Intro

This is an example demonstrating the error described in Dune and js_of_ocaml setup from the discuss.ocaml.org, with failing to resolve child_process and fs.

The OCaml setup ocaml/ is very simple. The JS uses Next.js. See js/pages/index.js for the entry point (this is the only relevant file on the JS side).

Instructions

cd js
npm install
npm run dev

On my computer (OCaml 4.13.1, js_of_ocaml 4.0.0) this produces:

Module not found: Can't resolve 'fs'
  934 |      {if(i >>> 0 >= s.l)caml_bytes_bound_error();
  935 |       return caml_bytes_unsafe_set(s,i,c)}
> 936 |     function MlNodeFile(fd){this.fs = require("fs");this.fd = fd}
      |                            ^
  937 |     MlNodeFile.prototype = new MlFile();
  938 |     MlNodeFile.prototype.truncate
  939 |     =

Import trace for requested module:
./pages/index.js

https://nextjs.org/docs/messages/module-not-found
Native Node.js APIs are not supported in the Edge Runtime. Found `fs` imported.

Fix

See the webpack-5-resolution branch.