ReactJS, no doubt, is the most popular web development library. ReactJS provided the solution that developers were looking for. It uses JSX (a unique syntax that allows HTML quotes as well as HTML tag syntax application for rendering specific subcomponents).
Part of this huge popularity comes from the fact that top corporations such as Facebook, PayPal, Uber, Instagram, and Airbnb use it to solve user interface related issues. This credibility has drawn a lot of people to the framework.
If you are a React Developer, you already know what are the key pillars of React. But, if you are a Quality Engineer and mostly focusing on the testing part of it, I highly suggest having some idea about React development.