fix(core): make generated files have unambiguous module types

[Josh-Cena]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

Related: #6520

I set up a new website and added "type": "module" to the root package.json. Unsurprisingly, the build failed with a multitude of reasons. Some of them are related to docusaurus.config.js and sidebars.js being seen as ES modules, which will be fixed in #7371. However, there are some generated files that use require but are seen as ES modules, therefore triggering "require is not defined in ES module scope" error. To fix this, we simply need to make them .cjs, and use CJS-exclusive APIs instead. This is recommended practice because it makes the module type unambiguous.

In addition, I've added .cjs to the resolvable extensions list.

Test Plan

I applied these changes to a locally set up site and it works. The same changes should be reflected in the deploy preview as well.

When locally serving a production build, I noticed a flash of "cannot find module" banner from the serve handler. We will need to check that.

Test links

Deploy preview: https://deploy-preview-_____--docusaurus-2.netlify.app/

Related issues/PRs

[netlify]

✅ [V2]

Name	Link
🔨 Latest commit	d79e8f9
🔍 Latest deploy log	https://app.netlify.com/sites/docusaurus-2/deploys/627f62ecc88ac200096639fb
😎 Deploy Preview	https://deploy-preview-7379--docusaurus-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 58	🟢 100	🟢 100	🟢 100	🟢 90	Report
/docs/installation	🟠 83	🟢 99	🟢 100	🟢 100	🟢 90	Report

[github-actions]

Size Change: -32.7 kB (-4%)

Total Size: 780 kB

Filename	Size	Change
website/build/assets/js/main.********.js	615 kB	+38 B (0%)
website/build/index.html	6.22 kB	-32.7 kB (-84%)	🏆

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	52.3 kB
website/build/assets/css/styles.********.css	106 kB

_{compressed-size-action}

[Josh-Cena]

Oh, I think I hit the same issue as in #7238 (comment) 😭 I don't know how to fix this... The server build can't find the assets as soon as you do non-trivial changes to the module system... What's interesting here is that the server build doesn't fail, it only silently outputs a "module not found" banner... I don't know what's causing that behavior It's because the theme-fallback/Loading component catches the error and displays the error banner. Maybe we should throw the error up during SSR, so that it becomes visible? This is almost impossible to happen in userland, though.

[Josh-Cena]

OK, this is caused by the same problem as #7238 (comment), but in a different way. Because we need babel-plugin-dynamic-import-node to transform dynamic imports to require, so that Webpack does not code-split, we need to include .cjs extension in the JS loader regex as well. I forgot about that.

[slorber]

Closing for now but feel free to reopen