Main Object in AJAX is XMLHttpRequest ,with this object,clients can submit and retrieve XML data to /from server without postbacks or reloading page.
var _reqObject= new XMLHttpRequest();
Every latest browser support this object however Internet explorer 6 or old versions doest not.To declare XMLHttpRequest for older browser compatibility,following active- X syntax is used as it would be treated as active-X control.
var _reqObject = new ActiveXObject("MSXML2.XMLHTTP.3.0");
So basically there is lot of workaround for browser checks in code.AJAX components in ASP.NET made it all easier.
Server side contains Controls, UpdatePanel,ScriptManager.
AJAX Library can also be used to call web service(.asmx extensions) .
Before processing to our sample, we need to download
ASPAJAXExtSetup.msi and restarting Visual studio, AJAX extensions is installed in toolbox.
AJAX Extensions contains server side controls, Following controls will be our target to build up a AJAX style Web page.
ScriptManager must be placed on page before placing any other AJAX server control o page, as it manages all AJAX Script libraries and files.
END of PART-1