mousewheel
<script type="text/javascript"> var EventUtil = { addHandler: function() {...}, getEvent: function(event) {...}, } EventUtil.addHandler(document, "mousewheel", function(event) { event = EventUtil.getEvent(event); alert(event.wheelDelta); }); </script>
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Role o botão do mouse para frente e depois para trás.
Funciona somente no IE, Opera, Safari e Chrome.