That was a lot of fun! One quick request - can the level-up popup not appear square in the middle of the screen? That can be a real problem if you happen to level while you're in the middle of a fight.

One other quick request, now I think of it - can the key event handler pass F11 through? Being able to un-fullscreen would be handy.

Awesome game! I look forward to the writeup on the tech stack and how it's done.