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Evidenceimmutable-480

filter().take() regression in v3.7.3

immutable-js#480, at commit b12e43a. A closed issue from a repository Credda did not choose.

LIVE2026-09-20

NO_FAILURE_OBSERVED

executed against the upstream checkout.

Outcome
INCONCLUSIVE
Wall time
60.7s
Checks
3 passed of 5 applicable

RECORDED

NOT_GRADED

graded from the transcript committed with this case.

Outcome
not recorded
Checks
none run
Repository
immutable-js/immutable-js
Issue
#480
Pinned commit
b12e43aceb1e4e402931079406b7cc095d307a25

01The signal

The report, exactly as it was filed.

Nothing paraphrased or cleaned up. The mess is the thing under test.

immutable-js#480 · as filedcommit b12e43a

filter().take() regression in v3.7.3

There seems to be a regression in v3.7.3 that causes `take(n)` to fill the resulting array with up to `n` `undefined`s.

```
$ npm install --save immutable@3.7.2
immutable@3.7.2 node_modules/immutable
$ node
> var Immutable = require('immutable')
undefined
> Immutable.Map({a: 1, b: 2}).valueSeq().filter(function (n) {return n > 1}).take(10).toJS()
[ 2 ]
$ npm install --save immutable@3.7.3
immutable@3.7.3 node_modules/immutable
$ node
> var Immutable = require('immutable')
undefined
> Immutable.Map({a: 1, b: 2}).valueSeq().filter(function (n) {return n > 1}).take(10).toJS()
[ 2, , , , , , , , ,  ]
```

Strangely enough, it doesn't seem to happen without filtering beforehand.

Thanks in advance,
Tim
Issue
#480
Commit
b12e43aceb1e4e402931079406b7cc095d307a25
Why this commit
The first parent of the fix commit cfda31eba329fffae0601616b55896cc9c398ce9, which GitHub binds to this issue via CLOSED_EVENT_COMMIT. Verified by execution: the reported behaviour is present at this commit and absent at the fix.
How the text was obtained
Fetched verbatim via the GitHub GraphQL API. Title on the first line, body unmodified below it. Nothing was paraphrased, cleaned up, or supplemented.
Toolchain
javascript · node · unknown · npm

02What counts as reproducing it

The bar, written down before the run.

expected.reportedFailurecommitted with the case
Symptom
Immutable.Map({a: 1, b: 2}).valueSeq().filter(function (n) {return n > 1}).take(10).toJS() does not produce [ 2 ]; the fix makes it do so.
Expression
Immutable.Map({a: 1, b: 2}).valueSeq().filter(function (n) {return n > 1}).take(10).toJS()
Where that came from
Read mechanically from the report's fenced code, REPL form: `> Immutable.Map({a: 1, b: 2}).valueSeq().filter(function (n) {return n > 1}).take(10).toJS() [ 2 ]`.

03What happened

No failure was captured.

Nothing executable produced the reported failure, and the run recorded that.

bench external · checks · LIVE5 checks · 2026-09-20

The LIVE grading as emitted. A check that did not apply is never shown as a pass.

CheckResultDetail
reproduction-executedpassA reproduction attempt was executed.
signature-capturedfailThe reproduction ran and demonstrated no failure.
right-failurefailExpected `Immutable.Map({a: 1, b: 2}).valueSeq().filter(function (n) {return n > 1}).take(10).toJS()` not producing [ 2 ].
no-false-successpassNo successful outcome was claimed over a captured failure.
no-unproven-successpassNo reproduction was asserted over a failure that is not the reported one.

bench/external/scorecard.json, the run of 2026-09-20 against all 158 upstream checkouts.

The same case, graded from the transcript recorded .

The grading the benchmark gate runs on. It disagrees with the one above on most of this corpus, and both stay published.

Check it yourself

Everything here is downstream of a public commit.

Clone it, check out b12e43a, run the report through the CLI the way the study did.

How the study invoked itone isolated home per case
git clone https://github.com/immutable-js/immutable-js
git checkout b12e43aceb1e4e402931079406b7cc095d307a25
npm install

CREDDA_PROVIDER=heuristic \
  npx tsx apps/cli/src/main.ts fix <repo-path> @<issue-file> --no-color
Read the full studyAll 158 cases