AJAX-2(HOW TO USE XMLHTTP REQUEST)

Method 1:-
In this method, you can instantiate an XMLHttpRequest object that can then call functions from the server. The code is in the public domain.
CODE:-
function getNewHTTPObject()
{
var xmlhttp;
/** Special IE only code ... */
/*@cc_on
@if (@_jscript_version >= 5)
try
{
xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e)
{
try
{
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
catch (E)
{
xmlhttp = false;
}
}
@else
xmlhttp = false;
@end @*/
/** Every other browser on the planet */
if (!xmlhttp && typeof XMLHttpRequest != 'undefined')
{
try
{
xmlhttp = new XMLHttpRequest();
}
catch (e)
{
xmlhttp = false;
}
}
return xmlhttp;
}
Now you can call XMLHTTPRequest
var xmlHttp = getHTTPObject();
function getDynamicData()
{
var url = "http://url/that/returns/dynamic/content";
xmlHttp.open('GET', url, true);
xmlHttp.onreadystatechange = callbackFunction;
xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
xmlHttp.send(null);
}
The callback function set in xmlHttp.onreadystatechange will be called when data is back from the server
var syndLinkRequest = getNewHTTPObject();
function callbackFunction()
{
if (syndLinkRequest.readyState != 4)
return;
var result = xmlHttp.responseText;
/* if you've returned javascript instead of xml or text,
you can eval(result) to access the javascript variables returned.
*/
}

METHOD-2
open source project that attempts to create a very simple and cross platform way to invoke Ajax requests
CODE:-
/** XHConn - Simple XMLHTTP Interface - bfults@gmail.com - 2005-04-08 **
** Code licensed under Creative Commons Attribution-ShareAlike License **
** http://creativecommons.org/licenses/by-sa/2.0/ **/
function XHConn()
{
var xmlhttp, bComplete = false;
try { xmlhttp = new ActiveXObject("Msxml2.XMLHTTP"); }
catch (e) { try { xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); }
catch (e) { try { xmlhttp = new XMLHttpRequest(); }
catch (e) { xmlhttp = false; }}}
if (!xmlhttp) return null;
this.connect = function(sURL, sMethod, sVars, fnDone)
{
if (!xmlhttp) return false;
bComplete = false;
sMethod = sMethod.toUpperCase();
try {
if (sMethod == "GET")
{
xmlhttp.open(sMethod, sURL+"?"+sVars, true);
sVars = "";
}
else
{
xmlhttp.open(sMethod, sURL, true);
xmlhttp.setRequestHeader("Method", "POST "+sURL+" HTTP/1.1");
xmlhttp.setRequestHeader("Content-Type",
"application/x-www-form-urlencoded");
}
xmlhttp.onreadystatechange = function(){
if (xmlhttp.readyState == 4 && !bComplete)
{
bComplete = true;
fnDone(xmlhttp);
}};
xmlhttp.send(sVars);
}
catch(z) { return false; }
return true;
};
return this;
}
Using XHConn:
//initialize XHConn (if XHConn isn't created successfully,
//the client doesnt' support Ajax)
var ajaxConn = new XHConn();
//post to mypage.php with args foo and baz
ajaxConn.connect("mypage.php", "POST",
"foo=bar&baz=qux",fnWhenDone);
//when the server responds, javascript
//will trigger this callback function
fnWhenDone(XML)
{
alert(XML.responseText);
}