var request = null;
try {
  request = new XMLHttpRequest(); //Mozilla,Safari...
} catch (trymicrosoft) { //IE
  try { //·sª©IE
    request = new ActiveXObject("Msxml2.XMLHTTP");
  } catch (othermicrosoft) {
    try { //廩IE
      request = new ActiveXObject("Microsoft.XMLHTTP");
    } catch (failed) {
      request = null;
    }
  }
}

if (request == null)
  //alert("Error creating request object!"); ÂsÄý¾¹¤£¤ä´©