var http_request=false;
  function send_request(url){//初始化，指定处理函数，发送请求的函数
    http_request=false;
        //开始初始化XMLHttpRequest对象
        if(window.XMLHttpRequest){//Mozilla浏览器
         http_request=new XMLHttpRequest();
         if(http_request.overrideMimeType){//设置MIME类别
           http_request.overrideMimeType("text/xml");
         }
        }
        else if(window.ActiveXObject){//IE浏览器
         try{
          http_request=new ActiveXObject("Msxml2.XMLHttp");
         }catch(e){
          try{
          http_request=new ActiveXobject("Microsoft.XMLHttp");
          }catch(e){}
         }
    }
        if(!http_request){//异常，创建对象实例失败
         window.alert("创建XMLHttp对象失败！");
         return false;
        }
        http_request.onreadystatechange=processrequest;
        //确定发送请求方式，URL，及是否同步执行下段代码
    http_request.open("GET",url,true);
        http_request.send(null);
  }
  //处理返回信息的函数
  function processrequest(){
   if(http_request.readyState==4){//判断对象状态
     if(http_request.status==200){//信息已成功返回，开始处理信息
          document.getElementById(reobj).innerHTML=http_request.responseText;
         }
         else{//页面不正常
          alert("您所请求的页面不正常！");
         }
   }
  }
  function usercheck(obj){
   var f=document.reg;
   var username=f.username.value;
   if(username==""){
   document.getElementById(obj).innerHTML=" <font color=red>用户名不能为空！</font>";
        f.username.focus();
        return false;
   }
   else{
   document.getElementById(obj).innerHTML="正在读取数据...";
   send_request('../sd_check_reg.asp?username='+username);
   reobj=obj;
   }
     
  }
