React JS is an open-source, cross-platform JavaScript-based library which helps ReactJS developers for building user interfaces specifically for developing responsive web and single page applications. ReactJS is fast & flexible backed by Facebook/Instagram & other community of developers.
React developers build web applications or use React Native to develop mobile apps on the client-side of development. This requires the use of core front-end technologies like JavaScript, HTML, and CSS. The day-to-day activities of a React developer can be quite diverse. React Native uses JavaScript to build cross-platform apps. JavaScript is a very popular language in the web community at the moment. It is commonly used with React and other popular JavaScript frameworks.