actual-asynchronous.js

var EventEmitter = require('events').EventEmitter;

EventEmitter.prototype.emit = function(type){
  console.log(type);//output : end
  var handler = this._events[type];
  
  /**
   *output: function(r, callback){
              callback(r);
            }
   *
   */
  console.log(handler);
  
  if(Array.isArray(handler)){
    var args = Array.prototype.slice.call(arguments, 1);
    var listeners = handler.slice();

    for(var i = 0 ;i< listeners.length ; i++){
      console.log(listeners[i]);
      listeners[i].apply(this, args);
    }

  }else if(typeof handler === 'function'){
    var args = Array.prototype.slice.call(arguments, 1);
    handler.apply(this, args);
  }
};

function Test(){
  this.on('end',function(r, callback){
    callback(r);
  });
}

Test.prototype = Object.create(EventEmitter.prototype);
Test.prototype.constructor = Test;

Test.prototype.factorial = function(n, callback){
  var self = this;
  var res = this.fact(n);
  setTimeout(function(){
    self.emit('end',res,callback);
  },50);
};

Test.prototype.fact = function(n){
  if(n == 1)
    return 1;

  return n * this.fact(n - 1);
};

var t = new Test();
var res;

t.factorial(5, function(result){
  res = result;
  console.log(res);//output : 120
});

console.log("last",res);//output : undefined

module.exports = Test;