What is a popular method of adding animation and interactivity to web pages?

The method known for adding animation and interactivity to web pages, particularly in a manner that has been widely adopted and integrated into modern web development, is JavaScript. JavaScript allows for dynamic content changes, user interaction handling, and the ability to manipulate HTML and CSS on the fly, making it crucial for creating an engaging user experience.

While Flash was historically used for animations and interactive content on the web, its usage has significantly declined due to security issues and the rise of HTML5, which natively supports multimedia elements. Additionally, HTML provides the structure for web pages but does not include functionality for animations by itself. CSS, on the other hand, can create transitions and animations, enhancing the presentation layer; however, it lacks the extensive interactivity capabilities that JavaScript offers. Hence, JavaScript stands out as the preferred method for incorporating both animation and interactivity into web pages.