JS创建Ajax的XMLHttpRequest对象的通用方法

 1 function createXMLHttpRequest() {
 2     var request = false;
 3     if(window.XMLHttpRequest) {
 4         request = new XMLHttpRequest();
 5         if(request.overrideMimeType) {
 6             request.overrideMimeType('text/xml');
 7         }
 8     } else if(window.ActiveXObject) {
 9         var versions = ['Microsoft.XMLHTTP', 'MSXML.XMLHTTP', 'Microsoft.XMLHTTP', 'Msxml2.XMLHTTP.7.0', 'Msxml2.XMLHTTP.6.0', 'Msxml2.XMLHTTP.5.0', 'Msxml2.XMLHTTP.4.0', 'MSXML2.XMLHTTP.3.0', 'MSXML2.XMLHTTP'];
10         for(var i=0; i<versions.length; i++) {
11             try {
12                 request = new ActiveXObject(versions[i]);
13                 if(request) {
14                     return request;
15                 }
16             } catch(e) {}
17         }
18     }
19     return request;
20 }