I'm using PureScript because it is purely functional and has a powerful type system like Haskell, but compiles to JS with easy FFI and I can use it with webpack. I'm writing both a backend API server and frontend app with it. It's been amazingly productive and a godsend for writing type-safe JS.

On the front-end, it has purescript-pux, which is pretty much a port of the Elm architecture. The language/community is really shaping up.