初始化XMLHttpRequest对象

function  createXmlHttpRequest(){

   varxmlHttp;

   try{   //Firefox, Opera 8.0+, Safari

           xmlHttp=newXMLHttpRequest();

    }catch (e){

           try{   //Internet Explorer

                  xmlHttp=newActiveXObject("Msxml2.XMLHTTP");

            }catch (e){

                  try{

                         xmlHttp=newActiveXObject("Microsoft.XMLHTTP");

                  }catch (e){} 

           }

    }

   returnxmlHttp;

 }