I see we both went with variable names like 'up' and 'left' for the subscripts in the "neighbor count" code. I'm always looking for ways to sidestep numerical array indexing because it's such a fertile ground for bugs. For example, I find it really hard to look at:

var up = i-1>0 ? -1 + i : -1 + h;

...and tell if it's correct. I used a mod_wrap function instead, which is an implementation of Python-like modulo, which 'wraps' negative numbers to the top of the range.