Ajax Design Patterns

Chapter 10. Browser-Server Dialogue

We’ve looked at the basic technologies for web remoting, which leads to questions about browser-server information flow. How will you deal with multiple calls? How will you keep the browser and the server synchronized? How will you access external domains?

Call Tracking is about tracking calls and dealing with the asynchronous nature of Ajax. The next three patterns concern synchronization. With Periodic Refresh, the browser keeps requesting fresh information from the server. The opposite is Submission Throttling, where the browser keeps uploading new information to the server. An alternative to Submission Throttling, Explicit Submission involves uploading only when the user performs some action.

All of those patterns help manage bandwidth, but keeping things in sync can still be quite complex when there are lots of entities in the server and a rich interface in the browser. Distributed Events help manage the complexity.

Finally, Cross-Domain Proxy is a technique for mediating the dialogue between the browser and external servers.

Call Tracking

⊙⊙⊙ Asynchronous, Follow, Monitor, Parallel, Tracking, XMLHttpRequest

Figure 10-1. Call Tracking

Developer Story

Dave is writing an Ajax chat client, and he’s concerned the more vocal users will hog server resources, so he decides to enforce a policy of no more than three pending server calls at any time. Thus, ...