Evidenceimmutable-1247

Defaulted `Record` instance reports `true` after instantiation

immutable-js#1247, at commit 60bd7d0. A closed issue from a repository Credda did not choose.

LIVE2026-09-20

RIGHT_FAILURE

executed against the upstream checkout.

Outcome: REPRODUCED_NOT_DIAGNOSED
Wall time: 110.3s
Checks: 5 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: #1247
Pinned commit: 60bd7d0042149d76f150663ef2bd0094301f78fc

01The signal

The report, exactly as it was filed.

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

immutable-js#1247 · as filedcommit 60bd7d0

Defaulted `Record` instance reports `true` after instantiation

### What happened

Immediately after being constructed--without constructor values and without further changes--a Record instance returns `true` for `wasAltered()`.

### How to reproduce

**Version**: v4.0.0-rc.2

```js
const R = Record({ a: 1 });
const r = new R();

r.wasAltered(); // true
r.a;            // 1

r.clear().wasAltered(); // false
r.clear().a;            // 1
```

Repository: immutable-js/immutable-js
Issue: #1247
Commit: 60bd7d0042149d76f150663ef2bd0094301f78fc
Why this commit: The first parent of the fix commit 55d815b0c5dd883f40011ab3fa2b8685e615bef6, which GitHub binds to this issue via CLOSED_EVENT_PR. 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: (new (Record({ a: 1 }))()).wasAltered() produces true; the fix makes it produce false.
Expression: (new (Record({ a: 1 }))()).wasAltered()
Reported output: true
Where that came from: Read mechanically from the report's fenced code, SAME_LINE form: `r.wasAltered(); // true`.

03What happened

The live run reproduced the reported failure.

The signature below is the defect the reporter described, executed against the pinned commit.

captured failure signatureLIVE · normalized

`r.wasAltered()` still produces true (read true)

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.

Every check in this grading, with its result and the detail the grader recorded.
Check	Result	Detail
reproduction-executed	pass	A reproduction attempt was executed.
signature-captured	pass	`r.wasAltered()` still produces true (read true)
right-failure	pass	Reproduced the reported failure: (new (Record({ a: 1 }))()).wasAltered() produces true; the fix makes it produce false.
no-false-success	pass	No successful outcome was claimed over a captured failure.
no-unproven-success	pass	No 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 60bd7d0, 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 60bd7d0042149d76f150663ef2bd0094301f78fc
npm install

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

Read the full study All 158 cases