These days virtually every language can be compiled to JavaScript in a very usable manner. For example, I've had a lot of success with js_of_ocaml[1], not really running into any of the problems people like to harp about regarding compiled-to-JS languages.
[1]: ocsigen.org/js_of_ocaml/
The argument for developer time--as well as decreased maintenance cost--is exactly why I went with OCaml over pure JavaScript. And so far it's certainly paid off!
Sure, but the language that _every_ developer will need to know is JavaScript, not OCaml or some other of the dozen alternatives that can be compiled to JS.
Besides, the ability to compile to JS is not enough; you will need to read it in JS, debug it in JS and let other developers work on it in JS (because they don't know OCaml).
[1]: ocsigen.org/js_of_ocaml/
The argument for developer time--as well as decreased maintenance cost--is exactly why I went with OCaml over pure JavaScript. And so far it's certainly paid off!