It's speculation what patents Facebook has for React or what they cover. I've heard of claims of prior art for vdom-like concepts, so it is possible even if Facebook has React-related patents, only narrower interpretations of any claims might hold up (if that). React has a specific way of updating state which, for example, Mithril does not use. So, it is possible other vdoms may be far enough away from React to not be covered by any patents claims Facebook might try to make. Granted, that is no 100% guarantee of anything.

To me, the most important part of a vdom library like Mithril is using the HyperScript API with it, a library which predates React: Aug 20, 2012: https://github.com/hyperhype/hyperscript/tree/9237f590f3bc82... May 2013: https://github.com/facebook/react/blob/75897c2dcd1dd3a6ca462...

Personally, I feel templating approaches to making JavaScript-powered UIs like React's JSX or Angular's own templating approach or the templating systems in many other UI systems are obsolete. Modern webapps can use Mithril+Tachyons+JavaScript/TypeScript to write components in single files where all the code is just JavaScript/TypeScript. Such apps don't need to be partially written in either CSS and some non-standard variant of HTML that reimplements part of a programming language (badly). (Well, there may be a tiny bit of custom CSS needed on top of Tachyons, but very little.)

Here is an example of a coding playground I wrote that way with several examples in it which use that approach: http://rawgit.com/pdfernhout/Twirlip7/master/src/ui/twirlip7...

So, by writing UIs using HyperScript (plus a vdom library), you can potentially (with some work) replace a backend like Mithril with almost any other vdom or even a non-vdom solution. So, that is another way I mitigate this risk when I have a choice.

Granted, I know many web developers grew up on tweaking HTML and love HTML-looking templates and so they love JSX or whatever and are happy to ignore how hard it is to refactor such non-code stuff in the middle of their applikcations or validate it (granted, some IDEs are getting better at that). But I came to web development from desktop and embedded development working with systems where you (usually) generated UIs directly from code (e.g. using Swing, Tk, wxWidgets, and so on). I like the idea that standard tools can help me refactor all the code I work on and detect many inconsistencies.

Maybe a deeper issue for me is that with BSD+PATENTS Facebook is redefining what "open source" means in a way that is harmful to the open source community -- and also free software community as well like with Automattic using React on top of a GPLd WordPress. Which is why the Apache Foundation rejected the React license.