构造函数

var obj1={
        name:‘xxx‘,
        age:‘xxx‘,
        sad:function(){}
    }

var obj2=new Object();
    obj2.name=‘xxx‘;
    obj2.age=20;
    obj2.say=function(){}

//构造函数Dog()
    function Dog(){
        this.name=‘xxxx‘;
        this.age=10;
        this.sad=function(){console.log(this.age)}
    }
    var dog1=new Dog();
    dog1.age=20;
    dog1.sad();//20
    //1 new操作符 :的内部原理
        1：创建一个空对象
        2：把this指向到这个空对象
        3：把空对象的内部原型指向构造函数的原型对象
        4：当前构造函数执行完成后，如果没有return的话，就会把当前的空对象返回，一般都没有return
    //1 new操作符原理：执行的时候类似在构造函数Dog()内部，过程可以如下去理解，实际不是！！
    function Dog(){
        var tt={};
        this=tt;
        tt.__proto__=Dog.prototype;
        this.name=‘xxxx‘;
        this.age=10;
        this.sad=function(){...}
        return tt;
    }
    //prototype只有函数才有的原型
    //__proto__所有的对象都有的
    dog1.__proto__===Dog.prototype;//true
    dog1.prototype===Dog.prototype;//false

function Dog(usename,age){
        this.name=usename;
        this.age=age;
        this.sad=function(){console.log(this.age)}
    }
    Dog.prototype.speak=function(){
        console.log(‘I am ‘+this.name+‘ ‘+‘今年 :‘+this.age);
    }
    var dog1=new Dog(‘dog1‘,20);
    var dog2=new Dog(‘dog2‘,100);
    dog1.sad();
    dog2.sad();

    dog1.speak();
    dog2.speak();

function Dog(option){
        this.name=option.name;
        this.age=option.age;
        this.sad=function(){console.log(this.age)}
    }
    Dog.prototype.speak=function(){
        console.log(‘I am ‘+this.name+‘ ‘+‘今年 :‘+this.age);
    }
    var dog1=new Dog({name:‘dog1‘,age:20});
    var dog2=new Dog({name:‘dog2‘,age:100});

    dog1.sad();
    dog2.sad();

    dog1.speak();
    dog2.speak();

function Dog(option){
        this.init(option);
    }
    //重新设定原型
    Dog.prototype={
        init:function(option){
            this.age=option.age||‘‘;
            this.name=option.name||‘‘;
            this.sad=function(){
                console.log(this.age);
            }
        },
        speak:function(){
            console.log(‘I am ‘+this.name+‘ ‘+‘今年 :‘+this.age);
        }
    }

    var dog1=new Dog({name:‘dog1‘,age:20});
    var dog2=new Dog({name:‘dog2‘,age:100});

    dog1.sad();
    dog2.sad();

    dog1.speak();
    dog2.speak();