How JS Prototype works

JS Prototyping

//See more here: http://stackoverflow.com/questions/572897/how-does-javascript-prototype-work

//Define a functional object to hold persons in JavaScript
var Person = function(name) {
    this.name = name;
};

//Add dynamically to the already defined object a new getter
Person.prototype.getName = function() {
    return this.name;
};

//Create a new object of type Person
var john = new Person("John");

//Try the getter
alert(john.getName());

//If now I modify person, also John gets the updates
Person.prototype.sayMyName = function() {
    alert('Hello, my name is ' + this.getName());
};

//Call the new method on john
john.sayMyName();

//Until now I've been extending the base object, now I create another object and then inheriting from Person.

//Create a new object of type Customer by defining its constructor. It's not 
//related to Person for now.
var Customer = function(name) {
    this.name = name;
};

//Now I link the objects and to do so, we link the prototype of Customer to 
//a new instance of Person. The prototype is the base that will be used to 
//construct all new instances and also, will modify dynamically all already 
//constructed objects because in JavaScript objects retain a pointer to the 
//prototype
Customer.prototype = new Person();     

//Now I can call the methods of Person on the Customer, let's try, first 
//I need to create a Customer.
var myCustomer = new Customer('Dream Inc.');
myCustomer.sayMyName();

//If I add new methods to Person, they will be added to Customer, but if I
//add new methods to Customer they won't be added to Person. Example:
Customer.prototype.setAmountDue = function(amountDue) {
    this.amountDue = amountDue;
};

Customer.prototype.getAmountDue = function() {
    return this.amountDue;
};

//Let's try:       
myCustomer.setAmountDue(2000);
alert(myCustomer.getAmountDue());

//While as said I can't call setAmountDue(), getAmountDue() on a Person.

//The following statement generates an error.
john.setAmountDue(1000);