Array.prototype.forEach = Array.prototype.forEach || function(callback) {
  var arr = this;
  for (var i = 0, len = arr.length; i < len; i++) {
    callback(arr[i], i);
  }
};

Object.create = Object.create || function(proto) {
    function F() {}
    F.prototype = proto;
    return new F;
}

function Emitter() {
  this._events =   {};
}

Emitter.prototype.on = function(evtype, fn) {
  this._events[evtype] = this._events[evtype] || [];
  if (this._events[evtype].indexOf(fn) !== -1) return;
  this._events[evtype].push(fn);
}
Emitter.prototype.off = function(evtype, fn) {
  if (evtype in this._events === false)  return;
  fn && this._events[evtype].splice(this._events[evtype].indexOf(fn), 1);
  !fn && delete this._events[evtype];
}
Emitter.prototype.emit = function(evtype, detail) {
  var self = this;
  if (!(evtype in this._events)) return;
  this._events[evtype].forEach(function(fn, i) {
      fn.apply(self, detail);
  });
}

Emitter.eventify = function(Klass) {
    Klass.prototype = Object.create(Klass.prototype);
    for (var attr in Emitter.prototype) {
        Klass.prototype[attr] = Emitter.prototype[attr]
    }
    return Klass;
}