JavaScript is a high-level, interpreted programming language commonly used for web and mobile applications. It allows for the manipulation of HTML and CSS, enabling dynamic content and user interaction on web pages. JavaScript supports both front-end and back-end development through frameworks like Node.js. Front-end development involves creating visual and interactive elements of a website, while back-end development focuses on the server-side. Both are essential for creating functional web applications and involve languages like Python, Ruby, PHP, and frameworks like Node.js. Node.js is a runtime environment that allows the execution of JavaScript code outside of a web browser. It is commonly used for building server-side applications, networking tools, and for running scripts to automate tasks. Node.js provides an event-driven architecture and a non-blocking I/O API, making it lightweight and efficient for real-time applications.