code: function(event, fn) {
          if (!this._callbacks[event]) {
              return;
          }
          var callbacks = this._callbacks[event];
          // Iterate through and delete the callback functions that match
          // They are spliced out when _runCallbacks is invoked, not here
          // (This function might be called in the middle of a callback, which complicates the logic)
          for (var i = 0; i < callbacks.length; i++) {
              if (!fn || callbacks[i] === fn) {
                  delete callbacks[i];
              }
          }
      }
docs: Unbind callbacks for the given event If fn is specified, only it will be removed; otherwise all callbacks will be