Why are helper methods frequently used in Javascript?

Question

New to Javascript, reading Crockford's Javascript: The Good Parts (among other things)

In the 4th chapter regarding functions Crockford is showing how to preserve this in the outer function for use in inner functions, which I understand.

My question is, in his example code and a ton more like it, why use this helper function:

myObject.double = function() {
  var that = this; 

  var helper = function () {
      that.value = add(that.value, that.value);
  }
  helper();
};

Is it maybe because add() is sitting out in global scope, while value is in myObject, so I need to copy this (myObject) then transfer to global where I can grab add()?

Otherwise I'm not sure why I need the helper function?

Answer 1

In that section of the book he is demonstrating that it is conventional to use that when accessing the this object of a function's parent.

It is not necessary to use a helper function do do what the code does. It is just an example to illustrate how to get around scoping issues with the this object.

Answer 2

Encapsulation. The helper() in your example only exist in the scope of myObject.double() it won't be available / visible outside of it. I believe that it is called private method instead of "helper" function.