feat: use require to load esm #5366

legendecas · 2025-05-13T13:26:38Z

PR Checklist

Addresses an existing open issue: fixes 🐛 Bug: Node.js v23 testing with .ts files #5314, fixes 🐛 Bug: Syntax error with @babel/register, JSX and latest Node.js 20 LTS (require ESM) only when run via Mocha #5317
That issue was marked as status: accepting prs
Steps in CONTRIBUTING.md were taken

Overview

This allows compilers based on require.extensions continue to work, like ts-node with Node.js built-in TypeScript support enabled.

Hopefully unblock nodejs/node#57298.

Fixes: #5314
Fixes: #5317

linux-foundation-easycla · 2025-05-13T13:26:43Z

The committers listed above are authorized under a signed CLA.

✅ login: legendecas / name: Chengzhong Wu (5cde7f5)

marco-ippolito · 2025-06-09T07:24:10Z

friendly ping @JoshuaKGoldberg

JoshuaKGoldberg · 2025-06-09T10:56:04Z

Hey thanks for the ping! I was out for a bit and am catching up on things now. I'm going to try to get to testing this thoroughly this week (hopefully tomorrow or so). But the more folks who can test this out, the better.

Note that we're pretty close to releasing Mocha 12 (#5357). I also have a vague memory of someone mentioning somewhere that once Mocha drops support for pre-require(esm) versions of Node.js, this whole area of code could be simplified. I don't have the time to spelunk for it right now, but will if nobody posts that soon.

IMO it might make sense to either...

⚡ Faster: Merge this in as a feature in Mocha 11.x, then take on the drastic simplification in Mocha 12
🦺 More careful: merge this in as a feature in Mocha 12.0, then file the simplification as a followup (either Mocha 12 or Mocha 13, depending on how breaking it is)

I'm personally leaning to ⚡ since this change is pretty targeted, and because of how broken things are at the moment for Node.js versions with type stripping. cc @mochajs/committers - WDYT?

JoshuaKGoldberg · 2025-06-09T10:59:22Z

Oh and @legendecas in the meantime, could you please try to fix the lint error? It's failing in CI.

This allows compilers based on `require.extensions` continue to work.

legendecas · 2025-06-09T12:15:01Z

Fixed lint issue.

"Merge this in as a feature in Mocha 11.x, then take on the drastic simplification in Mocha 12" sounds good to me!

JoshuaKGoldberg

💯 Fantastic! Thanks for sending this in, it's really clean and I haven't been able to break it locally when testing on a bunch of real-world repos.

We should definitely get another review from @mochajs/committers if possible just to be safe. But no blockers from me on merging to main in v11.

Copilot

Pull Request Overview

This PR adds support for loading ESM syntax via Node’s require(esm) feature while preserving require.extensions hooks, and provides integration tests for both .js and .ts compilers.

Introduce tryImportAndRequire and requireModule in esm-utils.js to choose between import() and require() based on process.features.require_module.
Add integration tests and fixtures under test/compiler-cjs and test/compiler-fixtures to validate require.extensions-based compilers.
Update ESLint config to include the new test file.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
lib/nodejs/esm-utils.js	Replace single `requireOrImport` with two strategies and conditional override
test/integration/compiler-cjs.spec.js	Add tests for `.js` and `.ts` extensions using fixtures
test/compiler-fixtures/js.fixture.js	Fixture to override `.js` loader and compile files
test/compiler-fixtures/ts.fixture.js	Fixture to override `.ts` loader and compile files
test/compiler-cjs/test.js	ESM source file for `.js` test
test/compiler-cjs/test.js.compiled	Compiled CJS output for `.js` test
test/compiler-cjs/test.ts	ESM source file for `.ts` test
test/compiler-cjs/test.ts.compiled	Compiled CJS output for `.ts` test
eslint.config.js	Include the newly added `test/compiler-cjs/test.js` in linting

Comments suppressed due to low confidence (4)

lib/nodejs/esm-utils.js:86

It looks like the closing }; for the original exports.requireOrImport arrow function is left behind after replacing it with tryImportAndRequire. Consider removing this stray closing brace and semicolon to avoid a syntax error.

