ZXing QR Reader

A QR code reader based on a wasm port of Zebra Crossing library by @nu-book.

Installation

npm install zxing-qr-reader

Demo

You can find the demo here

Usage

Instantiate the QrReader class by passing a canvas context to the constructor.
The way this was designed means you shouldn't need a react to use it :D.
NOTE: The resolution of the camera feed is the same as the size of the canvas.

import React from 'react';
import { QrReader } from 'zxing-qr-reader';

class App extends React.Component {
	componentDidMount() {
		const canvas = document.getElementById('canvas');//get canvas
		const context = canvas.getContext('2d');//get canvas context

		this.qr_reader = new QrReader(context);//instantiate qr reader

		this.qr_reader.scan();//start scan

		this.qr_reader.on('found', (result) => {
			console.log(result.text); //called when qr code was found
		});
    	}
    
	componentWillUnmount() {
		this.qr_reader.stop();
	}
	render() {
		return (
			<div>
				<canvas id="canvas" width={480} height={852}></canvas> //480p resolution in portrait on mobile
			</div>
		);
	}
}

A cover calculation is done when the image is drawn to the canvas meaning supplying one resolution for mobile devices and one other for desktop devices should suffice.
Typically a 600x600 resolution for desktop and 480x852 resolution for mobile does the trick. This gives fullscreen image on mobile and a large enough image on most desktop monitors.

QR Code From File

const file = e.target.files[0];
const result = this.qr_reader.readBarCodeFromFile(file);

Error Handling

this.qr_reader.on('error', (e) => {
	console.log(e);
});

Errors

Stream already initialised. Occurs when scan() method is called contiguously.

DOM Exception. Permission denied. Occurs when the user has not given your site permission. Error. Permission denied. Please update browser permissions to access camera. is written to the canvas in this event. Notifying the user.

Browser does not support getUserMedia Occurs when a browser does not support webRTC. Error. Your browser does not support camera access. Use a modern browser or update your browser. is written to the canvas in this event. Notifying the user.

Stream was not initialised Occurs when stop() method is called before scan() method.

Reader isn't initialised Occurs when readBarCodeFile is called before wasm module is loaded. (Uncommon)

Known Issues

Trying to set a canvas size that is of a higher resolution than the device camera can deliver, undefined behaviour occurs.

Calling stop() before the reader could fully initialise causes a bug where the last stream is always on. Meaning the user camera stays on and calling stop() changes nothing.