[lbatchelor]

Edit: I've actually managed to get the javascript down to a measly 859 bytes now. Pretty happy with some of the code golfing techniques I came up with

[gabrielsroka]

You should be able to change

  e.addEventListener("keyup"...

to

  e.onkeyup=...

but I haven't tested it.

[lbatchelor]

Ooh! Don't know how I missed that, I'll give it a go! Cheers!