Sometimes the thick veneer of C-like syntax over JavaScript's inner functionality can be enough to make you want to switch to another functional language. Well, you can!
Clojure and ClojureScript
Closure is a modern Lisp implementation and a full-featured functional language
ClojureScript trans-compiles Clojure into JavaScript
CoffeeScript
CoffeeScript is the name of both a functional language and a compiler for trans-compiling the language into JavaScript
1-to-1 mapping between expressions in CoffeeScript and expression in JavaScript
There are many more out there, including Pyjs, Roy, TypeScript, UHC and more.