[spion]

Try TypeScript or ReasonML or ScalaJS. They all compile to JS and have dead-easy FFI so you can still use the ecosystem stuff you're used to, but you learn something new. In the case of ReasonML and Scala you get to use them later with different backend ecosystems too.

TS will give you a nice balance between learning new stuff (types) and sticking to what you know (most JS patterns are supported), whereas ReasonML and ScalaJS would be a bit more adventurous.

Also try playing with dotnet languages (F# maybe?) via EdgeJS: https://github.com/tjanczuk/edge (but I don't know if thats production-stable)