function onScanSuccess(decodedText, decodedResult) {
  // handle the scanned code as you like, for example:
  console.log(`Code matched = ${decodedText}`, decodedResult);
}

function onScanFailure(error) {
  // handle scan failure, usually better to ignore and keep scanning.
  // for example:
  console.warn(`Code scan error = ${error}`);
}

let html5QrcodeScanner = new Html5QrcodeScanner('reader', { fps: 10, qrbox: { width: 250, height: 250 } }, /* verbose= */ false);
html5QrcodeScanner.render(onScanSuccess, onScanFailure);