I am one of the authors of BuckleScript, you can try BuckleScript in the browser: http://bloomberg.github.io/bucklescript/js-demo/ Click Examples see how the JS code generated, questions are welcome!
From a practical standpoint, what's the difference between js_of_ocaml?
bucklescript doesn't respect the OCaml memory model and runtime semantics, which makes it incompatible with some part of the ecosystem.
Js_of_ocaml already has various features that bucklescript doesn't have: dynlink, support for concurrency libraries such as lwt and async, etc. It's also much more stable and battle-tested.