It's quite a can of worms - there are many different keyboard layouts in common use (QEWRTZ, AZERTY, etc).

If you can find a way to make it work using only layout-independent keys (arrow keys, ctrl, alt, enter, space, esc, etc) you will save yourself a lot of headaches.

That's a good idea. Thanks.

Better to provide an options screen to let people choose the keys they want to use.

I would prefer to find a set of keys that work for most people. An options screen sounds too heavyweight for a web game.