JavaScript & jQuery: The Missing Manual, 3rd 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, watch videos, and click links to move to other web pages with more text, pictures, and videos. 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, effective, and useful.

Note

Actually, HTML5 does add some smarts to HTML—including basic form validation. But because 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, most user-friendly and interactive forms. You can learn more about HTML5 and web forms in Ben Henick’s HTML5 Forms (O’Reilly) and Gaurav Gupta’s Mastering HTML5 Forms (Packt Publishing).

Figure 1-1. The Interactive Ear (http://www.amplifon.co.uk/interactive-ear/), an interactive ...