Tracking issue: require(esm) #52697

joyeecheung · 2024-04-25T21:25:06Z

Before it's unflagged

Figure out default export interop with transpilers, either adding __esModule to required ESM on our end (module: add __esModule to require()'d ESM #52166), or transpilers update themselves to check the result returned by require():
conditional exports for module, regardless of whether it's loaded by require or import. Something like module which is recognized by Webpack and Rollup would be good (maybe this doesn't need to block unflagging, but should be done before stablization) module: implement the "module-sync" exports condition #54648
Move experimental warning to where require() is actually handling a ESM

Before it is promoted to be stable:

Implement detection module: support ESM detection in the CJS loader #52047
Some marker to customize the default exports returned by require(esm) module: support 'module.exports' interop export name in require(esm) #54563
Support module customization hooks doc: add synchronous hooks proposal loaders#198

Nice-to-haves:

Bug fixes & changes:

Related features that interoperate with require(esm) and need to be considered when being backported together:

For v22.x backport (see a summary of regression analysis in #55217 (comment))

The text was updated successfully, but these errors were encountered:

GeoffreyBooth · 2024-04-30T19:16:14Z

@nodejs/loaders

jakebailey · 2024-05-07T22:00:30Z

I just wanted to note it here, but it would be super super awesome if (once stable) this were backported to Node 20/22 or even Node 18 if still in support. I'd love to be able to propose a change to switch TypeScript to ESM (given I have it working without breaking CJS consumers), but the time horizon of Node 22 being the oldest supported version is pretty daunting.

It also seems like there is a hacky way using multiple entrypoints that could allow for TS to grab Node's builtins conditionally without #52599/#52762, though none of that is possible without require(ESM), of course.

Even without TypeScript's use case, I think the feature itself is a really important one for the ecosystem. Backporting would really make ESM changeovers a lot less painful.

Andarist · 2024-05-07T22:07:50Z

IIRC from some Twitter threads - there is a plan to backport this once the feature stabilizes.

joyeecheung · 2024-07-11T23:16:42Z

Regarding the conditional exports, @guybedford suggested to implement just the module condition that Rollup and Webpack already recognize. I have a WIP but need to do some testing which involves many combinations of test cases 😵‍💫 but will also do some npm crawling to see if it can be picked up/is in conflict with any existing popular packages.

GeoffreyBooth · 2024-07-11T23:41:11Z

@guybedford suggested to implement just the module condition that Rollup and Webpack already recognize.

The module top level field, or within exports?

Personally I think require-module makes more sense, as it would complement the existing require and import keys that Node supports.

joyeecheung · 2024-08-29T22:54:36Z

Opened PR for "module" in #54648

Personally I think require-module makes more sense, as it would complement the existing require and import keys that Node supports.

If we are starting from scratch, yes, but then the "module" condition has already been adopted by bundlers that support require(esm) in the wild, so it seems better to go along with the existing convention. See https://gist.github.com/sokra/e032a0f17c1721c71cfced6f14516c62

This patch implements a "module-sync" exports condition for packages to supply a sycnrhonous ES module to the Node.js module loader, no matter it's being required or imported. This is similar to the "module" condition that bundlers have been using to support `require(esm)` in Node.js, and allows dual-package authors to opt into ESM-first only newer versions of Node.js that supports require(esm) while avoiding the dual-package hazard. ```json { "type": "module", "exports": { "node": { // On new version of Node.js, both require() and import get // the ESM version "module-sync": "./index.js", // On older version of Node.js, where "module" and // require(esm) are not supported, use the transpiled CJS version // to avoid dual-package hazard. Library authors can decide // to drop support for older versions of Node.js when they think // it's time. "default": "./dist/index.cjs" }, // On any other environment, use the ESM version. "default": "./index.js" } } ``` We end up implementing a condition with a different name instead of reusing "module", because existing code in the ecosystem using the "module" condition sometimes also expect the module resolution for these ESM files to work in CJS style, which is supported by bundlers, but the native Node.js loader has intentionally made ESM resolution different from CJS resolution (e.g. forbidding `import './noext'` or `import './directory'`), so it would be semver-major to implement a `"module"` condition without implementing the forbidden ESM resolution rules. For now, this just implments a new condition as semver-minor so it can be backported to older LTS. Refs: https://webpack.js.org/guides/package-exports/#target-environment-independent-packages PR-URL: #54648 Fixes: #52173 Refs: https://github.com/joyeecheung/test-module-condition Refs: #52697 Reviewed-By: Jacob Smith <[email protected]> Reviewed-By: Jan Krems <[email protected]> Reviewed-By: Chengzhong Wu <[email protected]>

