Add inheritance to JavaScript

addInheritance.js

(function ()
{
	if (!Function.prototype.inherit)
	{
		Function.prototype.inherit = function (p_parent)
		{
			if (p_parent.constructor == Function)
			{
				// Normal Inheritance
				this.prototype = new p_parent();
				this.prototype.constructor = this;
				this.prototype.supr = p_parent.prototype;
			}
			else
			{
				// Virtual Inheritance
				this.prototype = p_parent;
				this.prototype.constructor = this;
				this.prototype.supr = p_parent;
			}
			return this;
		}
	}
	
	if (!Object.prototype.inherit)
	{
		Object.prototype.inherit = function ()
		{
			if (arguments.length > 0)
			{
				this.supr.constructor.apply(this, arguments);
			}
			else
			{
				this.supr.constructor.call(this);
			}
		}
	}
})()

/*
Usage:
function Mammal(p_speech)
{
	Mammal.prototype.speak = function (p_phrase)
	{
		if (p_phrase)
		{
			console.log(p_phrase);
		}
	}

	this.speak(p_speech);
}

function Dog()
{
	this.inherit("I'm a dog!");
	this.speak("Woof woof!");
}
Dog.inherit(Mammal);

function Cat()
{
	Cat.prototype.speak = function ()
	{
		console.log("Augmenting the ancestor's speak function!");
		
		this.supr.speak.apply(this, arguments);
	}
	
	this.inherit("I'm a cat!");
	this.speak("Meow!");
}
Cat.inherit(Mammal);

new Dog();
new Cat();

Output:
I'm a dog!
Woof woof!
Augmenting the ancestor's speak function!
I'm a cat!
Augmenting the ancestor's speak function!
Meow!
*/