Object Oriented JavaScript: Polymorphism with examples

Again this is not the advance topic of JavaScript but it relies under Object Oriented JavaScript & polymorphism is one of the tenets of Object Oriented Programming (OOP), we all know what is Polymorphism from other languages (like C#, Java etc) but we always think when to use it, why to use it and how to this, and most of us are still in confusion that should we really use it? blah !!!.

JavaScript is dynamically typed language [a big issue to discuss], but for understanding purpose:

When: It is used when we want a function’s (let say function HOLA) interface to be flexible enough to accept different types or number of parameters. Also, based on changing parameters types or numbers, we might want the function HOLA to behave differently (morphism).

How: use case- Take the old example of Person & Employee, where all employees are people, but all people are not employees. Which is to say that people will be the super class, and employee the sub class. People may have ages and weights, but they do not have salaries. Employees are people so they will inherently have an age and weight, but also because they are employees they will have a salary.

Polymorphism takes advantage of inheritance in order to make this happen.

Lets jump into code samples: take the basic shapes things:

	var shape = function (){};
	shape.prototype.draw = function(){
		return "i am generic shape";
	}
	//circle
	var circle = function(){}
	circle.prototype = Object.create(shape.prototype);
	circle.prototype.draw= function(){
		return "i am a circle";
	}
	//triangle
	var triangle = function (){}
	triangle.prototype = Object.create(shape.prototype);
	triangle.prototype.draw= function(size){
		return "this is triangle";
	}
	//printing shapes
	var shapes = [new shape(), new circle(), new triangle(23)];
	shapes.forEach (function (shapeList){
		console.log(shapeList.draw());
	});

Stay tuned….