The wheel event fires when the user rotates a wheel button on a pointing device (typically a mouse).
This event replaces the non-standard deprecated mousewheel event.
Note: Don't confuse the wheel event with the scroll event. The default action of a wheel event is implementation-specific, and doesn't necessarily dispatch a scroll event. Even when it does, the delta* values in the wheel event don't necessarily reflect the content's scrolling direction. Therefore, do not rely on the wheel event's delta* properties to get the scrolling direction. Instead, detect value changes of scrollLeft and scrollTop of the target in the scroll event.
Syntax
Use the event name in methods like addEventListener(), or set an event handler property.
Returns an unsigned long representing the unit of the delta* values' scroll amount. Permitted values are:
Constant
Value
Description
WheelEvent.DOM_DELTA_PIXEL
0x00
The delta* values are specified in pixels.
WheelEvent.DOM_DELTA_LINE
0x01
The delta* values are specified in lines. Each mouse click scrolls a line of content, where the method used to calculate line height is browser dependent.
WheelEvent.DOM_DELTA_PAGE
0x02
The delta* values are specified in pages. Each mouse click scrolls a page of content.
9The onwheel event handler property is not supported. To listen to this event, use element.addEventListener('wheel', function() {});. See IE bug 782835.