Before few years ago, JavaScript is used for frontend development like validation to form. But now a days, People are using it for frontend as well as backend development. So it is being popular. You don’t need to server side language like PHP, .Net for developing web and mobile application because it is possible to make whole application by using JavaScript. Today we will discuss about ReactJS which is front end JavaScript library developed by Facebook. It is currently most popular JavaScript libraries for front end development and facilitate the creation of interactive and reusable UI components. React gives you a template language and some function hooks to essentially render HTML. That's all React outputs, HTML.