wc-scratch

wc-scratch

A fun scratch card native web component without any dependencies.

Installation

Install it ith npm:

npm i wc-scratch

Or link it using a script tag:

<script type="module" src="https://unpkg.com/wc-scratch@latest/dist/wc-scratch.js"></script>

Usage

Import the component - this will also register it as a custom element with the tag name <wc-scratch>:

import 'wc-scratch'

Now you can use the component in your markup:

<wc-scratch>
  <h1 style="margin: 0">Scratch me free!</h1>
</wc-scratch>

Configuration

Slot

Slot name	Description
default	The content to be scratched free.
scratch-source	Used to pass an image that acts as a scratch-color replacement.

Example on how to use the scratch-source slot:

<wc-scratch>
  <h1>Scratch me!</h1>
  <img slot="scratch-source" crossorigin style="display: none;" src="https://example.com/example.jpeg" alt="image" />
</wc-scratch>

• To get the best experience make sure that your content is the same size as the image used to hide it.
• You need to set display: none on this image so the original is getting hidden. We only read its image data and paint it on the canvas.
• For images fetched over the internet you also need to set crossorigin if you want to use the percentage-update feature or else the CanvasRenderingContext2D: getImageData() will throw an error.

Props

Property	Type	Default	Description
brush-size	number	10	Defines the lineWidth attribute.
brush-shape	string	'round'	Defines the lineJoin attribute.
scratch-color	string	'#000000'	The color you want to scratch away with your scratch card. Can be any valid CSS color.
percentage-update	boolean	false	Flag to toggle the percentage-update event emitter on or off.

Events

Name	Type	Description
percentage-update	{ detail: number }	Emits a custom event with the cleared amount as a percentage.

Example:

<script>
  const scratch = document.querySelector('wc-scratch[percentage-update]')
  scratch.addEventListener('percentage-update', ({ detail }) => console.log(detail))
</script>

Caveats

1. Please avoid using margin on a content element since it can lead to improper sizing of the canvas element and therefore the content might be visible.

2. Calculation of the cleared area is rounded with a 150 pixel error margin.