};

test/compiler-cjs/test.ts:3

[nitpick] The test title uses cts which can be confusing—consider renaming to ts written in esm for clarity and consistency with the file extension.

describe('cts written in esm', () => {

test/compiler-cjs/test.ts.compiled:3

[nitpick] The compiled test also uses cts in its description; update this to ts written in esm to match the source and avoid confusion.

describe('cts written in esm', () => {

test/integration/compiler-cjs.spec.js:58

[nitpick] This expectation references cts written in esm; after renaming the test titles to ts written in esm, update this expectation string accordingly.

          'cts written in esm should work',

eslint.config.js

JoshuaKGoldberg · 2025-06-18T01:34:23Z

Just to be safe, I ran this PR's changes through another set of tests today on:

https://github.com/eslint/eslint
https://github.com/Microsoft/TypeScript
https://github.com/legendecas/mocha-register-node-v23 (from 🐛 Bug: Node.js v23 testing with .ts files #5314)
https://github.com/mbtts/babel-node-mocha-test (from 🐛 Bug: Syntax error with @babel/register, JSX and latest Node.js 20 LTS (require ESM) only when run via Mocha #5317)

...across Node.js versions:

18.18.0
20.9.0
21.1.0
22.16.0
23.11.1
24.2.0

Confirmed that this fixes both of those issues and generally works. Great! I'll merge this now and publish a new release. Thanks a bunch @legendecas for the clean fix and patience with us on the PR review, this is great work! Additional shoutout to @marco-ippolito from the Node.js side and for helping push it forward. 🔥

JoshuaKGoldberg · 2025-06-18T01:40:31Z

Released as 11.7.0:

🎉

AviVahl · 2025-06-18T11:08:23Z

This PR has the unfortunate side-effect of removing support for setups that use asynchronous Node.js loaders/hooks.

Before this PR:
try import(). if that fails- try require().

After this PR:
try require(). if that fails and error is ERR_REQUIRE_ASYNC_MODULE- try import().
if require() fails for any other reason (e.g. needing the hooks being registered), it won't even try to import(), not making use of any asynchronous hooks.

queengooborg · 2025-06-18T12:08:54Z

Looks like this change had broken testing on MDN's browser-compat-data: https://github.com/mdn/browser-compat-data/actions/runs/15731639024/job/44333918076?pr=27094

Exception during run: Error: Transform failed with 1 error:
/home/runner/work/browser-compat-data/browser-compat-data/index.ts:56:15: ERROR: Top-level await is currently not supported with the "cjs" output format

Also affecting the mdn-bcd-collector project in the same way: https://github.com/openwebdocs/mdn-bcd-collector/actions/runs/15732266958/job/44335981656?pr=2479

Not sure if it's an issue with tsx in particular, but something seems to be blocking us from upgrading to Mocha v11.7. Will try to dig in to see if it's something with our setup tomorrow!

JoshuaKGoldberg · 2025-06-18T12:53:12Z

Lovely. Thanks @AviVahl and @queengooborg, that's good to know. Any investigation you can do would be greatly appreciated. Fixing this area is a high priority for Mocha right now.

This reverts commit 41e24a2.

mshima · 2025-06-20T20:36:06Z

@JoshuaKGoldberg it breaks mocha with custom ts loader. jhipster/generator-jhipster#29827
It's probably because the required module doesn't exist so it does not fallback to import due to condition.
Typescript loaders takes a non existing .js module and tries to load .ts alternative and I think there is no loader support for require.
I will do some test.

MuTsunTsai · 2025-06-23T01:58:34Z

It also breaks @hyperse/ts-node/register. It was working in Mocha 11.6.0.

JoshuaKGoldberg · 2025-06-23T15:24:25Z

We believe we have a fix:

test: add esm loader test #5383: adds a test that exercises at least one of the kinds of cases now failing in 11.7.0
fix: always fallback to import() if require() fails #5384 fixes at least all of the cases that have been reported:

If anybody is seeing a new error as of Mocha 11.7.0 that's not in any of those issues (and doesn't reproduce on Mocha 11.6.0) please do file a new issue.

marco-ippolito approved these changes May 13, 2025

View reviewed changes

legendecas marked this pull request as ready for review May 26, 2025 00:56

feat: use require to load esm

5cde7f5

This allows compilers based on `require.extensions` continue to work.

