Fireplace.vim is an nREPL client, and nREPL does not support CLJS out of
the box. From what I understand, Chas Emerick has been doing some work
to bridge nREPL and the CLJS REPL:
https://github.com/cemerick/piggieback
I haven't been doing much work on the web recently, but I plan on
checking this out when I get the chance.
guns