Some prior knowledge of HTML will be helpful before reading this book. As we progress, we’ll tackle some more advanced topics, such as APIs and offline applications. To follow these sections, you should be familiar with HTML and the fundamentals of JavaScript and the Document Object Model (DOM). It’s unnecessary to have deep knowledge of JavaScript. Still, you should understand event handling, JavaScript data types, and control structures such as while loops and if-else conditionals. We’ll keep our script examples simple, though, and explain them line by line.