Prototype in JavaScript. Blog post: http://www.miguelmota.com/blog/understanding-prototype-in-javascript

prototype-demo.js

//----------------------------------
// Prototype Demo
// ---------------------------------

// Define functional object constructor called Quadrilateral
// with width and height as parameters.
var Quadrilateral = function(width, height) {
	this.width = width;
	this.height = height;

	return this;
}

// Define method to return width.
Quadrilateral.prototype.getWidth = function() {
	return this.width;
}

// Define new object of type Quadrilateral.
var mysquare = new Quadrilateral(4,4);

// Call the getWidth method.
console.log(mysquare.getWidth()); // returns 4

// Define method to set dimensions.
Quadrilateral.prototype.setDimensions = function(width, height) {
	this.width = width;
	this.height = height;

	return this;
}

// Set the dimensions of mysquare.
mysquare.setDimensions(7,7);

// Output mysquare width.
console.log(mysquare.getWidth()); // returns 7

// Define functional object constructor called Rectangle
// with width and height as parameters.
var Rectangle = function(width, height){
	this.width = width;
	this.height = height;

	return this;
};

// Inherit methods and properties from Quadrilateral object.
Rectangle.prototype = new Quadrilateral();

// Define new object of type Rectangle.
var myrectangle = new Rectangle(6,2);

// Output myrectangle width.
console.log(myrectangle.getWidth()); // returns 6

// Test Quadrilateral and Rectangle method properties
console.log(Quadrilateral.prototype.hasOwnProperty('getWidth')); // returns true
console.log(Rectangle.prototype.hasOwnProperty('getWidth')); // returns false

// Test mysquare inheritance
console.log(mysquare instanceof Quadrilateral); // returns true
console.log(mysquare instanceof Rectangle); //return false

// Test myrectangle inheritance
console.log(myrectangle instanceof Quadrilateral); // returns true
console.log(myrectangle instanceof Rectangle); //return true

// Test inheritance from global Object object
console.log(Quadrilateral instanceof Object); // returns true
console.log(Rectangle instanceof Object); //return true
console.log(mysquare instanceof Object); // returns true
console.log(myrectangle instanceof Object); //return true

// Check if a global method exists, if not create our own
if (!Array.prototype.forEach) {
  Array.prototype.forEach = function(fn, scope) {
    for(var i = 0, len = this.length; i < len; ++i) {
      fn.call(scope, this[i], i, this);
    }
  }
}

//EOF