Chapter 3. Functions

Mastering functions is an important skill when you learn any programming language and even more so when it comes to JavaScript. This is because JavaScript has many uses for functions, and much of the language's flexibility and expressiveness comes from them. Where most programming languages have a special syntax for some object-oriented features, JavaScript just uses functions. This chapter will cover:

• How to define and use a function

• Passing parameters to a function

• Pre-defined functions that are available to you "for free"

• The scope of variables in JavaScript

• The concept that functions are just data, albeit a special type of data

Understanding these topics will provide a solid base that will allow you to dive into the second part of the chapter, which shows some interesting applications of functions:

• Using anonymous functions

• Callbacks

• Self-invoking functions

• Inner functions (functions defined inside functions)

• Functions that return functions

• Functions that redefine themselves...