mousewheel event is fired asynchronously when mouse wheel or similar device is operated. It's represented by the
The document in MSDN: onmousewheel event
|Feature||Chrome||Firefox (Gecko)||Internet Explorer||Opera||Safari|
|Basic support||(Yes)||Not supported||6.0||(Yes)||(Yes)|
|Feature||Android||Firefox Mobile (Gecko)||IE Mobile||Opera Mobile||Safari Mobile|
|Basic support||?||Not supported||?||?||?|
wheelDelta attribute value is abstract value which indicates how far the wheel turned. If the wheel has rotated away from the user, it's positive. Otherwise, negative. This means that the delta value sign is different from DOM Level 3 Events'
On either IE or WebKit on Windows: The value is multiplies of 120 when the user is using a wheel with notches and its driver doesn't support high resolution scrolling. Otherwise, could be smaller than 120.
On Opera on Windows: The value is multiplies of 40 per line. If the scroll speed is 3 lines per notch (default setting on Windows), this value becomes same as IE and WebKit.
Horizontal wheel operation
Neither IE nor Opera fires this event by horizontal wheel operation. On the other hand, WebKit fires it for horizontal wheel operation too.