Force Touch events are a proprietary, Apple-specific feature which makes possible (where supported by the input hardware) new interactions based on how hard the user clicks or presses down on the touchscreen or trackpad.

webkitmouseforcewillbegin Non-standard

This event is fired before the mousedown event. Its main use is that it can be Event.preventDefault()ed.

webkitmouseforcedown Non-standard

This event is fired after the mousedown event as soon as sufficient pressure has been applied for it to qualify as a "force click".

webkitmouseforceup Non-standard

This event is fired after the webkitmouseforcedown event as soon as the pressure has been reduced sufficiently to end the "force click".

webkitmouseforcechanged Non-standard

This event is fired each time the amount of pressure changes. This event first fires after the mousedown event and stops firing before the mouseup event.

The following property is known to be available on the webkitmouseforcewillbegin, mousedown, webkitmouseforcechanged, webkitmouseforcedown, webkitmouseforceup, mousemove, and mouseup event objects:

MouseEvent.webkitForce Non-standard Read only

The amount of pressure currently being applied to the trackpad/touchscreen.

These constants are useful for determining the relative intensity of the pressure indicated by MouseEvent.webkitForce:

MouseEvent.WEBKIT_FORCE_AT_MOUSE_DOWN Non-standard Read only

Minimum force necessary for a normal click.

MouseEvent.WEBKIT_FORCE_AT_FORCE_MOUSE_DOWN Non-standard Read only

Minimum force necessary for a force click.

Not part of any specification. Apple has a description at the Mac Developer Library.