At one point I hand-wrote a simple Brainfuck interpreter in both WAT (called WAST at the time...) and asm.js. Both are extremely tedious, but it seems WAT has improved a bit ergonomically since...

https://github.com/magcius/bfasm/blob/master/bfasm.js

https://github.com/magcius/bfasm/blob/master/bfwasm.wast