AJAX judges the browser, ie5, ie6 use ActiveX object

Older versions of Internet Explorer (IE5 and IE6) used ActiveX objects:

variable=new ActiveXObject("Microsoft.XMLHTTP");

For all modern browsers, including IE5 and IE6, please check if the browser supports the XMLHttpRequest object. If supported, an XMLHttpRequest object is created. If not supported, create ActiveXObject:

var xmlhttp;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }