstNum(2), you are not catching the return-value (which is a function). If I run your code in Node.js REPL, here is what it looks like:

> var firstNum = outMost(1);
undefined
> firstNum(2);
[Function]
> firstNum((3));
[Function]

Try this in the end instead:

var firstNum = outMost(1);
var secondNum = firstNum(2);
secondNum(3);

Here is what it looks like in Node.js REPL:

> var firstNum = outMost(1);
undefined
> var secondNum = firstNum(2);
undefined
> secondNum(3);
6
undefined

Please note that assignment evaluates to undefined. Also, since innerInnerMost doesn't return anything, there is an implicit return undefined in the end.

edited Sep 21, 2014 at 19:24

answered Sep 21, 2014 at 19:15

Harry Pehkonen

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2 Comments

rahul2001 Over a year ago

Thank you very much Harry -- makes more sense now.

rahul2001 Over a year ago

I did, can you please give my question a couple points. Thank you.

NSNoob · Accepted Answer · 2016-06-09 09:41:44Z

0

function firstFunc(x){
    return function secondFunc(y){
            return function thirdFunc(z){
                    console.log(x+y+z);
                }
        }
}

Calling:

var ff = firstFunc(1);

var sf = ff(2);

sf(3);

edited Jun 9, 2016 at 9:41

NSNoob

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answered Jun 9, 2016 at 9:10

Dhiraj Gophane

1

Comments

MEAbid · Accepted Answer · 2016-10-13 11:57:27Z

very easy look at this example

if you have this type in ES6

  let f = () => {
  return () => {
    console.log('First function called');
    return () => {
      console.log('Second function called');
    }
  }
}

you have two way to call every function, first of all, I want to call the First function in this way f()() and then I want to call the Second function f()()(). First of all, you will be seeing in console

First function called

and then

Second function called

and another way you can use this technic

let f1 = f();
let f2 = f1();

you will be seeing

First function called

if you want to the second function call

let f1 = f();
let f2 = f1();
let f3 = f2();

and then you will be seeing

Second function called

if you want to change this code to ES5

var f = function() {
  return function() {
    console.log('First function');
    return function(){
      console.log('Second function');
    }
  }
}

two way of call

var f1 = f();
var f2 = f1();
var f3 = f2();

f()()();

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