All our mobile stuff is thin web-layers that consume our core APIs, so it's all js. I started looking at WebSharper and FunScript for a more strongly-typed and robust web-development experience, but they're all a bit too 'awkward'.
I keep meaning to look into Elm as it appears to be a more thoughtful approach to functional programming on the client.
I avoid JS, not because I don't like it, but there are other choices. Then again, it's much easier to find JS devs than Elm devs.
I've played with Elm, but not made anything of note with it yet. The Elixir/Phoenix crowd are getting hopped up about it lately as a good fit for them.
I keep meaning to look into Elm as it appears to be a more thoughtful approach to functional programming on the client.