// JavaScript Document

/*attach-add event listener*/
function hookEvent(element, eventName, callback)
{
  if(typeof(element) == "string")
    element = document.getElementById(element);
  if(element == null)
    return;
  if(element.addEventListener)
  {
    if(eventName == 'mousewheel')
    {
      element.addEventListener('DOMMouseScroll',
        callback, false); 
    }
    element.addEventListener(eventName, callback, false);
  }
  else if(element.attachEvent)
    element.attachEvent("on" + eventName, callback);
}

/* detach-remove event listener */
function unhookEvent(element, eventName, callback)
{
  if(typeof(element) == "string")
    element = document.getElementById(element);
  if(element == null)
    return;
  if(element.removeEventListener)
  {
    if(eventName == 'mousewheel')
    {
      element.removeEventListener('DOMMouseScroll',
        callback, false); 
    }
    element.removeEventListener(eventName, callback, false);
  }
  else if(element.detachEvent)
    element.detachEvent("on" + eventName, callback);
}