Only restore the initial value when it was actually destroyed - #1096
Only restore the initial value when it was actually destroyed#1096christianaurichzm wants to merge 1 commit into
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useField's mount effect treated a missing FieldState as "the field was destroyed" and wrote initialValues[name] back. Final Form drops fields[name] on the last unregister either way, so that is also what a field mounting at a path written through form.change() looks like, and the write-back discarded live data. Restore only when the value was really destroyed, meaning destroyOnUnregister plus an empty path. The changed initialValue path gets its own explicit write-back instead of depending on that reset as a side effect. Fixes final-form#1095
📝 WalkthroughWalkthrough
ChangesuseField registration behavior
Estimated code review effort: 3 (Moderate) | ~20 minutes Mergeability Score: 🟡 Moderate · up to Changing field metadata or an initial value can discard a user-edited field value when the field re-registers with destroyOnUnregister enabled. Merge should wait until that value-preservation behavior is fixed or explicitly accepted. Possibly related PRs
Suggested reviewers: Poem
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Inline comments:
In `@src/useField.ts`:
- Around line 165-176: The re-registration logic in useField must preserve the
current field value when its effect reruns due to data or initialValue changes,
rather than restoring an initial value after destroyOnUnregister cleanup.
Capture the value before cleanup, distinguish dependency-driven re-registration
from genuine unmounts, and reuse the captured value during reseeding; add
regression coverage for changed data and non-matching initialValue with
destroyOnUnregister enabled.
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src/useField.issue-1095.test.jssrc/useField.ts
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Fixes #1095.
useField's mount effect treats a missingFieldStateas "the field was destroyed" and writesinitialValues[name]back. Final Form dropsfields[name]on the last unregister whether or notdestroyOnUnregisteris set, so that is equally what it looks like when a field mounts at a path written throughform.change(), whether by a parent field, an earlier wizard step, or a sibling effect. The write-back discards it.Two guards that look right don't work:
currentValue === undefinedon its own cannot tell a destroyed value from one that is legitimately absent. It still overwrites after an intentionalform.change(name, undefined), and it restores stale entries in array fields whose indices shifted, whereinitialValues[1]still holds the item that used to be there.form.destroyOnUnregisteron its own breaks Fix #984: useField returns stale values when sibling updates form in useEffect #1085. Since Radio button remains dirty after submit becauseinitialValuedoes not update to newly saved value despiteinitialValueprop changing #988/Fix #984: useField returns stale values when sibling updates form in useEffect #1085 this block has a second owner:initialValueis in the effect's deps, so changing that prop re-registers the field, and the write-back is what makesregisterField'svalue === current initialprecondition hold, which is what applies the newinitialValue.So the two cases are separated. The mount effect restores only when the value was really destroyed, meaning
destroyOnUnregisterand an empty path. The changedinitialValuepath gets its own explicit write-back, placed in the effect that knows the prop changed, instead of depending on the reset firing on every re-registration.That second
form.changeis the part worth a close look. It runs only insideif (isEqual(currentValue, initialValue)), so the current value already equals the newinitialValue, andregisterFieldwrites it straight back on the next line. There is no window in which typed input can be lost.Two side effects of the same root cause are fixed along with it, both present on
maintoday. Changing thedataprop, which is pure metadata surfaced onmeta.data, wiped a modified field back to its initial value. And a non-matchinginitialValueprop overwrote a modified field, something Final Form's ownregisterFielddeliberately refuses to do.Tests:
src/useField.issue-1095.test.js, 13 cases covering both directions. Values that must survive a late mount, and the #1069/#1031 behaviour that must keep working: initial values from the form and from the field restored afterdestroyOnUnregisterwipes them, StrictMode's double mount, and seeding a genuinely empty path. I could not find existing coverage for the #1031 behaviour, sinceStrictModeand1031do not appear undersrc/*.test.js, so it seemed worth freezing while touching this block. Removing either half of the new guard turns tests red.Full suite 171/171.
tsc --project tsconfig.build.json --noEmitandeslintare clean; the oneexhaustive-depswarning onconfigRefis pre-existing.Summary by CodeRabbit
undefinedupdates and existing form values during field re-registration.