// xhr in progress or url not provided -> exit
if ( !( (xhr_done == true || xhr_done == null) && url ) ) return;
if ( typeof XMLHttpRequest !== 'undefined' )
{
xhr = new XMLHttpRequest();
}
else
{
try
{
xhr = new XMLHttpRequest("MSXML2.XmlHttp.5.0") || new XMLHttpRequest("MSXML2.XmlHttp.4.0") ||
new XMLHttpRequest("MSXML2.XmlHttp.3.0") || new XMLHttpRequest("MSXML2.XmlHttp.2.0") ||
new XMLHttpRequest("Microsoft.XmlHttp");
} catch ( e ) {}
}
// if xhr object does not supported or url not given, exit
xhr.onre