Input components

To make your code more readable, we recommend that you develop your own input components if you are not using a prebuilt UI library. There you can encapsulate logic to display error messages, for example.

If you're already a bit more experienced, you can use the input components we developed for our playground as a starting point. You can find the code in our GitHub repository here.

Why input components?

Currently, your fields might look something like this:

<Field of={loginForm} path={['email']}>
  {#snippet children(field)}
    <div>
      <label for={field.props.name}>Email</label>
      <input
        {...field.props}
        id={field.props.name}
        value={field.input}
        type="email"
        required
      />
      {#if field.errors}
        <div>{field.errors[0]}</div>
      {/if}
    </div>
  {/snippet}
</Field>

If CSS and a few more functionalities are added here, the code quickly becomes confusing. In addition, you have to rewrite the same code for almost every form field.

Our goal is to develop a TextInput component so that the code ends up looking like this:

<Field of={loginForm} path={['email']}>
  {#snippet children(field)}
    <TextInput
      {...field.props}
      type="email"
      label="Email"
      input={field.input}
      errors={field.errors}
      required
    />
  {/snippet}
</Field>

Create an input component

In the first step, you create a new file for the TextInput component and, if you use TypeScript, define its properties.

<script lang="ts">
  type TextInputProps = {
    name: string;
    type: 'text' | 'email' | 'tel' | 'password' | 'url' | 'date';
    label?: string;
    placeholder?: string;
    input: string | undefined;
    errors: [string, ...string[]] | null;
    required?: boolean;
    onfocus?: (event: FocusEvent) => void;
    oninput?: (event: InputEvent) => void;
    onchange?: (event: Event) => void;
    onblur?: (event: FocusEvent) => void;
  };

  let {
    name,
    type = 'text',
    label,
    placeholder,
    input,
    errors,
    required,
    onfocus,
    oninput,
    onchange,
    onblur,
  } = $props<TextInputProps>();
</script>

Component markup

In the next step, add the component markup to display the input and error messages.

<script lang="ts">
  // ... types and props definition ...
</script>

<div>
  {#if label}
    <label for={name}>
      {label}
      {#if required}<span>*</span>{/if}
    </label>
  {/if}
  <input
    {name}
    {type}
    {placeholder}
    id={name}
    value={input ?? ''}
    aria-invalid={!!errors}
    aria-errormessage={`${name}-error`}
    {onfocus}
    {oninput}
    {onchange}
    {onblur}
  />
  {#if errors}
    <div id={`${name}-error`}>{errors[0]}</div>
  {/if}
</div>

Next steps

You can now build on this code and add CSS, for example. You can also follow the procedure to create other components such as Checkbox, Slider, Select and FileInput.

Final code

Below is an overview of the entire code of the TextInput component.

<script lang="ts">
  type TextInputProps = {
    name: string;
    type: 'text' | 'email' | 'tel' | 'password' | 'url' | 'date';
    label?: string;
    placeholder?: string;
    input: string | undefined;
    errors: [string, ...string[]] | null;
    required?: boolean;
    onfocus?: (event: FocusEvent) => void;
    oninput?: (event: InputEvent) => void;
    onchange?: (event: Event) => void;
    onblur?: (event: FocusEvent) => void;
  };

  let {
    name,
    type = 'text',
    label,
    placeholder,
    input,
    errors,
    required,
    onfocus,
    oninput,
    onchange,
    onblur,
  } = $props<TextInputProps>();
</script>

<div>
  {#if label}
    <label for={name}>
      {label}
      {#if required}<span>*</span>{/if}
    </label>
  {/if}
  <input
    {name}
    {type}
    {placeholder}
    id={name}
    value={input ?? ''}
    aria-invalid={!!errors}
    aria-errormessage={`${name}-error`}
    {onfocus}
    {oninput}
    {onchange}
    {onblur}
  />
  {#if errors}
    <div id={`${name}-error`}>{errors[0]}</div>
  {/if}
</div>

Next steps

Now that you know how to create reusable input components, continue to the handle submission guide to learn how to process form data when the user submits the form.