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    1.3.0 • Public • Published

    QR Scanner

    Javascript QR Code Scanner based on Cosmo Wolfe's javascript port of Google's ZXing library.

    In this library, several improvements have been applied over the original port:

    • Web cam scanning support out of the box
    • Uses the browser's native BarcodeDetector if available
    • Lightweight: ~50.5 kB (~13.0 kB gzipped) minified with Google's closure compiler. If the native BarcodeDetector is available, only ~6.8 kB (~2.7 kB gzipped) are loaded.
    • Improved performance and reduced memory footprint.
    • Runs in a WebWorker which keeps the main / UI thread responsive.
    • Can be configured for better performance on colored QR codes.

    According to our benchmarking this project's scanner engine's detection rate is about 2-3 times (and up to 8 times) as high as the one of the most popular javascript QR scanner library LazarSoft/jsqrcode. Also the other library oftentimes misreads the content of QR codes, while for this project no misreads occurred in the benchmarking.

    The library supports scanning a continuous video stream from a web cam as well as scanning of single images.

    The development of this library is sponsored by nimiq, world's first browser based blockchain.



    See https://nimiq.github.io/qr-scanner/demo/


    To install via npm:

    npm install --save qr-scanner

    To install via yarn:

    yarn add qr-scanner

    Or simply copy qr-scanner.min.js and qr-scanner-worker.min.js to your project.


    The QR Scanner consists of two files.

    Setting up the API

    qr-scanner.min.js is the main API as an es6 module and can be imported as follows:

    import QrScanner from 'path/to/qr-scanner.min.js'; // if using plain es6 import
    import QrScanner from 'qr-scanner'; // if installed via package and bundling with a module bundler like webpack or rollup

    This requires the importing script to also be an es6 module or a module script tag, e.g.:

    <script type="module">
        import QrScanner from 'path/to/qr-scanner.min.js';
        // do something with QrScanner

    If your project is not based on es6 modules you can

    import('path/to/qr-scanner.min.js').then((module) => {
        const QrScanner = module.default;
        // do something with QrScanner
    • use qr-scanner.umd.min.js for direct usage as non-module script
    <script src="path/to/qr-scanner.umd.min.js"></script>
        // do something with QrScanner
    • bundle qr-scanner.umd.min.js directly with your non-module code with tools like gulp or grunt.
    • bundle the lib with require based bundlers like browserify:
    const QrScanner = require('qr-scanner'); // if installed via package
    const QrScanner = require('path/to/qr-scanner.umd.min.js'); // if not installed via package
    // do something with QrScanner

    Setting up the worker

    qr-scanner-worker.min.js is a plain Javascript file for the separate worker thread and needs to be copied over to your project. You should then point QrScanner.WORKER_PATH to the location where it will be hosted:

    QrScanner.WORKER_PATH = 'path/to/qr-scanner-worker.min.js';

    Webpack specific worker setup

    If you're using Webpack to bundle your project, the file-loader or raw-loader might be interesting for you for handling the qr-scanner-worker.min.js dependency. Which one to choose depends on your use case.

    Using file-loader

    The file-loader automatically copies the worker script into your build and provides the path where it will be located in the build. At runtime, the worker will then be lazy-loaded from there when needed. Due to its ability to lazy-load the worker, using the file-loader is the preferred approach if you do not expect the QR scanner to be used every time a user uses your app or if the QR scanner is not launched right after loading the app.

    You can add the file-loader to your project via:

    npm install --save-dev file-loader

    You can then use it to copy the worker file and obtain the WORKER_PATH:

    import QrScannerWorkerPath from '!!file-loader!./node_modules/qr-scanner/qr-scanner-worker.min.js';
    QrScannerLib.WORKER_PATH = QrScannerWorkerPath;

    Note that the path to the worker file has to be set relatively to the source file where you use it. For example, if your source file using the QrScanner sits in /src/components, the correct import would be import QrScannerWorkerPath from '!!file-loader!../../node_modules/qr-scanner/qr-scanner-worker.min.js';.

    Using raw-loader

    The raw-loader bundles the worker as string into your build, thus no separate file gets generated in your build output. While this simplifies the build output and avoids an additional network request, it increases your bundle size and removes the ability to lazy-load the worker file only when needed.

    You can add the raw-loader to your project via:

    npm install --save-dev raw-loader

    You can then use it to load the worker file and set the WORKER_PATH:

    import qrScannerWorkerSource from '!!raw-loader!./node_modules/qr-scanner/qr-scanner-worker.min.js';
    QrScanner.WORKER_PATH = URL.createObjectURL(new Blob([qrScannerWorkerSource]));

    Note that the path to the worker file has to be set relatively to the source file where you use it. For example, if your source file using the QrScanner sits in /src/components, the correct import would be import qrScannerWorkerSource from '!!raw-loader!../../node_modules/qr-scanner/qr-scanner-worker.min.js';.


    Web Cam Scanning

    1. Create HTML

    Create a <video> element where the web cam video stream should get rendered:


    2. Create a QrScanner Instance

    const qrScanner = new QrScanner(videoElem, result => console.log('decoded qr code:', result));

    As an optional third parameter an error handler to be invoked on decoding errors can be specified. The default is QrScanner._onDecodeError.

