What is AJAX ?

AJAX stands for Asynchronous Java And XML.
* AJAX is a set of technologies,supported by a web browser ,including following elements :
* HTML & CSS for Presenting.
JavaScript ( ECMAscript ) for local processing & DOM ( Document Object Model ) to access data inside the page or to access elements of XML file read on the server (with the getElement by TagName method for example).......

The XML http Request class reads or sends data on the server asynchronously.

Why We Use AJAX ?

AJAX is the acronym for Asynchronous Java And XML
* Unlike older approach , which required reloading of the entire page with every postback,
AJAX uses the JavaScript DOM, the XML http Request Object ,XML, and CSS to download &
displays just the content that needs to change.
* AJAX rich clients in the real world.
* Loading data asynchronously using XML technologies.
* Third party libaries & frameworks.
* Working with the server side.
* Security & performance with AJAX.

How Does AJAX Works ?

AJAX uses a programming model with displays & events. These events r Users actions, they call
function associated to element of the web page.
Interactive is achieved with forms & buttons . DOM allow to link elements of the page with actions & also to extract data from XML files provided by the server.
To get data on the server ,XML http request provides two methods -
#open: create a connection.
#send: send a request to the server.
Data furnished by the server will b found in the attributes of the XMLHttpRequest

OBJECT:
* responseXml for Xml file.
* response Text for a simple text.

A New XMLHttpsRequest object has to b created for new files to load.
we Have to wait for the data to b availbale to process it & in this purpose , the state of available of data is given by the ready state attribute of XMLHttpRequest.

The Purpose Of Using AJAX

The purpose of AJAX is that of giving illusion tht websites r responsive.It achieves this by processing request which involves yhe sending & recieving of small packets of data without refreshing the web browser. AJAX is founded on:
* XHTML - A rigid subset of HTML which is used to mark -up or to style the information.
* DOM - The Document Object Modelwhich can b accessed by the client browser.
* XMLHttpRequest - The object which is used to exchange the information asynchronously.
* XML - The format which is used to transfer the data from the server to the client.

Advantage Of AJAX

Bandwidth Utilisation:
By generating the HTML locally within the browser & only bringing down javascript calls & the actual data from the AJAX web pages can appear to load quickly since the payload coming down is much smaller in size . An example of this technique is a large result set where multiple pages of data exit. With AJAX , the HTML of the page eg : a table control & related TD & TR tag can b produced locally in the browser & not brought down with yhe first page of data. If the user click other pages, only the data is brought & populated into the HTML generated in the browser.

Interactivity:
AJAX application is mainly executed on the users machine , by manipulating the current page withn their browser using document object model methods. AJAX can b used for a multiple of task such sa updating or deleting records, expanding web forms , returing simple search queries or editing category treesall without the requirement to fetch a full page of HTML each time a change is made. Generally only small request need to b sent to the server & relatively short response are sent back. This permits the development of more interactive application featuring more responsive user interfaces due to use of DHTML techniques.

I Hope u understand What Is AJAX ?

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