(JS) app progressive

[Werwolfe]

Salve ragazzi, ho creato un app progressiva, e ho realizzato, prendendo da web un lettore di barcode, che funziona, ha solo due problemi e risolti quelli, sono riuscito a creare una cosa davvero carina.

Problema 1)
Il lettore scannerizza il qrcode, vorrei che il risultato venisse inserito in un campo di input, ho modificato il file in questo modo:

var barcode_result = document.getElementById('input#dbr');

ma non lo inserisce se metto <span id='dbr'></span>

funziona.

Problema 2) vitale
Quando accedo alla fotocamera mi da sempre quella frontale, io vorrei quella posteriore, per una questione di comodità, non devo fare un self al barcode, ma scannerizzarlo con serenità.

C'è una select ma mette sempre la camera 1 , il codice completo dello script è questo:

var videoElement = document.querySelector('video');
var canvas = document.getElementById('pcCanvas');
var mobileCanvas = document.getElementById('mobileCanvas');
var ctx = canvas.getContext('2d');
var mobileCtx = mobileCanvas.getContext('2d');
var videoSelect = document.querySelector('select#videoSource');
var videoOption = document.getElementById('videoOption');
var buttonGo = document.getElementById('go');
var barcode_result = document.getElementById('input#dbr');

var isPaused = false;
var videoWidth = 640,
  videoHeight = 480;
var mobileVideoWidth = 240,
  mobileVideoHeight = 320;
var isPC = true;

var ZXing = null;
var decodePtr = null;

var tick = function () {
  if (window.ZXing) {
    ZXing = ZXing();
    decodePtr = ZXing.Runtime.addFunction(decodeCallback);
  } else {
    setTimeout(tick, 10);
  }
};
tick();

var decodeCallback = function (ptr, len, resultIndex, resultCount) {
  var result = new Uint8Array(ZXing.HEAPU8.buffer, ptr, len);
  console.log(String.fromCharCode.apply(null, result));
  barcode_result.textContent = String.fromCharCode.apply(null, result);
  buttonGo.disabled = false;
  if (isPC) {
    canvas.style.display = 'block';
  } else {
    mobileCanvas.style.display = 'block';
  }
};

// check devices
function browserRedirect() {
  var deviceType;
  var sUserAgent = navigator.userAgent.toLowerCase();
  var bIsIpad = sUserAgent.match(/ipad/i) == "ipad";
  var bIsIphoneOs = sUserAgent.match(/iphone os/i) == "iphone os";
  var bIsMidp = sUserAgent.match(/midp/i) == "midp";
  var bIsUc7 = sUserAgent.match(/rv:1.2.3.4/i) == "rv:1.2.3.4";
  var bIsUc = sUserAgent.match(/ucweb/i) == "ucweb";
  var bIsAndroid = sUserAgent.match(/android/i) == "android";
  var bIsCE = sUserAgent.match(/windows ce/i) == "windows ce";
  var bIsWM = sUserAgent.match(/windows mobile/i) == "windows mobile";
  if (bIsIpad || bIsIphoneOs || bIsMidp || bIsUc7 || bIsUc || bIsAndroid || bIsCE || bIsWM) {
    deviceType = 'phone';
  } else {
    deviceType = 'pc';
  }
  return deviceType;
}

if (browserRedirect() == 'pc') {
  isPC = true;
} else {
  isPC = false;
}

// stackoverflow: http://stackoverflow.com/questions/4998908/convert-data-uri-to-file-then-append-to-formdata/5100158
function dataURItoBlob(dataURI) {
  // convert base64/URLEncoded data component to raw binary data held in a string
  var byteString;
  if (dataURI.split(',')[0].indexOf('base64') >= 0)
    byteString = atob(dataURI.split(',')[1]);
  else
    byteString = unescape(dataURI.split(',')[1]);

  // separate out the mime component
  var mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0];

  // write the bytes of the string to a typed array
  var ia = new Uint8Array(byteString.length);
  for (var i = 0; i < byteString.length; i++) {
    ia[i] = byteString.charCodeAt(i);
  }

  return new Blob([ia], {
    type: mimeString
  });
}

// add button event
buttonGo.onclick = function () {
  if (isPC) {
    canvas.style.display = 'none';
  } else {
    mobileCanvas.style.display = 'none';
  }

  isPaused = false;
  scanBarcode();
  buttonGo.disabled = true;
};

// scan barcode
function scanBarcode() {
  barcode_result.textContent = "";

  if (ZXing == null) {
    buttonGo.disabled = false;
    alert("Barcode Reader is not ready!");
    return;
  }

  var data = null,
    context = null,
    width = 0,
    height = 0,
    dbrCanvas = null;

  if (isPC) {
    context = ctx;
    width = videoWidth;
    height = videoHeight;
    dbrCanvas = canvas;
  } else {
    context = mobileCtx;
    width = mobileVideoWidth;
    height = mobileVideoHeight;
    dbrCanvas = mobileCanvas;
  }

  context.drawImage(videoElement, 0, 0, width, height);

  var vid = document.getElementById("video");
  console.log("video width: " + vid.videoWidth + ", height: " + vid.videoHeight);
  var barcodeCanvas = document.createElement("canvas");
  barcodeCanvas.width = vid.videoWidth;
  barcodeCanvas.height = vid.videoHeight;
  var barcodeContext = barcodeCanvas.getContext('2d');
  var imageWidth = vid.videoWidth, imageHeight = vid.videoHeight;
  barcodeContext.drawImage(videoElement, 0, 0, imageWidth, imageHeight);
  // read barcode
  var imageData = barcodeContext.getImageData(0, 0, imageWidth, imageHeight);
  var idd = imageData.data;
  var image = ZXing._resize(imageWidth, imageHeight);
  console.time("decode barcode");
  for (var i = 0, j = 0; i < idd.length; i += 4, j++) {
    ZXing.HEAPU8[image + j] = idd[i];
  }
  var err = ZXing._decode_any(decodePtr);
  console.timeEnd('decode barcode');
  console.log("error code", err);
  if (err == -2) {
    setTimeout(scanBarcode, 30);
  }
}
// https://github.com/samdutton/simpl/tree/gh-pages/getusermedia/sources 
var videoSelect = document.querySelector('select#videoSource');

navigator.mediaDevices.enumerateDevices()
  .then(gotDevices).then(getStream).catch(handleError);

videoSelect.onchange = getStream;

function gotDevices(deviceInfos) {
  for (var i = deviceInfos.length - 1; i >= 0; --i) {
    var deviceInfo = deviceInfos[i];
    var option = document.createElement('option');
    option.value = deviceInfo.deviceId;
    if (deviceInfo.kind === 'videoinput') {
      option.text = deviceInfo.label || 'camera ' +
        (videoSelect.length + 1);
      videoSelect.appendChild(option);
    } else {455
      console.log('Found one other kind of source/device: ', deviceInfo);
    }
  }
}

function getStream() {
  buttonGo.disabled = false;
  if (window.stream) {
    window.stream.getTracks().forEach(function(track) {
      track.stop();
    });
  }

  var constraints = {
    video: {
      deviceId: {exact: videoSelect.value}
    }
  };

  navigator.mediaDevices.getUserMedia(constraints).
    then(gotStream).catch(handleError);
}

function gotStream(stream) {
  window.stream = stream; // make stream available to console
  videoElement.srcObject = stream;
}

function handleError(error) {
  console.log('Error: ', error);
}

Vi ringrazio in anticipo per l'aiuto