The term AJAX, originally coined by Jesse James Garrett of Adaptive Path in his essay AJAX: A New Approach To Web Applications, is an acronym for "Asynchronous JavaScript And XML." That's a bit of a mouthful, but it's simply describing a technique that uses JavaScript to refresh a page's contents from a web server without having to reload the entire page. This is different from the traditional method of updating web pages, which requires the browser to refresh the entire page in order to display any changes to the content.
Similar techniques have been around in one form or another (often achieved with the help of some clever hacks) for quite a while. But the increasing availability of the XMLHttpRequest class in browsers, the coining of the catchy term AJAX, and the advent of a number of high-profile examples such as Google Maps, Gmail, Backpack, and Flickr, have allowed these kinds of highly interactive web applications to begin to gain traction in the development world.
As the term AJAX has become more widespread, its definition has expanded to refer more generally to browser-based applications that behave much more dynamically than old-school web apps. This new crop of AJAX web applications make more extensive use of interaction techniques like edit-in-place text, drag-and-drop, and CSS animations or transitions to effect changes within the user interface. This tutorial will explain those techniques, and show you how to develop AJAX web applications of your own.
AJAX Web Applications
AJAX can be a great solution for many web development projects -- it can empower web apps to step up and take over a lot of the ground that previously was occupied almost exclusively by desktop applications.All the same, it's important to keep in mind that AJAX is not a sort of magic fairy dust that you can sprinkle on your app to make it whizzy and cool. Like any other new development technique, AJAX isn't difficult to mis-use, and the only thing worse than a horrible, stodgy, old-school web app is a horrible, poorly executed AJAX web app.
When you apply it to the right parts of your web application, in the right ways, AJAX can enhance users' experience of your application significantly. AJAX can improve the interactivity and speed of your app, ultimately making that application easier, more fun, and more intuitive to use.
Often, AJAX applications are described as being "like a desktop application in the browser." This is a fairly accurate description -- AJAX web apps are significantly more responsive than traditional, old-fashioned web applications, and they can provide levels of interactivity similar to those of desktop applications. But an AJAX web app is still a remote application, and behaves differently from a desktop application that has access to local storage. Part of your job as an AJAX developer is to craft applications that feel responsive and easy to use despite the communication that must occur between the app and a distant server. Fortunately, the AJAX toolbox gives you a number of excellent techniques to accomplish exactly that.
Defining AJAX and its Benefits Plus Sucess and Failure
AJAX development is such an enormous leap forward for web development: instead of having to send everything to the server in a single, huge mass, then wait for the server to send back a new page for rendering, web developers can communicate with the server in smaller chunks, and selectively update specific areas of the page based on the server's responses to those requests. This is where the word asynchronous in the AJAX acronym originated.
It's probably easiest to understand the idea of an asynchronous system by considering its opposite -- a synchronous system. In a synchronous system, everything occurs in order. If a car race was a synchronous system, The car that started first on the grid would be the first across the finish line, followed by the car that started second, and so on. There would be no overtaking, and if a car broke down, the traffic behind would be forced to stop and wait while the mechanics made their repairs. Traditional web apps use a synchronous system: you must wait for the server to send you the first page of a system before you can request the second page, as shown in Figure 1.1.
Figure 1.1. A traditional web app is a synchronous system
As an example An asynchronous car race would be a lot more exciting. The car in pole position could be overtaken on the first corner, and the car that starts from the back of the grid could weave its way through the field and cross the finish line in third place. The HTTP requests from the browser in an AJAX application work in exactly this way. It's this ability to make lots of small requests to the server on a needs-basis that makes AJAX development so cool. Figure 1.2 shows an AJAX application making asynchronous requests to a web server.
Figure 1.2. An AJAX web app is an asynchronous system
The end result is an application that feels much more responsive, as users spend significantly less time waiting for requests to process, and don't have to wait for an entire new web page to come across the wire, and be rendered by their browsers, before they can view the results.
Because Ajax applications are more difficult to build than classic web applications, they must contain certain Success that make them worth it. Applications built with Ajax have much more responsive interfaces. Users experience changes in a way that feels instantaneous. In traditional web applications, multiple connection threads are used to speed up deliveries between client and server. But this only affects content. All scripts and format information are communicated through a single connection thread, which negatively impacts performance. Ajax uses multiple connections to load basic scripts and CSS files; the rest is requested as content.
The primary failure of AJAX include increased development time and costs, even though using Ajax can be more difficult to use when building applications rather than traditional client server web applications. However, this is tempered by the fact that most of the technologies that make up Ajax are already known. Ajax’s asynchronous nature can also cause conflict because it interferes with traditional ways of navigating the web and book marking sites.
References:http://www.helium.com/items/580436-advantages-and-disadvantages-of-ajax[Accessed 20/01/2011]
No comments:
Post a Comment