That’s part of the strangeness of this whole debate: nobody knows. The list of Facebook’s patents is public, but I’m not aware of anyone publicly going and doing the research to see which of them, if any, are likely to apply to React. (Possibly because of the whole treble damages thing - along with the fact that Facebook has thousands of patents to look through.) Facebook’s lawyers may or may not have done that research, but it’s in their best interest to keep things as vague as possible (at least up to the point where they actually threaten to sue someone), to avoid workarounds.

Facebook can sue anyone for patent infringement whether or not they use React. Many people seem to believe that they can't ever be sued by Facebook for any reason as long as they don't use React although that is not the case.

The list of contributors to React, and Facebook patent holders are both public. If someone cared to they could cross reference both and narrow down the search area.

The ones that haven't been finalized by the patent office yet.

Do you really think they don't have a pending patent for some part of React? I bet they've got at least one covering virtual DOM.

And don't worry about prior art. As long as some part of it can weasel through a patent it's enough. Doesn't have to be the whole thing.