This is a cookbook that contains a list of recipes explaining step-by-step how to use JavaScript in Moodle. The first two chapters concentrate on the basics of how to start working with JavaScript and the YUI while the later chapters show how to use these techniques as a basis for implementing more complete functionality. This book is aimed at developers and administrators comfortable with customizing Moodle with the use of plugin modules, themes, and patches who want to make their site more dynamic. If you have prior knowledge of HTML, PHP, and CSS and a good working knowledge of the underlying structure of Moodle, then this book is for you. No prior experience with JavaScript is needed.