This unflags --experimental-require-module so require(esm) can be used without the flag. For now, when require() actually encounters an ESM, it will still emit an experimental warning. To opt out of the feature, --no-experimental-require-module can be used. There are some tests specifically testing ERR_REQUIRE_ESM. Some of them are repurposed to test --no-experimental-require-module. Some of them are modified to just expect loading require(esm) to work, when it's appropriate. PR-URL: #55085 Refs: #52697 Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Marco Ippolito <[email protected]> Reviewed-By: Rafael Gonzaga <[email protected]> Reviewed-By: Yagiz Nizipli <[email protected]> Reviewed-By: LiviaMedeiros <[email protected]> Reviewed-By: Antoine du Hamel <[email protected]> Reviewed-By: Filip Skokan <[email protected]> Reviewed-By: Michael Dawson <[email protected]> Reviewed-By: Richard Lau <[email protected]>

This patch implements a "module-sync" exports condition for packages to supply a sycnrhonous ES module to the Node.js module loader, no matter it's being required or imported. This is similar to the "module" condition that bundlers have been using to support `require(esm)` in Node.js, and allows dual-package authors to opt into ESM-first only newer versions of Node.js that supports require(esm) while avoiding the dual-package hazard. ```json { "type": "module", "exports": { "node": { // On new version of Node.js, both require() and import get // the ESM version "module-sync": "./index.js", // On older version of Node.js, where "module" and // require(esm) are not supported, use the transpiled CJS version // to avoid dual-package hazard. Library authors can decide // to drop support for older versions of Node.js when they think // it's time. "default": "./dist/index.cjs" }, // On any other environment, use the ESM version. "default": "./index.js" } } ``` We end up implementing a condition with a different name instead of reusing "module", because existing code in the ecosystem using the "module" condition sometimes also expect the module resolution for these ESM files to work in CJS style, which is supported by bundlers, but the native Node.js loader has intentionally made ESM resolution different from CJS resolution (e.g. forbidding `import './noext'` or `import './directory'`), so it would be semver-major to implement a `"module"` condition without implementing the forbidden ESM resolution rules. For now, this just implments a new condition as semver-minor so it can be backported to older LTS. Refs: https://webpack.js.org/guides/package-exports/#target-environment-independent-packages PR-URL: nodejs#54648 Fixes: nodejs#52173 Refs: https://github.com/joyeecheung/test-module-condition Refs: nodejs#52697 Reviewed-By: Jacob Smith <[email protected]> Reviewed-By: Jan Krems <[email protected]> Reviewed-By: Chengzhong Wu <[email protected]>

This unflags --experimental-require-module so require(esm) can be used without the flag. For now, when require() actually encounters an ESM, it will still emit an experimental warning. To opt out of the feature, --no-experimental-require-module can be used. There are some tests specifically testing ERR_REQUIRE_ESM. Some of them are repurposed to test --no-experimental-require-module. Some of them are modified to just expect loading require(esm) to work, when it's appropriate. PR-URL: nodejs#55085 Refs: nodejs#52697 Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Marco Ippolito <[email protected]> Reviewed-By: Rafael Gonzaga <[email protected]> Reviewed-By: Yagiz Nizipli <[email protected]> Reviewed-By: LiviaMedeiros <[email protected]> Reviewed-By: Antoine du Hamel <[email protected]> Reviewed-By: Filip Skokan <[email protected]> Reviewed-By: Michael Dawson <[email protected]> Reviewed-By: Richard Lau <[email protected]>

voxpelli · 2024-10-03T12:53:10Z

Raised a question on Twitter to @joyeecheung on my conclusions in https://github.com/voxpelli/investigation-esm-require where it seems like Node 22.9.0 may unintentionally allow some ESM-files to be loaded even without the flag: https://twitter.com/voxpelli/status/1841818608713826693

