Instascan select camara to scan qr - html

Question

My website reads QR CODES using the mobile phone. I have used that library
https://github.com/schmich/instascan
<div class="select">
<label for="videoSource">Video source: </label><select id="videoSource"></select>
</div>
<video autoplay muted playsinline></video>
<script async src="js/main.js"></script>
Because the mobile phone has many camaras I want to let the user to select which camara wants for scanning the qr code.
main.js:
https://simpl.info/getusermedia/sources/
https://github.com/samdutton/simpl/blob/gh-pages/getusermedia/sources/js/main.js
'use strict';
var videoElement = document.querySelector('video');
var videoSelect = document.querySelector('select#videoSource');
videoSelect.onchange = getStream;
getStream().then(getDevices).then(gotDevices);
function getDevices() {
// AFAICT in Safari this only gets default devices until gUM is called :/
return navigator.mediaDevices.enumerateDevices();
}
function gotDevices(deviceInfos) {
window.deviceInfos = deviceInfos; // make available to console
console.log('Available input and output devices:', deviceInfos);
for (const deviceInfo of deviceInfos) {
const option = document.createElement('option');
option.value = deviceInfo.deviceId;
if (deviceInfo.kind === 'videoinput') {
option.text = deviceInfo.label || `Camera ${videoSelect.length + 1}`;
videoSelect.appendChild(option);
}
}
}
function getStream() {
if (window.stream) {
window.stream.getTracks().forEach(track => {
track.stop();
});
}
const videoSource = videoSelect.value;
const constraints = {
video: {deviceId: videoSource ? {exact: videoSource} : undefined}
};
return navigator.mediaDevices.getUserMedia(constraints).
then(gotStream).catch(handleError);
}
function gotStream(stream) {
window.stream = stream; // make stream available to console
videoSelect.selectedIndex = [...videoSelect.options].
findIndex(option => option.text === stream.getVideoTracks()[0].label);
videoElement.srcObject = stream;
}
function handleError(error) {
console.error('Error: ', error);
}
Then I want to start the scanner to the camara the user has selected because I want to obtaint the QR-CODE:
<script type="text/javascript">
let scanner = new Instascan.Scanner({ video: document.getElementById('preview'),mirror: false });
scanner.addListener('scan', function (content) {
alert("qr result " + content);
});
Instascan.Camera.getCameras().then(function (cameras) {
if (cameras.length > 0) {
scanner.start(cameras[0]); //I want to scanner.start the camara that the user has selected.
} else {
console.error('No cameras found.');
}
}).catch(function (e) {
console.error(e);
});
</script>