A little JS Game

I was having some fun making a little game in javascript that I wanted to share with you. Please have a play and let me know what you think. The game, called Sokoban, was originally created in 1981 and all appropriate copyright/licensing belongs to the original owner (details here).

There are still a few things that at some point I'd like to add, such as multiple levels and a countdown to let you know how many crates you still have left to put in place.

Instructions

You are a warehouseman ("@"). The goal of the game is to move all of the crates ("o") into place by pushing them, one at a time onto their places (".") with keys as follows: