Forms

This guide covers the useLiveForm composable for building complex forms with server-side validation, nested objects, and dynamic arrays in LiveVue.

New to LiveVue? Check out Basic usage for fundamental patterns before diving into forms.

Quick example

Here’s how a typical form setup looks with useLiveForm:

<script setup lang="ts">
import { useLiveForm, type Form } from 'live_vue'

type UserForm = {
  name: string
  email: string
  profile: {
    bio: string
    skills: string[]
  }
}

const props = defineProps<{ form: Form<UserForm> }>()

const form = useLiveForm(() => props.form, {
  changeEvent: 'validate',     // Send validation requests on changes
  submitEvent: 'submit',       // Event sent on form submission
  debounceInMiliseconds: 300   // Debounce validation requests
})

const nameField = form.field('name')
const emailField = form.field('email')
const bioField = form.field('profile.bio')
const skillsArray = form.fieldArray('profile.skills')
</script>

<template>
  <div>
    <!-- Basic field with validation -->
    <input
      v-bind="nameField.inputAttrs.value"
      :class="{ error: nameField.isTouched.value && nameField.errorMessage.value }"
    />
    <div v-if="nameField.errorMessage.value">
      {{ nameField.errorMessage.value }}
    </div>

    <!-- Array field with add/remove -->
    <div v-for="(skillField, index) in skillsArray.fields.value" :key="index">
      <input v-bind="skillField.inputAttrs.value" placeholder="Enter skill" />
      <button @click="skillsArray.remove(index)">Remove</button>
    </div>
    <button @click="skillsArray.add('')">Add Skill</button>

    <!-- Form actions -->
    <button @click="form.submit()" :disabled="!form.isValid.value">
      Submit
    </button>
  </div>
</template>

Why useLiveForm?

Traditional client-side forms present several challenges:

Validation synchronization between client and server
Complex state management for nested objects and arrays
Type safety for deeply nested form structures
Accessibility and proper ARIA attributes
User experience patterns like field states and error handling

The useLiveForm composable solves these problems by:

Providing seamless server-side validation with debouncing
Offering type-safe field access for complex structures
Managing all form state reactively (dirty, touched, valid)
Automatically generating proper input attributes and accessibility features
Handling nested objects and dynamic arrays with ease

Form API reference

useLiveForm()

Creates a reactive form instance with validation and state management.

function useLiveForm<T extends object>(
  form: MaybeRefOrGetter<Form<T>>,
  options?: FormOptions
): UseLiveFormReturn<T>

Parameters:

form - Reactive reference to the form data from LiveView (typically () => props.form)
options - Configuration object for form behavior

Options:

Option	Type	Default	Description
`changeEvent`	`string \| null`	`null`	Event sent on field changes (set to `null` to disable validation events)
`submitEvent`	`string`	`"submit"`	Event sent on form submission
`debounceInMiliseconds`	`number`	`300`	Debounce delay for change events to reduce server load
`prepareData`	`function`	`(data) => data`	Transform data before sending to server

Returns:

Form instance properties

Form-level state:

Property	Type	Description
`isValid`	`Ref<boolean>`	No validation errors exist
`isDirty`	`Ref<boolean>`	Form values differ from initial
`isTouched`	`Ref<boolean>`	At least one field has been interacted with
`isValidating`	`Readonly<Ref<boolean>>`	Whether validation requests are in progress
`submitCount`	`Readonly<Ref<number>>`	Number of submission attempts
`initialValues`	`Readonly<Ref<T>>`	Original form values for reset

Field factory functions:

Method	Description
`field(path, options?)`	Get a typed field instance for the given path
`fieldArray(path)`	Get an array field instance for managing dynamic lists

Form actions:

Method	Description
`submit()`	Submit form to server (returns Promise)
`reset()`	Reset to initial values and clear state

FormField

Individual form field with reactive state and helpers:

Field properties

Reactive state:

Property	Type	Description
`value`	`Ref<T>`	Current field value
`errors`	`Readonly<Ref<string[]>>`	Validation errors from server
`errorMessage`	`Readonly<Ref<string \| undefined>>`	First error message
`isValid`	`Ref<boolean>`	No validation errors
`isDirty`	`Ref<boolean>`	Value differs from initial
`isTouched`	`Ref<boolean>`	Field has been blurred

Input binding:

Property	Description
`inputAttrs`	Object containing `value`, event handlers, `name`, `id`, and accessibility attributes. Use with `v-bind`

Navigation methods:

Method	Description
`field(key)`	Access nested object field
`fieldArray(key)`	Access nested array field

Field actions:

Method	Description
`blur()`	Mark field as touched

FormFieldArray

Array field with additional methods for array manipulation:

Array field properties

Array operations:

Method	Description
`add(item?)`	Add new item to array. Returns a promise.
`remove(index)`	Remove item by index. Returns a promise.
`move(from, to)`	Move item to different position. Returns a promise.

