It would be interesting to see at least a simple Hello World example in JavaScript, but I suspect the library is too dependent on CoffeeScript, and a compatible JS code would be too convoluted (I'd be glad to be proven wrong though).
If a version of hexagonal targeted java then it would be "hexagonal.java". But .coffee and .js target the same "binary" so .js is the correct designation. It's about the runtime not the language.
There's nothing that makes this approach impossible to use with JS. The code samples are Coffee, because that's what we write our production apps in.