Draggables.prototype = Object.extend(Draggables, {
  _cacheObserverCallbacks: function() {
    ['onStart','onEnd','onDrag','onClick'].each( function(eventName) {
      Draggables[eventName+'Count'] = Draggables.observers.select(
        function(o) { return o[eventName]; }
      ).length;
    });
  }
});