Chapter 17. Functionality

THIS CHAPTER CONTAINS A NUMBER OF HIGHER-LEVEL PATTERNS THAT ARE MORE GEARED TOWARD offering new functionality than modifying the user interface. Technical barriers have prevented these from being used much on the Web, but Ajax technologies are helping to break down the barrier.

Lazy Registration addresses the issue of managing the lifecycle of a user profile. Instead of a binary "you're registered or you're not" perspective, Lazy Registration advocates a more gradual accumulation of user data and authentication credentials. A related pattern is Direct Login, which explains how to let the user securely log in without forcing a page refresh. It incorporates browser-side encryption, a theme at the heart of the next pattern, Host-Proof Hosting. The purpose of this pattern is to encrypt and decrypt data within the browser so that it can't be inspected by the hosting organization.

The next two patterns address monitoring the user's activity level. Timeout uses event-handling and scheduling to decide when the user is no longer active. Heartbeat is similar, but it brings the server into the equation; the browser keeps sending a heartbeat message to tell the server that the user is still active and that the application is still sitting in the browser.

Finally, Unique URLs restores some functionality that Ajax, to some degree, takes away. Bookmarkable URLs and browser history have always been an issue on the Web, but Ajax exacerbates the problem when developers choose not to use page refreshes. The Unique URLs pattern identifies a range of tricks to handle bookmarking, deep linking, the Back button, and related concerns.