`form.getFieldState` is corrupted after removing element `arrays.remove`

[zizizi17]

Are you submitting a bug report or a feature request?

bug report

What is the current behavior?

I have the form with FIeldArray component inside.

• "append customer" ie adding new element to array.
• click on the Set Field Data Here span -> it set the data: { disabled: true }(check in console after next step to ensure data is set) to the the element with 0 index
• then append a new one(index 1).
• click Set Field Data Here
• after that - click X to delete the element with index 0.

In console - check for the the the logging of the zero element(previous first one) -> data: {}.

What is the expected behavior?

In console - check for the the the logging of the zero element -> data: { disabled: true }.

Sandbox Link

https://codesandbox.io/s/react-final-form-field-arrays-forked-dythr?file=/index.js

What's your environment?

sandbox

Other information

Tried as described in issue #128, but it did not help.

[erikras-richard-agent]

Initial Investigation

I've been investigating this issue and here's what I've found so far:

Testing the underlying mutator:

I created a test in final-form-arrays to verify that the remove mutator preserves the data property when shifting fields down. The test PASSES, which means the internal field state IS preserving the data correctly.

The actual issue:

The problem appears to be with form.getFieldState(), which returns field.lastFieldState rather than the internal field state. The lastFieldState is only updated when field subscribers are notified.

Hypothesis:

When arrays.remove is called:

1. Fields are shifted down in the internal state (with data preserved)
2. lastFieldState is set to undefined to force renotification
3. If form.getFieldState() is called before the next notification cycle, it returns undefined
4. If called after notification, it should return the updated lastFieldState with data preserved

Next steps:

I need to:

1. Create a full integration test that reproduces the exact scenario from your CodeSandbox
2. Verify the timing of when getFieldState is called vs when notifications happen
3. Determine if this is a timing issue or if there's a bug in how data is published

Question:

In your reproduction steps, when exactly are you calling form.getFieldState()? Is it:

• Immediately after calling arrays.remove?
• In a useEffect after the remove?
• In the render function?

This timing detail is crucial to understanding the root cause.

I'll continue investigating and will update once I have a definitive fix.