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Evidencedayjs-244

dayjs() instanceof dayjs = false

dayjs#244, at commit 36c4e94. A closed issue from a repository Credda did not choose.

LIVE2026-09-20

RIGHT_FAILURE

executed against the upstream checkout.

Outcome
PATCH_REJECTED
Wall time
417.5s
Checks
5 passed of 5 applicable

RECORDED

NOT_GRADED

graded from the transcript committed with this case.

Outcome
not recorded
Checks
none run
Repository
iamkun/dayjs
Issue
#244
Pinned commit
36c4e94f014a78c186b354f003c048fdb5562464

01The signal

The report, exactly as it was filed.

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

dayjs#244 · as filedcommit 36c4e94

dayjs() instanceof dayjs = false

Hi,
I tried to replace moment with dayjs,but some old code have this condition:
```
if (aMomentDate instanceof moment) {
//do something
}
```
if this meet dayjs, it would be false and the `if` can not be enter.

after I found the problem , I tried this:
```
moment() instanceof moment
//true
```
and this:
```
dayjs() instanceof dayjs
//false
```

So, is it necessary to be fixed?
Repository
iamkun/dayjs
Issue
#244
Commit
36c4e94f014a78c186b354f003c048fdb5562464
Why this commit
The first parent of the fix commit 6e155b8cc6801b5e33886a683889d33b7dd8a5e2, 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
dayjs() instanceof dayjs produces false; the fix makes it produce true.
Expression
dayjs() instanceof dayjs
Reported output
false
Where that came from
Read mechanically from the report's fenced code, NEXT_LINE form: `dayjs() instanceof dayjs //false`.

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
`dayjs() instanceof dayjs` still produces false (read false)
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-capturedpass`dayjs() instanceof dayjs` still produces false (read false)
right-failurepassReproduced the reported failure: dayjs() instanceof dayjs produces false; the fix makes it produce true.
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 36c4e94, 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/iamkun/dayjs
git checkout 36c4e94f014a78c186b354f003c048fdb5562464
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