when to use prototypes

* For object creation optimization

Built-in prototype object is if you'll be duplicating an object multiple times that will share common functionality. By attaching methods to the prototype, you can save on duplicating methods being created per each new instance. But when you attach a method to the prototype, all instances will have access to those methods

* use prototypes if we need to declare a "non-static" method of the object.

var myObject = function () {

};

myObject.prototype.getA = function (){

  alert("A");

};

myObject.getB = function (){

  alert("B");

};

myObject.getB();  // This works fine

myObject.getA();  // Error!