# Range Slider

> A two-thumb slider for picking a range, with a thumb at each end that can meet but not pass the other.

`<slab-range-slider>` · Form · built on `[role=slider]`

## Install

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

## Usage

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

<slab-range-slider label="Price" name="price" min="0" max="500" start-value="100" end-value="300"></slab-range-slider>
```

## Example

Here's a styled version, `<slab-styled-range-slider>`. 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-range-slider label="Slump" max="7" min="2" step="0.5" start-value="3" end-value="5">
  <span slot="description">Inches. Most slabs pour between 3 and 5.</span>
</slab-styled-range-slider>
```

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 thumb is named by `label` and then its own label, "Minimum" and "Maximum" unless you set `start-label` and `end-label`, so a screenreader reads "Price Minimum". The form gets two entries under `name`, the start and then the end. Give the track a size, since the thumbs and the range between them are placed along it.

## Keyboard

| Key                   | What it does                                                                                   |
| --------------------- | ---------------------------------------------------------------------------------------------- |
| Left, Down, Right, Up | Steps the focused thumb down or up by `step`. Left and Right move it the way the arrow points. |
| Page Up, Page Down    | Steps it by a tenth of the range.                                                              |
| Home, End             | Moves it as far as it can go: to `min` or `max`, or to the other thumb.                        |

## Behavior

A two-thumb slider with no visual styles, for picking a range, such as a price from one amount to another. It follows the APG multi-thumb slider pattern: each thumb is a `[role=slider]`, and each one's minimum or maximum is the other thumb, so the two can meet but not pass each other.

A range input has only one thumb, so the thumbs are elements of their own rather than two range inputs on top of each other, which can't report each other as their bounds and fight over the pointer where they overlap.

`start-value` and `end-value` are the range, and they're always between `min` and `max`, on a `step` from `min`, and in order. Unset, they're `min` and `max`, so the whole range is picked. Like a native input's `value`, their attributes are the defaults and their properties the current values.

The group is named by `label`, and each thumb by it and its own label, so a screenreader reads "Price Minimum" and "Price Maximum". The arrow keys move a thumb by `step`, Page Up and Page Down by a tenth of the range, and Home and End as far as it can go. Drag a thumb, or press the track to bring the nearer thumb there.

Placing the thumbs and the range between them along the track is what a slider does, so that's functional and done here: each thumb is centered on its value, and the range spans from one to the other. Give the track a size, and style the rest through its parts and through `:state(disabled)` and `:state(dragging)`.

## API

### `<slab-range-slider>`

#### Attributes

| Name | Type | Default | Description |
| --- | --- | --- | --- |
| `label` (required) | `string` |  | Names the group. Each thumb is named by it and its own label. |
| `disabled` | `boolean` | `false` |  |
| `end-label` | `string` |  | Names the end thumb, after `label`. "Maximum" when unset. |
| `end-value` | `number` | `undefined` | Like a native input's `value`, the attribute is the default and the property is the current value. Between `start-value` and `max`, on a step. `max` when unset. |
| `hide-label` | `boolean` | `false` |  |
| `max` | `number` | `100` |  |
| `min` | `number` | `0` |  |
| `name` | `string` | `''` | Submitted twice, with the start value and then the end value. |
| `start-label` | `string` |  | Names the start thumb, after `label`. "Minimum" when unset. |
| `start-value` | `number` | `undefined` | Like a native input's `value`, the attribute is the default and the property is the current value. Between `min` and `end-value`, on a step. `min` when unset. |
| `step` | `number` | `1` |  |
| `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` |  |

#### Events

| Name | Type | Description |
| --- | --- | --- |
| `input` | `Event` |  |
| `change` | `Event` |  |

#### Slots

| Name | Type | Description |
| --- | --- | --- |
| `description` | `Element \| string` | Text about the slider, such as a hint |

#### CSS parts

| Name | Description |
| --- | --- |
| `container` | The label, the track and the description |
| `description` | Text about the slider, such as a hint |
| `end` | The end thumb |
| `label` | The label |
| `range` | The part of the track between the thumbs |
| `start` | The start thumb |
| `track` | The thumbs and the range between them |

## Copy and own it

`<slab-styled-range-slider>` 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.

### range-slider.ts

```ts
import { customElement } from 'lit/decorators.js';
import RangeSlider from 'slab-elements/range-slider.js';
import styles from './range-slider.styles.js';
import tokens from './tokens.styles.js';

declare global {
  interface HTMLElementTagNameMap {
    'slab-styled-range-slider': StyledRangeSlider;
  }
}

/**
 * Range Slider, styled: Slider's look, with an ember range between two
 * brick-shaped thumbs.
 */
@customElement('slab-styled-range-slider')
export default class StyledRangeSlider extends RangeSlider {
  static override styles = [tokens, styles];
}
```

### range-slider.styles.ts

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

/*
  The thumbs are centered on their values, so at either end of the track half
  of one hangs off it. The track is inset by half a thumb so they stay inside
  the host.
*/
export default css`
  :host {
    color: var(--ink);
    display: grid;
    font-family: var(--font-body);
  }

  [part~='container'] {
    display: grid;
    gap: 0.5rem;
  }

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

  [part~='track'] {
    background-color: var(--paper);
    block-size: 0.875rem;
    border: var(--border);
    box-sizing: border-box;
    cursor: pointer;
    margin-block: 0.5rem;
    margin-inline: 0.5rem;
  }

  [part~='range'] {
    background-color: var(--ember);
  }

  [part~='start'],
  [part~='end'] {
    background-color: var(--ink);
    block-size: 1.875rem;
    border: 2px solid var(--paper);
    box-shadow: 0 0 0 2px var(--ink);
    box-sizing: border-box;
    inline-size: 1rem;

    &:focus-visible {
      outline: 3px solid var(--ember);
      outline-offset: 3px;
    }
  }

  [part~='description'] {
    color: var(--ash);
    display: block;
    font-size: 0.875rem;
  }

  :host(:state(disabled)) [part~='track'] {
    cursor: not-allowed;
    opacity: 0.5;
  }
`;
```

### 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);
  }
`;
```