Cannot build my app, Vite says: "Module externalized for browser compatibility"

[fernandocanizo]

Hi everybody, I'm unable to build my app, Vite gives a bunch of warnings regarding Node.js imports that are only used in the backend, no client code is using this, but still gaves me the message "Module externalized for browser compatibility".

The error though is about not being able to find fields on imported Node.js modules that are there, like for example process.env.

pnpm build
# gives a bunch of messages like this one:
[plugin:vite:resolve] Module "node:process" has been externalized for browser compatibility, imported by "config.js". See https://vitejs.dev/guide/troubleshooting.html#module-externalized-for-browser-compatibility for more details.
# ...
Error [RollupError]: "env" is not exported by "__vite-browser-external", imported by "config.js".
file: config.js:2:9
1: import "dotenv/config"
2: import { env } from "node:process"
                    ^

I checked my whole code base to see if maybe I'm importing config.js from a client module, but not. All the modules that use config.js like under app/only.server/ folder, except for the entry point, which lives at the root of the project: server.js. It's an Express template-based app.

I thought maybe Vite is confused and renamed config.js to config.server.js, and then the error became:

Error: [commonjs--resolver] Server-only module referenced by client

    '~/../config.server' imported by 'app/only.server/fetchers.ts'

  See https://remix.run/docs/en/main/future/vite#splitting-up-client-and-server-code

I don't get why I'm getting this error, I thought that by naming my folder only.server I was covered from this kind of errors.

What can I do to further investigate this problem and, hopefully, solve it? Cause right now I cannot deploy my app, which is critical.

[fernandocanizo]

Ok, I thought no client code was importing config.js, but after further inspection I found that app/fileSessions.ts is using config.js and is being imported by client code.

Now the problem is I'm loading the cookie secret from config.js, I'll need to see in which ways can I send the cookie secret to the client code without exposing it.

[fernandocanizo]

Found the bug: we were exporting a back-end only function from a resource route in addition to the loader. A simple mistake overlooked on first inspection.