SOURCE

var Animal = function(name) {
    this.name = name;
};
Animal.prototype = {
    getName: function() {
        return this.name;
    }
};
var Cat = function(name) {
    this.name = name;
    // 继承构造函数父类中的属性和方法
    // Animal.call(this, name);
};
function extends(sub, sup) {
	var F = function() {};
    F.prototype = sup.prototype;
	sub.prototype = new F();
    sub.prototype.constructor = sub;
    sub.sup = sup.prototype;
    if(sup.prototype.constructor === Object.prototype.constructor) {
        // 检测超类原型的构造器是否为原型自身
        sup.prototype.constructor = sup;
    }
};