Javascript Absolute Beginner's Guide, 3rd Edition

48

Variable and Function Hoisting

In this Chapter

• Understand the relationship between when a variable is declared, initialized, and used

• Impress your friends with knowledge about the temporal dead zone, a source of many a gnarly error!

One of the quirkiest things about JavaScript is this thing known as hoisting. We’ll get to what it means in a bit, but let’s set the stage for it by looking at some examples and figuring out what the right behavior should be. For our first example, take a look at the following code:

function foo() {
  return "Yay!";
}
 
console.log(foo());

What do you think is going to be displayed in our console when this code runs? Here are three choices:

1. undefined

2. Error—foo isn’t referenced

3. Yay!

If you guessed Yay!, you ...