说出this的三个应用

1.this是javascript中的一个关键字，它代表函数运行时，自动生成的一个内部对象，只能在函数内部使用。 2.随着函数使用场合的不同，this的值会发生变化，但是有一个原则，就是this指的是调用函数的那个对象。 3.this分类 1）纯粹的函数调用 这时的this指向window。（函数没有所属对象：指向全局对象） eg: var x=1; function test(){ alert(this.x); } test();

 2)作为对象方法的调用 这时的this指向上级对象。（函数有所属对象时：指向所属对象） eg: function test(){ alert(this.x) } var o={}; o.x=1; o.m=test; o.m(); 3)作为构造函数调用 构造函数，就是通过这个函数生成一个新对象。这时的this指向这个新对象。（构造器中的 this：指向新对象） eg: function test(){ this.x=1; } var o=new test(); alert(o.x);

 var x=2; function test(){ this.x=1; } var o=new test(); alert(x);

 function foo(){return this.a}; var a=2; var o={a:3,foo:foo}; var p={a:4}; console.log(o.foo()); p.foo=o.foo; console.log(p.foo()); console.log(foo());

 4)apply或者call的调用 是改变函数对象的一个方法，作用是改变函数的调用对象。 eg: var x=0; function test(){ alert(this.x); } var o={}; o.x=1; o.m=test; o.m(); o.m.apply();

例题

//1 var point={     x:0,     y:0,     moveTo:function(x,y){         this.x=this.x+x;             this.y=this.y+y;             alert(this.x);    //1          alert(this.y);  //1     } } point.moveTo(1,1);

 //2    var myObject = {value: 100};    myObject.getValue = function () {        console.log(this.value);        console.log(this);        return this.value;    };    console.log(myObject.getValue());   // 100 object{value: 100} 100 

 //3    var myObject = {value: 100};    myObject.getValue = function () {        var foo = function () {            console.log(this.value);            console.log(this);        };        foo();        return this.value;    };    console.log(myObject.getValue());  //undefined window 100

 //4    var SomeClass = function(){        this.value = 100;    }    var myCreate = new SomeClass();    console.log(myCreate.value);     //100

 //5    var myObject = {value: 100};    var foo = function(){        console.log(this);    };    foo();          //window    foo.apply(myObject);  //object{value: 100}    foo.call(myObject);   //object{value: 100}

 //6var name = "clever coder";var person = {    name : "foocoder",    hello : function(sth){        var sayhello = function(sth) {            console.log(this.name + " says " + sth);        };        sayhello(sth);    }}person.hello("hello world");  //clever coder says hello world

 //7var name = "clever coder";var person = {    name : "foocoder",    hello : function(sth){        var that = this;        var sayhello = function(sth) {            console.log(that.name + " says " + sth);        };        sayhello(sth);    }}person.hello("hello world");  ////foocoder says hello world

//1 var point={     x:0,     y:0,     moveTo:function(x,y){         this.x=this.x+x;         this.y=this.y+y;         console.log(this.x);         console.log(this.y);     } }; point.moveTo(1,1);  //1 1

//2   var myObject = {value: 100};   myObject.getValue = function () {       console.log(this.value);       console.log(this);       return this.value;   };   console.log(myObject.getValue());  //100 object 100

//3   var myObject = {value: 100};   myObject.getValue = function () {       var foo = function () {           console.log(this.value);           console.log(this);       };       foo();       return this.value;   };   console.log(myObject.getValue());//undefined window 100

//4   var SomeClass = function(){       this.value = 100;   }   var myCreate = new SomeClass();   console.log(myCreate.value);  //100

//5   var myObject = {value: 100};   var foo = function(){       console.log(this);   };   foo();   //window   foo.apply(myObject);//Object   foo.call(myObject); //Object

 //6var name = "clever coder";var person = {    name : "foocoder",    hello : function(sth){        var sayhello = function(sth) {            console.log(this.name + " says " + sth);        };        sayhello(sth);    }}person.hello("hello world");  //clever coder says hello world

 //7var name = "clever coder";var person = {    name : "foocoder",    hello : function(sth){        var that = this;        var sayhello = function(sth) {            console.log(that.name + " says " + sth);        };        sayhello(sth);    }}person.hello("hello world");  //foocoder says hello world

//8var name="window";var Bob={    name:"Bob",    showName:function(){        alert(this.name);    }};var Tom={    name:"Tom",    showName:function(){        var fun=Bob.showName;        fun();    }}Tom.showName();  //window

//9var name="Bob";var nameObj={    name:"Tom",    showName:function(){        alert(this.name);    },    waitShowName:function(){        !function(__callback){            __callback();        }(this.showName);    }}nameObj.waitShowName(); //Bob

 var name="Bob"; var nameObj={     name:"Tom",     showName:function(){         alert(this.name);     },     waitShowName:function(){         var that=this;         setTimeout(function(){             that.showName();         },1000);     } };nameObj.waitShowName(); //Tom