Reactive array:

Property	Description
`fields`	Array of field instances for iteration (`FormField<T>[]`)

Individual array item access:

Method	Description
`field(path)`	Get individual array item fields (e.g., `field(0)`, `field('[0].name')`)
`fieldArray(path)`	Get nested array fields within array items

Working with fields

Field state

Each field provides reactive state that updates automatically:

<script setup>
const nameField = form.field('name')

// Reactive field state
console.log(nameField.value.value)        // Current value
console.log(nameField.errors.value)       // Array of error strings
console.log(nameField.errorMessage.value) // First error or undefined
console.log(nameField.isValid.value)      // true if no errors
console.log(nameField.isDirty.value)      // true if changed from initial
console.log(nameField.isTouched.value)    // true if user interacted
</script>

<template>
  <!-- Display field state -->
  <div class="field-debug">
    <p>Value: {{ nameField.value.value }}</p>
    <p>Valid: {{ nameField.isValid.value }}</p>
    <p>Dirty: {{ nameField.isDirty.value }}</p>
    <p>Touched: {{ nameField.isTouched.value }}</p>
    <p>Errors: {{ nameField.errors.value }}</p>
  </div>
</template>

Input binding

The inputAttrs property provides all necessary attributes for form inputs:

<template>
  <!-- Automatic binding with all attributes -->
  <input v-bind="nameField.inputAttrs.value" />

  <!-- Error message with proper ID linking -->
  <div
    v-if="nameField.errorMessage.value"
    :id="nameField.inputAttrs.value.id + '-error'"
    class="error"
  >
    {{ nameField.errorMessage.value }}
  </div>
</template>

Checkbox fields

LiveVue supports three checkbox patterns:

Boolean checkbox
Single with value
Multiple checkboxes

For simple true/false fields:

<script setup>
const acceptTerms = form.field('acceptTerms', { type: 'checkbox' })
</script>

<template>
  <label>
    <input v-bind="acceptTerms.inputAttrs.value" />
    I accept the terms and conditions
  </label>
</template>

For fields that should have a specific value when checked:

<script setup>
const plan = form.field('plan', { type: 'checkbox', value: 'premium' })
</script>

<template>
  <label>
    <input v-bind="plan.inputAttrs.value" />
    Upgrade to Premium ($9.99/month)
  </label>
  <!-- When checked: plan.value = 'premium', when unchecked: plan.value = null -->
</template>

When you create multiple checkboxes for the same field path with different values:

<script setup>
const emailPref = form.field('preferences', { type: 'checkbox', value: 'email' })
const smsPref = form.field('preferences', { type: 'checkbox', value: 'sms' })
const pushPref = form.field('preferences', { type: 'checkbox', value: 'push' })
</script>

<template>
  <fieldset>
    <legend>Notification Preferences</legend>
    
    <label>
      <input v-bind="emailPref.inputAttrs.value" />
      Email notifications
    </label>
    
    <label>
      <input v-bind="smsPref.inputAttrs.value" />
      SMS notifications  
    </label>
    
    <label>
      <input v-bind="pushPref.inputAttrs.value" />
      Push notifications
    </label>
  </fieldset>
  <!-- e.g., preferences.value = ['email', 'push'] -->
</template>

Nested fields

Access nested object fields using dot notation:

type UserProfile = {
  name: string
  email: string
  address: {
    street: string
    city: string
    country: string
  }
  preferences: {
    newsletter: boolean
    theme: 'light' | 'dark'
  }
}

const form = useLiveForm<UserProfile>(/* ... */)

// Access nested fields with full type safety
const nameField = form.field('name')                           // FormField<string>
const streetField = form.field('address.street')               // FormField<string>
const themeField = form.field('preferences.theme')             // FormField<'light' | 'dark'>

Complex nested structures

<script setup lang="ts">
type CompanyForm = {
  name: string
  headquarters: {
    address: {
      street: string
      city: string
      postal_code: string
    }
    contact: {
      phone: string
      email: string
    }
  }
}

const form = useLiveForm<CompanyForm>(/* ... */)

const companyNameField = form.field('name')
const hqStreetField = form.field('headquarters.address.street')
const hqPhoneField = form.field('headquarters.contact.phone')
</script>

