[Irfaan]

I think I see a way of shaving another byte:

instead of "0<x%n&", you should be able to do "x%n&&". Works for me on Chrome.

My goal is to shave 2 bytes, so you can change the key handler back to onkeydown. :P

[amenghra]

There are 5 possible collisions: top edge, left edge, right edge, bottom edge and the tail.

Your proposal does not cover the top edge.