The WheelEvent interface represents events that occur due to the user moving a mouse wheel or similar input device.
Note: This is the standard wheel event interface to use. Old versions of browsers implemented the non-standard and non-cross-browser-compatible MouseWheelEvent and MouseScrollEvent interfaces. Use this interface and avoid the non-standard ones.
Note: Do not confuse the wheel event with the scroll event. The default action of a wheel event is implementation-defined. Thus, a wheel event doesn't necessarily dispatch a scroll event. Even when it does, that doesn't mean that the delta* values in the wheel event necessarily reflect the content's scrolling direction. Therefore, do not rely on delta* properties to get the content's scrolling direction. Instead, detect value changes to scrollLeft and scrollTop of the target in the scroll event.
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.