# Number

> A number field built on the native one, with stepping and validation included.

`<slab-number>` · Form · built on `<input type=number>`

## Install

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

## Usage

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

<slab-number label="Quantity" name="quantity" min="1" max="10" value="1"></slab-number>
```

## Example

Here's a styled version, `<slab-styled-number>`. 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-number label="Cubic yards" max="200" min="1" step="0.5" value="38">
  <span slot="description">Order about 10% over the slab's volume.</span>
</slab-styled-number>
```

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.

## Keyboard

| Key      | What it does                           |
| -------- | -------------------------------------- |
| Up, Down | Steps the value, as on a number input. |

## Behavior

A number field with no visual styles, around a native `<input type=number>`, so it is typed into, stepped, focused, and read the way one is. Its spin buttons, arrow-key stepping and `spinbutton` role are the input's own.

The label and the input are both in the shadow root, so a plain `for` reference names it without crossing out of one. The host delegates focus, so clicking anywhere on it, or a `<label for>` pointing at it, focuses the input.

Validity is the native input's. `required`, `min`, `max` and `step` are passed through to it, and whatever it decides is mirrored onto the host, so `valueMissing`, `rangeUnderflow`, `rangeOverflow`, `stepMismatch` and `badInput` all mean what they mean on an `<input>`. Nothing is computed twice.

`value` is a string, as it is on the input, so an empty field and one a person is partway through typing aren't forced into a number.

Style it through its parts and through `:state(disabled)`, `:state(error)`, `:state(readonly)` and `:state(required)`. Where the label sits relative to the input is layout, so it's left to the styles around it.

## API

### `<slab-number>`

#### Attributes

| Name | Type | Default | Description |
| --- | --- | --- | --- |
| `label` (required) | `string` |  |  |
| `autocomplete` | `HTMLInputElement['autocomplete']` |  |  |
| `disabled` | `boolean` | `false` |  |
| `hide-label` | `boolean` | `false` |  |
| `max` | `number` |  |  |
| `min` | `number` |  |  |
| `name` | `string` | `''` |  |
| `placeholder` | `string` |  |  |
| `readonly` | `boolean` | `false` |  |
| `required` | `boolean` | `false` |  |
| `step` | `number \| 'any'` |  | A number, or "any" to allow any value. Left unset, the input's own default of 1 applies. |
| `value` | `string` | `''` | Like a native input, the attribute is the default value and the property is the current one, so the attribute doesn't change as the field is typed into. |
| `version` | `string` |  |  |

#### Properties

| Name | Type | Description |
| --- | --- | --- |
| `form` (read-only) | `HTMLFormElement \| null` |  |
| `validity` (read-only) | `ValidityState` |  |
| `valueAsNumber` | `number` | `value` as a number, or `NaN` when empty, as on a native input. |

#### Methods

| Signature | Description |
| --- | --- |
| `checkValidity(): boolean` |  |
| `click(): void` |  |
| `focus(options?: FocusOptions): void` |  |
| `reportValidity(): boolean` |  |
| `resetValidityFeedback(): void` | Clears the validity feedback without changing `validity`. |
| `select(): void` |  |
| `setCustomValidity(message: string): void` |  |
| `setValidity(flags?: ValidityStateFlags, message?: string): void` |  |
| `stepDown(count?: number): void` | Steps `value` down by `step` times `count`. Like a native input's, it dispatches no events, and throws when `step` is "any". |
| `stepUp(count?: number): void` | Steps `value` up by `step` times `count`. Like a native input's, it dispatches no events, and throws when `step` is "any". |

#### Events

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

#### Slots

| Name | Type | Description |
| --- | --- | --- |
| `description` | `Element \| string` |  |

#### CSS parts

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

## Copy and own it

`<slab-styled-number>` 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.

### number.ts

```ts
import { customElement } from 'lit/decorators.js';
import NumberField from 'slab-elements/number.js';
import textInput from './text-input.styles.js';
import tokens from './tokens.styles.js';

declare global {
  interface HTMLElementTagNameMap {
    'slab-styled-number': StyledNumberField;
  }
}

/**
 * Number, styled: Text Field's look, with the browser's own stepper.
 */
@customElement('slab-styled-number')
export default class StyledNumberField extends NumberField {
  static override styles = [tokens, textInput];
}
```

### text-input.styles.ts

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

/*
  The look shared by everything typed into: Text Field, Textarea, Number, Date
  Field and Combobox, whose fields are "::part(input)", or "::part(textarea)"
  for Textarea. File Drop starts from it too, for its label and description.
*/
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: 0.375rem;
  }

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

  [part~='input'],
  [part~='textarea'] {
    background-color: var(--paper);
    block-size: 3rem;
    border: var(--border);
    border-radius: 0;
    box-sizing: border-box;
    color: inherit;
    font: inherit;

    /* A fixed height, shared with Select, so fields line up in a row. */
    padding: 0 0.75rem;
    transition:
      background-color 100ms,
      border-color 100ms,
      box-shadow 100ms,
      translate 100ms;

    &::placeholder {
      color: var(--ash);
    }

    /*
      The outline is transparent rather than gone, so it still shows in forced
      colors, where box shadows don't.
    */
    &:focus-visible {
      box-shadow: 4px 4px 0 var(--ember);
      outline: 2px solid transparent;
      translate: -2px -2px;
    }

    &:disabled {
      background-color: var(--chalk);
      border-style: dashed;
      color: var(--ash);
      cursor: not-allowed;
    }
  }

  [part~='textarea'] {
    block-size: auto;
    min-block-size: 7rem;
    padding: 0.625rem 0.75rem;
    resize: vertical;
  }

  :host(:state(readonly)) [part~='input'],
  :host(:state(readonly)) [part~='textarea'] {
    background-color: var(--chalk);
  }

  :host(:state(error)) [part~='input'],
  :host(:state(error)) [part~='textarea'] {
    border-color: var(--ember-deep);
  }

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

  ::slotted([slot='description']) {
    margin-block-start: 0.375rem;
  }

  [part~='validity-message'] {
    color: var(--ember-deep);
    font-weight: 600;
    margin-block-start: 0.375rem;

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

  @media (prefers-reduced-motion: reduce) {
    [part~='input'],
    [part~='textarea'] {
      transition: none;
    }
  }
`;
```

### 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);
  }
`;
```