Como crear clases y herencias en JS

formas.js

var Forma = function(){};
Forma.prototype = {
	getArea: function()
	{
		console.log('Get Area from Forma');
	}
};

var Cuadrado = function()
{
	var __super__ = Forma;
	__super__.apply(this);
	__super__ = null;
};

Cuadrado.prototype = new Forma();
Cuadrado.prototype = {
	getArea: function()
	{
		console.log('Get Area from Cuadrado');
	}
};

var Circulo = function()
{
	var __super__ = Forma;
	__super__.apply(this);
	__super__ = null;
};

Circulo.prototype = new Forma();
Circulo.prototype = {
	getArea: function()
	{
		console.log('Get Area from Circulo');
	}
};

var Triangulo = function()
{
	var __super__ = Forma;
	__super__.apply(this);
	__super__ = null;
};

Triangulo.prototype = new Forma();
Triangulo.prototype = {
	getArea: function()
	{
		console.log('Get Area from Triangulo');
	}
};

(new Forma()).getArea();
(new Cuadrado()).getArea();
(new Circulo()).getArea();
(new Triangulo()).getArea();