（2）基于原型的类继承

1 version 1

var Animal = function(){
        this.init(this,arguments);
    };

    //init
    Animal.prototype.init = function(color){
        this.color = color;
    };
    Animal.prototype.breath = function(){
        console.log("breath");
    };

    var Dog = function(){};
    Dog.prototype = new Animal();

    Dog.prototype.init("white");

    Dog.prototype.getColor = function(){
        console.log(this.color);
    };

    var dog = new Dog();
    dog.breath();//breath
    dog.getColor();//white

（1） Dog类继承Animal类，这种继承属于原型继承，那就是说Dog的原型里面拥有Animal类的实例

2 version 2 类库添加继承

var Class = function(parent){
        var klass = function(){
            this.init.apply(this,arguments);
        };
        if(parent){
            var subClass = function(){};
            subClass.prototype = parent.prototype;
            klass.prototype = new subClass();
        }
        //init
        klass.prototype.init = function(){};
        klass.fn = klass.prototype;
        klass.fn.parent = klass;
        //add class property
        klass.extend = function(obj){
            var extended = obj.extended;
            for(var i in obj){
                klass[i] = obj[i];
            }
            if(extended) extended(klass);
        };
        //add prototype property
        klass.include = function(obj){
            var included = obj.included;
            for(var i in obj){
                klass.fn[i] = obj[i];
            }
            if(included) included(klass);
        };
        return klass;
    };

    var Animal = new Class();

    Animal.include({
        breath:function(){
            console.log('breath');
        }
    });

    var Cat = new Class(Animal);
    var tommy = new Cat();
    tommy.breath();

可以仔细看这段代码

 if(parent){
            var subClass = function(){};
            subClass.prototype = parent.prototype;
            klass.prototype = new subClass();
        }

再次将Animal这个function传回去，新建一个局部的subClass的原型指向Animal的原型，再将klass的原型指向subClass的实例，防止了原型污染