JavaScript is a versatile programming language that is primarily used for adding interactivity to websites. It is a key technology for front-end web development, allowing developers to create dynamic and interactive user interfaces. JavaScript is supported by all major web browsers, making it a fundamental component of web development.

In addition to its role in front-end development, JavaScript is also used on the server side (Node.js) to build scalable and efficient web applications. This versatility makes JavaScript an essential language for full-stack developers, as they can work on both the client and server sides of an application using the same language.