Bug: setFieldValue crashes with "Cannot read properties of undefined (reading 'onServer')" in v1.27.5 #1947
Description
Describe the bug
Calling form.setFieldValue() on a field that has not been mounted/registered yet can cause a runtime crash in TanStack Form v1.27.5 with the following error:
Cannot read properties of undefined (reading 'onServer')
This appears to be a regression introduced in v1.27.5.
The same behavior works without crashing in v1.27.4.
Your minimal, reproducible example
https://codesandbox.io/p/sandbox/sf3wq2
Steps to reproduce
import { useEffect, useState } from 'react';
import { useForm } from '@tanstack/react-form';
type DetailItem = {
id: number;
qty: number;
};
export function BugRepro() {
const [mountDetailsFields, setMountDetailsFields] = useState(false);
const form = useForm({
defaultValues: { details: [] as DetailItem[] },
validators: {
onSubmit: ({ value }) => {
if (!value.details.length) {
return {
details: 'Details is required',
};
}
return {};
},
},
});
const handleAddItem = () => {
const current = form.state.values.details ?? [];
// Update field before it is mounted
form.setFieldValue('details', [...current, { id: 1, qty: 10 }]);
setMountDetailsFields(true);
};
useEffect(() => {
if (!mountDetailsFields) return;
// Trigger sync validation after field mounts
const id = setTimeout(() => {
(form as any).validateSync('change');
}, 0);
return () => clearTimeout(id);
}, [form, mountDetailsFields]);
return (
<div>
<button onClick={handleAddItem}>Add Item</button>
{mountDetailsFields ? (
<>
<form.Field name="details">{() => null}</form.Field>
<form.Field name="details[0].id">{() => null}</form.Field>
<form.Field name="details[0].qty">{() => null}</form.Field>
</>
) : null}
</div>
);
}- Install @tanstack/[email protected]
- Render the component above
- Click “Add Item”
- Application crashes with:
Cannot read properties of undefined (reading 'onServer')
Expected behavior
Calling setFieldValue should not crash the application, even if the field is updated before being mounted.
This behavior worked as expected in v1.27.4.
How often does this bug happen?
Every time
Screenshots or Videos
No response
Platform
Windows
TanStack Form adapter
react-form
TanStack Form version
1.27.5
TypeScript version
5.9.3
Additional context
No response