I’m trying to use react navigation 5 in my Krell RN app, however, I’m having difficulties loading it in my cljs files. On their “Getting started” page, they say that we have to use:

import { NavigationContainer } from '@react-navigation/native';

(ns my-app.core (:require ["@react-navigation/native" :refer [NavigationContainer]]))

(require '["@react-navigation/native" :refer [NavigationContainer]])

Unexpected error (IllegalArgumentException) compiling at (REPL:1).
Don't know how to create ISeq from: java.lang.Character

(js/require "@react-navigation/native")

npm install @react-navigation/native
npm install react-native-reanimated react-native-gesture-handler react-native-screens react-native-safe-area-context @react-native-community/masked-view

@michael.w.jung did you check if you need to import $default

there's no magic way us to detect that you need to look at the library and see how it's exported

@dnolen You mean like this?

(ns my-app.core (:require ["@react-navigation/native$default" :refer [NavigationContainer]]))

@michael.w.jung you need to know about 🙂

I’m using this library, with shadow-cljs, and it works. I’m not saying that it’s a krell/shadow-cljs thing. It’s probably something to do with your setup… If you want to see what is available when you require a given library, require it in the REPL:

(require "@your-lib")

examine the the library, see if exports default and something else

@michael.w.jung also (js/require "@react-navigation/native") if that doesn't work as you said above then something else is probably wrong

oh sorry - but you can't do that anyway

React Native is not Node.js you have to understand this

if Metro can't see it - you cannot require it

Metro is never going to see your ClojureScript files - so that will never work

To avoid issues like you have to understand what Krell must do to satisfy Metro

1. Compiling your project will detect Node modules - this gets dumped into a file that Metro does see in the output directory

2. If your Node import isn't in that file - it's never going to work

look at output-dir/npm_deps.js

It seems to be there:

module.exports = {                                                                                                                                                                                                                                                              
  npmDeps: {                                                                                                                                                                                                                                                                    
    "react-native": require('react-native'),                                                                                                                                                                                                                                    
    "react-dom": require('react-dom'),                                                                                                                                                                                                                                          
    "@react-navigation/native": require('@react-navigation/native'),                                                                                                                                                                                                            
    "react": require('react')  }                                                                                                                                                                                                                                                
}; 

so

if it's there then

A) it was in node_modules ... good

B) Krell saw it ... good

so you're running out of possibilities of what could be wrong

did you reload your RN app? new npm dependencies cannot be hot-reloaded or REPL require'd in without being there by the initial load first

right there's absolutely nothing dynamic about Metro

you have recompile ClojureScript & reload the entire app if you import something from node_modules

(for the first time)

node_modules/@react-navigation/native/lib/module/index.js looks like this:

export * from '@react-navigation/core';                                                                                                                                                                                                                                         
export { default as NavigationContainer } from './NavigationContainer';                                                                                                                                                                                                         
...

Yes, I think I reloaded / rebuilt everything.

I threw away the whole target directory and reran clj -M -m krell.main -co build.edn -c

another way to debug is the edit index.js and console.log this library that you're trying to use

there's nothing especially magical about the way Krell works

whenever you're done debugging you can always restore index.js by running a compile

Ok, I added the following to index.js

import { NavigationContainer } from '@react-navigation/native';                                                                                                                                                                                                                 
console.log(NavigationContainer);
console.log(typeof(NavigationContainer));
console.log(NavigationContainer === undefined);

{"$$typeof": Symbol(react.forward_ref), "render": [Function NavigationContainer]}
object
false

ok - so now fix up your :require to the way you originally had it

now if you look at the generated JS for that namespace you should see something that looks sensible

the one magic Krell trick here is this

there is no such thing as dynamic require in Metro - so we just monkey patch a global JS require function that will return the library then you invoke it

this is how you can get a handle on modules and assets even though Metro never saw ClojureScript

@michael.w.jung before you go look at though

console logging the npm_deps.js import in index.js is probably more useful - it's a JS object that will be used by ClojureScript to "import" those libraries

if somehow the library is null in there - then of course it can't work

Very odd. Now the library is no longer in npm_deps.js...

so this would be source of the bug if there is one

if it disappears from there - of course it won't work

but npm_deps.js will only get rewritten if you somehow run another compile

I deleted the target folder and reran clj -M -m krell.main -co build.edn -c. Still gone.

here's the one other thing

your ClojureScript require cannot be in some random file outside of the entry point dep graph

i.e. a.core is the app entrypoint and you have some side file b.core which imports Node library

which is never required by a.core

Ok, that’s why it was gone. I commented out some stuff before and it no longer was in that dependency graph. It is back now that I fixed this.

you are now a Krell expert 🙂

there's no other rules than the above

Well, I certainly don’t feel like one 😄

It seems to work now

I have no idea what I changed. It probably really was because I removed the require of the file that imported the lib when I tried to debug the issue.

✨

Thank you very much for your help @dnolen. I was about to give up on this. Much appreciated!

No problem

But hopefully the above shows Krell works in a way intentionally to make debugging issues relatively straightforward

And I haven’t seen a library that can’t be used

Yes, it definitly did. I specifically chose Krell because it seemed rather simple and straightforward. I did some experiments with re-natal and expo in the past, but that was a complete mystery to me. I’m still pretty much a newbie in both CLJS and JS.

I have added another library to my project. This time with a default export. And again, I was having quite some trouble until I finally managed to get it to run. I think I’m still missing a piece of the picture: When I add a new dependency, which steps do I need to take? I thought I have to do this: 1. npm add my-lib 2. Require the library in cljs 3. Recompile using clj -M -m krell.main -co build.edn -c 4. Restart the Android app But I think this wasn’t enough. I also did the following things in some order I don’t remember: • Delete and rebuild the target dir • Restart metro with npx react-native start • Reinstall the Android app with npx react-native run-android (I’m not building for iOS at the moment)

Metro also has caching problems - but otherwise I don't think any of those other steps should be necessary

definitely have gotten into funny situations w/ Metro which have nothing to do w/ Krell that requires a whole cycle

whatever is on disk is the truth - and if it's still not working, I think the likelihood the problem is in Krell is quite low

but happy to take a specific set of steps to reproduce if you can come up w/ them - I dev on Android less so maybe it's spottier there