[gurgunday]

Determining the format of a .js or .ts module calls getPackageScopeConfig(), which spreads the deserialized package configuration and therefore invokes its lazy exports and imports getters

Every resolved module parses those maps again so load time and memory grows with the number of modules in a package times the size of its exports map

Instead of crating yet another cache, use getPackageType() for format detection and only look up the package.json path when warning about a typeless package

Build	exports=0	exports=700 (~130 KB map)
main 91c4436	12–14 ms, 65 MB	55–66 ms, 134–157 MB
this branch	10–12 ms, 64–65 MB	11–13 ms, 66–67 MB

Both date-fns and drizzle-orm are affected by this and should improve the same way

Supersedes #65812 and fixes #66485

[nodejs-github-bot]

Review requested:

• @nodejs/loaders

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.59%. Comparing base (91c4436) to head (ac7d34f).
⚠️ Report is 115 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66982      +/-   ##
==========================================
- Coverage   92.93%   90.59%   -2.35%     
==========================================
  Files         428      797     +369     
  Lines      195236   278301   +83065     
  Branches    30176    53520   +23344     
==========================================
+ Hits       181442   252115   +70673     
- Misses      13467    16556    +3089     
- Partials      327     9630    +9303     

Files with missing lines	Coverage Δ
lib/internal/modules/esm/get_format.js	98.64% <100.00%> (+24.67%)	⬆️
lib/internal/modules/package_json_reader.js	99.34% <100.00%> (+11.59%)	⬆️

... and 499 files with indirect coverage changes

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[mcollina]

lgtm

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/78664/

[ljharb]

This seems good, but needs nonzero tests.

[gurgunday]

@ljharb what should I test? Memory usage? Changes are already covered by tests and for the performance improvement, I can port this if you'd like

[nodejs-github-bot]

Landed in 45df6b7

[TylerNRobertson]

Thanks for fixing this! Could it be backported to v26.x and v24.x?

It has a big effect on test runners that start a fresh process per test file. With date-fns 4.4.0 (864 files, 741 exports entries), a cold import('date-fns') takes ~605 ms on 24.22.1 and ~550 ms on 26.13.0, against ~90 ms and ~50 ms for require('date-fns'). In a CPU profile, ~450 ms of that is the lazy exports getter fired by the ...data spread in getPackageScopeConfig.

Under Vitest's default pool (a new process per test file), that cost is paid once per file. On our 500-file suite, Vitest takes ~78 s locally against ~7 s for Jest.