@lion/button

Button

lion-button provides a button component that is easily styleable and is accessible.

import { html } from 'lit-html';

import './lion-button.js';
import iconSvg from './docs/assets/icon.svg.js';

export default {
  title: 'Buttons/Button',
};

export const main = () => html` <lion-button>Default</lion-button> `;

Features

• Clickable area that is bigger than visual size
• Works with native form / inputs
• Has integration for implicit form submission similar to how native <form>, <input> and <button> work together.

How to use

Installation

npm i --save @lion/button

import { LionButton } from '@lion/button';
// or
import '@lion/button/lion-button.js';

Example

<lion-button>Button Text</lion-button>

Buttons

With click handler

export const handler = () => html`
  <lion-button @click="${ev => console.log('clicked/spaced/entered', ev)}">
    Click | Space | Enter me and see log
  </lion-button>
`;

Icon button

export const iconButton = () => html` <lion-button>${iconSvg(html)} Bug</lion-button> `;

Icon only button

export const iconOnly = () =>
  html` <lion-button aria-label="Bug"> ${iconSvg(html)} </lion-button> `;

Disabled button

export const disabled = () => html` <lion-button disabled>Disabled</lion-button> `;

Usage with native form

Supports the following use cases:

• Submit on button click
• Reset native form fields when using type="reset"
• Submit on button enter or space keypress
• Submit on enter keypress inside an input

export const withinForm = () => html`
  <form
    @submit=${ev => {
      ev.preventDefault();
      console.log('submit handler');
    }}
  >
    <label for="firstNameId">First name</label>
    <input id="firstNameId" name="firstName" />
    <label for="lastNameId">Last name</label>
    <input id="lastNameId" name="lastName" />
    <lion-button @click=${() => console.log('click handler')}>Submit</lion-button>
  </form>
`;

Important notes:

• A (lion)-button of type submit is mandatory for the last use case, if you have multiple inputs. This is native behavior.
• @click on <lion-button> and @submit on <form> are triggered by these use cases. We strongly encourage you to listen to the submit handler if your goal is to do something on form-submit.
• To prevent form submission full page reloads, add a submit handler on the form @submit with event.preventDefault(). Adding it on the <lion-button> is not enough.

Considerations

Why a Web Component?

There are multiple reasons why we used a Web Component as opposed to a CSS component.

• Target size: The minimum target size is 40 pixels, which makes even the small buttons easy to activate. A container element was needed to make this size possible.
• Advanced styling: There are advanced styling options regarding icons in buttons, where it is a lot more maintainable to handle icons in our button using slots. An example is that a sticky icon-only buttons may looks different from buttons which have both icons and text.
• Native form integration: The lion button works with native <form> submission, and even implicit form submission on-enter. A lot of delegation logic had to be created for this to work.

Event target

We want to ensure that the event target returned to the user is <lion-button>, not button. Therefore, simply delegating the click to the native button immediately, is not desired. Instead, we catch the click event in the <lion-button>, and ensure delegation inside of there.

Flashing a native button click as a direct child of form

By delegating the click() to the native button, it will bubble back up to <lion-button> which would cause duplicate actions. We have to simulate the full .click() however, otherwise form submission is not triggered. So this bubbling cannot be prevented. Therefore, on click, we flash a <button> to the form as a direct child and fire the click on that button. We then immediately remove that button. This is a fully synchronous process; users or developers will not notice this, it should not cause problems.

Native button & implicit form submission

Flashing the button in the way we do solves almost all issues except for one. One of the specs of W3C is that when you have a form with multiple inputs, pressing enter while inside one of the inputs only triggers a form submit if that form has a button of type submit.

To get this particular implicit form submission to work, having a native button in our <lion-button> is a hard requirement. Therefore, not only do we flash a native button on the form to delegate <lion-button> trigger to <button> and thereby trigger form submission, we also add a native button inside the <lion-button> whose type property is synchronized with the type of the <lion-button>.