Basic javascript event dispatcher

dispatcher.js

/**
 * Usage:
 *   var callback = function(event) { console.log(event); };
 *   EventDispatcher.addEventListener('event_type', callback);
 *   EventDispatcher.dispatch('event_type', eventData);
 *   EventDispatcher.removeEventListener('event_type', callback);
 */
 
var EventDispatcher = (function() {
  var _callbacks = {};

  return {
    addEventListener: function(eventType, callback) {
      if(!_callbacks.hasOwnProperty(eventType)) {
        _callbacks[eventType] = [];
      }

      _callbacks[eventType].push(callback);
    },

    removeEventListener: function(eventType, callback) {
      if(!_callbacks.hasOwnProperty(eventType)) {
        return;
      }

      var index = _callbacks[eventType].indexOf(callback);
      _callbacks[eventType].splice(index, 1);
    },

    dispatch: function(eventType, event) {
      if(!_callbacks.hasOwnProperty(eventType)) {
        return;
      }

      for(var i in _callbacks[eventType]) {
        _callbacks[eventType][i](event);
      }
    }
  };
})();