JavaScript is a text-based programming language used both on the client-side and server-side that allows you to make web pages interactive. Where HTML and CSS are languages that give structure and style to web pages, JavaScript gives web pages interactive elements that engage a user. JavaScript can be used for different things which are 1.Adding interactive behavior to web pages. JavaScript allows users to interact with web pages. ... 2.Creating web and mobile apps. Developers can use various JavaScript frameworks for developing and building web and mobile apps. ... 3.Building web servers and developing server applications. ... 4.Game development. Why is javascript important? JavaScript codes are the important elements to develop websites, especially when it comes to handling user inputs and validation. You can use JavaScript to develop back-end of the web application. Developers prefer to use NodeJs for the web It helps to increase the performance of front-end and web application.