[javascript]对象原型prototype用法大杂烩

function Box(){

this.test="test";

};

Box.prototype.username="jet";

Box.prototype.age=29;

Box.prototype.run=function(){

return this.username+this.age+"岁发大财";

};

var boxa=new Box();

var boxb=new Box();

//alert(boxa.run==boxb.run);                //指向相同

//alert(boxa.prototype);                    //无法访问 undefined

//alert(JSON.stringify(boxa.__proto__));    //指针指向Box prototype

//alert(boxa.__proto__.run());              //可运行

//alert(boxa.constructor);                  //构造函数本身Box

//alert(boxa.constructor.prototype.run());  

var boxc=new boxa.constructor;

//alert(boxc.run()); //可运行

//alert(boxc instanceof Box);   //true

boxa.username='chow';

//alert(boxa.username);  //就近原则，不读指针原型

delete boxa.username;  //删除实例属性，就读原型属性

//alert(boxa.username);  //删除实例属性，就读原型属性

//alert(boxa.hasOwnProperty("username"));   //判断是否存在指定的实例属性，如果上方执行了delete就返回false

//alert("username" in boxa);   //判断实例或者原型是否包含指定属性。无论实例还是原型有，都会返回true

//判断是否只有对象原型是否包含指定属性

function isproperty(object,username){

return !object.hasOwnProperty(username) && username in object;

}

//alert(isproperty(boxa,"username"));

//boxa.kk='kk';

//alert(isproperty(boxa,"kk"));

//prototype原型对象化

function Boxtwo(){};

Boxtwo.prototype={

username:"jet",

age:29,

run:function(){

return this.username+this.age+"岁发大财";

},

}

var Boxtwoa = new Boxtwo();

//alert(Boxtwoa.run()); 

//构造函数 + prototype原型混合使用

function Boxthree(username,age,doing){

this.username=username;

this.age=age;

this.doing=doing;

if(typeof Boxthree.prototype.run != "function"){ //判断是否初始化话原型

//alert("初始化原型");

Boxthree.prototype.run=function(){

return this.username+this.age+this.doing;

};

}

};

var Boxthreea = new Boxthree("jet",29,"岁发大财");

var Boxthreeb = new Boxthree("chou",30,"岁行大运");

var Boxthreec = new Boxthree("baby",5,"岁了，身体越来越棒！");

// alert(Boxthreea.run());

// alert(Boxthreeb.run());

// alert(Boxthreec.run());

//原型链继承

function Boxfour(){

this.username="jet"; 

this.age=29;

};

Boxfour.prototype.run=function(){

return this.username+this.age+"岁发大财";

};

function Boxfive(){};

Boxfive.prototype=new Boxfour();        //Boxfive原型继承了Boxfour的构造属性和原型属性

var Boxfivea = new Boxfive();

//alert(Boxfivea.username)              //jet  继承成功

//alert(Boxfivea.run())                 //正常运行

//alert(Boxfivea instanceof Boxfive);   //true

//alert(Boxfivea instanceof Boxfour);   //true

//对象冒充继承

function Boxsix(username,age){

this.username=username; 

this.age=age;

};

Boxsix.prototype.run=function(){

return this.username+this.age+"岁发大财";

};

function Boxseven(username,age){ 

Boxsix.call(this,username,age);

};

var Boxsevena = new Boxseven("jet",29);

//alert(Boxsevena.username);//jet              //构造属性继承成功

//alert(Boxsevena.run);//undefined             //对象原型prototype无法继承

//alert(Boxsevena instanceof Boxseven);        //true

//alert(Boxsevena instanceof Boxsix);          //false

 Boxseven.prototype=new Boxsix();              //使用原型链继承run + 上面的对象冒充继承实例属性，则可以正常运行

 var Boxsevenb = new Boxseven("jet",29);

// alert(Boxsevenb.run());                     //正常运行