Are you aware of GHCJS, Haskell-to-JS, compiler? In the new and rather popular "build/dependency manager"[1] for Haskell, named Stack, you can now quite easily install this compiler.
And I think it is only a matter of time till someone writes a Swift-to-JS compiler (Apple might already have it on it's radar).
[1]: I know it is not a "build/dependency manager", but I don't know how to call better in for sake of this discussion.