element.onmousewheel = handlerFunction; var handlerFunction = element.onmousewheel;
handlerFunction should be either
See the DOM event handlers page for information on working with
mousewheel event is fired asynchronously when a mouse wheel or similar device is operated. It's represented by the
mousewheel event documentation for more information about the event.
|WHATWG HTML Living Standard
The definition of 'mousewheel' in that specification.