Htmx/docs/Components/Textarea.md

# Textarea

A styled multi-line text input. Use it when you need more than a single line of text — comments, descriptions, notes, bio fields, or message composition.

---

## Quick example

```csharp
new Textarea(
    id:          "comment",
    name:        "comment",
    placeholder: "Write a comment…",
    label:       "Comment",
    rows:        5)
```

---

## All the options

```csharp
public Textarea(
    string id,
    string name         = "",
    string placeholder  = "",
    string label        = "",
    string description  = "",
    string defaultValue = "",
    string extraClasses = "",
    string hxAttrs      = "",
    int    rows         = 3)
```

| Parameter | What it does |
|---|---|
| `id` | The element id. Also used by the `<label for="...">`. |
| `name` | Form field name. |
| `placeholder` | Greyed-out hint inside the field when it is empty. |
| `label` | Visible text label above the field. |
| `description` | Small hint below the field (e.g. character limits). |
| `defaultValue` | Pre-filled content. |
| `extraClasses` | Additional Tailwind classes on the `<textarea>`. |
| `hxAttrs` | Extra HTML attributes appended verbatim. |
| `rows` | How many lines tall the field is initially. Default is 3. |

---

## Real-world examples

### Bio field (editing an existing value)

```csharp
new Textarea(
    id:           "bio",
    name:         "bio",
    label:        "Bio",
    description:  "Max 280 characters",
    defaultValue: System.Web.HttpUtility.HtmlEncode(user.Bio ?? ""),
    rows:         4)
```

### Auto-growing field (expands as the user types)

Pass a small `oninput` handler through `hxAttrs`:

```csharp
new Textarea(
    id:      "notes",
    name:    "notes",
    label:   "Notes",
    rows:    3,
    hxAttrs: """oninput="this.style.height=''; this.style.height=this.scrollHeight+'px'"""")
```

### Reading on the server

```csharp
public record Command(
    [property: FromForm] string Bio
);
```

---

## How it works

Textarea renders a standard HTML `<textarea>` element. The `defaultValue` is placed between the opening and closing tags (not in `value` like an `<input>`). Always HTML-encode any user-supplied `defaultValue` before passing it in.
new Textarea(
    id:      "draft",
    name:    "content",
    label:   "Draft",
    hxAttrs: """hx-post="/drafts/save" hx-trigger="keyup changed delay:500ms" hx-include="[name='content']"""")
```

### Reading in a form handler

```csharp
public record Command([property: FromForm] string Comment);

// command.Comment contains the textarea value
```

---

## Tips and tricks

- HTML-encode the `defaultValue` if it contains user-supplied content — it is placed directly inside the `<textarea>` element.
- `rows` controls the initial visible height but the user can resize vertically. For a fixed-height textarea, add `resize-none` in `extraClasses`.
- For a character counter, add `maxlength` via `hxAttrs` and pair with a small JS snippet or a sibling `<span>` updated on `input`.
- `placeholder` text is not submitted — always use `defaultValue` for edit forms where existing content should be pre-filled.
- `placeholder` text is not submitted — always use `defaultValue` for edit forms where existing content should be pre-filled.

---

## Complete page example

**`Templates/FeedbackPage.htmx`**
```html
<div class="max-w-lg mx-auto py-10">
  <h1 class="text-2xl font-bold mb-2">Send feedback</h1>
  <p class="text-sm text-muted-foreground mb-6">We read every message.</p>
  <form method="post" action="/feedback">
  $$AntiforgeryToken$$
  <div class="space-y-5 mb-6">
    $$SubjectInput$$
    $$MessageArea$$
  </div>
  $$SubmitBtn$$
  </form>
  $$SuccessAlert$$
</div>
```

**`Templates/FeedbackPage.htmx.cs`**
```csharp
namespace Htmx.ApiDemo.Templates;

public sealed class FeedbackPage : FeedbackPageBase
{
  private readonly IHtmxComponent _subject;
  private readonly IHtmxComponent _message;
  private readonly IHtmxComponent _submit;
  private readonly IHtmxComponent _success;
  private readonly byte[] _afToken;

  public FeedbackPage(
    IAntiforgery af,
    HttpContext ctx,
    string subjectError  = "",
    string messageError  = "",
    bool   submitted     = false)
  {
    var tokens = af.GetAndStoreTokens(ctx);
    _afToken = $"""<input type="hidden" name="{tokens.FormFieldName}" value="{tokens.RequestToken}">""".ToUtf8Bytes();

    _subject = new Components.Input(
      id:          "subject",
      name:        "subject",
      label:       "Subject",
      placeholder: "What's on your mind?",
      errorMessage: subjectError);

    _message = new Components.Textarea(
      id:           "message",
      name:         "message",
      label:        "Message",
      rows:         6,
      placeholder:  "Describe your feedback in detail…",
      errorMessage: messageError);

    _submit  = new Components.Button("Send feedback", type: "submit");
    _success = submitted
      ? new Components.Alert(title: "Thank you!", description: "Your feedback has been received.")
      : HtmxEmpty.Instance;
  }

  protected override void RenderAntiforgeryToken(HtmxRenderContext ctx) => ctx.Writer.WriteUtf8(_afToken);
  protected override void RenderSubjectInput(HtmxRenderContext ctx)     => _subject.Render(ctx.Next());
  protected override void RenderMessageArea(HtmxRenderContext ctx)      => _message.Render(ctx.Next());
  protected override void RenderSubmitBtn(HtmxRenderContext ctx)        => _submit.Render(ctx.Next());
  protected override void RenderSuccessAlert(HtmxRenderContext ctx)     => _success.Render(ctx.Next());
}
```

**POST handler**
```csharp
[Handler]
[MapPost("/feedback")]
public static partial class PostFeedbackHandler
{
  public record Command(
    [property: FromForm] string Subject,
    [property: FromForm] string Message);

  private static Task<IResult> HandleAsync(
    [AsParameters] Command cmd, HttpContext ctx, IAntiforgery af, CancellationToken ct)
  {
    if (string.IsNullOrWhiteSpace(cmd.Subject))
      return ctx.WriteHtmxPage(
        new FeedbackPage(af, ctx, subjectError: "Subject is required."), title: "Feedback");

    if (string.IsNullOrWhiteSpace(cmd.Message))
      return ctx.WriteHtmxPage(
        new FeedbackPage(af, ctx, messageError: "Message is required."), title: "Feedback");

    // Persist feedback…
    return ctx.WriteHtmxPage(
      new FeedbackPage(af, ctx, submitted: true), title: "Feedback");
  }
}
```

**`AppJsonSerializerContext.cs`**
```csharp
[JsonSerializable(typeof(PostFeedbackHandler.Command), TypeInfoPropertyName = "FeedbackCommand")]
```