the nativ QR-Code feature is only for mobile devices, if you want to decode the QR-Code in your Web Application, you’re going to need a external library (you can try this one https://github.com/LazarSoft/jsqrcode) for it.
Afterwards you can build a videostream to scan the QR-Code or you can upload the QR-Code as image and decode it with your chosen library.