Mentioning here for sake of completeness, if deemed a correct observation a proper issue will be created

voxpelli · 2024-10-04T07:46:34Z

The above resulted in a PR to fix it: #55250

This patch implements a "module-sync" exports condition for packages to supply a sycnrhonous ES module to the Node.js module loader, no matter it's being required or imported. This is similar to the "module" condition that bundlers have been using to support `require(esm)` in Node.js, and allows dual-package authors to opt into ESM-first only newer versions of Node.js that supports require(esm) while avoiding the dual-package hazard. ```json { "type": "module", "exports": { "node": { // On new version of Node.js, both require() and import get // the ESM version "module-sync": "./index.js", // On older version of Node.js, where "module" and // require(esm) are not supported, use the transpiled CJS version // to avoid dual-package hazard. Library authors can decide // to drop support for older versions of Node.js when they think // it's time. "default": "./dist/index.cjs" }, // On any other environment, use the ESM version. "default": "./index.js" } } ``` We end up implementing a condition with a different name instead of reusing "module", because existing code in the ecosystem using the "module" condition sometimes also expect the module resolution for these ESM files to work in CJS style, which is supported by bundlers, but the native Node.js loader has intentionally made ESM resolution different from CJS resolution (e.g. forbidding `import './noext'` or `import './directory'`), so it would be semver-major to implement a `"module"` condition without implementing the forbidden ESM resolution rules. For now, this just implments a new condition as semver-minor so it can be backported to older LTS. Refs: https://webpack.js.org/guides/package-exports/#target-environment-independent-packages PR-URL: #54648 Fixes: #52173 Refs: https://github.com/joyeecheung/test-module-condition Refs: #52697 Reviewed-By: Jacob Smith <[email protected]> Reviewed-By: Jan Krems <[email protected]> Reviewed-By: Chengzhong Wu <[email protected]>

targos · 2024-10-05T09:38:54Z

It looks like npm itself triggers the warning:

$ make lint
cd tools/eslint && if [ -x ""/Users/mzasso/git/nodejs/node/node"" ] && [ -e ""/Users/mzasso/git/nodejs/node/node"" ]; then ""/Users/mzasso/git/nodejs/node/node"" /Users/mzasso/git/nodejs/node/./deps/npm/bin/npm-cli.js ci; elif [ -x `command -v node` ] && [ -e `command -v node` ] && [ `command -v node` ]; then `command -v node` /Users/mzasso/git/nodejs/node/./deps/npm/bin/npm-cli.js ci; else echo "No available node, cannot run \"node /Users/mzasso/git/nodejs/node/./deps/npm/bin/npm-cli.js ci\""; exit 1; fi;
npm warn cli npm v10.8.3 does not support Node.js v23.0.0-pre. This version of npm supports the following node versions: `^18.17.0 || >=20.5.0`. You can find the latest version at https://nodejs.org/.
(node:45192) ExperimentalWarning: Support for loading ES Module in require() is an experimental feature and might change at any time
    at emitExperimentalWarning (node:internal/util:269:11)
    at loadESMFromCJS (node:internal/modules/cjs/loader:1388:5)
    at Module._compile (node:internal/modules/cjs/loader:1517:5)
    at Module._extensions..js (node:internal/modules/cjs/loader:1672:16)
    at Module.load (node:internal/modules/cjs/loader:1328:32)
    at Module._load (node:internal/modules/cjs/loader:1138:12)
    at TracingChannel.traceSync (node:diagnostics_channel:315:14)
    at wrapModuleLoad (node:internal/modules/cjs/loader:218:24)
    at Module.require (node:internal/modules/cjs/loader:1350:12)
    at require (node:internal/modules/helpers:138:16)

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joyeecheung · 2024-10-05T20:24:06Z

Yes, because of debug, which I covered in #55217 (comment) and addressed in the last commit of the backport PR. In the last TSC meeting we agreed to silence the warning when require() comes from node_modules on v22 and keep it on v23 to help people notice and update them (with #55241)

This unflags --experimental-require-module so require(esm) can be used without the flag. For now, when require() actually encounters an ESM, it will still emit an experimental warning. To opt out of the feature, --no-experimental-require-module can be used. There are some tests specifically testing ERR_REQUIRE_ESM. Some of them are repurposed to test --no-experimental-require-module. Some of them are modified to just expect loading require(esm) to work, when it's appropriate. PR-URL: nodejs#55085 Refs: nodejs#52697 Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Marco Ippolito <[email protected]> Reviewed-By: Rafael Gonzaga <[email protected]> Reviewed-By: Yagiz Nizipli <[email protected]> Reviewed-By: LiviaMedeiros <[email protected]> Reviewed-By: Antoine du Hamel <[email protected]> Reviewed-By: Filip Skokan <[email protected]> Reviewed-By: Michael Dawson <[email protected]> Reviewed-By: Richard Lau <[email protected]>

