This is at a pre-pre-alpha stage. Alpha release is currently projected for summer. The WebXR API is very unstable right now and development is in a minor limbo while waiting for that work to solidify. For simple sketches, mobile VR works relatively well in Chrome when served locally (ie use something like https://www.npmjs.com/package/http-server on shared wifi with your phone). Once WebXR stabilizes a bit and the non-polyfill spec is more predictable, this will work in more scenarios such as with the p5 online editor.
As stated above, this is currently not guaranteed to work. All of the manual examples work well on a Samsung Galaxy S7 in Chrome. Much more in the way of testing, stabilization, optimization, and features to come.
to build package:
npm install
npm run build
to build docs:
npm run docs
you may need to enable the WebXR flag in your browser by going to chrome://flags/#webxr
in your url bar