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fix: detect esm only pkg w/ main and module fields#1494

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ghostdevv merged 1 commit intonpmx-dev:mainfrom
jonchurch:legacy-dual-detection
Feb 14, 2026
Merged

fix: detect esm only pkg w/ main and module fields#1494
ghostdevv merged 1 commit intonpmx-dev:mainfrom
jonchurch:legacy-dual-detection

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@jonchurch
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@jonchurch jonchurch commented Feb 14, 2026 •
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Problem

In the Compare feature, the heuristic for legacy fallback for dual vs esm only detection has a bug currently where it assumes main contains CJS when the package also has a module field.

That reports ESM only packages w/ both esm main and module fields like lodash-es as dual packages.

  "type": "module",
  "jsnext:main": "lodash.js",
  "main": "lodash.js",
  "module": "lodash.js",

Above is an ESM only package description, but currently that will be reported as "ESM + CJS"

Solution

Infer if the main field should be CJS or ESM. If main is .cjs extension then we for sure know it's CJS. If we have a .js file and no "type": "module" then we have a CJS file.

📸

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codecov bot commented Feb 14, 2026

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines Patch % Lines
shared/utils/package-analysis.ts 0.00% 0 Missing and 2 partials ⚠️

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coderabbitai bot commented Feb 14, 2026 •
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📝 Walkthrough

Walkthrough

The changes modify the module format detection logic in detectModuleFormat within the package analysis utility. Previously, when both module and main fields were present, the function always returned 'dual'. The new implementation conditionally returns 'dual' or 'esm' based on whether the main field ends with .cjs or .js (when package type is not module). Test cases have been added to verify both dual and ESModule detection scenarios with type, module, and main fields present.

Suggested reviewers

  • danielroe
  • ghostdevv
🚥 Pre-merge checks | ✅ 2
✅ Passed checks (2 passed)
Check name Status Explanation
Merge Conflict Detection ✅ Passed ✅ No merge conflicts detected when merging into main
Description check ✅ Passed The pull request description clearly explains the bug in module format detection and provides a specific solution aligned with the code changes.

✏️ Tip: You can configure your own custom pre-merge checks in the settings.

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@ghostdevv ghostdevv added this pull request to the merge queue Feb 14, 2026
Merged via the queue into npmx-dev:main with commit d7de1e7 Feb 14, 2026
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github-actions bot commented Feb 14, 2026

Thanks for your first contribution, @jonchurch! 💪

We'd love to welcome you to the npmx community. Come and say hi on Discord! And once you've joined, visit npmx.wamellow.com to claim the contributor role.

@jonchurch jonchurch deleted the legacy-dual-detection branch February 14, 2026 17:07
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@jonchurch @ghostdevv