AJAX 实质

//创建对象,IE - ActiveXObject,firefox - XMLHttpReuqest.
function createXMLHttpRequest(){
if(window.ActiveXObject){
  xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");   
}
else if(window.XMLHttpRequest){
  xmlHttp = new XMLHttpRequest();
}
}

//前台界面事件调用的函数
function checkName(){
createXMLHttpRequest();
xmlHttp.onreadystatechange = handleStateChange;
var strCon = "getInfo.aspx?";
xmlHttp.open("GET",strCon,true);
xmlHttp.send(null);
}

//和服务器交互期间执行的函数
function handleStateChange(){
if(xmlHttp.readyState == 4){
  if(xmlHttp.status == 200){  
  document.getElementById("dix").innerHTML = xmlHttp.responseText;
  }
}
}