javascript实现继承

function Mammal(name) {
		this.name = name;
		this.offspring = [];
	}
	Mammal.prototype.haveABaby = function() {
		var newBaby = new Mammal('Baby ' + this.name);
		this.offspring.push(newBaby);
		return newBaby;
	}

	Mammal.prototype.toString = function() {return '[Mammal "' + this.name + '"]';}

	Cat.prototype = new Mammal();
	Cat.prototype.constructor = Cat;
	function Cat(name) {this.name = name;}
	Cat.prototype.toString = function() {
		return '[Cat " ' + this.name + '"]';
	}

	var someAnimal = new Mammal('Mr. Biggles');

	var myPet = new Cat('Felix');

	myPet.haveABaby();