In addition to the Ocaml recommendations I suggest Haxe, which is basically "Ocaml concepts transposed into a compiler targeting various GC runtimes". (Compiler is also written in Ocaml - it's not kidding around) Easy to pick up if you already know JS syntax, and basically covers the "best-of" of static inferred type systems, but you can easily break out of it if you need dynamic or low-level behavior.

Downside is that it's not convenient if you just want one standard library and runtime because it targets all of them. You have to justify the trade-offs involved in that, but it's a good secret weapon.