React Native using shadow-cljs in 3 minutes

The fastest way a ClojureScript coder can get started with React Native. Prove me wrong.

This is an example project using: shadow-cljs, React Native, Expo, Reagent, and re-frame.

Here follows instructions for getting started either using Calva or the command line or, and assuming you have stuff like XCode, or whatever is the Android equivalents, installed:

Using Calva

Open the project in VS Code. Then:

1. In a Terminal pane, execute npm install -g expo-cli
2. Then yarn and wait for it to finish.
3. Run the Calva command Start a Project REPL and Connect (aka Jack-in)
   1. Select the project type shadow-cljs.
   2. Select to start the :app build.
   3. Wait for shadow to build the project.
4. Then Start build task. This will start Expo and the Metro builder. Wait for it to fire up Expo DevTools in your browser.
   1. Start the app on your phone or in a simulator or in browser.
   2. In the Expo settings for your app (shake or force touch with two fingers), disable Live Reloadinhg and Hot Reloading. (Don't worry, shadow-cljs will take care of hot reloading for you, in the most beautiful way.)
5. When the app is running in your phone/simulator the Calva CLJS REPL can be used.
6. Hack away!

Using Emacs with CIDER

Open Emacs and a bash shell:

1. In the shell, execute npm install -g expo-cli shadow-cljs

2. Then yarn and wait for it to finish.

3. Then run shadow-cljs compile :app to perform an initial build of the app.

4. In Emacs open one of the files in the project (deps.edn is fine)

5. From that buffer, do cider-jack-in-clojurescript [C-c M-J] to launch a REPL. Follow the series of interactive prompts in the minibuffer:

   1. select shadow-cljs as the command to launch
   2. select shadow as the repl type
   3. select :app as the build to connect
   4. and optionally answer y or n to the final question about opening the shadow-cljs UI in a browser. At this point shadow-cljs will be watching the project folder and running new builds of the app if any files are changed. You'll also have a REPL prompt, however the REPL doesn't work because it isn't connected to anything. The app isn't running yet.

6. In a shell run yarn ios (same as expo start -i). This starts the Metro bundler, perform the bundling, launch the iPhone simulator, and transmit the bundled app. Be patient at this step as it can take many seconds to complete. When the app is finally running expo will display the message:

   WebSocket connected!
   REPL init successful
   

7. Once you see that the REPL is initalized, you can return to Emacs and confirm the REPL is connected and functional:

   cljs.user> (js/alert "hello world!")

   Which should pop-up a modal alert in the simulator, confirming the app is running and the REPL is connected end to end.

Using Vim with Fireplace

Follow the steps in the Command line section below then come back here.

Open a file like src/main/example/app.cljs in vim. Find the nrepl port printed by the previous watch command (here 38369) and:

:Connect 38369
=>
Connected to nrepl://localhost:38369/
Scope connection to: ...
(ENTER)

Then enter into the CLJS session:

:CljEval (shadow/nrepl-select :app)
=>
To quit, type: :cljs/quit
[:selected :app]
(ENTER)

More explanations in the doc for shadow-cljs

Now enjoy fireplace commands!

For example to increment the counter add this snippet in the file (no need to save the file):

(comment
  (rf/dispatch [:inc-counter]))

Place your cursor somewhere on the "rf/dispatch" and hit cpp. The counter should be incremented on your phone.

Or the Command line

$ npm install -g expo-cli
$ yarn
$ yarn watch app
# wait for first compile to finish or expo gets confused 
# on another terminal tab/window:
$ yarn start

This will run Expo DevTools at http://localhost:19002/

To run the app in browser using expo-web (react-native-web), press w in the same terminal after expo devtools is started. This should open the app automatically on your browser after the web version is built. If it does not open automatically, open http://localhost:19006/ manually on your browser.

Note that you can also run the following instead of yarn start to run the app in browser:

# same as expo start --web
$ yarn web

# or

# same as expo start --web-only
$ yarn web-only

Then use your editor of choice to hook up the REPL and such.

Using ClojureScript REPL

Once the app is deployed and opened in phone/simulator/emulator/browser, connect to the nrepl on port printed by the watch command and run the following:

(shadow/nrepl-select :app)

(js/alert "Hello from Repl")

Production builds

A production build invloves first asking shadow-cljs to build a relase, then to ask Expo to work in Production Mode.

NB: Currently there's a bug in the metro bundler that causes release builds to fail in Production Mode. This project includes a way to patch it (nicked from here). Patch by executing: patch node_modules/metro/src/JSTransformer/worker.js ./etc/metro-bundler.patch

1. Kill the watch and expo tasks.
2. Execute shadow-cljs release app
3. Start the expo task (as per above)
   1. Enable Production mode.
   2. Start the app.

If you get complaints about Module HMRClient is not a registered callable module*, you probably have Hot reloading enabled. Disable it and try again.

"Known good" toolchain configurations

This repository provides a baseline setup for a React Native application. However newcomers may still have problems getting up in running "in 3 minutes" because of obscure dependencies on supporting tools such as the Java and Node runtimes. So while we can't definitively show every viable configuration, we can at least maintain what's known to work, especially when dependencies are bumped.

Expo SDK	35	35
clojure	1.10.1	1.10.1
clojurescript	1.10.520	1.10.597
expo-cli	3.4.1	3.9.1
expo	35.0.0	35.0.0
jdk	openjdk 1.8.0_222	openjdk 1.8.0_222
node	10.17.0	10.17.0
re-frame	0.11.0-rc2	0.11.0-rc3
react	16.9.0	16.9.0
react-native	0.59.8	0.59.8
reagent	0.9.0-rc2	0.9.0-rc3
shadow-cljs (cli)	2.8.69	2.8.78
shadow-cljs (jar)	2.8.69	2.8.78
yarn	1.19.1	1.19.1

When in doubt, a script is provided in this repo (etc/toolchain-report) to query what versions you have. This script is NOT needed for app development, building, or releasing, but may come in handy if you're having trouble getting up and running. toolchain-report requires joker, a portable and fast dialect of clojure implemented in go. See the joker repo on github for installation instructions.

Some notes from Thomas Heller

(This project is built from this example of his: https://github.com/thheller/reagent-expo)

The :app build will create an app/index.js. In release mode that is the only file needed. In dev mode the app directory will contain many more .js files.

:init-fn is called after all files are loaded and in the case of expo must render something synchronously as it will otherwise complain about a missing root component. The shadow.expo/render-root takes care of registration and setup.

You should disable the expo live reload stuff and let shadow-cljs handle that instead as they will otherwise interfere with each other.

Source maps don't seem to work properly. metro propably doesn't read input source maps when converting sources as things are correctly mapped to the source .js files but not their sources.

Initial load in dev is quite slow since metro processes the generated .js files.

reagent.core loads reagent.dom which will load react-dom which we don't have or need. Including the src/main/reagent/dom.cljs to create an empty shell. Copied from re-natal.