Starting to AJax

Abstract
The basic elements for an application using the AJAX technologies, JavaScript and the XMLHttpRequest object, are not difficult to understand and there are many articles on the web that show how to use this object and declare that being AJAX. I think there are a lot more topics that should be understood and talked about. The right selection from the available technologies as well as a suitable abstraction in using these elements is important for the success of the realization of an application.

One main goal behind the architecture of the AJAX engine was to build an AJAX framework that you can reuse every time you want some asynchronous processing or when you need a smart way to refresh information on the current web page. When targeting applications with some hundred sides and WebServices and with in sum about a thousand methods the developer must have a clear and simple kind and pattern for coding the JavaScript code on the client to avoid errors and to not think about the implementation details. Only by using a simple approach a good quality and maintenance can be achieved. The idea of the AJAX engine on the client is the simplification of the implementation of the code that we need for implementing a specific functionality on the client. Like with the WebService framework of ASP.NET on the server the details of communication over SOAP on the client are completely hidden from the developer and also the recurring code portion is only realized once in a central place. Also all details about the different implementations of the XMLHttpRequest object in Internet Explorer or the Firefox browsers are hidden from your code. By using web controls or tag-libraries again a higher level of abstraction and more productivity for the developer can be reached. Because these web controls have to deploy JavaScript code to the client to avoid round-trips and enable the local functionality in the browser the JavaScript technology, especially JavaScript Behaviors are a substantial part of an AJAX infrastructure. The visual effects library adds some more polished User interface elements that can be used together with AJAX or as standalone client side components.

Asynchronous programming
This first part is about the problems that arise in simple but long running application tasks and processes and the possible solutions to that general problem. In the end we see how asynchronous programming can be done in web applications. The mechanism shown here are part of the principles used by AJAX and other Web 2.0 technologies. If you are an advanced JavaScript programmer already you might already understand how to split long running actions into smaller pieces and working with timers and internal event handlers so you just skip this chapter and start with the chapter Native AJAX Programming.