How to add the rear camera to options with getUserMedia?

Question

I've just found "say-cheese" JS to open phone cam in a webpage.
https://github.com/Kephson/html5qrcodereader

My project is to read QR Codes with a smartphones camera and enter the data into a input field on a website.

The JS library works just fine!

My problem is that the code only uses the default camera (front), and i want to use the rear camera also.

How can i implement this code:
https://github.com/samdutton/simpl/blob/gh-pages/getusermedia/sources/js/main.js

Into this code: https://github.com/Kephson/html5qrcodereader/blob/master/js/say-cheese.js

HTML SELECT

<!--SELECT CAMERA-->
<select id="videoSource">
   <option selected>Default Camera</option>
</select>

Some random code from say-cheese.js

//Get Cameras?!
navigator.getUserMedia = (navigator.getUserMedia ||
        navigator.webkitGetUserMedia ||
        navigator.mozGetUserMedia ||
        navigator.msGetUserMedia ||
        false);

SayCheese = function SayCheese(element, options) {
    this.snapshots = [],
            this.video = null,
            this.events = {},
            this.stream = null,
            this.options = {
                videoSource: null,
                snapshots: true,
                audio: false,
                width: 320
            };


return navigator.getUserMedia({video: { 
            optional: [{
                    sourceId: this.options.videoSource
                }]

Is it somewhere in the code above i should put something like:

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

As you can tell i do not know so much about JS.
I'm using Jquery to almost everything i need.