A BBC navigation bar component broke depending on the external monitor

This seems like a self-inflicted bug resulted from incorrect heuristics (assumption that positive screenX/Y values represent mouse event), and the investigation was complicated by inadequate tracing/logging.

Instead of checking the more appropriate property that other commenters have suggested (pointerType), I'm a bit surprised that the solution given by the author is to patch up the shaky heuristics even more:

> We could deduce from our final two clues the solution: we need to check for negative numbers as well as positive numbers when checking the screenX and screenY coordinates.

Actually that is what we're going to do. I'm hoping to merging in code, soon, that will change it to use pointerId === -1 and then fall back to screenX === 0.

At the time this code was originally written four years ago or whenever it was, not all browsers used PointerEvent for click.