Head First JavaScript Programming, 2nd Edition

Chapter 6. Interacting with your web page: Getting to know the DOM

You’ve come a long way with JavaScript. In fact, you’ve evolved from a newbie to a scripter to, well, a programmer. But, there’s something missing. To really begin leveraging your JavaScript skills, you need to know how to interact with the web page your code lives in. Only by doing that are you going to be able to write pages that are dynamic, pages that react, that respond, that update themselves after they’ve been loaded. So how do you interact with the page? By using the DOM, otherwise known as the document object model. In this chapter, we’re going to break down the DOM and show you how you can use it, along with JavaScript, to teach your pages a few new tricks.

In the last chapter, we left you with a little challenge...the “crack the code challenge”

You were given some HTML with code in an external file, captured from Dr. Evel’s website, that looked like this:

And you needed to figure out Dr. Evel’s passcode using your deductive powers on this code.

So what does the code do?

Let’s walk through this code to see how Dr. Evel is generating his passcodes. After we break down each step, you’ll start to ...