function isok(theform)
{

if (theform.username.value=="")

  {
    alert("请输入用户名！");
    theform.username.focus();
    return (false);
  }
  
if (theform.userpass.value=="")

  {
    alert("请输入密码！");
    theform.userpass.focus();
    return (false);
  }

return (true);
}