clj -R:nrepl -m nrepl.cmdline --middleware "[cider.piggieback/wrap-cljs-repl]"
in Emacs, cider-connect
user> (require '[oops.core :refer [oset!]])
nil
user> (oset! (js-obj) :mood "a happy camper")
IllegalStateException Can't change/establish root binding of: *cljs-warnings* with set clojure.lang.Var.set (Var.java:223)