一.函数调用,此时this是全局的也就是window
  var c=function(){
   alert(this==window)
  }
  c()//true

二.方法调用
 var myObj={
  value:2,
  inc:function(num){
   alert(this.value+num);
  }
 }

myobject.inc(1); //结果3，因为this指向myObj

注意：内部匿名函数不属于当前对象的函数，因此this指向了全局对象window

var myObj={name:'myObject',value:0,increment:function(num){this.value += typeof(num) ==='number'? num:0;},toString:function(){return '[object:'+this.name+'{value:'+this.value+'}]';},getInfo:function(){return (function(){return this.toString();//内部匿名函数不属于当前对象的函数，因此this指向了全局对象window})();}}
alert(myObj.getInfo());//[object window];
点击看结果
解决方法：var myObj={name:'myObject',value:0,increment:function(num)   {this.value += typeof(num) ==='number' ? num : 0;},toString:function()   {return '[object:'+this.name+'{value:'+this.value+'}]';},getInfo:function(){var This=this;//先把当前的this指向存起来return (function(){ return This.toString();})();}}
alert(myObj.getInfo());//[Object:myObject {value:0}]点击看结果 

三.用new关键字来新建一个函数对象的调用,this指向被绑定到构造函数的实例上var fn = function (status){this.status = status;}fn.prototype.get_status = function(){return this.status;}var test = new fn('my status');alert(test.get_status);//my status,this指向test
四.apply/call调用function MyObject(name){this.name=name ||'MyObject';this.value=0;this.increment=function(num){this.value += typeof(num) === 'number' ? num : 0;};this.toString=function(){return '[Object:'+this.name+' {value:'+this.value+'}]';};this.target=this;}function getInfo(){return this.toString();}var myObj=new MyObject();alert(getInfo.apply(myObj));//[Object:MyObject {value:0}],this指向myObjalert(getInfo.apply(window));//[object Window],this指向window通过call和apply可以重新定义函数的执行环境，即this的指向，这对于一些应用当中是十分常用的。
点击看结果