Simple Event Emitter

event.js

function EventEmitter(){
  this.events = {};
}

EventEmitter.prototype.on = function(event,fn){
  if(!(event in this.events)) this.events[event] = [];
  this.events[event].push(fn);
}

EventEmitter.prototype.emit = function(event){
  if(!event in this.events) return;
  var args = [];
  for(var i=0,l=arguments.length;i<l;i++) args[i] = arguments[i];
  var listeners = this.events[event];
  for(var i=0,l=listeners.length;i<l;i++){
    listeners[i].apply(listeners[i],args);
  }
}

EventEmitter.prototype.off = function(event,fn){
  if(!(event in this.events)) return;
  if(!fn){
    delete this.events[event];
  }
  var listeners = this.events[event];
  
  for(var i=0,l=listeners.length;i<l;i++){
    if(fn === listeners[i]){
      listeners.splice(i,1);
      return;
    }
  }
}