build,deps: replace cjs-module-lexer with merve #61456

anonrig · 2026-01-20T21:21:34Z

Initially started a couple of years ago, the new cjs module lexer is 25% faster for cold importing cjs files. This change introduces a new dependency and removes the old one.

Benchmark CI: https://ci.nodejs.org/view/Node.js%20benchmark/job/benchmark-node-micro-benchmarks/1784/console

                                                                                                                                                                confidence improvement accuracy (*)
esm/detect-esm-syntax.js n=10000 type='with-package-json'                                                                                                              ***      1.47 %       ±0.40%
esm/detect-esm-syntax.js n=10000 type='without-package-json'                                                                                                           ***      0.64 %       ±0.35%
esm/esm-legacyMainResolve.js resolvedFile='node_modules/non-exist' packageConfigMain='./index.js' packageJsonUrl='node_modules/test/package.json' n=10000                *      0.95 %       ±0.92%
esm/esm-legacyMainResolve.js resolvedFile='node_modules/non-exist' packageConfigMain='' packageJsonUrl='node_modules/test/package.json' n=10000                                -0.06 %       ±0.95%
esm/esm-legacyMainResolve.js resolvedFile='node_modules/test/index.js' packageConfigMain='./index.js' packageJsonUrl='node_modules/test/package.json' n=10000                  -0.72 %       ±1.02%
esm/esm-legacyMainResolve.js resolvedFile='node_modules/test/index.js' packageConfigMain='' packageJsonUrl='node_modules/test/package.json' n=10000                             0.33 %       ±0.62%
esm/esm-legacyMainResolve.js resolvedFile='node_modules/test/index.json' packageConfigMain='./index.js' packageJsonUrl='node_modules/test/package.json' n=10000                 0.38 %       ±0.98%
esm/esm-legacyMainResolve.js resolvedFile='node_modules/test/index.json' packageConfigMain='' packageJsonUrl='node_modules/test/package.json' n=10000                   **      0.84 %       ±0.61%
esm/esm-legacyMainResolve.js resolvedFile='node_modules/test/index.node' packageConfigMain='./index.js' packageJsonUrl='node_modules/test/package.json' n=10000                 0.66 %       ±1.04%
esm/esm-legacyMainResolve.js resolvedFile='node_modules/test/index.node' packageConfigMain='' packageJsonUrl='node_modules/test/package.json' n=10000                           0.21 %       ±0.92%
esm/esm-loader-defaultResolve.js specifier='./relative-existing.js' n=1000                                                                                                     -1.93 %       ±5.48%
esm/esm-loader-defaultResolve.js specifier='./relative-nonexistent.js' n=1000                                                                                                  -0.48 %       ±1.94%
esm/esm-loader-defaultResolve.js specifier='node:os' n=1000                                                                                                                    -8.43 %       ±9.28%
esm/esm-loader-defaultResolve.js specifier='node:prefixed-nonexistent' n=1000                                                                                                  -8.48 %      ±10.15%
esm/esm-loader-defaultResolve.js specifier='unprefixed-existing' n=1000                                                                                                         0.56 %       ±3.21%
esm/esm-loader-defaultResolve.js specifier='unprefixed-nonexistent' n=1000                                                                                                     -0.08 %       ±1.73%
esm/esm-loader-import.js specifier='./relative-existing.js' n=1000                                                                                                       *      5.62 %       ±5.09%
esm/esm-loader-import.js specifier='./relative-nonexistent.js' n=1000                                                                                                           1.53 %       ±2.90%
esm/esm-loader-import.js specifier='data:text/javascript,{i}' n=1000                                                                                                            1.47 %       ±2.73%
esm/esm-loader-import.js specifier='node:os' n=1000                                                                                                                             0.43 %       ±7.59%
esm/esm-loader-import.js specifier='node:prefixed-nonexistent' n=1000                                                                                                           2.29 %       ±3.67%
esm/import-cjs.js type='cold'                                                                                                                                          ***     26.83 %       ±0.58%
esm/import-cjs.js type='warm'                                                                                                                                          ***     11.95 %       ±0.14%
esm/import-esm-reload.js n=1000 count=1                                                                                                                                         0.08 %       ±1.04%
esm/import-esm-reload.js n=1000 count=100                                                                                                                                *      0.99 %       ±0.92%
esm/import-meta.js valuesToRead='dirname-and-filename' n=1000                                                                                                           **      1.11 %       ±0.75%
esm/import-meta.js valuesToRead='dirname' n=1000                                                                                                                                0.50 %       ±0.67%
esm/import-meta.js valuesToRead='filename' n=1000                                                                                                                       **      1.17 %       ±0.76%
esm/import-meta.js valuesToRead='url' n=1000                                                                                                                                   -0.57 %       ±0.77%
esm/require-esm.js n=1000 exports='default' type='access'                                                                                                                       0.77 %       ±1.21%
esm/require-esm.js n=1000 exports='default' type='all'                                                                                                                          1.31 %       ±1.75%
esm/require-esm.js n=1000 exports='default' type='load'                                                                                                                         0.06 %       ±1.96%
esm/require-esm.js n=1000 exports='named' type='access'                                                                                                                         0.79 %       ±1.05%
esm/require-esm.js n=1000 exports='named' type='all'                                                                                                                           -0.54 %       ±1.98%
esm/require-esm.js n=1000 exports='named' type='load'                                                                                                                          -0.90 %       ±2.32%

