# Breadcrumb

> The trail of links to the current page, as an ordered list in a navigation landmark. Separators are yours to add.

`<slab-breadcrumb>` · Navigation · built on `<nav> + <ol>`

## Install

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

## Usage

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

<slab-breadcrumb>
  <a href="/">Home</a>
  <a href="/docs/">Docs</a>
  <a href="/docs/install/">Install</a>
</slab-breadcrumb>
```

## Example

Here's a styled version, `<slab-styled-breadcrumb>`. 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-breadcrumb>
  <a href="#jobs">Jobs</a>
  <a href="#alder">14 Alder Lane</a>
  <a href="#foundation">Foundation</a>
</slab-styled-breadcrumb>
```

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.

## Behavior

A breadcrumb with no visual styles: a `<nav>` around an `<ol>` of the links slotted into it, the last of which is the current page.

An `<ol>` may only hold `<li>`s, so each slotted element gets an `<li>` of its own: it's put in a slot inside one, through the `slot` attribute, which Breadcrumb sets. The last element gets `aria-current="page"` unless it has an `aria-current` already.

Separators are a design's, so there are none. Each `<li>` is `::part(item)`, and every one but the first starts with a `::part(separator)`, which is hidden from screenreaders and has no content until you give it some. The `<ol>` keeps its numbers and indent until your styles take them off.

## API

### `<slab-breadcrumb>`

#### Attributes

| Name | Type | Default | Description |
| --- | --- | --- | --- |
| `label` | `string` |  | Names the navigation. "Breadcrumb" when unset. |
| `version` | `string` |  |  |

#### Properties

| Name | Type | Description |
| --- | --- | --- |
| `items` (read-only) | `Element[]` |  |

#### Slots

| Name | Type | Description |
| --- | --- | --- |
| `(default)` | `Element` | The links, from the first page to the current one |

#### CSS parts

| Name | Description |
| --- | --- |
| `item` |  |
| `list` | The links |
| `nav` | The navigation |
| `separator` |  |

## Copy and own it

`<slab-styled-breadcrumb>` 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.

### breadcrumb.ts

```ts
import { customElement } from 'lit/decorators.js';
import Breadcrumb from 'slab-elements/breadcrumb.js';
import styles from './breadcrumb.styles.js';
import tokens from './tokens.styles.js';

declare global {
  interface HTMLElementTagNameMap {
    'slab-styled-breadcrumb': StyledBreadcrumb;
  }
}

/**
 * Breadcrumb, styled: slab-serif links underlined in ember, divided by ember
 * slashes, with the current page in bold.
 */
@customElement('slab-styled-breadcrumb')
export default class StyledBreadcrumb extends Breadcrumb {
  static override styles = [tokens, styles];
}
```

### breadcrumb.styles.ts

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

/*
  The links are the consumer's own, slotted in, so they're styled through
  "::slotted()". Breadcrumb marks the last one with "aria-current".
*/
export default css`
  [part~='list'] {
    align-items: center;
    display: flex;
    flex-wrap: wrap;
    font-family: var(--font-display);
    font-size: 1.0625rem;
    gap: 0.5rem;
    list-style: none;
    margin: 0;
    padding: 0;
  }

  [part~='item'] {
    align-items: center;
    display: flex;
    gap: 0.5rem;
  }

  [part~='separator']::before {
    color: var(--ember);
    content: '/';
    font-weight: 700;
  }

  ::slotted(a) {
    color: var(--ink);
    text-decoration-color: var(--ember);
    text-decoration-line: underline;
    text-decoration-thickness: 2px;
    text-underline-offset: 0.25em;
  }

  ::slotted(a:hover) {
    background-color: var(--ink);
    color: var(--paper);
    text-decoration-line: none;
  }

  ::slotted(a:focus-visible) {
    outline: 3px solid var(--ember);
    outline-offset: 2px;
  }

  ::slotted([aria-current='page']) {
    font-weight: 700;
    text-decoration-line: 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);
  }
`;
```