is it really running hashes, or is it probing your browser to see if your video card drivers look like phantomjs

I was actually quite curious about that and I found this.

>With a JS challenge, Cloudflare presents challenge page that requires no interaction from a visitor, but rather JavaScript processing by their browser.

>The visitor will have to wait until their browser finishes processing the JavaScript, which should be less than five seconds.

https://developers.cloudflare.com/fundamentals/get-started/c...

WebGL, an important part of browser fingerprinting, takes a long time. Im sure there are other APIs being 'abused' for this purpose that take a while. This doesnt quite prove the PoW.

that permits both possibilities