To anyone concerned about React's virtual DOM and diff'ing stuff, and a potential Facebook patent thereof, in early 2012 I wrote and published (under a GLPv3 license) a virtual DOM implementation with efficient diff'ing when I forked SproutCore[0] to become Blossom.[1]

So even if Facebook tries to patent that particular invention/innovation, it may not stand up to legal scrutiny depending on the filing date. AFAIK, Facebook didn't do a provisional patent for virtual DOM stuff before July 2012 (long after I released Blossom), because that patent filing would have become public AT THE LATEST on January 1st, 2016 and nothing has come to light that I'm aware of.

So…you should be safe (IANAL).

[0] Ironically given the subsequent popularity of React, the SproutCore team rejected my virtual DOM approach which is why I had to fork it. Live and learn. I actually came up with the specific virtual DOM + diff design in spring 2008, but didn't get around to writing the code for it until someone paid me to do it (I had asked Apple and they declined). Eventually, the copyright owner of SproutCore (Strobe, Inc.) got bought by Facebook, though I don't recall when…

[1] https://github.com/erichocean/blossom