Button: Use Cases

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>
`;

Disabled button

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

Minimum click area

The minimum click area needs to be at least 44px by 44px according to WCAG Success Criterion 2.5.5 Target Size (Enhanced).

export const minimumClickArea = () => html` <style>
    .small {
      padding: 4px;
      line-height: 1em;
    }
    .small::before {
      border: 1px dashed #000;
    }
  </style>
  <lion-button class="small">xs</lion-button>`;

Usage with native form

<lion-button-reset> and <lion-button-submit> are especially created to supports the following use cases:

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

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

Important notes:

• A <lion-button-submit> is mandatory for the last use case, if you have multiple inputs. This is native behaviour.
• @click on <lion-button-submit> 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-submit> 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-submit> 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-reset> and <lion-button-submit> 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-submit> is a hard requirement. Therefore, not only do we flash a native button on the form to delegate <lion-button-submit> trigger to <button> and thereby trigger form submission, we also add a native button inside the <lion-button-submit> whose type property is synchronized with the type of the <lion-button-submit>.