Oh gosh, there are debug options under some secret keys but they all should've been disabled for this release. I can't really help you at the moment but I'll add a few changes for graceful handling of fatal errors and come back to you once the game is updated.
One thing though - if you could get the error to happen again, open the developer console (Usually F12 or Ctrl+Shift+i), then open the "Console" tab and make a screenshot of the whole error message with the stack trace, the whole red thingy that will appear.
Otherwise you'll probably have to clear the save (which can be done in the aforementioned console by running the command `localStorage.clear()` and refreshing the page) but until I come up with the update you'll have to play the early levels again... And avoid pressing any curious key combinations :).