legendecas force-pushed the require-esm branch from e089426 to 5cde7f5 Compare June 9, 2025 12:13

mark-wiemer self-requested a review June 10, 2025 02:15

JoshuaKGoldberg approved these changes Jun 11, 2025

View reviewed changes

mark-wiemer approved these changes Jun 12, 2025

View reviewed changes

voxpelli requested a review from Copilot June 12, 2025 07:44

Copilot AI reviewed Jun 12, 2025

View reviewed changes

eslint.config.js Show resolved Hide resolved

JoshuaKGoldberg mentioned this pull request Jun 12, 2025

🧹 Versioning: Bump minimum Node.js version from 18.18.0 to 20.19.0 #5358

Open

JoshuaKGoldberg merged commit 41e24a2 into mochajs:main Jun 18, 2025
75 of 76 checks passed

github-actions bot mentioned this pull request Jun 18, 2025

chore(main): release 11.7.0 #5378

Merged

legendecas deleted the require-esm branch June 18, 2025 09:51

legendecas added a commit to legendecas/mocha that referenced this pull request Jun 18, 2025

Revert "feat: use require to load esm (mochajs#5366)"

eed332c

This reverts commit 41e24a2.

legendecas mentioned this pull request Jun 18, 2025

fix: revert "feat: use require to load esm (#5366)" #5381

Closed

3 tasks

JoshuaKGoldberg mentioned this pull request Jun 18, 2025

🛠 Repo: Add tests for issues discovered with native import() requiring #5382

Open

5 tasks

voxpelli mentioned this pull request Jun 18, 2025

🐛 Bug: Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: Package subpath './esm-register' is not defined by "exports #5380

Closed

4 tasks

Borewit mentioned this pull request Jun 22, 2025

🐛 Bug: Mocha 11.7.0 introduces issues loading ECMAScript Modules (ESM) with ts-node/esm #5388

Closed

4 tasks

voxpelli mentioned this pull request Jun 23, 2025

🐛 Bug: Mocha v11.7.0 fails with error ERR_REQUIRE_ESM #5387

Closed

4 tasks

mshima mentioned this pull request Jun 23, 2025

fix: always fallback to import() if require() fails #5384

Merged

3 tasks

This was referenced Jul 2, 2025

🐛 Bug: chai-as-promised with top-level-await in setup file no longer applies #5392

Closed

📌 Mocha 12 Release Plan #5357

Open

AlexCannonball mentioned this pull request Jul 10, 2025

Enable consuming of ES modules in extensions microsoft/vscode#130367

Open

joyeecheung mentioned this pull request Aug 6, 2025

node 22.18 breaks npm package because of experimental-strip-types enabled nodejs/node#59364

Open

azu mentioned this pull request Aug 9, 2025

chore: Node.js maintenance updates textlint/textlint#1682

Merged

3 tasks

This was referenced Aug 13, 2025

chore(deps): update dependency mocha to v11.7.1 open-telemetry/opentelemetry-js#5850

Open

fix: load mjs files correctly #5429

Open

Uh oh!

feat: use require to load esm #5366

feat: use require to load esm #5366

Uh oh!

Conversation

legendecas commented May 13, 2025 • edited by JoshuaKGoldberg Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

PR Checklist

Overview

Uh oh!

linux-foundation-easycla bot commented May 13, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

marco-ippolito commented Jun 9, 2025

Uh oh!

JoshuaKGoldberg commented Jun 9, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

JoshuaKGoldberg commented Jun 9, 2025

Uh oh!

legendecas commented Jun 9, 2025

Uh oh!

JoshuaKGoldberg left a comment • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull Request Overview

Reviewed Changes

Uh oh!

Uh oh!

JoshuaKGoldberg commented Jun 18, 2025

Uh oh!

Uh oh!

JoshuaKGoldberg commented Jun 18, 2025

Uh oh!

AviVahl commented Jun 18, 2025

Uh oh!

queengooborg commented Jun 18, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

JoshuaKGoldberg commented Jun 18, 2025

Uh oh!

mshima commented Jun 20, 2025

Uh oh!

MuTsunTsai commented Jun 23, 2025

Uh oh!

JoshuaKGoldberg commented Jun 23, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

legendecas commented May 13, 2025 •

edited by JoshuaKGoldberg

Loading

linux-foundation-easycla bot commented May 13, 2025 •

edited

Loading

JoshuaKGoldberg commented Jun 9, 2025 •

edited

Loading

JoshuaKGoldberg left a comment •

edited

Loading

queengooborg commented Jun 18, 2025 •

edited

Loading

JoshuaKGoldberg commented Jun 23, 2025 •

edited

Loading