I think any solution needs to check that only one finger was touched - some solutions forget this check. An iOS quirk to be careful of is that the event.touched array count for a touch event on an element is different if there is also a touch event registered on document (spooky interaction, but true).

Also I would check no modifier key (ctrl,alt,shift,meta) is down to handle mixed keyboard/touch devices. This check is often missed for mouse events, and causes various UI faults in pages.