EventTarget mixin module

event_target.js

// draft

(function(exports) {
  var ArrayProto = Array.prototype;

  var nativeSlice = ArrayProto.slice,
      nativeFilter = ArrayProto.filter;

  /* Internal: filters the collection. (extracted from underscore.js)
   *
   * Returns the filtered list, given a function condition.
   */
  function filter(obj, iterator, context) {
    var results = [];
    if (obj === null) return results;
    if (nativeFilter && obj.filter === nativeFilter) return obj.filter(iterator, context);
    for (var i = 0, l = obj.length; i < l; ++i) {
      if (iterator.call(context, obj[i], i)) results.push(obj[i]);
    }
    return results;
  }

  function EventTarget() {}

  var fn = EventTarget.prototype;

  fn.contructor = EventTarget;

  fn.on(type, fn, context) {
    if (!this.hasOwnProperty('_listeners')) {
      this._listeners = {};
    }

    if (!this._listeners.hasOwnProperty(type)) {
      this._listeners[type] = [];
    }

    this._listeners[type].push({ fn: fn, context: context || null });
  };

  fn.trigger = function(type) {
    if (this._listeners && this._listener[type] instanceof Array) {
      var args = nativeSlice.call(arguments, 1),
          listeners = this._listeners[type];
      for (var i = 0, len = listeners.length; i < len; i++) {
        listeners[i].fn.apply(listeners[i].context, args);
      }
    }
  };

  fn.off = function(type, fn) {
    if (this._listeners && this._listeners[type] instanceof Array) {
      var listeners = this._listeners[type];
      this._listeners[type] = filter(this._listeners[type], function(subscription) {
        return subscription.fn !== fn;
      });
    }
  };

  exports.EventTarget = EventTarget;
})(window);