The second part of my comment is probably more applicable (maybe I should've just excluded the point about private patent applications). Even if a React-related patent was public, it wouldn't be called "Patent on React Framework". It probably wouldn't even use the words JavaScript, HTML, or DOM. You would need to hire a patent lawyer for an extended period of time to have a reasonable amount of certainty that no such patent exists (and even then, it's just an educated guess).