创建ajax方法

var xmlHttp;
function makeRequest(queryString) {
 var msXml = new Array();
 msXml[0] = "Microsoft.XMLHTTP";
 msXml[1] = "MSXML2.XMLHTTP.5.0";
 msXml[2] = "MSXML2.XMLHTTP.4.0";
 msXml[3] = "MSXML2.XMLHTTP.3.0";
 msXml[4] = "MSXML2.XMLHTTP";
 if (window.xmlHttpRequest) {
  xmlHttp = new XMLHttpRequest();
 } else {
  for (var i = 0; i < msXml.length; i++) {
   try {
    xmlHttp = new ActiveXObject(msXml[i]);
    break;
   } catch (e) {
    xmlHttp = new xmlHttpRequest();
   }
  }
 }
 xmlHttp.onreadystatechange = getRequest;
 xmlHttp.open('post', 'seo.php', true);
 xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
 xmlHttp.send(queryString);
}
function getRequest() {
 if(xmlHttp.readyState==4) {
  if(xmlHttp.status==200) {
   $('seo_result').innerHTML =  xmlHttp.responseText;
  }
 } 
}