Great article! I spot a few bugs with event handling, but in some ways that adds to the premise.

The implementation assumes that onpointerup is mutually exclusive to the other two, but it fires in addition to mouse/touch events. Only onpointerup is needed, if you include onmouseup and ontouchstart then the button action will fire twice.

However, you also need an onpointerdown handler to verify that the pointer press started inside the button. Without it, the button would activate if you started holding down the mouse button outside the button area, and then releasing inside the button area.