Question

Can someone explain why the private variable, _a, isn’t being updated with the setter? I must be missing something really obvious but can’t see it.

var f = function(a){
   var _a = a;

   return {
       getA : _a,
       setA : function(e){
          _a = e;
       }
   }        
};    

var d = f(1);
console.log(d.getA); // 1

d.setA(2);
console.log(d.getA); // 1

I thought that the second call should return 2

code here – http://jsfiddle.net/JUKWN/

Answer 1

For the second call to work, you need this:

var f = function(a){
   var _a = a;

   return {
       getA : function() {
           return(_a);
       },
       setA : function(e){
          _a = e;
       }
   }        
}; 

Your code is putting a static representation of the value of _a into the data structure that it’s returning, not dynamically getting it’s value from the actual source. You need a getter function in order to dynamically get it’s value for all data types. What you had would actually work if _a had an array or object in it (because they are always by reference), but not when it’s a simple type like a number or string (which is not by reference).

The code I’ve suggested will work for all values of _a.