Slab
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Form

Form

A <form> that Slab's controls submit, reset, and validate with — just like native ones.

Element
<slab-form>
Built on
<form>
As Markdown
form.md

Example

Here's a styled version, <slab-styled-form>. 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
HTML
<slab-styled-form label="Schedule a pour">
  <slab-styled-text-field label="Job name" name="job" value="14 Alder Lane foundation" required></slab-styled-text-field>
  <slab-styled-date-field label="Pour date" name="date" required></slab-styled-date-field>
  <slab-styled-number label="Cubic yards" min="1" name="yards" value="38"></slab-styled-number>
  <div>
    <button class="styled-button styled-button--primary">Schedule</button>
  </div>
</slab-styled-form>
HTML
<slab-form label="Schedule a pour">
  <slab-text-field label="Job name" name="job" value="14 Alder Lane foundation" required></slab-text-field>
  <slab-date-field label="Pour date" name="date" required></slab-date-field>
  <slab-number label="Cubic yards" min="1" name="yards" value="38"></slab-number>
  <div>
    <button class="styled-button styled-button--primary">Schedule</button>
  </div>
</slab-form>

Usage

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

<slab-form label="Sign up" action="/sign-up" method="post">
  <slab-text-field label="Email" name="email" type="email" required></slab-text-field>
  <button>Sign up</button>
</slab-form>

A plain <form> works with Slab’s controls too. Reach for Form when you want what it adds: a label that makes the form a landmark, and a checkValidity() that doesn’t show errors, just like a native one.

Keyboard

Key What it does
Enter In a field, submits the form, as in a native one.

Behavior

A form with no visual styles, around a native <form>, so it's submitted, reset and validated the way one is.

The <form> is in the light DOM, not the shadow root. A control's form owner is its nearest <form> ancestor in its own tree, and that doesn't cross a shadow boundary: a <form> in the shadow root with a <slot> inside it would own nothing slotted into it, and every control would submit to no form at all. So Form appends a <form> as its only child and moves its other children into it, on connect and whenever one is added. The shadow root holds a single <slot>, which the <form> is slotted into.

Everything else is the <form>'s. Slab's controls are form-associated through ElementInternals, so they submit, reset, and report their validity to it the way a native <input> does, and nothing here walks them. checkValidity(), reportValidity(), requestSubmit(), reset() and submit() are the <form>'s, and "submit" and "reset" bubble from it through the host.

A native <form>'s checkValidity() fires "invalid" at each invalid control but shows nothing, and so does this one's: Form marks its own <form> while its checkValidity() runs, whether it's called on Form or on form, and Slab's controls stay out of their error state. Only that <form> is marked. HTMLFormElement.prototype is left alone, so a consumer's own plain <form> gets no such marking, and its checkValidity() puts Slab's invalid controls into their error state as reportValidity() does.

label, when set, names the <form>, which is what makes it a form landmark. The <form> is reachable as form and styled as any light-DOM element is.

API

<slab-form>

Attributes
Name Type Default Description
action string
autocomplete 'on' | 'off'
enctype string
label string Names the form, which makes it a landmark.
method 'get' | 'post' | 'dialog'
name string
novalidate boolean false
target string
version string
Properties
Name Type Description
elements Read-only HTMLFormControlsCollection
form Read-only HTMLFormElement The native form, in the light DOM
Methods
Signature Description
checkValidity(): boolean
reportValidity(): boolean
requestSubmit(submitter?: HTMLElement | null): void
reset(): void
submit(): void
Slots
Name Type Description
(default) Element | string Moved into the form

Copy and own it

<slab-styled-form> 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.

form.ts 
import { customElement } from 'lit/decorators.js';
import Form from 'slab-elements/form.js';
import styles from './form.styles.js';
import tokens from './tokens.styles.js';

declare global {
  interface HTMLElementTagNameMap {
    'slab-styled-form': StyledForm;
  }
}

/**
 * Form, styled: its fields stacked, with room between them.
 */
@customElement('slab-styled-form')
export default class StyledForm extends Form {
  static override styles = [tokens, styles];
}
form.styles.ts 
import { css } from 'lit';

/*
  Form moves its children into a "<form>" of its own, in the light DOM, and
  slots that in. So the form is what's laid out.
*/
export default css`
  ::slotted(form) {
    display: grid;
    gap: 1.5rem;
  }
`;
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);
  }
`;