JavaScript is responsible for the "interactive layer" of a web page, complementing the "structural" layer provided by markup and "presentational" layer provided by CSS. JavaScript lets developers modify the structure and presentation of a page by adding, removing, and altering markup and styles in response to any combination of user interaction and internal logic. JavaScript can give you a tremendous amount of control over the rendering and behavior of a web page, even letting you alter some of the browser's built-in behaviors.
This course covers the fundamentals of JavaScript, from the basic rules that govern how the language is written to the built-in methods and properties it provides.