<template>
  <div>
    <input v-bind="companyNameField.inputAttrs.value" />

    <fieldset>
      <legend>Headquarters</legend>
      <input v-bind="hqStreetField.inputAttrs.value" />
      <input v-bind="form.field('headquarters.address.city').inputAttrs.value" />
      <input v-bind="hqPhoneField.inputAttrs.value" />
    </fieldset>
  </div>
</template>

Array fields

Basic array operations

<script setup lang="ts">
type TagsForm = {
  title: string
  tags: string[]
}

const form = useLiveForm<TagsForm>(/* ... */)
const tagsArray = form.fieldArray('tags')

const addTag = () => tagsArray.add('')
const removeTag = (index: number) => tagsArray.remove(index)
</script>

<template>
  <div>
    <fieldset>
      <legend>Tags</legend>
      <div v-for="(tagField, index) in tagsArray.fields.value" :key="index">
        <input v-bind="tagField.inputAttrs.value" placeholder="Enter tag" />
        <button @click="removeTag(index)">Remove</button>
      </div>
      <button @click="addTag()">Add Tag</button>
    </fieldset>
  </div>
</template>

If calling add() on an array field does not add a new item, it often means that your Ecto changeset is filtering out empty or invalid values. Make sure your changeset doesn’t consider the value you’re trying to add as empty, or provide a valid initial value when adding.

Complex array structures

Handle arrays of objects with nested properties:

<script setup lang="ts">
type ProjectForm = {
  name: string
  team_members: Array<{
    name: string
    email: string
    role: string
    skills: string[]
  }>
}

const form = useLiveForm<ProjectForm>(/* ... */)
const membersArray = form.fieldArray('team_members')

const addMember = () => {
  membersArray.add({
    name: '',
    email: '',
    role: 'developer',
    skills: []
  })
}
</script>

<template>
  <div>
    <fieldset>
      <legend>Team Members</legend>
      <div v-for="(memberField, memberIndex) in membersArray.fields.value" :key="memberIndex">
        <h4>Member {{ memberIndex + 1 }}</h4>
        
        <input v-bind="memberField.field('name').inputAttrs.value" />
        <input v-bind="memberField.field('email').inputAttrs.value" />
        
        <!-- Skills array (nested array) -->
        <fieldset>
          <legend>Skills</legend>
          <div
            v-for="(skillField, skillIndex) in memberField.fieldArray('skills').fields.value"
            :key="skillIndex"
          >
            <input v-bind="skillField.inputAttrs.value" />
            <button @click="memberField.fieldArray('skills').remove(skillIndex)">Remove</button>
          </div>
          <button @click="memberField.fieldArray('skills').add('')">Add Skill</button>
        </fieldset>

        <button @click="membersArray.remove(memberIndex)">Remove Member</button>
      </div>

      <button @click="addMember()">Add Team Member</button>
    </fieldset>
  </div>
</template>

Server-side integration

Ecto changeset integration

LiveVue forms work seamlessly with Ecto changesets:

defmodule MyApp.User do
  use Ecto.Schema
  import Ecto.Changeset

  schema "users" do
    field :name, :string
    field :email, :string
    field :age, :integer

    embeds_one :profile, Profile do
      field :bio, :string
      field :skills, {:array, :string}, default: []
    end
  end

  def changeset(user, attrs) do
    user
    |> cast(attrs, [:name, :email, :age])
    |> validate_required([:name, :email])
    |> validate_format(:email, ~r/@/)
    |> validate_number(:age, greater_than: 0)
    |> cast_embed(:profile, with: &profile_changeset/2)
  end

  defp profile_changeset(profile, attrs) do
    profile
    |> cast(attrs, [:bio, :skills])
    |> validate_length(:bio, max: 500)
  end
end

LiveView form handling

defmodule MyAppWeb.UserFormLive do
  use MyAppWeb, :live_view

  def handle_event("validate", %{"user" => user_params}, socket) do
    user = socket.assigns.user || %User{}

    changeset =
      user
      |> User.changeset(user_params)
      # Setting :action is crucial - without it, the changeset won't expose errors
      |> Map.put(:action, :validate)

