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Book excerpt: Ajax and the dynamic double combo

This chapter download demonstrates how to enhance HTML forms with Ajax to create double-combination linked lists.

Although Ajax is neither new (debuting in 1998 with Outlook Web Access) nor a technology (in fact, it's a way to use established Web technologies), Ajax programming requires a learning curve surpassing that of a new technology, since it requires as much unlearning as learning. Ajax also attracts different types of IT professionals; there are enterprise developers who want to brush up on improving presentation layers, there are graphic designers and desktop developers aiming to build back-end applications, and there are system admins called on by end users to build nifty UIs.

Ajax in Action by Dave Crane and Eric Pascarello with Darren James, the latest installment of Manning Publication Co.'s In Action series, reaches out to each type of Ajax-ready developer. The book is divided into four parts that provide an overview of why Ajax can be successful, explain the core technologies behind Ajax, describe how to build production-ready software and present five step-by-step projects that use Ajax. Client-side code examples are JavaScript, the underlying language behind Ajax, while server-side code is present in PHP, Java, C#, and Visual Basic .NET.

Chapter 9, "Dynamic double combo," is the first of the chapters that presents a step-by-step development project. The title refers to a double-combination linked list, in which the contents of one selection are dependent on what has been selected in a second list. The project outlined in this chapter enhances simple HTML forms with Ajax by using the data entered in one drop-down list to populate a second list by making a background request to the server. The chapter covers the client-side JavaScript, the server-side Visual Basic .NET and the data exchange format needed for this solution, describes how to refactor the code and make it a reusable component, and shows how to create dynamic select boxes.

Read this sample chapter from Ajax in Action in this PDF.

Learn more about Ajax application security in this Q&A with co-author Eric Pascarello.


Excerpted from Ajax in Action by Dave Crane and Eric Pascarello with Darren James (ISBN: 1-932-3946-13). Copyright 2005, Manning Publications Co.. All rights reserved.

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