What WheelEvent.deltaZ refers to?

Question

While I was working on JavaScript events, I found a troubling element on the wheel event: the deltaZ member.

I understood what was deltaX as horizontal scroll (available with some devices like a touchpad) and deltaY as vertical scroll (that is what any standard wheel do) but for deltaZ, the documentation says:

The WheelEvent.deltaZ read-only property is a double representing the scroll amount along the z-axis

But still I cannot see what deltaZ refers to ? What kind of device can simulate a scroll on depth direction ? Even a joystick has only two axis, right ?

But as it is implemented on most web browsers, it has to have a meaning ? So which one ?

Answer 1

There are a class of relatively new devices known as 3d-mice. These devices function like a standard 3 button mouse in addition to having extra capabilities.

An example of the input provided by such a device is shown below in an image from leapaust.com.au/3d-connexion-mouse.

Such input is most commonly made use of in 3d content-creation applications.