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What Is Ajax

   
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AJAX, while becoming increasing popular in web development today, is not actually a new technology but can date back more than a decade. The term is actually an acronym for Asynchronous JavaScript and XML, and it concerns the interrelationship between two web development languages. Today it is growing in popularity due to its ability to create interactive websites, however this is only part of the issue. Truth be told, the number one reason that it took so long to become popular is actually due to browser compatibility. In most cases compatibility issues can be blamed on the Internet Explorer side, however in the case of AJAX it is Mozilla and Safari where the issues have been.

It was back in 1996 when the introduction of the iFrame was introduced to the world. Only available in Internet Explorer, this started off as another one of Microsoft’s proprietary web developments. Thanks to this iFrame, a website could use the client side technology of JavaScript to retrieve data from the website without interference to the currently opened page element. By 1999, Microsoft introduced another technology which further increased the capabilities of AJAX when they released Internet Explorer 5 with the XMLHttpRequest object through Active X.

Soon after this occurred, Mozilla and Safari caught up and were able to also handle the interactions. However it would not be until 2006 that the World Wide Web Consortium would officially recognise the object and designate it with its official ISO.

It is important to firstly remember that while the acronym stands for asynchronous connectivity between the two languages, it is not a requirement. Today though, the term goes much further to describe a large group of technologies which can be utilised in the creation of AJAX environments. For starters, it can be used not only for XHTML presentation, but it can also be used for CSS presentations. Furthermore, it consists of the Active X object that allows for the interaction and displaying of the data; the XML or even the XSLT to allow for the interchanging, display as well as manipulation of the data with respect to the XMLHttpRequest. However when it comes to the XMLHttpRequest, this is really only used in asynchronous communication and as stated previously AJAX does not have to be asynchronous. Last but not least, you have the JavaScript which acts as the glue that holds all of the technology together into a seamless interactive experience.

At the time that AJAX was first coined, the only real client side technology available was that of JavaScript. However times have changed and now AJAX can also be done using VBScript in the place of JavaScript. Likewise, the technology used for the interchanging and displaying of the data use to be only XML, however this is once again not the only thing as it can be replaced by the JavaScript Object Notation or JSON as well as plain old HTML.

In the older days of web development, if pages had replicated content on them such as navigation and much more, every time a page was loaded this data too was loaded resulting in increased bandwidth use. When using AJAX on a website, the technology can load only certain parts, especially those specified by the visitor and whose settings are tracked via a cookie. Likewise, this also reduced the number of requests that a visitor’s browser makes to the server because of caching of both CSS and JavaScript and as such further reduces bandwidth usage.

Unfortunately, this dynamically created content is not truly registered into the web browser’s history and thus one cannot simply make use of the back button to return to previous information. However this can be fixed by using invisible iFrames in order to fool the browser into adding it to the history. Furthermore, because of this fact it is also not possible to bookmark the data retrieved through AJAX.

Then you have the issue of search engines which do not browse JavaScript, which means that any data loaded through AJAX, which is only accessible through the technology is not indexed by the search engines and if the technology is used improperly, the entire webpage could fail to be indexed.

AJAX is not really a supported feature on mobile phones or PDA, likewise since its use can also disable the JavaScript in his or her web browser, they would not be able to access the application or the data retrieved by it. As for those who are blind or have a vision impairment, screen readers are also not capable of reading the content loaded through AJAX making it inaccessible to them.

While AJAX is not yet fully supported by the World Wide Web Consortium, within time it may be, however until then if you plan on making use of the technology, please make sure that the data is also available through other means as well as checking it for any security issues. The last part is of utmost importance because with the use of client side scripting, you are giving hackers a means of accessing your server if it is not checked and protected.

Original Authors: Nick
Edit Update Authors: M.A.Harris
Updated On:
30/01/2009

 



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