[pharmakom]

It depends on the language. Elm does not allow you to call JS directly, but ReasonML and Fable (F#) both do. This means with a little effort you can use any JS library.

I think the advantage of these functional web languages is in small but high-skill teams where robust code can be written in a minimal number of lines (more expressive, type checked, etc) and everyone on the team is able to pick up new things quickly. The big caveat is that you need to have a solid understanding of JS before learning these languages on top. This makes the barrier too high for all but the best junior developers.

Another point is that Node is not particularly good at vertical scaling, so if you care about this and want a shared language between client and server, F# and OCaml (ReasonML) are much better bets.