Function with multiple nested functions returned

Question

I'm new to javascript and I have a trouble to understand the following javascript code. So is it possible for you guys to shed me the light on what is the purpose of having multiple functions nested inside the return. What is it for, why we need it and when we should use it.

Many thanks in advance

function create() {
   var counter = 0;
   return {
      increment: function() {
         counter++;
      },

      print: function() {
         console.log(counter);
      }
   }
}
var c = create();
c.increment();
c.print();

Err. The functions do different things, so there are more than one of them. And its an *object* holding multiple functions that is returned. — Quentin, May 18 '15 at 09:52
this separates public and private api - eg. counter is private, and the returned api is public — amdixon, May 18 '15 at 09:53
Reading some books/tutorials about not-easy parts of JavaScript will help to understand. — Regent, May 18 '15 at 09:54
@guruvn nope, I can not (I actually didn't read any books about JS), but Google can suggest many books, and some of them are supposed to be good ones. — Regent, May 18 '15 at 10:04

score 0 · Accepted Answer · edited May 23 '17 at 12:30

To understand this you need to understand two key concepts:

In JavaScript functions are first class objects
closures.

The create function returns an object that has two fields who's values are actually functions and that both have a closure that contains the counter variable. So the c variable is assigned an object (which is created by the create function) and that object has two functions that you can simply call that both reference the same counter variable.

Function with multiple nested functions returned

1 Answers1