hoverer.js

var Hoverer = {
  current: null,
  delay: 0.5,
  timer: null,

  handler: function(event) {
    var element = event.findElement('div.nav_menu');
    if (!element)
      return Hoverer.leave();
    if (element == Hoverer.current)
      return Hoverer.stopTimer();
    Hoverer.enter(element)
  },
  
  observe: function() {
    document.observe('mouseover', Hoverer.handler);
  },
  
  stopObserving: function() {
    document.stopObserving('mouseover', Hoverer.handler);
  },
  
  enter: function(element) {
    Hoverer.stopTimer();
    if (Hoverer.current) Hoverer.fireMouseExited(Hoverer.current);
    element.fire('mouse:entered');
    Hoverer.current = element;
  },
  
  leave: function() {
    if (!Hoverer.current || Hoverer.timer) return;
    Hoverer.timer = Hoverer.fireMouseExited.curry(Hoverer.current).delay(Hoverer.delay)
  },
  
  fireMouseExited: function(element) {
    element.fire('mouse:exited');
    Hoverer.current = null;
  },
  
  stopTimer: function() {
    if (!Hoverer.timer) return;
    window.clearTimeout(Hoverer.timer);
    Hoverer.timer = null;
  }
};

//Hoverer.observe();