nodejs-github-bot · 2026-01-20T21:21:39Z

Review requested:

@nodejs/gyp
@nodejs/security-wg

codecov · 2026-01-21T17:21:34Z

Codecov Report

❌ Patch coverage is 78.84615% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.78%. Comparing base (98d2331) to head (474c7e1).
⚠️ Report is 53 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_cjs_lexer.cc	77.55%	8 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61456      +/-   ##
==========================================
- Coverage   89.85%   89.78%   -0.07%     
==========================================
  Files         671      673       +2     
  Lines      203166   203822     +656     
  Branches    39057    39183     +126     
==========================================
+ Hits       182554   183001     +447     
- Misses      12967    13139     +172     
- Partials     7645     7682      +37

Files with missing lines	Coverage Δ
lib/internal/modules/esm/translators.js	`92.58% <100.00%> (-0.39%)`	⬇️
src/node_binding.cc	`82.74% <ø> (ø)`
src/node_builtins.cc	`76.33% <ø> (+0.14%)`	⬆️
src/node_metadata.cc	`92.75% <100.00%> (+0.32%)`	⬆️
src/node_cjs_lexer.cc	`77.55% <77.55%> (ø)`

... and 72 files with indirect coverage changes

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❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

mcollina · 2026-01-22T06:27:32Z

Where does this new dep live?

anonrig · 2026-01-22T12:29:52Z

Where does this new dep live?

Currently, under my github account. Is anybody interested in helping me maintain it? github.com/anonrig/merve

configure.py

guybedford · 2026-01-22T21:28:34Z

Per current process it would make sense to move merve into the Node.js org as well. I can then add a note to the cjs-module-lexer readme that future bugs should be posted there. I'd value also having permissions to the new repo to continue to provide support.

lemire

Next step, name a library after your cat.

LICENSE

doc/api/process.md

richardlau

Please also update these references to the removed cjs-module-lexer:

node/doc/api/packages.md

Line 190 in f700203

Such modules are passed through the `cjs-module-lexer` to try to identify named
node/doc/api/esm.md

Line 630 in f700203

and build tool and transpiler outputs. See [cjs-module-lexer][] for the exact

and

node/doc/api/esm.md

Line 1285 in f700203



and

node/doc/api/esm.md

Line 1323 in f700203

[cjs-module-lexer]: https://github.com/nodejs/cjs-module-lexer/tree/2.0.0
doc/contributing/maintaining/maintaining-cjs-module-lexer.md

References to the above maintaining doc

node/doc/contributing/maintaining/maintaining-dependencies.md

Line 17 in f700203

* [cjs-module-lexer][]

node/doc/contributing/maintaining/maintaining-dependencies.md

Lines 241 to 246 in f700203

    
           ### cjs-module-lexer 
        
           The [cjs-module-lexer](https://github.com/nodejs/node/tree/HEAD/deps/cjs-module-lexer) 
        
           dependency is used within the Node.js ESM implementation to detect the 
        
           named exports of a CommonJS module. 
        
           See [maintaining-cjs-module-lexer][] for more information.

node/.github/workflows/tools.yml

Line 22 in f700203

- cjs-module-lexer

and

node/.github/workflows/tools.yml

Lines 108 to 115 in f700203

    
                     - id: cjs-module-lexer 
        
                       subsystem: deps 
        
                       label: dependencies 
        
                       run: | 
        
                         ./tools/dep_updaters/update-cjs-module-lexer.sh > temp-output 
        
                         cat temp-output 
        
                         tail -n1 temp-output | grep "NEW_VERSION=" >> "$GITHUB_ENV" || true 
        
                         rm temp-output

richardlau

Same as #61456 (comment), I would prefer the dependency was in the Node.js org (as the dep it is replacing, cjs-module-lexer, is).

anonrig · 2026-01-27T20:02:06Z

cc @nodejs/tsc are we all ok with moving https://github.com/anonrig/merve to node.js organization? my only ask is to keep the name and don't change it in the future.

aduh95 · 2026-01-27T21:02:11Z

cc @nodejs/tsc are we all ok with moving https://github.com/anonrig/merve to node.js organization? my only ask is to keep the name and don't change it in the future.

