What is the primary purpose of JavaScript in a web browser?

The primary purpose of JavaScript in a web browser is to add interactivity. JavaScript allows developers to create dynamic and engaging user experiences by enabling interactive elements on web pages, such as forms that respond in real-time, animations, and updates that happen without needing to refresh the browser. Through JavaScript, various user actions, like clicks or keyboard events, can trigger changes in the content or behavior of a web page, making it more responsive and user-friendly.

While other languages play roles in web development, JavaScript specifically focuses on enhancing interactivity. For instance, HTML is primarily used to structure the content of a webpage, and CSS is utilized for styling the visual aspects. Encrypting web communications, on the other hand, is typically handled by protocols like HTTPS, rather than being a function of JavaScript within the browser itself.