Private, privileged and public accessors in Javascript

Definition of Javascript class with accessors mentioned in subject could be pretty easy:

 1 var TestClass = (function(){
 2
3     // parameterized constructor
 4     TestClass = function(message){
 5         // private field
 6         var message = message;
 7
8         // private function, can't be read by public prototype functions
 9         function readMessage(){
10             return message;
11         }
12
13         // privileged method, can access private fields and functions
14         // can be called by public prototypes methods
15         this.getMessage = function(){
16             return readMessage();
17         }
18     }
19
20     // public method
21     TestClass.prototype.displayMessage = function(){
22         return this.getMessage();
23     }
24
25     return TestClass;
26 })();

Usage of such class is following:

1 var test= new TestClass('test');
2 alert(test.displayMessage());