nREPL – Starting shadow-cljs from lein or clojure

This is a tiny example project for setting up development usingnREPLandshadow-cljs.TheClojureScriptapp is rendered usingReagent.

By default the project usesdeps.ednfor dependencies. There is aLeiningensetup as well.

Install npm dependencies

npm i

(Oryarn,whatever you fancy.)

Using a Clojure editor

If you are using something likeCalvaorCIDER,just jack in to the project as ashadow-cljsproject type, and hack away.

Starting the project w/o an editor

The following instructions are for working with the project without an editor. You probably wouldn't do that. The point is mostly to demystify what the editors are doing when starting and attaching to a shadow-cljs project. So, you could say it is for educational purposes. Since it's pretty quick, why not try it out?

You can start this project using eithershadow-cljs,clojure,orlein.As you are doing this to maybe learn something, please consider trying all three options.

With the shadow-cljs npm executable

npx shadow-cljs -d cider/cider-nrepl:0.28.5 clj-repl
...
shadow.user=>

NB: If you useshadow-cljsit will in turn useclojureto start Clojure and the nREPL server. (Orleinif you editshadow-cljs.ednand change this.)

With deps/clojure

To start the project and the nREPL server withclojure,in one terminal:

% clojure -Sdeps '{:deps {nrepl/nrepl {:mvn/version, "1.0.0" },cider/cider-nrepl {:mvn/version, "0.28.5" }}}' -m nrepl.cmdline --middleware "[cider.nrepl/cider-middleware,shadow.cljs.devtools.server.nrepl/middleware]"

Attach to the nREPL server in another terminal:

% clojure -Sdeps '{:deps {reply/reply {:mvn/version "0.5.1" }}}' -M -m reply.main --attach `<.nrepl-port`
...
user=>

Or, since thedeps.ednfile specifies thenrepldependency:

% clj -M -m nrepl.cmdline -c --port `<.nrepl-port`
...
user=>

With Leiningen

To start the project and the nREPL server with Leiningen, in one terminal:

lein update-in:dependencies conj '[nrepl, "1.0.0" ]' -- update-in:dependencies conj '[cider/cider-nrepl, "0.28.5" ]' -- update-in:plugins conj '[cider/cider-nrepl, "0.28.5" ]' -- update-in '[:repl-options,:nrepl-middleware]' conj '[cider.nrepl/cider-middleware,shadow.cljs.devtools.server.nrepl/middleware]' -- repl:headless

NB: This doesn't properly inject the shadow-cljs nREPL middleware for some reason.You'll need to add this toproject.clj:

:repl-options{:nrepl-middleware[shadow.cljs.devtools.server.nrepl/middleware]}

Attach to the nREPL server in another terminal:

% lein repl:connect
...
main.server=>

Starting shadow-cljs

(Not needed if if you started the REPL using the shadow-cljs executable.)

user=> (do(require'shadow.cljs.devtools.server) (shadow.cljs.devtools.server/start!))
shadow-cljs - HTTP server available at http://localhost:8700
shadow-cljs - server version:2.19.9 running at http://localhost:9632
shadow-cljs - nREPL server started on port57770
:shadow.cljs.devtools.server/started
user=>

(Never mind the second nREPL server started here.)

At this point the shadow-cljs dev browser is running and serving on port 8700, but your ClojureScript app is not running. It is not even compiled. As you'll see if you visithttp://localhost:8700with your browser.

Start the shadow-cljs watcher

(Therequireis not needed if you started the REPL with the shadow-cljs executable.)

user=> (do(require'shadow.cljs.devtools.api) (shadow.cljs.devtools.api/watch:app))
[:app] Configuring build.
[:app] Compiling...
[:app] Build completed. (170files,0compiled,0warnings,1.35s)
:watching
user=>

Start the ClojureScript app

Openhttp://localhost:8700in a web browser. (Or refresh if you opened it in an earlier step.)

Confirm that the shadow-cljs watcher is running by editing some hiccup insrc/main/core.cljsand save the file.

Attach to the ClojureScript REPL

(Therequireis not needed if you started the REPL with the shadow-cljs executable.)

user=> (do(require'shadow.cljs.devtools.api) (shadow.cljs.devtools.api/nrepl-select:app))
To quit, type::cljs/quit
[:selected:app]
cljs.user=>

(If you instead of[:selected:app]see:missing-nrepl-middleware,you are probably using Leiningen and missed a note above.)

Confirm that your REPL is attached to the app in the browser:

cljs.user=> (js/alert"BOOM!")

(You need to dismiss the alert in the browser to get the prompt back.)

Something more interesting could be to update the app state, maybe?

cljs.user=> (load-file"src/main/core.cljs")
[]
cljs.user=> (in-ns'main.core)
nil
main.core=> (swap!app-state update:textstr"UPDATED")
{:text"Hello world! UPDATED"}

(Check the app in the browser.)

Notes

If you use this project as a base for something, then edit.gitignoreand removepackage-lock.json.

The reason the Leiningen project file is not including the shadow nrepl middleware configuration is that I thinkthe failure to inject via the command line is a bug in Leiningenand that it will eventually be fixed.