How to change webcam focus while streaming?

Question

I’m creating an electronic point system based on Qrcode and ended up locking because I can’t focus Qrcode when I’m on a mobile phone for example. I say this because on webcam there is the possibility to focus far or near rotating her screen, on mobile need to do this via software.

I’m using Ciro Costa’s Qcodedecode API that uses Html5 and I believe it uses getUserMedia for the stream: http://cirocosta.github.io/qcode-decoder/

But I couldn’t find anything to change camera focus like javascript...

I believe it is not impossible, there are Qrcode readers apps that make the autofocus with the android camera.