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[Bug]: .esm.js is ignored in extensionsToTreatAsEsm

See original GitHub issue

Version

27.1.0

Steps to reproduce

Set extensionsToTreatAsEsm to ['.esm.js'].
Import a path that points to a file named something.esm.js.

Expected behavior

The imported file should be treated as esm.

Actual behavior

The imported file will be treated as CommonJS.

Additional context

AFAICT the culprit is this snippet in packages/jest-resolve/src/shouldLoadAsEsm.ts:

  const extension = extname(path);

  if (extension === '.mjs') {
    return true;
  }

  if (extension === '.cjs') {
    return false;
  }

  if (extension !== '.js') {
    return extensionsToTreatAsEsm.includes(extension);
  }

Which assumes only the last part of the file name needs to be checked against the configured extensions.

Environment

System:
    OS: Linux 5.4 Ubuntu 20.04.2 LTS (Focal Fossa)
    CPU: (8) x64 Intel(R) Xeon(R) Gold 6152 CPU @ 2.10GHz
  Binaries:
    Node: 14.17.1 - ~/.nvm/versions/node/v14.17.1/bin/node
    npm: 6.14.13 - ~/.nvm/versions/node/v14.17.1/bin/npm
  npmPackages:
    jest: ^27.1.0 => 27.1.0

Issue Analytics

State:
Created 2 years ago
Comments:6

Top GitHub Comments

1reaction

SimenBcommented, Feb 23, 2022

If you use .js, the closest package.json needs to include type: module, this won’t change.

Also, TypeScript’s tslib uses tslib.es6.js for its ESM build. I would say that’s a pretty common library to have…

Of course, jest could also be smart enough to recognize that tslib’s package.json has "module": "tslib.es6.js", indicating that tslib.es6.js is an ESM. But since it doesn’t even recognize the "module" field without a custom resolver (#2702), that’s probably a stretch…

Jest respects import export condition (as of https://github.com/facebook/jest/releases/tag/v27.3.0), which tslib uses, together with a package.json with the required type: module.

https://github.com/microsoft/tslib/blob/c827964226e85118e2fd35b1cc68d4a5ad867f39/package.json#L32 https://github.com/microsoft/tslib/blob/c827964226e85118e2fd35b1cc68d4a5ad867f39/modules/package.json

We have also come across this issue because Swiper v7 uses .esm.js.

Almost the same thing, but e.g. swiper/react (https://www.runpkg.com/?swiper@8.0.6/package.json#91) support is only available in Jest 28 (currently alpha.4), ref #9771. Only . subpath is support in v27.3.

0reactions

igneosaurcommented, Feb 23, 2022

We have also come across this issue because Swiper v7 uses .esm.js.

https://github.com/nolimits4web/swiper/issues/4871

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