Being able to scan barcodes using a web app is pretty cool. I used something similar when I was tinkering with transmitting data visually for the handshake step of webrtc: http://franklinta.com/2014/10/19/serverless-webrtc-using-qr-....

I used Lazarsoft's javascript QR code scanner which worked, but it wasn't very robust since it was a manual port of an early version of zxing. It is pretty easy to compile the c++ branch of zxing v2.3 using emscripten but it is a pain to optimize: https://github.com/fta2012/zxing-emscripten (or demo link: http://fta2012.github.io/zxing-emscripten/).