Example how to define a javascript class

closure_example.js

// a sample class decleration showing javascript closure examples.
// Keep in mind: prototyped properties affect all objects of the 
// same constructor, simultaneously, even if they already exist.
function Knight(hp){  
  // public attribute of Knight
  this.hp = hp; 
  
  // private attribute of Knight
  var secreteHP = hp+1;
  
  // Privileged method: may access private members but is public accessible
  // notice that it is not possible to extend a class (ignoring eval() magic)
  // by a priviliged method
  this.getSecreteHP = function() {
    return "I have " + secreteHP.toString() + " secrete HP";
  }
} 
 
// this is a public method which cannot access any private member of Knight instances.
// Note that using this kind of syntax allows a user to extend the class Knight
// with additional public members (i.e. methods or attributes)
// keep in mind that a public method only can access public members of its corresponding class
Knight.prototype.getHP = function(){ 
  return "I have " + this.hp.toString() + " secrete HP";
}; 

// this means, that a method invocation from a Knight instance, 
// defined using prototypes, e.g.:
/*
Knight.prototype.getIdPr = function(){ 
  return "I have " + secreteHP.toString() + " secrete HP";
}; 
*/
// does not work, since we cannot call secreteHP from a prototype's scope, 
// since it is a private attribute.

knight = new Knight(100);

knight.getHP();
>> "I have 100 secrete HP"

knight.getSecreteHP();
>> "I have 101 secrete HP"