I've been doing client-side JavaScript development for more than a decade, and have been creating React-powered UIs for more than five years. I wrote Fluxxor, the first flux library.
I'm familiar with other data management libraries and techniques, as well as many other libraries in the React ecosystem (such as React Router, React DnD, Redux, Recoil, Overmind, etc.) I also have experience with a wide variety of other client-side frameworks and libraries aside from React.
I'm also familiar with a variety of back-end technologies; I'm proficient with Node.js and Elixir, relatively proficient in Ruby, and Python, and have had some experience in PHP, Java, and a number of others.