This unflags --experimental-require-module so require(esm) can be used without the flag. For now, when require() actually encounters an ESM, it will still emit an experimental warning. To opt out of the feature, --no-experimental-require-module can be used. There are some tests specifically testing ERR_REQUIRE_ESM. Some of them are repurposed to test --no-experimental-require-module. Some of them are modified to just expect loading require(esm) to work, when it's appropriate. PR-URL: nodejs#55085 Backport-PR-URL: nodejs#55217 Refs: nodejs#52697 Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Marco Ippolito <[email protected]> Reviewed-By: Rafael Gonzaga <[email protected]> Reviewed-By: Yagiz Nizipli <[email protected]> Reviewed-By: LiviaMedeiros <[email protected]> Reviewed-By: Antoine du Hamel <[email protected]> Reviewed-By: Filip Skokan <[email protected]> Reviewed-By: Michael Dawson <[email protected]> Reviewed-By: Richard Lau <[email protected]>

This is faster and more consistent with other places using the regular expression to detect node_modules. PR-URL: nodejs#55243 Backport-PR-URL: nodejs#55217 Reviewed-By: Antoine du Hamel <[email protected]> Reviewed-By: Jacob Smith <[email protected]> Reviewed-By: Richard Lau <[email protected]> Reviewed-By: Marco Ippolito <[email protected]> Refs: nodejs#52697

Some packages have been using try-catch to load require(esm) in environments that are available. In 23, where require(esm) is unflagged, we emit an experimental warning when require() is used to load ESM. To backport require(esm) to older LTS releases, however, this could break existing CLI output. To reduce the disruption for LTS, on older release lines, this commit is applied to skip the warning if require(esm) comes from node_modules. This warning will be eventually removed when require(esm) becomes stable. PR-URL: nodejs#55217 Refs: nodejs#52697 Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Antoine du Hamel <[email protected]>

When a ESM module cannot be loaded by require due to the presence of TLA, its module status would be stopped at kInstantiated. In this case, when it's imported again, we should allow it to be evaluated asynchronously, as it's also a common pattern for users to retry with dynamic import when require fails. PR-URL: #55502 Fixes: #55500 Refs: #52697 Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Chemi Atlow <[email protected]>

This tracks the asynchronicity in the ModuleWraps when they turn out to contain TLA after instantiation, and throw the right error (ERR_REQUIRE_ASYNC_MODULE) when it's required again. It removes the freezing of ModuleWraps since it's not meaningful to freeze this when the rest of the module loader is mutable, and we can record the asynchronicity in the ModuleWrap right after compilation after we get a V8 upgrade that contains v8::Module::HasTopLevelAwait() instead of searching through the module graph repeatedly which can be slow. PR-URL: #55520 Fixes: #55516 Refs: #52697 Reviewed-By: Paolo Insogna <[email protected]> Reviewed-By: Antoine du Hamel <[email protected]> Reviewed-By: Chengzhong Wu <[email protected]> Reviewed-By: Jacob Smith <[email protected]>

When a ESM module cannot be loaded by require due to the presence of TLA, its module status would be stopped at kInstantiated. In this case, when it's imported again, we should allow it to be evaluated asynchronously, as it's also a common pattern for users to retry with dynamic import when require fails. PR-URL: nodejs#55502 Fixes: nodejs#55500 Refs: nodejs#52697 Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Chemi Atlow <[email protected]>

This tracks the asynchronicity in the ModuleWraps when they turn out to contain TLA after instantiation, and throw the right error (ERR_REQUIRE_ASYNC_MODULE) when it's required again. It removes the freezing of ModuleWraps since it's not meaningful to freeze this when the rest of the module loader is mutable, and we can record the asynchronicity in the ModuleWrap right after compilation after we get a V8 upgrade that contains v8::Module::HasTopLevelAwait() instead of searching through the module graph repeatedly which can be slow. PR-URL: nodejs#55520 Fixes: nodejs#55516 Refs: nodejs#52697 Reviewed-By: Paolo Insogna <[email protected]> Reviewed-By: Antoine du Hamel <[email protected]> Reviewed-By: Chengzhong Wu <[email protected]> Reviewed-By: Jacob Smith <[email protected]>