React.js is a JavaScript library used in web development to build interactive elements on websites. Coursera's React.js skill catalogue teaches you about this dynamic interface tool leveraged by many leading tech companies. You'll learn everything from fundamental concepts like component architecture, state and props, to more advanced topics like lifecycle methods, hooks, and context API. In addition, you'll also explore how to manage application state with Redux and connect to external APIs. With React.js skills, you can create rich, responsive user interfaces and single-page applications that are fast, scalable, and simple to maintain.