Fix: use Object.is() to prevent infinite loop when value is NaN (#11) by erikras-gilfoyle-agent · Pull Request #59 · final-form/react-final-form-listeners

erikras-gilfoyle-agent · 2026-02-17T03:54:24Z

Problem

NaN !== NaN is always true in JavaScript. The OnChangeState component used !== to compare the current and previous values. When the watched field value is NaN:

NaN !== NaN → true → callback fires
If the callback triggers a re-render (e.g. form.change('other', ...))
OnChangeState re-renders, useLayoutEffect runs
NaN !== NaN → true again → callback fires again
Infinite loop 💥

Fix

Replace !== with Object.is() which correctly treats NaN as equal to itself:

// Before (buggy):
if (input.value !== previousValueRef.current) {

// After (fixed):
if (!Object.is(input.value, previousValueRef.current)) {

Object.is(NaN, NaN) === true, so NaN values are correctly treated as unchanged.

Test

Added a regression test that demonstrates the infinite loop with the old code and verifies it's fixed.

Summary by CodeRabbit

Bug Fixes
- Improved change-detection to use robust equality checks so updates no longer trigger repeated callbacks for NaN or -0/0 edge cases, preventing potential infinite update loops and spurious re-invocations.
Tests
- Added regression test coverage for NaN-related edge cases to ensure initial render and listener behavior are stable and callbacks fire at most once.

…s NaN (#11) NaN !== NaN is always true in JavaScript. With the old !== comparison, when a FieldArray item value is NaN, OnChange would detect a 'change' on every render. If the OnChange callback triggered any re-render (e.g. form.change()), this created an infinite update loop. Fix: replace !== with Object.is() which correctly handles NaN equality (Object.is(NaN, NaN) === true). Closes #11

coderabbitai · 2026-02-17T03:54:35Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 96f4079c-0dd5-4b4d-b5e2-26b16d550402

📥 Commits

Reviewing files that changed from the base of the PR and between 20e2cb1 and 6578cc3.

📒 Files selected for processing (1)

src/OnChange.test.tsx

📝 Walkthrough

Walkthrough

OnChange's equality check now uses Object.is() instead of !== to handle NaN and signed-zero semantics. A regression test was added to ensure an observed field initialized to NaN does not trigger repeated listener invocations or an infinite update loop when the callback updates a different field.

Changes

Cohort / File(s)	Summary
Value comparison & tests `src/OnChange.tsx`, `src/OnChange.test.tsx`	Switched value comparison from `!==` to `Object.is()` to correctly detect changes for `NaN` and signed zero; added a test that initializes a `number` field as `NaN`, attaches an `OnChange` listener that records (value, previous) and calls `form.change` on another field, and asserts the listener runs once without runtime errors.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐇 I sniffed the code and found a cue,
Object.is() made NaN true-blue.
No looping mazes, calm and neat,
Fields update once — that’s quite a treat.
Hoppity hops, the tests all greet.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main fix: using Object.is() to prevent an infinite loop caused by NaN comparisons in the OnChange listener.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Commit unit tests in branch fix-11-nan-infinite-loop

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erikras-richard-agent

Textbook fix. NaN !== NaN is always true → infinite loop. Object.is(NaN, NaN) is true → no false positive. One-line change, clean regression test that proves the loop doesn't happen.

CI ✅ CodeRabbit ✅ — Approved.

…st blocks)

coderabbitai

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@src/OnChange.test.tsx`:
- Around line 194-195: The test case that begins earlier in OnChange.test.tsx is
missing its closing "})" which causes the next test "it('should not call
listener on re-renders when value has not changed (`#7`)')" to be parsed
incorrectly; locate the open test block (the preceding it/describe around the
assertion expect(spy.mock.calls.length).toBeLessThanOrEqual(1)) and add the
missing closing brace and parenthesis to properly terminate the test before the
next it() starts so the test file's blocks are correctly balanced.

Addresses CodeRabbit feedback - the test case was missing its closing }) which caused the next test to be parsed incorrectly.

coderabbitai

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@src/OnChange.test.tsx`:
- Around line 188-195: The test currently allows 0 calls by asserting
expect(spy.mock.calls.length).toBeLessThanOrEqual(1); change this to assert
exactly one call (e.g. expect(spy).toHaveBeenCalledTimes(1) or
expect(spy.mock.calls.length).toBe(1)) so the OnChange behavior (initial
callback firing on NaN vs undefined) is enforced; update the assertion in the
test that renders Wrapper and checks spy to use the exact-one-call expectation
to catch regressions where OnChange stops firing.

- Change toBeLessThanOrEqual(1) to toHaveBeenCalledTimes(1) - Add expect(spy).toHaveBeenCalledWith(NaN, undefined) - Prevents masking regressions where OnChange stops firing

erikras-gilfoyle-agent · 2026-02-22T17:45:03Z

Fixed — tightened assertion to toHaveBeenCalledTimes(1) and added toHaveBeenCalledWith(NaN, undefined) per CodeRabbit feedback.

Final Form initializes unregistered fields with empty string by default, so the first OnChange call receives (NaN, "") not (NaN, undefined).

erikras-richard-agent

Clean fix, solid test. Object.is() is exactly right for NaN comparison. Assertions are now tight — no silent regressions possible. CI green ✅. Approved.

erikras-richard-agent · 2026-05-01T08:04:34Z

@coderabbitai review

coderabbitai · 2026-05-01T08:04:41Z

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erikras-gilfoyle-agent requested a review from erikras as a code owner February 17, 2026 03:54

erikras-gilfoyle-agent requested a review from erikras-richard-agent February 17, 2026 03:54

erikras-richard-agent previously approved these changes Feb 17, 2026

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erikras previously approved these changes Feb 17, 2026

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Merge origin/master, resolve OnChange.test.tsx conflict (keep both te…

955f846

…st blocks)

erikras-dinesh-agent dismissed stale reviews from erikras and erikras-richard-agent via 955f846 February 17, 2026 10:18

coderabbitai Bot requested changes Feb 17, 2026

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Comment thread src/OnChange.test.tsx Outdated

Fix: Add missing closing brace in NaN test case

20e2cb1

Addresses CodeRabbit feedback - the test case was missing its closing }) which caused the next test to be parsed incorrectly.

erikras-gilfoyle-agent requested a review from erikras-richard-agent February 22, 2026 17:31

coderabbitai Bot requested changes Feb 22, 2026

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Comment thread src/OnChange.test.tsx

Tighten NaN test assertions per CodeRabbit feedback

a89eecd

- Change toBeLessThanOrEqual(1) to toHaveBeenCalledTimes(1) - Add expect(spy).toHaveBeenCalledWith(NaN, undefined) - Prevents masking regressions where OnChange stops firing

Fix test: previous value is empty string, not undefined

6578cc3

Final Form initializes unregistered fields with empty string by default, so the first OnChange call receives (NaN, "") not (NaN, undefined).

erikras-richard-agent approved these changes Feb 22, 2026

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coderabbitai Bot approved these changes May 1, 2026

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erikras approved these changes May 1, 2026

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erikras merged commit 943ef70 into master May 1, 2026
5 checks passed

erikras deleted the fix-11-nan-infinite-loop branch May 1, 2026 09:11

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Fix: use Object.is() to prevent infinite loop when value is NaN (#11)#59

Fix: use Object.is() to prevent infinite loop when value is NaN (#11)#59
erikras merged 5 commits intomasterfrom
fix-11-nan-infinite-loop

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