Prototype Property in JavaScript

The prototype property allows us to add properties and methods to an object.

Please note that we are not talking about the Prototype JavaScript Framework  implemented in  prototype.js


Prototype Property and  Dynamic inheritance:


The functions in JavaScript are objects and prototype is one of is  property.
   

• You cause a class to inherit using ChildClassName.prototype = new ParentClass();.
• You need to remember to reset the constructor property for the class using ChildClassName.prototype.constructor=ChildClassName.
• You can call ancestor class methods which your child class has overridden using the Function.call() method.
• Javascript does not support protected methods.

 Eg.
 >>>var boo = function(){};>>>typeof boo.prototype
returns "object"


Prototypes can be augmented
>>> boo.prototype.a = 1;
>>> boo.prototype.sayAh = function(){};

Prototypes can be overwritten

>>> boo.prototype = {a: 1, b: 2};


How is the prototype used?

when a function is invoked as a constructor

var Person = function(name) {
  this.name = name;
};
Person.prototype.say = function() {
  return this.name;
}


>>> var dude = new Person('dude');
>>> dude.name;
"dude"
>>> dude.say();
"dude"


say() is a property of the prototype object
but it behaves as if it's a property of the dude object

Can we tell the difference? Own properties vs. prototype’s:

>>> dude.hasOwnProperty('name');
true
>>> dude.hasOwnProperty('say');
false


isPrototypeOf():

>>> Person.prototype.isPrototypeOf(dude);
true
>>> Object.prototype.isPrototypeOf(dude);
true

__proto__:

__proto__ is a secret link to the prototype The secret link is exposed in Firefox it does not exist in Internet Explorer,
__proto__ is not the same as prototype. __proto__ is a property of the instances, whereas prototype is a property of the constructor functions.

>>> dude.__proto__.hasOwnProperty('say')
true
>>> dude.prototype
??? // Trick question
>>> dude.__proto__.__proto__.hasOwnProperty('toString')
true

In Object oriented client side programming prototype property is highly used.Inheretence can be achieved by prototyping.