I assume you mean the cljs getting started repl? I’m not too sure what is behind it for the “Welcome” app (though I don’t see any evidence of shadow, so my guess is vanilla), but ClojureScript is the compiler that compiles the cljs to js. https://clojurescript.org/ If you look at the sources tab under the element inspector, you can even see the js that gets returned, though it’s far from human readable.

Yes, it's vanilla ClojureScript.

When does the cljs got compiled to js?

The REPL is started like on https://clojurescript.org/ , the minimal cljs project.

I see. You were referring to this: https://clojurescript.org/guides/quick-start

Thanks! I was not at the computer. Anyway, I choose to use a vanilla ClojureScript REPL for this in the hope that newcomers will better understand the role of shadow-cljs and Figwheel, if they are not led directly there.