114CHAPTER 3

Introducing order to Ajax

Ruby on Rails

Ruby on Rails is a web development framework written in the Ruby programming language. It bundles together solutions for mapping server-side objects to a database and presenting content using templates, very much in the style of the server-side MVC that we discussed in section 3.4. Ruby on Rails claims very fast development of simple to medium websites, since it uses code-generation techniques to generate a lot of common code. It also seeks to minimize the amount of configuration required to get a live application running.

In recent versions, Rails has provided strong Ajax support through the Prototype library. Prototype and Rails are a natural fit, since the JavaScript code for Prototype is generated from a Ruby program, and the programming styles are similar. As with Echo2, using Ajax with Rails does not require a strong knowledge of Ajax technologies such as JavaScript, but a developer who does understand JavaScript can extend the Ajax support in new ways.

This concludes our overview of third-party frameworks for Ajax. As we’ve already noted, this is currently a fast-moving area, and most of the frameworks that we have discussed are under active development.

Many of the libraries and frameworks have their own coding idioms and styles, too. In writing the code examples for this book, we have sought to provide a feel for the breadth of Ajax technologies and techniques and have avoided leaning too heavily on any particular framework. Nonetheless, you will encounter some of the products that we have discussed here, sprinkled lightly throughout the rest of the book.

3.6 Summary

In this chapter, we’ve introduced the concept of refactoring as a way of improving code quality and flexibility. Our first taste of refactoring was to roll up the XMLHttpRequest object—the very core of the Ajax stack—into a simple, reusable object.

We’ve looked at a number of design patterns that we can apply to solve commonly encountered problems when working with Ajax. Design patterns provide a semiformal way of capturing the knowledge of the programmers who have gone before us and can help us to refactor toward a concrete goal.

Façade and Adapter provide useful ways of smoothing over the differences between varying implementations. In Ajax, these patterns are especially useful in providing an insulating layer from cross-browser incompatibilities, a major and longstanding source of worry for JavaScript developers.

Resources 115

Observer is a flexible pattern for dealing with event-driven systems. We’ll return to it in chapter 4 when looking at the UI layers of our application. Used together with Command, which offers a good way of encapsulating user interactions, it is possible to develop a robust framework for handling user input and providing an undo facility. Command also has its uses in organizing client/server interactions, as we will see in chapter 5.

Singleton offers a straightforward way of controlling access to specific resources. In Ajax, we may usefully use Singleton to control access to the network, as we will see in chapter 5.

Finally, we introduced the Model-View-Controller pattern, an architectural pattern that has a long history (in Internet time, at least!) of use in web applications. We discussed how the use of MVC can improve the flexibility of a server-side application through use of an abstracted data layer and a template system.

Our garment store example also demonstrated the way in which design patterns and refactoring go hand in hand. Creating a perfectly designed piece of code the first time round is difficult, but refactoring an ugly-but-functional bit of code such as listing 3.4 to gradually bring in the benefits of design patterns is possible, and the end results are every bit as good.

Finally, we looked at third-party libraries and frameworks as another way of introducing order to an Ajax project. A number of libraries and frameworks are springing up at present, from simple cross-browser wrappers to complete widget sets to end-to-end solutions encompassing both client and server. We reviewed several of the more popular frameworks briefly, and we will return to some of them in later chapters.

In the following two chapters, we’ll apply our understanding of refactoring and design patterns to the Ajax client and then to the client/server communication system. This will help us to develop a vocabulary and a set of practices that will make it easier to develop robust and multifeatured web applications.

3.7 Resources

Martin Fowler (with coauthors Kent Beck, John Brant, William Opdyke, and Don Roberts) wrote the seminal guide to refactoring: Refactoring: Improving the Design of Existing Code (Addison-Wesley Professional, 1999).

Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides (also known as “The Gang of Four”) wrote the influential Design Patterns (Addison-Wesley Professional, 1995).

116CHAPTER 3

Introducing order to Ajax

Gamma later went on to become architect for the Eclipse IDE/platform (see appendix A), and discusses both Eclipse and design patterns in this recent interview: www.artima.com/lejava/articles/gammadp.html.

Michael Mahemoff has recently set up a website devoted to cataloging Ajax design patterns: www.ajaxpatterns.org.