touch-pad

Track drags and touches on an element, a bit like a touchpad or trackpad.

Demo

The best way to understand how touch-pad works is to try it. But the GIF below may give you a quick idea.

Installation

npm install touch-pad

Usage

This package provides a web component and an event processor class. In both cases TouchPadMoveEvents are emitted when the user drags or touches the element. The event detail property contains an x and y property with the current position of the touch or drag relative to the top left corner of the element as a fraction of the element's width and height.

As a Web Component

import 'touch-pad/define'

The touch-pad/define module automatically registers the touch-pad custom element. You can now use it in your HTML.

<touch-pad>
  <interactive-element><interactive-element>
</touch-pad>

If you prefer to do your own registration, you can instead import { TouchPad } from 'touch-pad' to get the class.

Now you can listen for touchpadmove events on the touch-pad element (or on its ancestors).

document.querySelector('touch-pad').addEventListener('touchpadmove', (event) => {
  console.log(event.detail)
})

As a Class

import { TouchPadEventProcessor } from 'touch-pad'

const eventProcessor = new TouchPadEventProcessor(
  document.querySelector('interactive-element')
)
eventProcessor.listen()

The <interactive-element> will now emit touchpadmove events when the user drags or touches it.

document.querySelector('interactive-element').addEventListener('touchpadmove', (event) => {
  console.log(event.detail)
})

If do not want your element to emit touchpadmove events into the DOM, you can specify an EventTarget as the second argument to the constructor.

const touchMoveTarget = new EventTarget()
touchMoveTarget.addEventListener('touchpadmove', (event) => {
  console.log(event.detail)
})

const eventProcessor = new TouchPadEventProcessor(
  document.querySelector('interactive-element'),
  touchMoveTarget
)
eventProcessor.listen()

Cleanup

If the source element is removed from the DOM, you should call eventProcessor.unlisten() to stop listening for events. Failure to do so may result in memory leaks, since it adds event listeners to the element’s document. This is not necessary for the web component usage pattern where this is handled for you.