create xmlhttprequest

 1 function createXHR() {
 2         if (typeof XMLHttpRequest != "undefined") {
 3             return new XMLHttpRequest();
 4         } else if (typeof ActiveXObject != "undefined") {
 5             if (typeof arguments.callee.activeXString != "string") {
 6                 var versions = ["MSXML2.XMLHttp.6.0", "MSXML2.XMLHttp.3.0", "MSXML2.XMLHttp"];
 7 
 8                 for (var i = 0, len = versions.length; i < len; i++) {
 9                     try {
10                         var xhr = new ActiveXObject(versions[i]);
11                         arguments.callee.activeXString = versions[i];
12                         return xhr;
13                     } catch (ex) {
14                         //omit
15                     }
16                 }
17             }
18             return new ActiveXObject(arguments.callee.activeXString);
19         } else {
20         throw new Error("no xhr object available.");
21         }
22     }