Javascript, redefine unlimited number of setters with same function

Suppose you have an object:

var o = {
 a: 3
 b: 4
}

And you want to save or do something with it whenever a property of this object is changed. This is possible by defining special setters in javascript.

Observe first that means we will need two object: one to actually store the data, one to contain the special getters. (Is there an elegant way to avoid it?)

However, the annoying thing is that - if you read the above API page, setters have to be set by hand. Luckily, Object.defineProperty will help us redefine unlimited number of setters as follow:

var create_custom_setter = function(destination, source, custom_setter){
 destination = destination || {};
 for(var prop in source){

 if(typeof(source[prop]) === "object"){
 var sub_destination = create_custom_setter({}, source[prop]);
 destination[prop] = sub_destination;
 }else{

 // javascript scope problem:
 var maker_set = function(source, prop){
 return function(value) {
 source[prop] = value;
 custom_setter(value, prop, destination, custom_setter); 
 }
 }

 // default setter:
 var maker_get = function(source, prop){
 return function(){
 return source[prop];
 }
 } 

 Object.defineProperty(destination, prop, {
 set: maker_set(source, prop),
 get: maker_set(source, prop)
 });
 }
 }
 return destination;
 }

The, I can create a front-facing object of o like this with a custom global setter:

var front_facing = create_custom_setter({}, o, function(value, prop){ 
 console.log(prop + " has been set"); 
})