AJAX In Action [10]
Licensed to jonathan zheng Licensed to jonathan zheng A new design for the Web This chapter covers ■ Asynchronous network interactions and usage patterns ■ The key differences between Ajax and classic web applications ■ The four fundamental principles of Ajax ■ Ajax in the real world 3 Licensed to jonathan zheng 4 CHAPTER 1 A new design for the Web Ideally, a user interface (UI) will be invisible to users, providing them with the options they need when they need them but otherwise staying out of their way, leaving users free to focus on the problem at hand. Unfortunately, this is a very hard thing to get right, and we become accustomed, or resigned, to working with suboptimal UIs on a daily basis—until someone shows us a better way, and we realize how frustrating our current method of doing things can be. The Internet is currently undergoing such a realization, as the basic web browser technologies used to display document content have been pushed beyond the limits of what they can sanely accomplish. Ajax (Asynchronous JavaScript + XML) is a relatively recent name, coined by Jesse James Garrett of Adaptive Path. Some parts of Ajax have been previously described as Dynamic HTML and remote scripting. Ajax is a snappier name, evoking images of cleaning powder, Dutch football teams, and Greek heroes suffering the throes of madness. It’s more than just a name, though. There is plenty of excitement surrounding Ajax, and quite a lot to get excited about, from both a technological and a business perspective. Technologically, Ajax gives expression to a lot of unrealized potential in the web browser technologies. Google and a few other major players are using Ajax to raise the expectations of the general public as to what a web application can do. The classical “web application” that we have become used to is beginning to creak under the strain that increasingly sophisticated web-based services are placing on it. A variety of technologies are lining up to fill the gap with richer, smarter, or otherwise improved clients. Ajax is able to deliver this better, smarter richness using only technologies that are already installed on the majority of modern computers. With Ajax, we are taking a bunch of dusty old technologies and stretching them well beyond their original scope. We need to be able to manage the complexity that we have introduced. This book will discuss the how-tos of the individual technologies but will also look at the bigger picture of managing large Ajax projects. We’ll introduce Ajax design patterns throughout the book as well to help us get this job done. Design patterns help us to capture our knowledge and experience with a technology as we acquire it and to communicate it with others. By introducing regularity to a codebase, they can facilitate creating applications that are easy to modify and extend as requirements change. Design patterns are even a joy to work with! Licensed to jonathan zheng Why Ajax rich clients? 5 1.1 Why Ajax rich clients? Building a rich client interface is a bit more complicated than designing a web page. What is the incentive, then, for going this extra mile? What’s the payoff? What is a rich client, anyway? Two key features characterize a rich client: it’s rich, and it’s a client. Let me explain a little more. Rich refers here to the interaction model of the client. A rich user interaction model is one that can support a variety of input methods and that responds intuitively and in a timely fashion. We could set a rather unambitious yardstick for this by saying that for user interaction to be rich, it must be as good as the current generation of desktop applications, such as word processors and spreadsheets. Let’s take a look at what that would entail. 1.1.1 Comparing the user experiences Take a few minutes to play with an application of your choice (other than a web browser), and count the types of user interaction that it offers. Come back here when you’ve finished. I’m going