Fix Aframe and Threejs error in my project.

Hi,
I have a build of a project in Aframe.js.
I want to display whatever the VR camera showing on an external canvas.
It works fine in normal mode but doesn't work when entering VR mode. The canvas turns black.
I found some solution written in threejs which could help but need to port in aframe.

https://discourse.threejs.org/t/webxr-mirroring-vr-view-on-web-page-canvas/12251

heres the jsfiddle
https://jsfiddle.net/tg31bqLs/

Thanks.