// REGISTRAZIONE EVENTO CROSSBROWSER
function addEvent(obj, evt, fn) {

  if(obj.addEventListener)
    obj.addEventListener(evt, fn, false);
  else if(obj.attachEvent)
    obj.attachEvent('on'+ evt, fn);
}

// RIMOZIONE EVENTO CROSSBROWSER
function removeEvent(obj, evt, fn) {

  if(obj.removeEventListener)
    obj.removeEventListener(evt, fn, false);
  else if(obj.detachEvent)
    obj.detachEvent('on'+ evt, fn);
}