@falcondev-oss/form

A framework-agnostic form-state library on top of @vue/reactivity. You give it a Standard Schema (zod v4, arktype, …) and reactive sourceValues; it gives you a reactive form handle with a tree of field accessors.

Three published packages — pick the one for the runtime, never import -core directly in app code:

useForm from the framework package wraps useFormCore — same options, same handle. Everything below is identical across frameworks except field binding and re-render (see reference/frameworks.md).

Two ideas that explain everything

1. Accessors are lazy paths; $use() materializes. form.fields.address.city is just a typed path proxy — no field object exists yet. Calling .$use() creates (and caches) the actual reactive FormField. Navigate with dot/.at(), then .$use() at the leaf you bind.

1. Form data is NullableDeep. While editing, every value can be null — a half-filled form has nulls everywhere. So form.data, field.value, and accessor types are the schema's input type made deeply nullable (objects → T | null, arrays → (T|null)[] | null). The validated output type (non-null) only appears in submit({ values }). Write UI against nullable types; trust submit for clean data.

Golden path

import { useForm } from '@falcondev-oss/form-vue' // or -react
import z from 'zod'

const form = useForm({
  schema: z.object({ name: z.string(), age: z.number() }),
  sourceValues, // initial data (NullableDeep); a value, getter, or ref — React needs a stable reference
  async submit({ values }) {
    // `values` is validated OUTPUT: { name: string, age: number }
    await api.save(values)
    // return nothing → { success: true }; return { success: false } to keep form dirty
  },
})

const nameField = form.fields.name.$use()
nameField.handleChange('Jane')   // programmatic write (validates, marks dirty)
// or write straight through the reactive data:
form.data.name = 'Jane'          // equivalent effect

await form.submit()              // validates whole schema, runs submit if valid

useForm(options)

• schema — any Standard Schema that also exposes Standard JSON Schema (zod v4, arktype). JSON Schema drives field.schema metadata and required-detection. Non-JSON-representable types (Date, bigint, Map…) need a codec/transform or metadata extraction silently degrades (a console warning fires).
• sourceValues — initial NullableDeep data. A value, a getter () => data, or (Vue) a ref. In React it must be a stable reference — see below. May be undefined → form is pending (isLoading/field.isPending true, data is undefined, writes ignored) until it resolves. When it later changes: if the form is not dirty, the form resets to the new values; if dirty, the update is skipped with a warning (except during submit).
• submit({ values }) — async, receives the validated output. Return void/{success:true} → form marked pristine; {success:false} → stays dirty. await everything that must finish before the form settles — most importantly cache/query invalidations, so fresh data flows back into sourceValues before the form is marked pristine (an un-awaited invalidation lets the form settle against stale data). With TanStack Query: await queryClient.invalidateQueries(...) directly in submit, or do it in the mutation's onSuccess and await mutateAsync(...) in submit (awaiting the mutation awaits onSuccess).
• disabled? — boolean | Ref | getter. Blocks handleChange/handleBlur/reset on all fields.
• hooks? — lifecycle hooks (see reference/patterns.md).

Writing sourceValues (do it this way)

Three ordered branches: still-loading → existing entity → blank defaults. Vue takes them as a getter; React takes them as a useMemoed value.

// Vue — getter, tracked reactively
useForm({
  schema,
  sourceValues: () => {
    if (isLoading.value) return undefined    // 1. source still loading → form is pending
    if (entity.value) return entity.value    // 2. edit: return the whole entity object
    return { name: null, age: null }         // 3. create: blank defaults
  },
  async submit({ values }) { /* … */ },
})

// React — same branches, wrapped in useMemo
const sourceValues = useMemo(() => {
  if (isLoading) return undefined
  if (entity) return entity
  return { name: null, age: null }
}, [isLoading, entity])

useForm({ schema, sourceValues, async submit({ values }) { /* … */ } })

In React sourceValues must be a stable reference. Never inline the object (or a getter) in the useForm call: React re-runs the component body every render, so a fresh object identity re-seeds the form on every render — resetting a clean form and warning on a dirty one. Memoize it (useMemo), or hoist a constant to module scope, or pass query data directly (sourceValues: query.data — already stable). Getters are worse than useless here: the adapter captures the getter once on mount, so one built over React state or props is frozen at its first-render closure and never sees an update.

• Return undefined while the source is loading (e.g. the fetch for the entity being edited is pending). This puts the form in the pending state instead of seeding it with a wrong/empty shape you'd have to overwrite later.
• Return the existing entity as one whole object — don't hand-build { name: entity?.name, age: entity?.age, … } with optional chaining per key. If the entity doesn't match the schema, spread and override just the divergent fields: return { ...entity, tags: entity.tags ?? [] }.
• Use null for fields with no meaningful default — not '' or 0 just because the type is string/number. NullableDeep makes null valid for every field; an empty string is a real value that reads as "the user typed nothing", which is different from "untouched".

The form handle

Field accessors

form.fields.user.email.$use()        // nested object
form.fields.tags.at(0).$use()        // array item (negative index ok: .at(-1))
form.fields.tags.$use()              // the array field itself
for (const item of form.fields.tags) item.$use()  // iterate (reactive)
form.fields.tags.delete(field.key)   // remove array item by its key (see below)
form.fields.$use()                   // root field = whole form value
form.fields['a.b'].$use()            // keys containing dots work (auto-escaped)

.at(i) accessor exists even before the array/index does — .$use().value is null until data arrives. .delete(key) must target an array item's key (items[2]), not a nested property — otherwise it throws.

The FormField (result of $use())

Two write paths (equivalent)

• field.handleChange(newValue) — explicit, what input handlers call.
• form.data.path = newValue — direct reactive mutation; on-change observes it and triggers the same validation.

Both mark the form dirty and re-validate. Use handleChange/model in components; direct writes are handy in tests and effects.

When validation runs

Whole-schema validation (not per-field), then issues are filtered to each field's path:

• on submit — always;
• on change — only if the field already has errors (so fixing an error clears it live);
• on blur — if the field was edited.

Errors clear while isLoading. A field also surfaces validation issues of nested paths that haven't been $used yet.

Gotchas

• Read/write nullable, submit non-null. Don't assume field.value is non-null in the UI.
• $use() is required to bind. Accessors alone are inert paths. In React, $use() re-renders the useForm-owning component; a child reading a field prop needs useField(field) or FormFieldMemo to re-render (see frameworks).
• sourceValues won't overwrite a dirty form (by design) — reset first if you need to force it.
• delete(key) needs an array-item key, and field.key changes when the array is replaced via handleChange (cache is cleared).
• Don't import from -core in a React/Vue app — you lose re-render/model integration.

Deeper reference

• Framework specifics (React re-render/useField/FormFieldMemo, Vue v-model/useFormHandles, using core standalone) → read reference/frameworks.md.
• Optional features — discriminated unions ($use({discriminator})), value translation ($use({translate})), field.schema metadata, and hooks → read reference/patterns.md.