Okay, maybe Racket and OCaml are relatively obscure options, but quite a lot of people know Java and Python. And I can't say Lua's not popular, too.

I'd expect Javascript programmers dwarf Lua programmers by a couple of orders of magnitude. At least one OOM if you want to limit to people who only know the language "well."

In the game programming industry (PC games, not iOS/Android games), the two most popular languages are C++ and Lua. That's probably part of the reason why these two languages keep getting brought up in this thread to compare against Javascript.