The World Wide Web officially celebrated its 20th birthday as I began writing this book. In one sense, it's hard to believe that the technology has been around this long already. At another level, it's amazing how much has happened in that short time. When I started teaching and writing about the Internet (long before the Web was practical), none of us had any idea what it was going to turn into one day.

If you're reading this book, I don't have to tell you that the Web is a big deal. It's come a long way, and it's doing very interesting things. What I want to show in this book is where the Web is going. Web technology is changing faster than ever, and people who don't understand these changes are going to have a hard time staying on top of things.

In the early days of the Web, we talked about Web pages, as if the Internet were a set of ordinary documents connected by links. This was true (and still is largely), but I don't think that's the best way to think of the Web any more. Today's Web is not about documents, but about applications. Users and developers expect their pages to do things, not just be glorified documents.

This book describes two critical and inter-related technologies: JavaScript and AJAX. JavaScript has been a part of the Web since the relatively early days. It is a simple but powerful programming language that was designed from the beginning to work within the context of a Web document. While JavaScript has been with us for a long time, it has recently ...

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