Closures in JavaScript!

Question

Hey, so I was working on a coding challenge, and part of the challenge required that I understand how to properly use closures.  I read through an MDN article here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Closures and it was helpful, but I don't really understand why my code works. 
Here is my closures function that I could use some help in understanding why it works. The part that I don't get is the way the second number is added to the end of addTogether(2)(9). 
```JavaScript
function addTogether() {
  var args = Array.prototype.slice.call(arguments);
  var isNumb = function Numb(args) {
    for (i = 0; i < args.length; i ++) {
      if (!Number.isInteger(args[i])) {
        return undefined;
      }
    }
    return true;
  };    
  var addNew = function(x) {
    return function(y) {
      if (!Number.isInteger(y)) {
        return undefined;
      }
      return x + y;
    };
  }; 
  var addTwo = function(a,b) {
    return a + b;
  };
  if (!isNumb(args)) {
    return;
  } else if (args.length === 1) {
      return addNew(args[0]);
  } else if (args.length > 1) {      
      return addTwo(args[0], args[1]);
  }   
}
addTogether(2)(3);
```

Steven Parker · Accepted Answer

This is a function that is returned by another function being called.
It looks odd, but think about it in  steps:
- the function addTogether is called and given the argument 2
- it returns another function (the anonymous one inside addNew)
- then that returned function is called and given the argument 9
Make sense now?

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Trevor Johnson

Trevor Johnson

Closures in JavaScript!

1 Answer

Steven Parker

Steven Parker

This is a function that is returned by another function being called.