fix(form-core): exclude undefined from FormState errors type by isaackaara · Pull Request #2066 · TanStack/form

isaackaara · 2026-03-06T04:51:49Z

The runtime code in FormApi.ts explicitly filters out undefined values from the error map when building the errors array:

fieldErrors = Object.values(currBaseMeta.errorMap ?? {}).filter(
  (val) => val !== undefined,
) as never

But the type definition allows undefined in the union, forcing consumers to add unnecessary undefined checks:

// Before: TypeScript thinks errors can contain undefined
errors.forEach(error => {
  console.log(error.length)  // TS error: Object is possibly 'undefined'
})

This wraps the error union types with NonNullable<> in both the FormState.errors type and the getAllErrors() return type, aligning the types with the runtime behavior.

// After: undefined is excluded from the type, matching runtime
errors.forEach(error => {
  console.log(error.length)  // Works
})

Fixes #2022

Summary by CodeRabbit

Refactor
- Tightened TypeScript typings for form error arrays to exclude null/undefined, improving compile-time safety and clearer error shapes.
- Updated type-level tests to reflect the stricter error array element types.

The runtime code filters out undefined values from the errorMap when building the errors array (via .filter(val => val !== undefined)), but the type definition allowed undefined in the union. This forced consumers to add unnecessary runtime undefined checks when iterating over errors. Wrapping the error union with NonNullable aligns the type with the actual runtime behavior. Fixes TanStack#2022

changeset-bot · 2026-03-06T04:52:00Z

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crutchcorn

This makes sense, thanks

coderabbitai · 2026-05-10T19:05:40Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: efbc88ac-6a37-4cbb-8ed4-6f161aa6e5fd

📥 Commits

Reviewing files that changed from the base of the PR and between 433005e and 3be9ee8.

📒 Files selected for processing (4)

packages/form-core/src/FormApi.ts
packages/form-core/tests/FieldApi.test-d.ts
packages/form-core/tests/FormApi.test-d.ts
packages/form-core/tests/formOptions.test-d.ts

🚧 Files skipped from review as they are similar to previous changes (1)

packages/form-core/src/FormApi.ts

📝 Walkthrough

Walkthrough

This PR tightens TypeScript type definitions for form error arrays by wrapping error element unions with NonNullable<...> in two locations: DerivedFormState.errors and FormApi.getAllErrors() return type. The changes reflect existing runtime filtering of undefined values, closing a type-definition mismatch.

Changes

Error Type Nullability

Layer / File(s)	Summary
Form Error Type Definitions `packages/form-core/src/FormApi.ts`	`DerivedFormState.errors` and `FormApi.getAllErrors()` return type's `form.errors` now wrap their error element unions in `NonNullable<...>`, excluding `null`/`undefined` from the type contract to match runtime filtering behavior.
Type-level Tests `packages/form-core/tests/FieldApi.test-d.ts`, `packages/form-core/tests/FormApi.test-d.ts`, `packages/form-core/tests/formOptions.test-d.ts`	Type assertions updated to expect error arrays without `undefined` in element unions (e.g., `'123'[]`, `'Too short!'[]`, `('Too short!'

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 With whiskers twitched and eyes alight,
We wrap the errors tight and right—
No nulls shall pass our type's defense,
Where runtime and the types now dance! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: wrapping error types with NonNullable to exclude undefined from the FormState errors type, directly matching the PR's core objective.
Description check	✅ Passed	The description clearly explains the type mismatch, provides before/after code examples, identifies the runtime filtering behavior, and references the fixed issue, meeting all template requirements.
Linked Issues check	✅ Passed	The PR fully addresses issue `#2022` by wrapping error union types with NonNullable<> in both FormState.errors and getAllErrors() return type, removing undefined from compile-time types to match runtime behavior.
Out of Scope Changes check	✅ Passed	All changes are scoped to the linked issue: three test files were updated to reflect the narrowed type expectations, and the FormApi.ts type definitions were modified to exclude undefined as required.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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nx-cloud · 2026-05-10T19:05:54Z

View your CI Pipeline Execution ↗ for commit 433005e

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☁️ Nx Cloud last updated this comment at 2026-05-10 19:15:22 UTC

pkg-pr-new · 2026-05-10T19:13:27Z

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commit: 3be9ee8

sentry · 2026-05-10T19:16:12Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.71%. Comparing base (6892ed0) to head (3be9ee8).
⚠️ Report is 195 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2066      +/-   ##
==========================================
+ Coverage   90.35%   90.71%   +0.36%     
==========================================
  Files          38       59      +21     
  Lines        1752     2198     +446     
  Branches      444      550     +106     
==========================================
+ Hits         1583     1994     +411     
- Misses        149      183      +34     
- Partials       20       21       +1

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crutchcorn approved these changes May 10, 2026

View reviewed changes

Merge branch 'main' into fix/form-errors-type-exclude-undefined

433005e

crutchcorn and others added 2 commits May 10, 2026 15:10

chore: fix build and test types

23fb417

ci: apply automated fixes and generate docs

3be9ee8

crutchcorn merged commit 43123f9 into TanStack:main May 10, 2026
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fix(form-core): exclude undefined from FormState errors type#2066

fix(form-core): exclude undefined from FormState errors type#2066
crutchcorn merged 4 commits into
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isaackaara:fix/form-errors-type-exclude-undefined

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