setTimeout()里的this

 1 window.id=‘windowid‘;
 2 function M(){
 3     this.id=‘Mid‘;
 4     this.f1=function(){console.log(this.id);}; 
 5     this.f2=function(){
 6         var that=this;
 7         setTimeout(that.f1,5000);
 8         };
 9 }  
10 var m=new M(); 
11 m.f2();        //‘windowid‘    

window.id=‘windowid‘;
function M(){
    this.id=‘Mid‘;
    this.f1=function(){console.log(this.id);}; 
    this.f2=function(){
        setTimeout(this.f1,5000);
        };
}  
var m=new M(); 
m.f2();        //‘windowid‘

window.id=‘windowid‘;
function M(){
    this.id=‘Mid‘;
    this.f1=function(){console.log(this.id);}; 
    this.f2=function(){
        setTimeout(function(){this.f1();},5000);
        };
}  
var m=new M(); 
m.f2();        //Error: undefined is not a function 

 1 window.id=‘windowid‘;
 2 function M(){
 3     this.id=‘Mid‘;
 4     this.f1=function(){console.log(this.id);}; 
 5     this.f2=function(){
 6         var that=this;
 7         setTimeout(function(){that.f1();},5000);
 8         };
 9 }  
10 var m=new M(); 
11 m.f2();        //‘Mid‘