PointerEvent: isPrimary property

The isPrimary read-only property of the PointerEvent interface indicates whether or not the pointer device that created the event is the primary pointer. It returns true if the pointer that caused the event to be fired is the primary one and returns false otherwise.

In a multi-pointer scenario (such as a touch screen that supports more than one touch point), this property is used to identify a master pointer among the set of active pointers for each pointer type. Only a primary pointer will produce compatibility mouse events. Authors who desire only single-pointer interaction can achieve that by ignoring non-primary pointers.

A pointer is considered primary if the pointer represents a mouse device. A pointer representing pen input is considered the primary pen input if its pointerdown event was dispatched when no other active pointers representing pen input existed. A pointer representing touch input is considered the primary touch input if its