UIEvent: sourceCapabilities property

The UIEvent.sourceCapabilities read-only property returns an instance of the InputDeviceCapabilities interface which provides information about the physical device responsible for generating a touch event. If no input device was responsible for the event, it returns null.

When a single user interaction with an input device generates a series of different input events, the sourceCapabilities property for all of them will point to the same instance of InputDeviceCapabilities. For example, when a user lifts their finger off of a touchscreen, several UIEvents may be generated including touchend, mousedown, click, and focus. All of these events must have the same sourceCapabilities representing the touchscreen.

A device is considered "responsible" for an event only when that interaction is part of the abstraction provided by the web platform. For example, many user agents allow a window to be resized with a mouse or a keyboard, but this detail is not exposed to the web platform in any way, and so the sourceCapabilities of a resize event will typically be null.