I would suggest adding something to control your keyboard movements. Trying to use arrow keys results in the screen sliding up and down (You have to go into full screen mode to play this). Since you are using an eventListener for the keys, you may want to include this in your event line (And substitute 'e' for whatever your variable is):
if(e.keyCode==32||e.keyCode==38||keyCode==40){e.preventDefault()}
Otherwise, I like the challenge of having to control both sides of the board at the same time. :D