# Checkbox Group

> A set of Checkboxes with one label, one value, and one validity between them.

`<slab-checkbox-group>` · Form · built on `[role=group]`

## Install

```sh
pnpm add slab-elements lit
```

## Usage

```html
<script type="module">
  import 'slab-elements/checkbox-group.js';
</script>

<slab-checkbox-group label="Toppings" name="toppings">
  <slab-checkbox label="Cheese" value="cheese"></slab-checkbox>
  <slab-checkbox label="Onions" value="onions"></slab-checkbox>
</slab-checkbox-group>
```

## Example

Here's a styled version, `<slab-styled-checkbox-group>`. It's not in the package — it's an example of what you can build with the headless element. Copy it and make it yours at the bottom of this page.

```html
<slab-styled-checkbox-group label="Before the pour">
  <slab-styled-checkbox label="The forms are level" value="forms" checked></slab-styled-checkbox>
  <slab-styled-checkbox label="The rebar is tied" value="rebar" checked></slab-styled-checkbox>
  <slab-styled-checkbox label="The vapor barrier is down" value="barrier"></slab-styled-checkbox>
  <slab-styled-checkbox label="The inspector signed off" value="inspection"></slab-styled-checkbox>
  <span slot="description">Check them off as the crew does.</span>
</slab-styled-checkbox-group>
```

Swap `slab-styled-` for `slab-` in that markup and you've got the same example as it ships: the headless elements with no CSS at all. That's your starting point.

Each item is a [Checkbox](checkbox.md).

## Keyboard

| Key   | What it does                                     |
| ----- | ------------------------------------------------ |
| Tab   | Moves between the Checkboxes, each its own stop. |
| Space | Checks or unchecks the focused one.              |

## Behavior

A group of Checkboxes with no visual styles, with one label and one validity for all of them.

Checkboxes are found by class rather than by tag name, so your subclass of Checkbox can be named anything. The group's `value` is the value of every Checkbox that is checked and enabled, in the order they were checked.

Style it through its parts and through `:state(disabled)`, `:state(error)`, and `:state(required)`. How the Checkboxes are arranged is layout, so it's left to the styles around them.

## API

### `<slab-checkbox-group>`

#### Attributes

| Name | Type | Default | Description |
| --- | --- | --- | --- |
| `label` (required) | `string` |  |  |
| `disabled` | `boolean` | `false` |  |
| `hide-label` | `boolean` | `false` |  |
| `name` | `string` | `''` |  |
| `required` | `boolean` | `false` |  |
| `value` | `string[]` | `[]` | The value of every checked and enabled Checkbox, in the order they were checked. Not reflected, to match a native control. |
| `version` | `string` |  |  |

#### Properties

| Name | Type | Description |
| --- | --- | --- |
| `form` (read-only) | `HTMLFormElement \| null` |  |
| `validity` (read-only) | `ValidityState` |  |

#### Methods

| Signature | Description |
| --- | --- |
| `checkValidity(): boolean` |  |
| `focus(options?: FocusOptions): void` |  |
| `reportValidity(): boolean` |  |
| `resetValidityFeedback(): void` | Clears the validity feedback without changing `validity`. |
| `setCustomValidity(message: string): void` |  |
| `setValidity(flags?: ValidityStateFlags, message?: string): void` |  |

#### Slots

| Name | Type | Description |
| --- | --- | --- |
| `(default)` | `Checkbox` |  |
| `description` | `Element \| string` |  |

#### CSS parts

| Name | Description |
| --- | --- |
| `description` | Text about the group, and its validity message when it has one |
| `group` | The Checkboxes |
| `label` | The label |
| `validity-message` |  |

## Copy and own it

`<slab-styled-checkbox-group>` isn't in the package. It's an example — copy it into your project and change whatever you want. Under the hood, it's just the headless element, subclassed, with `styles` set. That's it. Keyboard, focus, ARIA, forms, and events all come from the headless element, and the styles only reach in through `::part()` and `:state()`, same as yours would.

To use it, copy these files, swap the tag in `@customElement()` for one of your own, and import it. `tokens.styles.ts` holds the colors and fonts every styled example shares, so you only need it once.

