Head First JavaScript Programming

Chapter 10. Liberated functions

First Class Functions

Know functions, then rock. Every art, craft, and discipline has a key principle that separates the intermediate players from the rock star virtuosos—when it comes to JavaScript, it’s truly understanding functions that makes the difference. Functions are fundamental to JavaScript, and many of the techniques we use to design and organize code depend on advanced knowledge and use of functions. The path to learning functions at this level is an interesting and often mind-bending one, so get ready... This chapter is going to be a bit like Willy Wonka giving a tour of the chocolate factory—you’re going to encounter some wild, wacky and wonderful things as you learn more about JavaScript functions.

Note

We’ll spare you the singing Oompa Loompas.

The mysterious double life of the function keyword

So far we’ve been declaring functions like this:

There are no surprises here, but let’s get our terminology down: formally, the first statement above is a function declaration, which creates a function that has a name—in this case quack—that can be used to reference and invoke the function.

So far so good, but the story gets more mysterious because, as you ...