重写表单的checkForm方法，并用if和else解决异步判断的问题。

function checkForm(){
     1 var flag = false;     2  3 $.ajaxSetup({async : false}); 4  5 $.post(
     ,'captcha='+document.getElementById("captcha").value,function(msg){
   if(!parseInt(msg)){layer.alert('验证码错误！',{time:1000});return flag;}else{ 6  7 $.post(
     ,'username='+document.getElementById("username").value+'&'+'password='+document.getElementById("password").value,function(msg){
   if(!parseInt(msg)){layer.alert('用户名或密码错误！',{time:1000});return flag;}else{ 8  9 flag = true;return flag;}});}});10 11 return flag; }