lib: include ESM loader in the built-in snapshot by joyeecheung · Pull Request #61769 · nodejs/node

joyeecheung · 2026-02-11T04:52:49Z

Benchmark number from an ARM64 Linux machine: empty/minimal CJS startup is now slightly slower in worker but other metrics get a slight boost (because they all incur ESM loader initialization). In reality ESM loading is likely to happen at some point in the lifetime of an application especially with the growing adoption of ESM and require(esm), so real-world applications that are more than just an empty script should get a bit of speed up from being able to just deserialize the ESM loader instead of initializing it from scrach.

                                                                                         confidence improvement accuracy (*)   (**)  (***)
misc/startup-core.js n=30 mode='process' script='benchmark/fixtures/empty.mjs'                  ***      6.06 %       ±0.60% ±0.80% ±1.04%
misc/startup-core.js n=30 mode='process' script='benchmark/fixtures/import-builtins.mjs'        ***      2.40 %       ±0.30% ±0.40% ±0.52%
misc/startup-core.js n=30 mode='process' script='benchmark/fixtures/require-builtins.js'        ***      0.57 %       ±0.32% ±0.42% ±0.55%
misc/startup-core.js n=30 mode='process' script='test/fixtures/semicolon.js'                            -0.22 %       ±0.56% ±0.75% ±0.97%
misc/startup-core.js n=30 mode='worker' script='benchmark/fixtures/empty.mjs'                   ***      1.89 %       ±0.26% ±0.34% ±0.44%
misc/startup-core.js n=30 mode='worker' script='benchmark/fixtures/import-builtins.mjs'         ***      0.74 %       ±0.28% ±0.38% ±0.49%
misc/startup-core.js n=30 mode='worker' script='benchmark/fixtures/require-builtins.js'         ***     -2.20 %       ±0.26% ±0.34% ±0.44%
misc/startup-core.js n=30 mode='worker' script='test/fixtures/semicolon.js'                     ***     -1.95 %       ±0.30% ±0.40% ±0.52%

nodejs-github-bot · 2026-02-11T04:52:54Z

Review requested:

@nodejs/loaders
@nodejs/performance
@nodejs/startup

mcollina

lgtm

codecov · 2026-02-11T05:55:33Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.77%. Comparing base (37ff1ea) to head (cdf427a).
⚠️ Report is 28 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61769      +/-   ##
==========================================
+ Coverage   89.74%   89.77%   +0.02%     
==========================================
  Files         675      674       -1     
  Lines      204735   204759      +24     
  Branches    39348    39355       +7     
==========================================
+ Hits       183737   183815      +78     
+ Misses      13269    13233      -36     
+ Partials     7729     7711      -18

Files with missing lines	Coverage Δ
lib/internal/bootstrap/switches/is_main_thread.js	`95.92% <100.00%> (+0.01%)`	⬆️
lib/internal/modules/esm/get_format.js	`94.83% <100.00%> (+1.68%)`	⬆️
lib/internal/modules/esm/loader.js	`98.76% <100.00%> (+1.79%)`	⬆️
lib/internal/modules/esm/resolve.js	`98.94% <100.00%> (+2.74%)`	⬆️
lib/internal/modules/esm/translators.js	`97.64% <100.00%> (+5.26%)`	⬆️
lib/internal/process/pre_execution.js	`95.98% <100.00%> (+0.01%)`	⬆️
lib/internal/repl/completion.js	`95.13% <100.00%> (ø)`

... and 59 files with indirect coverage changes

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watilde

One question for my understanding: I noticed defaultResolve and defaultLoadSync are still lazy-loaded with ??= while translators was moved to pre-loading. Is this because:

These are only used when there are no custom loader hooks (less common path)?
Their dependencies are heavier and would hurt startup more?
Or is this something that could be optimized similarly in the future?

Just curious about the design rationale

joyeecheung · 2026-02-11T18:53:49Z

I noticed defaultResolve and defaultLoadSync are still lazy-loaded with ??= while translators was moved to pre-loading.