Yeah, just follow the process described in https://github.com/nodejs/admin/blob/main/transfer-repo-into-the-org.md. Happy to help if needed!

anonrig · 2026-01-27T21:04:01Z

cc @nodejs/tsc are we all ok with moving https://github.com/anonrig/merve to node.js organization? my only ask is to keep the name and don't change it in the future.

Yeah, just follow the process described in https://github.com/nodejs/admin/blob/main/transfer-repo-into-the-org.md. Happy to help if needed!

Appreciate any help @aduh95, I'll give you admin rights to the repo.

github-actions · 2026-01-28T03:56:03Z

The notable-change PRs with changes that should be highlighted in changelogs. label has been added by @anonrig.

Please suggest a text for the release notes if you'd like to include a more detailed summary, then proceed to update the PR description with the text or a link to the notable change suggested text comment. Otherwise, the commit will be placed in the Other Notable Changes section.

anonrig · 2026-01-28T03:56:24Z

let's land this pull request and i'll follow up with the changes to move the repo to nodejs organization and update references.

nodejs-github-bot · 2026-01-28T04:27:51Z

CI: https://ci.nodejs.org/job/node-test-pull-request/71086/

nodejs-github-bot · 2026-01-28T07:30:00Z

Landed in 37e4004

nodejs-github-bot added build Issues and PRs related to build files or the CI. dependencies Pull requests that update a dependency file. needs-ci PRs that need a full CI run. labels Jan 20, 2026

anonrig force-pushed the yagiz/experiment-with-cjs-lexer branch 3 times, most recently from ae6ab98 to 5e69495 Compare January 21, 2026 16:24

anonrig force-pushed the yagiz/experiment-with-cjs-lexer branch 13 times, most recently from 9bfb358 to 1da16dd Compare January 21, 2026 19:44

anonrig changed the title ~~[DO NOT MERGE] experiment with commonjs-lexer~~ build,deps: replace cjs-module-lexer with merve Jan 21, 2026

anonrig requested a review from guybedford January 21, 2026 19:46

anonrig force-pushed the yagiz/experiment-with-cjs-lexer branch 5 times, most recently from 66e99b4 to d687c0a Compare January 21, 2026 20:29

anonrig requested a review from mcollina January 21, 2026 20:56

richardlau reviewed Jan 22, 2026

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build,deps: replace cjs-module-lexer with merve

b2ec704

anonrig force-pushed the yagiz/experiment-with-cjs-lexer branch from d687c0a to b2ec704 Compare January 22, 2026 15:24

anonrig requested review from jasnell, lemire and richardlau January 22, 2026 15:25

guybedford approved these changes Jan 22, 2026

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fixup! build,deps: replace cjs-module-lexer with merve

474c7e1

anonrig requested a review from richardlau January 26, 2026 19:14

richardlau approved these changes Jan 27, 2026

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anonrig added the notable-change PRs with changes that should be highlighted in changelogs. label Jan 28, 2026

anonrig added commit-queue Add this label to land a pull request using GitHub Actions. request-ci Add this label to start a Jenkins CI on a PR. labels Jan 28, 2026

github-actions bot removed the request-ci Add this label to start a Jenkins CI on a PR. label Jan 28, 2026

nodejs-github-bot removed the commit-queue Add this label to land a pull request using GitHub Actions. label Jan 28, 2026

nodejs-github-bot merged commit 37e4004 into nodejs:main Jan 28, 2026
70 of 71 checks passed

	### cjs-module-lexer

	The [cjs-module-lexer](https://github.com/nodejs/node/tree/HEAD/deps/cjs-module-lexer)
	dependency is used within the Node.js ESM implementation to detect the
	named exports of a CommonJS module.
	See [maintaining-cjs-module-lexer][] for more information.

	- id: cjs-module-lexer
	subsystem: deps
	label: dependencies
	run: \|
	./tools/dep_updaters/update-cjs-module-lexer.sh > temp-output
	cat temp-output
	tail -n1 temp-output \| grep "NEW_VERSION=" >> "$GITHUB_ENV" \|\| true
	rm temp-output

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build,deps: replace cjs-module-lexer with merve #61456

build,deps: replace cjs-module-lexer with merve #61456

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