function requestStatus(verifycode){  var req=createRequest();  req.open("POST","getVerifycode.do?isVerify=1&verifycode="+verifycode);  req.onreadystatechange=function(){callback(req);}  req.send(null); } function createRequest(){  if(window.XMLHttpRequest){   return new XMLHttpRequest();  }else{   try{    return new ActiveXObject("Msxm12.XMLHTTP");   }catch(e){    return new ActiveXObject("Microsoft.XMLHTTP");   }  }  return null; } //回调函数 function callback(req){  if(req.readyState==4){   if(req.status==200){    //获取返回值    var data=req.responseText;    if(data==1){     loginSubmit();    }else{     alert('验证码输入有误');     document.getElementById('verifycode').value='';     getVerifycode();    }    return;   }  } }