Cross browser scroll event handler, with a consistant delta.

scrollEvt.js

var mousewheelevt=(/Firefox/i.test(navigator.userAgent))? "DOMMouseScroll" : "mousewheel";

if (document.attachEvent)
  document.attachEvent("on"+mousewheelevt, function(e){scroller(e)});
else if (document.addEventListener)
  document.addEventListener(mousewheelevt, function(e){scroller(e)},false);

function scroller(evt)
{
  //Guess the delta.
  var delta = 0;
  if (!evt) evt = window.event;
  if (evt.wheelDelta) {
    delta = evt.wheelDelta/120;
  } else if (evt.detail) {
    delta = -evt.detail/3;
  }
  if (evt.preventDefault) evt.preventDefault();
  evt.returnValue = false;

  //Do the magic.
  //callback(delta);
}