function GE(a){return document.getElementById(a);} 
function Check(){ 
 if(GE('yourname').value==''){GE('msg').innerHTML='please type your name!';return false} 
 if(GE('youremail').value==''){GE('msg').innerHTML='please type your email!';return false} 
 var url = "reg.php";
 var postStr = "yourname="+ GE('yourname').value +"&youremail="+ GE('youremail').value;
          var ajax = false;
         //开始初始化XMLHttpRequest对象
         if(window.XMLHttpRequest) { //Mozilla 浏览器
                 ajax = new XMLHttpRequest();
                 if (ajax.overrideMimeType) {//设置MiME类别
                         ajax.overrideMimeType("text/xml");
                 }
         }
         else if (window.ActiveXObject) { // IE浏览器
                 try {
                         ajax = new ActiveXObject("Msxml2.XMLHTTP");
                 } catch (e) {
                         try {
                                 ajax = new ActiveXObject("Microsoft.XMLHTTP");
                         } catch (e) {}
                 }
         }
         if (!ajax) { // 异常，创建对象实例失败
                 window.alert("fail to create XMLHttpRequest object.");
                 return false;
         }

ajax.open("POST", url, true); 

//定义传输的文件HTTP头信息
ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 

//发送POST数据
ajax.send(postStr);

//获取执行状态
ajax.onreadystatechange = function() { 
   //如果执行状态成功，那么就把返回信息写到指定的层里
   if (ajax.readyState == 4 && ajax.status == 200) { 
    alert(ajax.responseText); 
   } 
} 

}