By default in a project using ClojureScript, the .repl/ directory is used to store compiled CLJS for the browser REPL. This compilation is skipped if the directory already exists (src/clj/cljs/repl/browser.clj:205:create-client-js-file). However, it really should be re-compiled if the version of ClojureScript is upgraded/changed or else the browser REPL may fail with some very difficult to interpret error messages. At the moment, it seems people simply know to delete .repl/ when changing ClojureScript versions (https://groups.google.com/forum/#!topic/clojure/C-H4gSWIUwc) but this can be extremely tough on new users when they upgrade ClojureScript for the first time.
We could append clojurescript-version to the directory name. Unfortunate that it generates a new directory each time a new version of CLJS/BrowserREPL combo is used, but shoudl not occur too often and makes it very explicit that :working-dir should be tied to CLJS version. Also developers utilizing ClojureScript though lein checkouts will still have to delete .repl/ since clojurescript-verion is only set by script/build.
See attached patch.
NOTE: I do not have a CA agreement on file, but one is in the mail.
NOTE: Sorry if this is bad form, but as a preceding commit, in cases where clojurescript-version is unbound I changed (clojurescript-version) to return "" instead of ". This is so that when clojurescript-version is unbound .repl/ will be used instead of .repl-./ Let me know if this should be considered as a separate issue.
Alternatively, we could remove the exists check entirely, and instead recompile client.js every time (repl-env) is called at the cost of slowing down browser REPL startup.