how to display name = "o_object"? Now the result is null why?

Question

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JavaScript

onload=function(){  
	 var o={
		name:"the o_object",
		 oo:{
			name:"zhuzhu",
			f1:function(){
				return function (){
					 return this.name;
				}
			}
		} 
	 };  
	 alert(o.oo.f1()());    
}

Posted 4-Oct-14 6:45am

snailPig

Updated 4-Oct-14 8:54am

Yvan Rodrigues

v2

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Sergey Alexandrovich Kryukov 4-Oct-14 15:30pm

Why doing such pointless tricks?
If f1 returned not the function but this.name, it would work.
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-10-04T09:34:00

This is because this.name is in the context of the function f1, but not in the function you returned from f1, which has different "this", the object which does not contain name property.

For example, compare:

JavaScript

o = {
   name: "the o_object", // irrelevant to the problem
   oo: {
      name: "zhuzhu",
      f1: function() {
         return this.name;
      }
   } 
}; 
alert(o.oo.f1()); //will show "zhuzhu"

[EDIT #1]

Now, let's figure out what is that "different this" used in return statement in f1. This is the function object f1 itself. To check it up, let's give it a property to identify it, and call this property innerName. Then out check-up will show the value of this property:

C#

o = {
   name:"the o_object",  // irrelevant to the problem
      oo: {
         name: "zhuzhu",
         f1: function(){
            innerName = "function itself";
            return function () {
                return this.innerName;
            }
         }
      } 
   };
alert(o.oo.f1()()); // will show "function itself"

[EDIT #2]

By the way, the second case presents the interesting example of closure, a very important concept in programming. Please see: http://en.wikipedia.org/wiki/Closure[^].

—SA