让火狐、谷歌支持Ajax

<script>
var xmlHttp;
---------------------------------------------------------------------------------------
        function createXMLHttpRequest()
        { 
  try
     {
    // Firefox, Opera 8.0+, Safari
     xmlHttp=new XMLHttpRequest();
     }
  catch (e)
     {

   // Internet Explorer
    try
       {
       xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
       }
    catch (e)
       {
       try
          {
          xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
          }
       catch (e)
          {
          alert("您的浏览器不支持AJAX！");
          return false;
          }
       }