HowTo: Components – howto-tooltip

By Ewa Gasperowicz

Ewa is a contributor to WebFundamentals

By Rob Dodson

Rob is a contributor to WebFundamentals

By Surma

Surma is a contributor to WebFundamentals

Summary

A <howto-tooltip> is a popup that displays information related to an element when the element receives keyboard focus or the mouse hovers over it. The element that triggers the tooltip references the tooltip element with aria-describedby.

The element self-applies the role tooltip and sets tabindex to -1, as the tooltip itself can never be focused.

Reference

Demo

View live demo on GitHub

Example usage

<div class="text">
   <label for="name">Your name:</label>
   <input id="name" aria-describedby="tp1"/>
   <howto-tooltip id="tp1">Ideally your name is Batman</howto-tooltip>
   <br>
   <label for="cheese">Favourite type of cheese: </label>
   <input id="cheese" aria-describedby="tp2"/>
   <howto-tooltip id="tp2">Help I am trapped inside a tooltip message</howto-tooltip>
</div>

Code

class HowtoTooltip extends HTMLElement {

The constructor does work that needs to be executed exactly once.
```
  constructor() {
```
```
    super();
```

These functions are used in a bunch of places, and always need to bind the correct this reference, so do it once.

    this._show = this._show.bind(this);
    this._hide = this._hide.bind(this);
  }

connectedCallback() fires when the element is inserted into the DOM. It's a good place to set the initial role, tabindex, internal state, and install event listeners.
```
  connectedCallback() {
```

    if (!this.hasAttribute('role'))
      this.setAttribute('role', 'tooltip');

    if (!this.hasAttribute('tabindex'))
      this.setAttribute('tabindex', -1);

    this._hide();

The element that triggers the tooltip references the tooltip element with aria-describedby.

    this._target = document.querySelector('[aria-describedby=' + this.id + ']');
    if (!this._target)
      return;

The tooltip needs to listen to focus/blur events from the target, as well as hover events over the target.

    this._target.addEventListener('focus', this._show);
    this._target.addEventListener('blur', this._hide);
    this._target.addEventListener('mouseenter', this._show);
    this._target.addEventListener('mouseleave', this._hide);
  }

disconnectedCallback() unregisters the event listeners that were set up in connectedCallback().
```
  disconnectedCallback() {
```

    if (!this._target)
      return;

Remove the existing listeners, so that they don't trigger even though there's no tooltip to show.

    this._target.removeEventListener('focus', this._show);
    this._target.removeEventListener('blur', this._hide);
    this._target.removeEventListener('mouseenter', this._show);
    this._target.removeEventListener('mouseleave', this._hide);
    this._target = null;
  }

  _show() {
    this.hidden = false;
  }

  _hide() {
    this.hidden = true;
  }
}

window.customElements.define('howto-tooltip', HowtoTooltip);