var xmlHttp = null;
try {
  xmlHttp = new XMLHttpRequest();
} catch (trymicrosoft) {
  try {
    xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
  } catch (othermicrosoft) {
    try {
      xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
    } catch (failed) {
      xmlHttp = null;}}}

if (xmlHttp == null)
  alert("Error creating request object!");