I'm a big fan of Elm but it's still experimental. Major non-backward-compatible changes to the languages still happen sometimes in new releases. Not the same thing, really.
(Don't know that much about the others.)
(Don't know that much about the others.)
Solid, mature, great libraries and one of the best languages out there, even when competing against real (in the sense of not compile-to-JavaScript-only) languages.
I haven't tried scala.js yet, but I've gone through some presentation slides...they're claiming compact code that runs as fast as javascript, clear error messages that point to the line of scala sourcecode, and even some advantages over jvm scala (though I forget the details). Don't know about compile speed.