To work on the function instrumentation for ClojureScript clone the malli repository and:

npm i
./node_modules/.bin/shadow-cljs watch instrument

Open an nREPL connection from your favorite editor to the port located in .shadow-cljs/nrepl.port

Open a browser to http://localhost:8000

the port is set in the shadow-cljs.edn file should you wish to change it.

In your editor evaluate:

(shadow/repl :instrument)

The dev-time code is located in the file: app/malli/instrument_app.cljs.