js 兼容ff ActiveXObject创建xmlhttp方法

js 兼容ff activexobject创建xmlhttp方法
*/

function createxmlhttpobject()
 {
  var xobject = null;
  try
  {
   xobject = new activexobject("msxml2.xmlhttp.4.0");
  }
  catch (e)
  {
   try
   {
    xobject = new xmlhttprequest();
    if(xobject.overridemimetype){
     xobject.overridemimetype('text/xml');
    }
   }
   catch (e)
   {
    try
    {
     xobject = new activexobject("msxml2.xmlhttp");
    }
    catch (e)
    {
     try
     {
      xobject = new activexobject("microsoft.xmlhttp");
     }
     catch (e)
     { 
      alert("error: unable to create xml http object!");
     }
    }
   }
  }
  return xobject;
 }
 
 function initrequest(){
  request = createxmlhttpobject();
 }