This is code that provides an interface to let you select the camera to be used with jsqrcode ( https://github.com/LazarSoft/jsqrcode ). To make it work, you will have to include said library and have elements with the IDs in the loadCommonHTMLElements method on your page. You may want to provide appropriate styling as well. This source code is …

QR Code Scanner

"use strict";
define(["require", "exports"], function (require, exports) {
    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    // Browser compatibility definitions
    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    navigator.getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    // Private state
    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    var qrcodescanner = null;
    var cameralist = null;
    var camerafeed = null;
    var camerastream = null;
    var canvas = null;
    var drawingcontext = null;
    var readtimeout = null;
    var scanfrequency = 333; //In milliseconds
    var nocameras = false;
    var ready = false;
    var closed = true;
    var successcallback = defaultSuccess;
    var failurecallback = defaultFailure;
    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    // Exports
    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    function load() {
        if (ready) {
            //Don't initialize twice
            return;
        }
        loadCommonHTMLElements();
        installEventListeners();
        //Find all cameras and add them to the dropdown
        MediaStreamTrack.getSources(function (sources) {
            //Find video sources
            var videosources = sources.filter(function (source) {
                return source.kind === "video";
            });
            //Check if there are any video sources
            if (videosources.length === 0) {
                //If there are no video sources at all, the scanner will not work.
                nocameras = true;
                return;
            }
            //Add all video sources to the dropdown for camera selection
            var unlabelledcameraindex = 1;
            videosources.forEach(function (videosource) {
                var option = document.createElement("option");
                option.value = videosource.id; //TODO: Apparently Chrome-specific; W3C specifies sourceId.
                //Establish the label for the current video source
                var cameralabel = videosource.label;
                if (cameralabel === "") {
                    cameralabel = "Camera " + unlabelledcameraindex;
                    ++unlabelledcameraindex;
                }
                if (videosource.facing) {
                    //The facing-property is Chrome-specific
                    cameralabel += " - " + videosource.facing;
                    if (videosource.facing === "environment") {
                        //Pre-select the video source facing the environment
                        option.selected = true;
                    }
                }
                option.text = cameralabel;
                //Add the video source to the dropdown
                cameralist.appendChild(option);
            });
            //Signal that the QR code scanner is now ready
            ready = true;
        });
    }
    exports.load = load;
    function scan(onsuccess, onfailure) {
        if (nocameras) {
            //If there are no cameras, the scanner cannot operate - fail right away
            failure("This device does not seem to have any cameras.");
            return;
        }
        if (!ready) {
            //If the scanner is not ready yet, try again later
            window.setTimeout(scan, 200);
            return;
        }
        //Default values for parameters
        if (onsuccess === undefined || typeof onsuccess !== "function") {
            onsuccess = defaultSuccess;
        }
        if (onfailure === undefined || typeof onfailure !== "function") {
            onfailure = defaultFailure;
        }
        //Set up callbacks
        successcallback = onsuccess;
        failurecallback = onfailure;
        //Set state to opened
        closed = false;
        //Clear the canvas (avoids re-scanning the previous QR code)
        drawingcontext.clearRect(0, 0, canvas.width, canvas.height);
        //Request camera access
        requestCameraAccess(cameralist.value);
        //Show the scanner
        qrcodescanner.style.display = "block";
    }
    exports.scan = scan;
    function close() {
        closed = true;
        window.clearTimeout(readtimeout);
        if (camerastream !== null) {
            camerastream.stop();
        }
        qrcodescanner.style.display = "none";
    }
    exports.close = close;
    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    // Private helper methods
    ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    function loadCommonHTMLElements() {

/* The types are as follows:
    qrcodescanner = <HTMLDivElement> document.getElementById("QRCodeScannerOverlay");
    cameralist    = <HTMLSelectElement> document.getElementById("cameraselection");
    camerafeed    = <HTMLVideoElement> document.getElementById("camerafeed");
    canvas        = <HTMLCanvasElement> document.getElementById("qr-canvas");
*/

        qrcodescanner = document.getElementById("QRCodeScannerOverlay");
        cameralist = document.getElementById("cameraselection");
        camerafeed = document.getElementById("camerafeed");
        canvas = document.getElementById("qr-canvas");
        //Not really an HTML element, but anyway
        drawingcontext = canvas.getContext("2d");
    }
    function installEventListeners() {
        //Add handler for camera selection
        cameralist.addEventListener("change", function () {
            requestCameraAccess(cameralist.value);
        });
        //Set up callback for QR code decoding success
        qrcode.callback = success;
    }
    function requestCameraAccess(sourceId) {
        if (camerastream !== null) {
            //The following is required to enable switching between cameras, as there cannot be multiple concurrent streams
            camerastream.stop();
        }
        //Request access to the specified camera
        navigator.getUserMedia({
            "video": {
                "optional": [
                    { "sourceId": sourceId }
                ]
            },
            "audio": false
        }, function (stream) {
            camerastream = stream;
            camerafeed.src = URL.createObjectURL(stream);
            tryQRCodeReading();
        }, function (error) {
            window["e"] = error;
            failure("Could not access the camera (" + error.name + "). " + error.message);
        });
    }
    function tryQRCodeReading() {
        try {
            drawingcontext.drawImage(camerafeed, 0, 0);
            try {
                qrcode.decode();
            }
            catch (e) {
                //Happens all the time if QR code scanning did not succeed
                //console.log("QR code decoding status: " + e);
                if (!closed) {
                    readtimeout = window.setTimeout(tryQRCodeReading, scanfrequency);
                }
            }
        }
        catch (e) {
            failure(e);
        }
    }
    function success(data) {
        navigator.vibrate([500]);
        close();
        successcallback(data);
    }
    function failure(errormessage) {
        close();
        failurecallback(errormessage);
    }
    function defaultSuccess(data) {
        alert(data);
    }
    function defaultFailure(errormessage) {
        alert("Error: " + errormessage);
    }
});