Did you mean in esm/loader.js? I believe I've removed them. If not could you leave a pointer to the line where it still remains? Happy to update them in this PR.

lib/internal/repl/completion.js

watilde · 2026-02-12T13:48:38Z

My code base in my local was very old, nvm. Thank you!

nodejs-github-bot · 2026-02-12T15:02:50Z

CI: https://ci.nodejs.org/job/node-test-pull-request/71322/

nodejs-github-bot · 2026-02-13T04:58:44Z

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- Loading data for nodejs/node/pull/61769
✔  Done loading data for nodejs/node/pull/61769
----------------------------------- PR info ------------------------------------
Title      lib: include ESM loader in the built-in snapshot (#61769)
Author     Joyee Cheung <[email protected]> (@joyeecheung)
Branch     joyeecheung:esm-in-snapshot -> nodejs:main
Labels     lib / src, needs-ci, commit-queue-rebase
Commits    3
 - lib: remove top-level getOptionValue() calls in lib/internal/modules
 - lib: reduce cycles in esm loader and load it in snapshot
 - benchmark: add startup benchmark for ESM entrypoint
Committers 1
 - Joyee Cheung <[email protected]>
PR-URL: https://github.com/nodejs/node/pull/61769
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Daijiro Wachi <[email protected]>
Reviewed-By: Geoffrey Booth <[email protected]>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/61769
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Daijiro Wachi <[email protected]>
Reviewed-By: Geoffrey Booth <[email protected]>
--------------------------------------------------------------------------------
   ℹ  This PR was created on Wed, 11 Feb 2026 04:52:49 GMT
   ✔  Approvals: 3
   ✔  - Matteo Collina (@mcollina) (TSC): https://github.com/nodejs/node/pull/61769#pullrequestreview-3782914586
   ✔  - Daijiro Wachi (@watilde): https://github.com/nodejs/node/pull/61769#pullrequestreview-3784562017
   ✔  - Geoffrey Booth (@GeoffreyBooth): https://github.com/nodejs/node/pull/61769#pullrequestreview-3787902819
   ✘  Last GitHub CI failed
   ℹ  Last Full PR CI on 2026-02-12T15:02:50Z: https://ci.nodejs.org/job/node-test-pull-request/71322/
- Querying data for job/node-test-pull-request/71322/
✔  Build data downloaded
- Querying failures of job/node-test-commit/85439/
✔  Data downloaded
   ✘  44 failure(s) on the last Jenkins CI run
--------------------------------------------------------------------------------
   ✔  Aborted `git node land` session in /home/runner/work/node/node/.ncu

https://github.com/nodejs/node/actions/runs/21975249143

joyeecheung · 2026-02-13T19:43:01Z

Looks like this got broken by #61665 which added filtering of internal frames but the regex couldn't understand async frames. Updated the regex to handle async frames. cc @legendecas

nodejs-github-bot · 2026-02-13T19:44:44Z

CI: https://ci.nodejs.org/job/node-test-pull-request/71334/

joyeecheung · 2026-02-14T00:17:13Z

Looks like the new regex didn't work with test runner outputs somehow. Updated. Can you take a look again? @legendecas Thanks!

test/common/assertSnapshot.js

Co-authored-by: Chengzhong Wu <[email protected]>

benchmark/fixtures/import-builtins.mjs

nodejs-github-bot · 2026-02-18T16:53:58Z

CI: https://ci.nodejs.org/job/node-test-pull-request/71361/

nodejs-github-bot · 2026-02-18T20:52:29Z

CI: https://ci.nodejs.org/job/node-test-pull-request/71363/

joyeecheung · 2026-02-18T20:54:46Z

Fixed the test-bootstrap-modules list for workers. Can you take a look again? Thanks!

@legendecas @mcollina @GeoffreyBooth @watilde @JakobJingleheimer @RafaelGSS

nodejs-github-bot · 2026-02-19T12:52:27Z

Landed in 9cd6630...53ac826

PR-URL: #61769 Reviewed-By: Matteo Collina <[email protected]> Reviewed-By: Daijiro Wachi <[email protected]> Reviewed-By: Geoffrey Booth <[email protected]> Reviewed-By: Chengzhong Wu <[email protected]> Reviewed-By: Rafael Gonzaga <[email protected]> Reviewed-By: Jacob Smith <[email protected]>

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joyeecheung added 4 commits February 13, 2026 20:42

test: allow filtering async internal frames in assertSnapshot

fa8161a

lib: remove top-level getOptionValue() calls in lib/internal/modules

92d6e40

lib: reduce cycles in esm loader and load it in snapshot

d00eeec

benchmark: add startup benchmark for ESM entrypoint

9cd87a2

joyeecheung force-pushed the esm-in-snapshot branch from 71c535a to 9cd87a2 Compare February 13, 2026 19:43

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sea: support ESM entry point in SEA #61813

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fixup! test: allow filtering async internal frames in assertSnapshot

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fixup! test: allow filtering async internal frames in assertSnapshot

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Co-authored-by: Chengzhong Wu <[email protected]>

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fixup! lib: reduce cycles in esm loader and load it in snapshot

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