    As an optional fourth parameter a method can be provided that determines a region to which scanning should be restricted as a performance improvement. This region can optionally also be scaled down before performing the scan as an additional performance improvement. The region is specified as x, y, width and height; the dimensions for the downscaled region as downScaledWidth and downScaledHeight. Note that the aspect ratio between width and height and downScaledWidth and downScaledHeight should remain the same. By default, the scan region is restricted to a centered square of two thirds of the video width or height, whichever is smaller, and scaled down to a 400x400 square.

    As an optional fifth parameter a preference for the camera to use can be specified. The preference can be either a device id as returned by listCameras or a facing mode specified as 'environment' or 'user'. The default is 'environment'. Note that there is no guarantee that the preference can actually be fulfilled.

    To use the default value for an optional parameter, omit it or use undefined.

    3. Start scanning


    Call it when you're ready to scan, for example on a button click or directly on page load. It will prompt the user for permission to use a camera. Note: to read from a Web Cam stream, your page must be served via HTTPS.

    4. Stop scanning


    If you want, you can stop scanning anytime and resume it by calling start() again.

    Single Image Scanning

        .then(result => console.log(result))
        .catch(error => console.log(error || 'No QR code found.'));

    Supported image sources are: HTMLImageElement, SVGImageElement, HTMLVideoElement, HTMLCanvasElement, ImageBitmap, OffscreenCanvas, File / Blob, Data URIs, URLs pointing to an image (if they are on the same origin or CORS enabled)

    As an optional second parameter a region defined by x, y, width and height can be specified to which the search for a QR code should be restricted. As a performance improvement this region can be scaled down before performing the scan by providing a downScaledWidth and downScaledHeight. By default, the region spans the whole image and is not scaled down.

    As an optional third parameter a manually created QR scanner engine instance to be reused can be specified. This improves performance if you're scanning a lot of images. An engine can be manually created via QrScanner.createQrEngine(QrScanner.WORKER_PATH) (async). By default, no engine is reused for single image scanning.

    As an optional fourth parameter a manually created canvas to be reused can be specified. This improves performance if you're scanning a lot of images. A canvas can be manually created via a <canvas> tag in your markup or document.createElement('canvas'). By default, no canvas is reused for single image scanning.

    As an optional fifth parameter you can request a provided canvas for reuse to not be resized, irrespective of the source image or source region dimensions. Note that the canvas and source region should have the same aspect ratio to avoid that the image to scan gets distorted which could make detecting QR codes impossible. By default, the canvas size is adapted to the source region dimensions for single image scanning.

    To use the default value for an optional parameter, omit it or use undefined.

    Checking for Camera availability

    This library provides a utility method for checking whether the device has a camera. This can be useful for determining whether to offer the QR web cam scanning functionality to a user.

    QrScanner.hasCamera(); // async

    Getting the list of available Cameras

    This library provides a utility method for getting a list of the device's cameras, defined via their id and label. This can be useful for letting a user choose a specific camera to use.

    You can optionally request the camera's labels. Note that this however requires the user's permission to acess the cameras, which he will be asked for if not granted already. If not specifically requested, device labels are determined on a best effort basis, i.e. actual labels are returned if permissions were already granted and fallback labels otherwise.

    QrScanner.listCameras(); // async; without requesting camera labels
    QrScanner.listCameras(true); // async; requesting camera labels, potentially asking the user for permission

    Specifying which camera to use

    You can change the preferred camera to be used. The preference can be either a device id as returned by listCameras or a facing mode specified as 'environment' or 'user'. Note that there is no guarantee that the preference can actually be fulfilled.

    qrScanner.setCamera(facingModeOrDeviceId); // async

    Color Inverted Mode

    The scanner by default scans for dark QR codes on a bright background. You can change this behavior to scan for bright QR codes on dark background or for both at the same time:


    Where inversionMode can be original, invert or both. The default for web cam scanning is original and for single image scanning both.

    Color Correction

    Change the weights for red, green and blue in the grayscale computation to improve contrast for QR codes of a specific color:

    qrScanner.setGrayscaleWeights(red, green, blue, useIntegerApproximation = true);

    Where red, green and blue should sum up to 256 if useIntegerApproximation === true and 1 otherwise. By default, these values are used.

    Flashlight support

    On supported browsers, you can check whether the currently used camera has a flash and turn it on or off. Note that hasFlash should be called after the scanner was successfully started to avoid the need to open a temporary camera stream just to query whether it has flash support, potentially asking the user for camera access.

    qrScanner.hasFlash(); // check whether the browser and used camera support turning the flash on; async.
    qrScanner.isFlashOn(); // check whether the flash is on
    qrScanner.turnFlashOn(); // turn the flash on if supported; async
    qrScanner.turnFlashOff(); // turn the flash off if supported; async
    qrScanner.toggleFlash(); // toggle the flash if supported; async.

    Clean Up

    You can destroy the QR scanner if you don't need it anymore:

    qrScanner = null;

    This will stop the camera stream and web worker and cleans up event listeners.

    Build the project

    The project is prebuild in qr-scanner.min.js in combination with qr-scanner-worker.min.js. Building yourself is only necessary if you want to change the code in the /src folder. NodeJs is required for building.

    Install required build packages:

    npm install


    npm run build


    npm i qr-scanner

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    • danimoh