登录的时候如果用户名密码错误就没事，如果正确就报错。代码如下： user.js: //根据用户名得到用户信息 User.getUserByUserName = function getUserNumByName(username, callback) {

    var getUserByUserName_Sql = "SELECT * FROM userinfo WHERE username = ?";

    connection.query(getUserByUserName_Sql, [username], function (err, result) {
        if (err) {
            console.log("getUserByUserName Error: " + err.message);
            return;
        }

        connection.release();

        console.log("invoked[getUserByUserName]");
        callback(err,result);
    });
};


login.js:
    User = require('../models/user.js'),
router.post('/', function(req, res) {
var userName = req.body['txtUserName'],
    userPwd = req.body['txtUserPwd'],
    isRem = req.body['chbRem'],
    md5 = crypto.createHash('md5');

User.getUserByUserName(userName, function (err, results) {

    if(results == '')
    {
        res.locals.error = '用户不存在';
        res.render('login',{title:TITLE_LOGIN});
        return;
    }

    userPwd = md5.update(userPwd).digest('hex');
    if(results[0].UserName != userName || results[0].UserPass != userPwd)
    {
        res.locals.error = '用户名或密码有误';
        res.render('login',{title:TITLE_LOGIN});
        console.log(1);
        return;
    }
    else
    {
        if(isRem)
        {
            res.cookie('islogin', userName, { maxAge: 60000 });
        }

        res.locals.username = userName;
        req.session.username = res.locals.username;
        console.log(req.session.username);
        res.redirect('/');
        return;
    }
});

});