Why is there a double bracket for function expression?

Question

JavaScript

Tell me why this code to execute alert ( Jsfiddle ):

var newclass = new Classname();
newclass.method.init();

function Classname () {
    this.method = function () {
        return {
            init: function () {
                alert();
            }
        }
    }()
}

And this code does not execute alert ( Jsfiddle ):

var newclass = new Classname();
newclass.method.init();

function Classname () {
    this.method = function () {
        return {
            init: function () {
                alert();
            }
        }
    }
}

Answer 1

In the first case, it this.methodwill be the result of executing the function:

{
  init: function () {
    alert();
  }
}

And in the second - the function itself.

Answer 2

Look in the console, there will be a hint.
In the first case, the function will be executed immediately and the object will get into this.method. The second will contain a function that must first be called jsfiddle.net/G3ybH/3

Answer 3

In the first case, encapsulation, in the second, no, in the second, init() must be called forcibly;