    {:noreply, assign(socket, form: to_form(changeset, as: :user))}
  end

  def handle_event("submit", %{"user" => user_params}, socket) do
    case save_user(socket.assigns.user, user_params) do
      {:ok, user} ->
        socket =
          socket
          |> put_flash(:info, "User saved successfully!")
          |> redirect(to: ~p"/users/#{user}")

        {:noreply, socket}

      {:error, changeset} ->
        {:noreply, assign(socket, form: to_form(changeset, as: :user))}
    end
  end
end

Form reset on successful submission

By default, useLiveForm does not automatically reset form state after submission. You can opt into automatic form reset by returning {:reply, %{reset: true}, socket} from your submit event handler:

def handle_event("submit", %{"contact" => contact_params}, socket) do
  case create_contact(contact_params) do
    {:ok, contact} ->
      socket =
        socket
        |> put_flash(:info, "Contact created successfully!")
        |> assign(:form, to_form(Contact.changeset(%Contact{}, %{}), as: :contact))

      # Tell the Vue component to reset form state
      {:reply, %{reset: true}, socket}

    {:error, changeset} ->
      {:noreply, assign(socket, form: to_form(changeset, as: :contact))}
  end
end

What gets reset:

Reset all field values to their current server state
Clear all touched states (isTouched becomes false)
Reset submit count to 0
Clear dirty states (isDirty becomes false)
Update initialValues to match current form values

Advanced patterns

Data transformation

Transform form data before sending to the server using prepareData:

<script setup>
type RawForm = {
  name: string
  tags: string
  price: string
}

type ProcessedForm = {
  name: string
  tags: string[]
  price: number
}

const form = useLiveForm<RawForm>(() => props.form, {
  changeEvent: 'validate',
  submitEvent: 'submit',
  prepareData: (data: RawForm): ProcessedForm => {
    return {
      name: data.name.trim(),
      tags: data.tags.split(',').map(tag => tag.trim()).filter(Boolean),
      price: parseFloat(data.price) || 0
    }
  }
})
</script>

Conditional field logic

Show/hide fields based on form state:

<script setup>
type UserForm = {
  account_type: 'personal' | 'business'
  name: string
  company_name?: string
  tax_id?: string
}

const form = useLiveForm<UserForm>(/* ... */)
const accountTypeField = form.field('account_type')

const isBusinessAccount = computed(() =>
  accountTypeField.value.value === 'business'
)

// Clear conditional fields when they become hidden
watch(isBusinessAccount, (isBusiness) => {
  if (!isBusiness) {
    form.field('company_name').value.value = ''
    form.field('tax_id').value.value = ''
  }
})
</script>

<template>
  <div>
    <select v-bind="accountTypeField.inputAttrs.value">
      <option value="personal">Personal</option>
      <option value="business">Business</option>
    </select>

    <!-- Business-only fields -->
    <div v-if="isBusinessAccount">
      <input v-bind="form.field('company_name').inputAttrs.value" />
      <input v-bind="form.field('tax_id').inputAttrs.value" />
    </div>
  </div>
</template>

Next steps

Configuration for advanced setup and customization options
Basic usage for fundamental patterns

Get Started

Core Usage

Advanced Topics

Help & Resources

Quick example

Why useLiveForm?

Form API reference

useLiveForm()

FormField

FormFieldArray

Working with fields

Field state

Input binding

Checkbox fields

Nested fields

Object navigation

Complex nested structures

Array fields

Basic array operations

Complex array structures

Server-side integration

Ecto changeset integration

LiveView form handling

Form reset on successful submission

Advanced patterns

Data transformation

Conditional field logic

Next steps

Build docs developers (and LLMs) love

Get Started

Core Usage

Advanced Topics

Help & Resources

​Quick example

​Why useLiveForm?

​Form API reference

​useLiveForm()

​FormField

​FormFieldArray

​Working with fields

​Field state

​Input binding

​Checkbox fields

​Nested fields

​Object navigation

​Complex nested structures

​Array fields

​Basic array operations

​Complex array structures

​Server-side integration

​Ecto changeset integration

​LiveView form handling

​Form reset on successful submission

​Advanced patterns

​Data transformation

​Conditional field logic

​Next steps

Build docs developers (and LLMs) love

Quick example

Why useLiveForm?

Form API reference

useLiveForm()

FormField

FormFieldArray

Working with fields

Field state

Input binding

Checkbox fields

Nested fields

Object navigation

Complex nested structures

Array fields

Basic array operations

Complex array structures

Server-side integration

Ecto changeset integration

LiveView form handling

Form reset on successful submission

Advanced patterns

Data transformation

Conditional field logic

Next steps