Checking Whether you browser supports XMLHTTP or Not.

function GetXmlHttpObject() {
var xmlHttp = null;
try {
// Firefox, Opera 8.0+, Safari
xmlHttp = new XMLHttpRequest();
}
catch (e) {
// Internet Explorer
try {
xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e) {
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}
}
return xmlHttp;
}
function CheckBrowser() {
xmlHttp = GetXmlHttpObject();
if (xmlHttp == null) {
alert("Your browser does not support AJAX!");
return;
}
}