function precheck(myform) {
  var username = myform.username.value;
  var password = myform.password.value;
  var rememberme = myform.rememberme.checked;
  
  if (username == "") {
    alert("您忘了输入用户代号。");
    myform.username.focus();
    return false;
  }
  if (password == "") {
    alert("您忘了输入登录密码。");
    myform.password.focus();
    return false;
  }
  
  if (rememberme) {
    if (isCookieEnabled()) {
      deleteCookie("username4save");  // Delete possible same cookies
      deleteCookie("password4save");
      setCookie("username4save", username, new Date(new Date().getTime() + (3600000*24*30*12)));  // expires in 12 months
      setCookie("password4save", password, new Date(new Date().getTime() + (3600000*24*30*12)));	
    } else {
      alert("要在本机记住您，您必须在您的浏览器中开放设置Cookie的功能。"); 
      rememberme.checked = false;
      return false;   	
    }	
  } else if (isCookieEnabled()) {
    deleteCookie("username4save");
    deleteCookie("password4save");	
  }
  return true;
}