Which programming language is primarily used to add dynamic elements to webpages?

JavaScript is the primary programming language used to add dynamic elements to webpages. It allows developers to create interactive content, control multimedia, animate images, and perform various tasks that respond to user actions without the need to refresh the entire page. This capability is crucial for modern web development, enabling features such as form validation, interactive maps, and real-time updates through technologies like AJAX.

HTML, while essential for structuring content on the web, is static and does not provide dynamic interactivity on its own. CSS primarily deals with the styling and layout of web pages, ensuring that they look good but lacks functionality for dynamic behavior. PHP is a server-side scripting language mainly used for backend processing. Even though it can be used to generate dynamic HTML content that is sent to the client, it operates on the server side rather than directly impacting the webpage's interactivity in the browser. In contrast, JavaScript operates on the client side, directly manipulating the document object model (DOM) and providing the user with a responsive experience.