Lightweight: ~33.7 kB (~12 kB gzipped) minified with Google's closure compiler.
Improved binarizer which makes it more tolerant to shades and reflections on the screen.
Can be configured for better performance on colored QR codes.
Runs in a WebWorker which keeps the main / UI thread responsive.
Works on higher resolution pictures by default.

Usage

You can either use the ready to use UI (index.html + qr-scanner.js + qr-scanner-wroker.min.js, based on the lightweight X-Element frontend framework) or use just the qr-scanner-wroker.min.js Webworker as follows:

Create a new Worker:

const qrWorker = new Worker('/path/to/qr-scanner-worker.min.js');

Send ImageData to the worker:

qrWorker.postMessage({
    type: 'decode',
    data: imageData
}, [imageData.data.buffer]);

Handle the result from the qr worker:

qrWorker.addEventListener('message', event => {
  const type = event.data.type;
  const data = event.data.data;
  if (type === 'qrResult') {
      if (data !== null) {
          alert(data);
      }
  }
});

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

qrWorker.postMessage({
    type: 'grayscaleWeights',
    data: {
        red: redWeight,
        green: greenWeight,
        blue: blueWeight
    }
});

To enable debug mode:

qrWorker.postMessage({
    type: 'setDebug',
    data: true
});

To handle the debug image:

qrWorker.addEventListener('message', event => {
  const type = event.data.type;
  const data = event.data.data;
  if (type === 'debugImage') {
      canvasContext.putImageData(data, 0, 0);
  }
});

Building the project

The project is prebuild in qr-scanner-worker.min.js. Building yourself is only neccessary if you want to change the code in the /src folder. Nodejs and Java are required for building.

Install required build packages:

npm install

Building:

gulp build