Slab

Selection

Combobox

A text input that filters a list of Options as you type.

Element
<slab-combobox>
Built on
<input role=combobox>
As Markdown
combobox.md

Example

Here's a styled version, <slab-styled-combobox>. 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. Switch to "As it ships" to see the same markup with the headless element and no CSS at all. That's your starting point.

Styled example As it ships
Alder Ready-Mix Basalt Concrete Co. Cascade Aggregates Delta Batch Plant Eagle Rock Materials
HTML
<slab-styled-combobox label="Supplier" placeholder="Start typing a name">
  <slab-styled-option value="alder">Alder Ready-Mix</slab-styled-option>
  <slab-styled-option value="basalt">Basalt Concrete Co.</slab-styled-option>
  <slab-styled-option value="cascade">Cascade Aggregates</slab-styled-option>
  <slab-styled-option value="delta">Delta Batch Plant</slab-styled-option>
  <slab-styled-option value="eagle" disabled>Eagle Rock Materials</slab-styled-option>
</slab-styled-combobox>
Alder Ready-Mix Basalt Concrete Co. Cascade Aggregates Delta Batch Plant Eagle Rock Materials
HTML
<slab-combobox label="Supplier" placeholder="Start typing a name">
  <slab-option value="alder">Alder Ready-Mix</slab-option>
  <slab-option value="basalt">Basalt Concrete Co.</slab-option>
  <slab-option value="cascade">Cascade Aggregates</slab-option>
  <slab-option value="delta">Delta Batch Plant</slab-option>
  <slab-option value="eagle" disabled>Eagle Rock Materials</slab-option>
</slab-combobox>

Usage

Install
pnpm add slab-elements lit
HTML
<script type="module">
  import 'slab-elements/combobox.js';
</script>

<slab-combobox label="Language" name="language">
  <slab-option value="en">English</slab-option>
  <slab-option value="es">Spanish</slab-option>
  <slab-option value="fr">French</slab-option>
</slab-combobox>

Its Options are the same ones Listbox uses.

Keyboard

Key What it does
Up, Down Opens the listbox and moves the active Option, stopping at each end and skipping disabled ones.
Alt+Down Opens the listbox without moving.
Alt+Up Closes the listbox.
Enter Selects the active Option and closes the listbox.
Escape Closes the listbox, and a second Escape clears the input.
Home, End Move the caret, as in any input.

Behavior

A text input that filters a list of Options as it's typed into, with no visual styles. It's the APG's editable combobox with list autocomplete.

Not <input list>. A <datalist> holds only text, can't be styled, and is drawn differently by every browser, down to whether it filters by prefix or by substring. So this is a real <input role="combobox"> with a <div role="listbox"> of slotted Options in a popover beside it.

The listbox is its own rather than a nested Listbox. A Listbox has a label, a Tab stop and a form value of its own, all of which a Combobox would have to switch off. What it shares with Listbox is Option, OptionsController, and the way the active Option is pointed at rather than focused: focus stays in the input, and the input's aria-activedescendant is set as an element, since an IDREF can't reach the slotted Options. Read or set it with activeOption.

Typing filters the Options by filter, a case-insensitive substring of each Option's text unless it's replaced, and opens the listbox. An Option that doesn't match is hidden, so it's out of the accessibility tree and skipped by the arrow keys. With none left, the listbox closes and the host matches :state(empty), for a "no results" message of your own.

ArrowDown and ArrowUp open the listbox and move the active Option, stopping at each end and skipping disabled Options. Alt with ArrowDown opens it without moving, and Alt with ArrowUp closes it. Enter and a click select the active Option and close the listbox. Escape closes it, and a second Escape clears the input. Home, End and the other caret keys stay the input's. A click or Tab elsewhere closes it, since either takes focus from the input.

value is the selected Option's value, not what's in the input, which shows that Option's text. Unless allow-custom is set, what's typed has to name an Option: when focus leaves, text that matches one's (ignoring case) selects it, an empty input clears the selection, and anything else goes back to the selected Option's text. With allow-custom, text that matches no Option is the value as typed. Either way, value is what's submitted, and "input" and "change" are dispatched together when it changes, as on a <select>, rather than on every keystroke.

Style it through its parts and through :state(disabled), :state(empty), :state(error), :state(open) and :state(required), and each Option through :state(active), :state(disabled) and :state(selected).

API

<slab-combobox>

Attributes
Name Type Default Description
label Required string
allow-custom boolean false Lets the value be text that matches no Option.
disabled boolean false
hide-label boolean false
name string ''
open boolean false
placeholder string
placement 'bottom' | 'top' 'bottom' The side of the input the listbox opens on, when there's room. It flips when there isn't.
required boolean false
value string '' The selected Option's value, or the typed text when allow-custom is set and it matches no Option. Setting it selects the Option with that value. Like a native input, the attribute is the default value and the property is the current one.
version string
Properties
Name Type Description
filter (option: Option, query: string) => boolean Whether an Option matches what's been typed. A case-insensitive substring of its text by default.
activeOption Option | null The Option the user is on, which Enter selects. It's pointed at rather than focused, so focus stays in the input.
form Read-only HTMLFormElement | null
options Read-only Option[]
selectedOption Read-only Option | 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
Events
Name Type Description
input Event
change Event
Slots
Name Type Description
(default) Option
description Element | string
CSS parts
Name Description
description Text about the Combobox, and its validity message when it has one
input
label The label
listbox The Options, in a popover beside the input
validity-message

Copy and own it

<slab-styled-combobox> 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.

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

declare global {
  interface HTMLElementTagNameMap {
    'slab-styled-combobox': StyledCombobox;
  }
}

/**
 * Combobox, styled: Text Field's input, with its Options in a panel that
 * casts a hard shadow, as Select's do.
 */
@customElement('slab-styled-combobox')
export default class StyledCombobox extends Combobox {
  static override styles = [tokens, textInput, styles];
}
text-input.styles.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;
    }
  }
`;
combobox.styles.ts
import { css } from 'lit';

/*
  Text Field's input, with the listbox in a panel beside it like Select's.
  The listbox is a popover, so a closed one isn't displayed, and its entrance
  runs each time it opens.
*/
export default css`
  [part~='listbox'] {
    animation: drop 150ms ease-out;
    background-color: var(--paper);
    border: var(--border);
    box-shadow: var(--shadow);
    box-sizing: border-box;
    color: var(--ink);
    margin-block: 0.5rem;
    max-block-size: 18rem;
    min-inline-size: anchor-size(inline);
    overflow-y: auto;
    padding: 0.25rem 0;
  }

  @keyframes drop {
    from {
      opacity: 0;
      translate: 0 -0.375rem;
    }
  }

  @media (prefers-reduced-motion: reduce) {
    [part~='listbox'] {
      animation: none;
    }
  }
`;
tokens.styles.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);
  }
`;