The second chapter provides the basics of the language like variables, data types, arrays, loops and conditionals.
The fourth chapter introduces objects. This chapter explains properties, methods and the various ways on how to create objects. After that, there’s an overview of the built-in objects (which are handled more in-depth in one of the appendices).
The fifth chapter is completely dedicated to the concept of prototypes. The author clearly explains the purpose of the prototype property and how to augment built-in objects.