Nice but:
1. Do not debug in production (console.log ...)
2. Secure the session (do not display the session ID in high-scores)
3. This is not infinite (in64 * in64) square + weird border :)
4. Balance the score for big discovered area
5. For the new players start the position on an playable area
6. Limit the total of high-scores returned by the ws
7. Limit the ws data as much as possible
...
Thanks and sorry :)