Professional ASP.NET Design Patterns

Chapter 9. The User Experience Layer

WHAT'S IN THIS CHAPTER?

• An explanation of what AJAX is

• Using JavaScript libraries to simplify your scripting needs

• The AJAX Periodic Refresh and Timeout patterns

• Maintaining history with the Unique URL pattern

• Client-side data binding with jTemplate

• The AJAX Predictive Fetch pattern

This chapter starts with a description of what AJAX is and what JavaScript libraries are available to make it easier to write AJAX applications. The chapter ends with common AJAX patterns that make up the user experience layer, with full exercises to see how these patterns are implemented.

WHAT IS AJAX?

AJAX (Asynchronous JavaScript and XML) is a way of programming to make asynchronous client callbacks from the browser to the server. Traditionally, data that the server returns is serialized into XML; however, more often JSON (JavaScript Object Notation) is used, because JSON is lightweight and therefore faster than XML.

The underlying technology used for AJAX is the XMLHttpRequest object. The XMLHttpRequest object allows client-side JavaScript code to send HTTP requests and handle responses. The ability to request data from a server asynchronously is half of the AJAX story, because now you need to update the browser page to show the new information. You can achieve this by using the Document Object Model (DOM). The DOM enables the page to be updated with the new data retrieved from the XMLHttpRequest object. These two pieces of technology are what make AJAX possible.

However, ...