I remember coming across a couple of comments saying that someone was forced to implement Zarith in JavaScript because BuckleScript wouldn’t compile the standard version, and thought I’d post this link to a BuckleScript port of Zarith: https://github.com/plow-technologies/bs-Zarith
From a quick glance, it doesn’t especially seem tied to BuckleScript, by the way. It might well be portable to JSOO.