js-inheritance

function Animal() {
	this.name = 'I am a generic Animal';
}

function Cat() {
	this.name = 'Cat'
	this.sound = 'purr';
}

Cat.prototype = new Animal();

Animal.prototype.isAnimal = function() { return true; };

var fluffy = new Cat();
fluffy.name; // Cat
fluffy.sound; // purr
fluffy.isAnimal(); // true