function AJAX() {
var o = false;
/*@cc_on @*/
/*@if (@_jscript_version >= 5)
try {
o = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
o = new ActiveXObject("Microsoft.XMLHTTP");
} catch (E) {
o = false;
}
}
@end @*/
if (!o && typeof XMLHttpRequest!='undefined') {
o = new XMLHttpRequest();
}
return o;
}

Sorry for the rough formatting.

Anyway, explanation is that it uses conditional compilation (all that @cc_on stuff) to do some serious browser/object forking. Hope that helps. If the function returns false, then the browser doesn’t support Ajax. Otherwise the return value is an Ajax object.

There’s a good chance that people who write browser sniffing Javascript have no idea what that code above is though (object literal notation). The first time I saw it, it looked a little cryptic and was taken aback.