fix(form-core): prevent runtime errors when using deleteField

[kusiewicz]

During implementing this and testing deleteField I found out that this method does not work.

When a form field has onChange validation and the deleteField method is called on it, an error appears.

FormApi.ts:1586 Uncaught TypeError: Cannot read properties of undefined (reading 'errorMap')
    at FormApi.ts:1586:27
    at functionalUpdate (utils.ts:26:8)
    at FormApi.ts:2058:20

error: https://bolt.new/~/vitejs-vite-ceu2fl73

I think flow look like this:

1. Remove button click => form.deleteField('firstName').
2. Delete function changes values so onChange validator runs.
3. This validator runs on the form level and still tries to set errors.fields.email = 'error message' - so validateSync tries to update metadata of deleted field.
4. setFieldMeta calls functionalUpdate with undefined (since field does not exists in fieldMetaBase).
5. Updater tries to do ...prev where prev now is undefined -> error.

So validateSync iterates through field list that already semes to be outdated. There is a check if (!fieldMeta) in this function but I guess we have to add as well if (!fieldMetaBase).

[nx-cloud]

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---

☁️ Nx Cloud last updated this comment at 2025-10-07 06:01:31 UTC

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commit: 842956e

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.44%. Comparing base (6892ed0) to head (842956e).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/form-core/src/FormApi.ts	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1706      +/-   ##
==========================================
+ Coverage   90.35%   90.44%   +0.09%     
==========================================
  Files          38       38              
  Lines        1752     1790      +38     
  Branches      444      453       +9     
==========================================
+ Hits         1583     1619      +36     
- Misses        149      151       +2     
  Partials       20       20              

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[kusiewicz]

Please, verify the idea. If I'm thinking in a proper direction I will proceed and add unit tests.

[kusiewicz]

@LeCarbonator? :)

[LeCarbonator]

Will try to review this in the coming days

[LeCarbonator]

I'm not convinced this would be the ideal solution, but this minor fix helps catch the irritating runtime errors. Thanks for the step-by-step explanation!

[changeset-bot]

🦋 Changeset detected

Latest commit: 842956e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 9 packages

Name	Type
@tanstack/form-core	Patch
@tanstack/angular-form	Patch
@tanstack/form-devtools	Patch
@tanstack/lit-form	Patch
@tanstack/react-form	Patch
@tanstack/solid-form	Patch
@tanstack/svelte-form	Patch
@tanstack/vue-form	Patch
@tanstack/react-form-devtools	Patch

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