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 :)