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You can modify classes after they have been defined and objects after they have been instantiated.

The above statement may seems strange to classic OOPs programmers. But JavaScript is prototype based language.

/* Class Person. */
function Person(name, age) { = name;
   this.age = age;
Person.prototype = {
   getName: function() {
 getAge: function() {
   return this.age;
/* Instantiate the class. */
var raja = new Person('Raja', 36);
var vinoj = new Person('Vinoj', 26);

/* Modify the class. */
Person.prototype.getGreeting = function() {
   return this.getName();
/* Modify a specific instance. */
raja.displayGreeting = function() {

/* Now raja alone have method displayGreetings */

In this example, the getGreetingmethod is added to the class after the two instances are created, but these two instances still get the method, due to the way the prototype object works. raja also gets the displayGreetingmethod, but no other instance does.


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