### TypeScript

These files are TypeScript, and `@customElement()` is one of Lit's decorators (TypeScript's experimental flavor). You'll need two options in your tsconfig, per [Lit's docs](https://lit.dev/docs/components/decorators/#decorators-typescript): `experimentalDecorators` to compile them, and `useDefineForClassFields` turned off so class fields don't stomp on the accessors Lit sets up.

```json
{
  "compilerOptions": {
    "experimentalDecorators": true,
    "useDefineForClassFields": false
  }
}
```

Using plain JavaScript? Drop the types and register the class with `customElements.define()` instead of the decorator.

### checkbox-group.ts

```ts
import { customElement } from 'lit/decorators.js';
import CheckboxGroup from 'slab-elements/checkbox-group.js';
import styles from './checkbox-group.styles.js';
import tokens from './tokens.styles.js';

declare global {
  interface HTMLElementTagNameMap {
    'slab-styled-checkbox-group': StyledCheckboxGroup;
  }
}

/**
 * Checkbox Group, styled: a slab-serif label over its Checkboxes, stacked.
 */
@customElement('slab-styled-checkbox-group')
export default class StyledCheckboxGroup extends CheckboxGroup {
  static override styles = [tokens, styles];
}
```

### checkbox-group.styles.ts

```ts
import { css } from 'lit';

export default css`
  :host {
    color: var(--ink);
    display: grid;
    font-family: var(--font-body);
  }

  [part~='label'] {
    font-family: var(--font-display);
    font-size: 1.0625rem;
    font-weight: 600;
    margin-block-end: 0.75rem;
  }

  :host(:state(required)) [part~='label']::after {
    color: var(--ember-deep);
    content: ' *' / '';
  }

  [part~='group'] {
    display: grid;
    gap: 0.75rem;
  }

  /*
    Spaced by what's in it rather than by a gap, so a description with
    nothing in it takes no room.
  */
  [part~='description'] {
    color: var(--ash);
    display: grid;
    font-size: 0.875rem;
  }

  ::slotted([slot='description']) {
    margin-block-start: 0.75rem;
  }

  [part~='validity-message'] {
    color: var(--ember-deep);
    font-weight: 600;
    margin-block-start: 0.75rem;

    &::before {
      content: '■ ' / '';
    }
  }
`;
```

### tokens.styles.ts

```ts
import { css } from 'lit';

/*
  The styled components' palette and type, taken from the logo: ink for the
  courses, ember for the base, paper behind them.

  Each is a short alias for a "--slab-styled-*" property, with the default as
  its fallback. Retheming is "--slab-styled-ember" and the rest on ":root",
  which every shadow root inherits. Were the defaults declared under those
  names here instead, each host's own declaration would shadow the page's.

  Each default is "light-dark()", so the components follow the page's
  "color-scheme": "dark" for dark, "light" for light, and "light dark" to
  follow the operating system. Ink and paper trade places in the dark, so
  ink is always the text and paper always what's behind it. Contrast is given
  as light, then dark.
*/
export default css`
  :host {
    /* Secondary text. 6.8:1 and 6.9:1 on paper. */
    --ash: var(--slab-styled-ash, light-dark(#5e5a55, #a8a19a));
    --border: 2px solid var(--ink);

    /* Behind disabled and read-only controls, and hovered rows. */
    --chalk: var(--slab-styled-chalk, light-dark(#f4f1ec, #2b2926));

    /*
      The logo's orange, brighter in the dark. 4.25:1 and 5.2:1 on paper is
      enough for borders, fills and large text, but not always for small text,
      which takes "--ember-deep".
    */
    --ember: var(--slab-styled-ember, light-dark(#d9492a, #ec5f3b));

    /*
      Orange for small text on paper, and for paper text on it. 5.7:1 and
      7.4:1.
    */
    --ember-deep: var(--slab-styled-ember-deep, light-dark(#b3381a, #ff8566));
    --font-body: var(
      --slab-styled-font-body,
      'IBM Plex Sans',
      system-ui,
      sans-serif
    );
    --font-display: var(
      --slab-styled-font-display,
      'Zilla Slab',
      rockwell,
      'Roboto Slab',
      serif
    );
    --font-mono: var(
      --slab-styled-font-mono,
      'IBM Plex Mono',
      ui-monospace,
      monospace
    );
    --ink: var(--slab-styled-ink, light-dark(#1c1c1c, #f4f1ec));
    --paper: var(--slab-styled-paper, light-dark(#fff, #1a1918));

    /* The hard, offset shadow a raised surface casts. */
    --shadow: 4px 4px 0 var(--ink);
  }
`;
```