JavaScript & jQuery: The Missing Manual, 2nd Edition

Chapter 1. Writing Your First JavaScript Program

By itself, HTML doesn’t have any smarts: It can’t do math, it can’t figure out if someone has correctly filled out a form, and it can’t make decisions based on how a web visitor interacts with it. Basically, HTML lets people read text, look at pictures, and click links to move to other web pages with more text and pictures. In order to add intelligence to your web pages so they can respond to your site’s visitors, you need JavaScript.

JavaScript lets a web page react intelligently. With it, you can create smart web forms that let visitors know when they’ve forgotten to include necessary information; you can make elements appear, disappear, or move around a web page (see Figure 1-1); you can even update the contents of a web page with information retrieved from a web server—without having to load a new web page. In short, JavaScript lets you make your websites more engaging and effective.

Figure 1-1. JavaScript lets web pages respond to visitors. On Amazon.com, mousing over the “Gifts & Wish Lists” link opens a tab that floats above the other content on the page and offers additional options.

Note

Actually, HTML5 does add some smarts to HTML–including basic form validation. But since not all browsers support these nifty additions (and because you can do a whole lot more with forms and JavaScript), you still need JavaScript to build the best, ...