feat: ESM configuration file

[thescientist13]

PR Checklist

• Addresses an existing open issue: fixes 🚀 Feature: ESM configuration file #5049
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Introduces the ability to use ESM configuration files for Mocha, leveraging the require(ESM) capability of Node >= 20.19.0

See a demo repo with these patches here - https://github.com/thescientist13/mocha-esm-config

TODO

1. Test Case
2. Documentation

---

Per my understanding of support require(ESM) is so far only in >= 20.19.0, so not sure how this will fare with test cases running on Node 18, and or if this is something to just call out in the documentation? Not sure if will get backported to 18.x at this point as it is EOL now...

Either way, let me know your thoughts on the current implementation and the implications of Node support. Happy to add a test case / docs once I make sure this changeset is heading in the right direction. 🫡

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: thescientist13 / name: Owen Buckley (1b8b91d, 7613e58, f9b77df)

[thescientist13]

Not sure if there's a better / more idiomatic way in Mocha to get the user's package.json file?

[JoshuaKGoldberg]

I would personally use something like package-up

But, determining whether the caller is CJS or ESM can be more tricky than that. My instinct is it'd be best to not add in specific logic for either. Using require(esm), we can do something simpler like packageJson.default ?? packageJson and call it a day.

[JoshuaKGoldberg]

👋 @thescientist13 just checking in, are you waiting on us for anything?

Now that #5358 is merged, this shouldn't have to worry about require(esm) not being supported. Though we are still seeing errors in other PRs (#5482, #5484, #5487) around that which we still need to debug. If you do see errors around CJS/ESM support you can ignore them for now.

[thescientist13]

hey @JoshuaKGoldberg , thanks for checking in!

Not waiting on anything per se, was just waiting to see what would happen with that other PR. I just rebased against main and pushed that up here with your feedback suggestion from earlier, so I can work on tests / docs if that's good with you.

[thescientist13]

Had some intermittent test failures locally, but none of them seemed related to the CLI changes here, so throwing this up to see what happens. 😅