The pointing meaning of this object

1. In the function:

function foo（）{
   return this;
}

Whoever calls the function points to it; the direct call points to the window;

2. In the event: in the html event, point to the window; in the dom0 event, point to the trigger of the event (the node of the bound element); in the dom2 event, point to the bound element node in non-IE; in IE, point directly to the window;

3. In closure: this points to window;

4. In object: this points to current object; if there are multiple levels of object wrapping , refers to the upper-level object;
(1).

var foo = {
         a:18,
        num:{
         a:10,
           num:function(){
          console.log(this.a);//10
                   }
               }
       }
  foo.num.num();

(2).

var foo = {
        a:18,
         num:{
         num:function(){
         console.log(this.a);//undefined
                   }
               }
       }
  foo.num.num();

5. The call function and the apply function can change the point of this, and the bind function can also change the function point;

6. Constructor module:

Summary : In the constructor, if the return value is a basic data type, then this points to the instance of the constructor; if the return value is an object, then this points to the object;

 function Foo(){           
     this.user = 'my';           
     return {};       
     }       
     var na = new Foo();       
     console.log(na.user);//返回值undefined;
 function Foo(){           
     this.user = 'my';           
     return 1;      
      }       
      var na = new Foo();       
      console.log(na.user);//返回值my

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