# Add form fields

> This document is the Markdown version of [formisch.dev/svelte/guides/add-form-fields/](https://formisch.dev/svelte/guides/add-form-fields/). For the complete documentation index, see [llms.txt](https://formisch.dev/llms.txt).

To add a field to your form, you can use the [`Field`](/svelte/api/Field.md) component or the [`useField`](/svelte/api/useField.md) rune. Both are headless and provide access to field state for building your form UI.

## Field component

The [`Field`](/svelte/api/Field.md) component has two mandatory properties: `of` which accepts the form store, and `path` which specifies which field to connect. If you use TypeScript, you get full autocompletion for the path based on your schema.

### Snippet syntax

Use Svelte's `{#snippet children(field)}` syntax to define how the field should render. The field store parameter includes the current value, error messages, and props to spread onto your input element.

```svelte
<script lang="ts">
  import { createForm, Field, Form } from '@formisch/svelte';
  import * as v from 'valibot';

  const LoginSchema = v.object({
    email: v.pipe(v.string(), v.email()),
    password: v.pipe(v.string(), v.minLength(8)),
  });

  const loginForm = createForm({
    schema: LoginSchema,
  });
</script>

<Form of={loginForm} onsubmit={(output) => console.log(output)}>
  <Field of={loginForm} path={['email']}>
    {#snippet children(field)}
      <input {...field.props} value={field.input} type="email" />
    {/snippet}
  </Field>
  <Field of={loginForm} path={['password']}>
    {#snippet children(field)}
      <input {...field.props} value={field.input} type="password" />
    {/snippet}
  </Field>
  <button type="submit">Login</button>
</Form>
```

> **Important:** The event handlers in `field.props` read the value from the DOM as a string. Fields with a non-string schema like `v.number()` or `v.date()` therefore need to be controlled to store the value with the correct type. See the [controlled fields](/svelte/guides/controlled-fields.md) guide to learn more.

> **Important:** If you plan to set initial values with `initialInput` or programmatically control field values using methods like [`setInput`](/methods/api/setInput.md) or [`reset`](/methods/api/reset.md), you must make your fields controlled by setting the appropriate attributes (like `value`, `checked`, or `selected`). See the [controlled fields](/svelte/guides/controlled-fields.md) guide to learn more.

### Headless design

The [`Field`](/svelte/api/Field.md) component does not render its own UI elements. It is headless and provides only the data layer of the field. This allows you to freely define your user interface. You can use HTML elements, custom components or an external UI library.

### Path array

The `path` property accepts an array of strings and numbers that represents the path to the field in your schema. For top-level fields, it's simply the field name wrapped in an array:

```svelte
<Field of={loginForm} path={['email']}>
  {#snippet children(field)}
    <input {...field.props} value={field.input} type="email" />
  {/snippet}
</Field>
```

For nested fields, the path reflects the structure of your schema:

```svelte
<!-- For a schema like: v.object({ user: v.object({ email: v.string() }) }) -->
<Field of={form} path={['user', 'email']}>
  {#snippet children(field)}
    <input {...field.props} value={field.input} type="email" />
  {/snippet}
</Field>
```

### Type safety

The API design of the [`Field`](/svelte/api/Field.md) component results in a fully type-safe form. For example, if you change your schema, TypeScript will immediately alert you if the path is invalid. The field state is also fully typed based on your schema, giving you autocompletion for properties like `field.input`.

## useField rune

For very complex forms where you create individual components for each form field, Formisch provides the [`useField`](/svelte/api/useField.md) rune. It allows you to access the field state directly within your component logic.

```svelte
<script lang="ts">
  import { useField } from '@formisch/svelte';
  import type { FormStore } from '@formisch/svelte';
  import * as v from 'valibot';

  type EmailInputProps = {
    form: FormStore<v.GenericSchema<{ email: string }>>;
  };

  let { form }: EmailInputProps = $props();

  const field = useField(form, { path: ['email'] });
</script>

<div>
  <input {...field.props} value={field.input} type="email" />
  {#if field.errors}
    <div>{field.errors[0]}</div>
  {/if}
</div>
```

### When to use which

- **Use [`Field`](/svelte/api/Field.md) component**: When defining multiple fields in the same component. It ensures you don't accidentally access the wrong field store.
- **Use [`useField`](/svelte/api/useField.md) rune**: When creating field components for single fields. It allows you to access field state in your component logic.

The [`Field`](/svelte/api/Field.md) component is essentially a thin wrapper around [`useField`](/svelte/api/useField.md) that allows you to access the field state within your snippet code.

## Field store

The field store provides access to the following properties:

- `path`: The path to the field within the form.
- `props`: Props to spread onto your input element (includes event handlers, name attribute, and `autofocus` to automatically focus fields with errors).
- `input`: The current input value of the field.
- `errors`: An array of error messages if validation fails.
- `isTouched`: Whether the field has been touched.
- `isEdited`: Whether the field's value has been changed.
- `isDirty`: Whether the current input differs from the initial input.
- `isValid`: Whether the field passes all validation rules.
- `onInput`: Sets the field input value programmatically. Use this when the field cannot be connected to a native HTML element (e.g., complex custom inputs or component libraries that don't expose the underlying element).

## Next steps

Now that you know how to add fields to your form, continue to the [input components](/svelte/guides/input-components.md) guide to learn about creating reusable input components for your forms.