Thank you!
Sorry about the exception. That's the crash bug I mention on the page. It only happens in the web build, so you could try the download version if you want to play further. (I haven't been able to figure out why it happens yet. It's hard to debug since it doesn't happen in the native versions. It seems to call some code that should be unreachable, but I don't have any unreachable code markers in my own code, so I think something goes wrong in the system library or in emscripten. Or maybe it's because the web build is 32-bit, I should investigate that)