React
From APIDesign
React.js is one of the most popular UI framework these days. Backed by Facebook, it appeals to masses - it has almost become a synonym for UI in the browser/mobile - especially between managers with only high-level knowledge.
JSX
React comes with enhanced version of JavaScript called JSX which mixes the code with DOM definition. Many love it. Some consider it crazy. Anyway it is certainly a challenge to convert such concept to another language like Java and to do it without enhancing the language - only with the help of AnnotationProcessors.
Can that be done? Yes, it can. See my react4jdemo tutorial or go directly to the project page.
What's Reactive on React Anyway?
The best way to learn about weaknesses of React is towatch rants by competitors. This one comes from Svelte: