A recent problem I ran into when importing a ESM module.
When using preserveModules in Rollup, the package creates a nested node_modules file with the relevant dependencies. Thus the entry point of the file had a relative import to said file, e.g.
import { clsx } from '../../node_modules/clsx/dist/clsx.js';
Even though the module was ESM, it would treat clsx.js as a CJS module, leading to errors. I'm not sure why it correctly treats the module as ESM, but the nested file as CJS.
When testing this behaviour with Node 20+, the issue goes away.
The easiest solution I've found for this is to rename the node_modules folder to something else, which for whatever reason stops this behaviour.
Alternatively you can choose to not bundle the dependency, if appropriate (#todo - link)
https://github.com/rollup/rollup/issues/3684 https://jeremyrichardson.dev/blog/vite-rollup-preservemodules-for-libraries
[[buildtooling]] [[js]] [[node]]