fun_with_closure.js

// Define a class
AwesomeClass = function () {
  this.hello = function(param) {
    console.log("[base method] ", param);
    return param;
  };
};

// Create an instance
awesome_object = new AwesomeClass();

// Extend the hello method by using a closure
awesome_object.hello = (function(){
  var oldHello = new AwesomeClass().hello;
  return function(param){
    oldHello(param);
    console.log("[closure] I'm here !");
    return "[closure] param: " + param;
  };
})();