lib: include ESM loader in the built-in snapshot

[joyeecheung]

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]

Review requested:

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

[mcollina]

lgtm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.79%. Comparing base (37ff1ea) to head (9cd87a2).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61769      +/-   ##
==========================================
+ Coverage   89.74%   89.79%   +0.04%     
==========================================
  Files         675      674       -1     
  Lines      204735   204688      -47     
  Branches    39348    39333      -15     
==========================================
+ Hits       183737   183795      +58     
+ Misses      13269    13191      -78     
+ Partials     7729     7702      -27     

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 30 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]

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.

[watilde]

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

[nodejs-github-bot]

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

[nodejs-github-bot]

Commit Queue failed

- 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 <joyeec9h3@gmail.com> (@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 <joyeec9h3@gmail.com>
PR-URL: https://github.com/nodejs/node/pull/61769
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/61769
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Geoffrey Booth <webadmin@geoffreybooth.com>
--------------------------------------------------------------------------------
   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
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   ℹ  Last Full PR CI on 2026-02-12T15:02:50Z: https://ci.nodejs.org/job/node-test-pull-request/71322/
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   ✔  Aborted `git node land` session in /home/runner/work/node/node/.ncu

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

[joyeecheung]

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]

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