Form Groups

When building a multi-stage form that has many stages, like so:

Form stepper

It's common for each step to have its own form. However, this complicates the form submission and validation process by requiring you to add complex logic.

Luckily, TanStack Form provides a way to build out sub-forms that make this kind of development trivial to implement: <form.FormGroup>.

Usage

To use a form group in TanStack Form, you'll use useForm to create a form variable, then reference its FormGroup component like you would a Field:

vue

<script setup lang="ts">
import { useForm } from '@tanstack/vue-form'

const form = useForm({
  defaultValues: {
    step1: {
      name: '',
    },
    step2: {
      age: 0,
    },
  },
})
</script>

<template>
  <form.FormGroup name="step1" v-slot="{ group: formGroup }">
    <!-- `formGroup` here has all of the form-like methods you'd expect like `deleteField` or `insertFieldValue` -->
    <!-- ... -->
  </form.FormGroup>
</template>

This becomes much more useful when paired with external state to conditionally render a FormGroup:

vue

<script setup lang="ts">
import { ref } from 'vue'
import { useForm } from '@tanstack/vue-form'

const step = ref(0)

const form = useForm({
  defaultValues: {
    step1: {
      name: '',
    },
    step2: {
      age: 0,
    },
  },
})

const onGroupSubmit = () => {
  step.value++
}

const onGroupSubmitInvalid = () => {
  // Or handle invalid submissions, just like a top-level form
}
</script>

<template>
  <form.FormGroup
    v-if="step === 0"
    name="step1"
    :onGroupSubmit="onGroupSubmit"
    :onGroupSubmitInvalid="onGroupSubmitInvalid"
    :onSubmitMeta="{} as SomeType"
    v-slot="{ group: formGroup }"
  >
    <form @submit.prevent.stop="formGroup.handleSubmit()">
      <!-- Use `formGroup.handleSubmit()` to submit the sub-form, but not the parent form -->
      <!-- ... -->
    </form>
  </form.FormGroup>
  <form.FormGroup
    v-if="step === 1"
    name="step2"
    :onGroupSubmit="() => form.handleSubmit()"
    v-slot="{ group: formGroup }"
  >
    <form @submit.prevent.stop="formGroup.handleSubmit()">
      <!-- Then, use `form.handleSubmit()` to submit the entire form -->
      <!-- ... -->
    </form>
  </form.FormGroup>
</template>

Form Group Validation

Form groups have a distinct validation proceedure that we think makes sense for sub-forms:

Form groups can have their own validation:

vue

<template>
  <form.FormGroup
    name="step1"
    :validators="{ onChange: () => 'Error' }"
    v-slot="{ group: formGroup }"
  >
    <!-- formGroup.state.meta.errorMap // {onChange: "Error" | undefined} -->
    <!-- formGroup.state.meta.errors // ("Error")[] -->
  </form.FormGroup>
</template>

Can set errors on sub-fields:

vue

<template>
  <form.FormGroup
    name="step1"
    :validators="{
      onChange: ({ value, groupApi }) => ({
        group: value.name === 'error' ? 'Group error' : undefined,
        fields: {
          // Must use the name of the field relative to the FormGroup as the error key,
          // to stay consistent with how standard schema works with form groups
          name: value.name === 'error' ? 'Field error' : undefined,
        },
      }),
    }"
  />
</template>

And can even accept standard schemas:

vue

<template>
  <form.FormGroup
    name="step1"
    :validators="{
      onChange: z.object({
        name: z.string().min(2),
      }),
    }"
  />
</template>

The reason we don't use the full path names for fields is so that you can compose your schemas like so:
ts
const step1Schema = z.object({
  name: z.string().min(2),
})

const schema = z.object({
  step1: step1Schema,
  step2: step2Schema,
})
And pass the step1Schema to a form group and schema to the parent form. That way, partially validated data will still flag errors if the group is bypassed.

Dynamic Group Validation

If you want to use dynamic validation (onDynamic) with a form group, do not rely on the onDynamic validator passed to useForm:

useForm({
  validationLogic: revalidateLogic(),
  validators: {
    // This validator will not run `onChange` when a sub-form is submitted;
    // it will only run `onChange` when the form itself is submitted.
    onDynamic: schema,
  },
})

Instead, pass your sub-schema for the group to the onDynamic validation of the FormGroup itself:

vue

<template>
  <form.FormGroup name="step1" :validators="{ onDynamic: step1Schema }" />
</template>

It will treat formGroup.submissionAttempts as the way to change what validator is ran before/after submit.

Form Group State

Just like you're able to access formGroup.state.meta.errors, you're also able to access the group's value using formGroup.state.value. Likewise, here are some valuable properties you can access in the formGroup.state.meta:

formGroup.state.meta.isFieldsValid: true when the field-level validators have no errors
formGroup.state.meta.isGroupValid: true when the group-level validators have no errors
formGroup.state.meta.isValid: true when both the field-level and group-level validators have no errors
formGroup.state.meta.isSubmitting: true when the group is in the process of being submitted