When an error occurs in a Clojure prepl the exception is caught at the outermost layer and returned with :tag :ret as well as :exception true. This allows tooling to handle the error responses accordingly.
If ClojureScript would return :exception true as well it would bring it inline with how the Clojure prepl works.
If this is considered valid I'll submit a patch for it today. As far as I can tell from all of my work with prepls over the last few months this is one of the last major outstanding features. Once is in we'll have reader conditionals in both Clojure and ClojureScript too.
The only thing I haven't been able to do is set the current line / column / file path for ClojureScript evals, but that's off topic.
CLJS-3096.patch passes CI
CLJS-3096.patch added to Patch Tender