TypeError: User.findById is not a function on deserializeUser

i was working with passport auth (local and google strategy) and now it tells me "User.findById is not a function" on the "deserializeUser" function.

passport.js

const passport = require('passport');
const request = require('request');
const LocalStrategy = require('passport-local').Strategy;
const GoogleStrategy = require('passport-google-oauth').

const OAuthStrategy = require('passport-oauth').OAuthStrategy;
const OAuth2Strategy = require('passport-oauth').OAuth2Strategy;

const User = require('../routes/user');

passport.serializeUser((user, done) => {
    done(null, user.id);
});

passport.deserializeUser(function(id, done) {
    User.findById(id, function(err, user) {
        done(err, user);
    });
});

/**
 * Sign in using Email and Password.
 */
passport.use(new LocalStrategy({ usernameField: 'email' }, (email, password, done) => {
    User.findOne({ email: email.toLowerCase() }, (err, user) => {
        if (err) { return done(err); }
        if (!user) {
            return done(null, false, { msg: `Email ${email} not found.` });
        }
        user.comparePassword(password, (err, isMatch) => {
            if (err) { return done(err); }
            if (isMatch) {
                return done(null, user);
            }
            return done(null, false, { msg: 'Invalid email or password.' });
        });
    });
}));

/**
 * OAuth Strategy Overview
 *
 * - User is already logged in.
 *   - Check if there is an existing account with a provider id.
 *     - If there is, return an error message. (Account merging not supported)
 *     - Else link new OAuth account with currently logged-in user.
 * - User is not logged in.
 *   - Check if it's a returning user.
 *     - If returning user, sign in and we are done.
 *     - Else check if there is an existing account with user's email.
 *       - If there is, return an error message.
 *       - Else create a new account.
 */


/**
 * Sign in with Google.
 */
passport.use(new GoogleStrategy({
    clientID: process.env.GOOGLE_ID,
    clientSecret: process.env.GOOGLE_SECRET,
    callbackURL: '/auth/google/callback',
    passReqToCallback: true
}, (req, accessToken, refreshToken, profile, done) => {
    if (req.user) {
        User.findOne({ google: profile.id }, (err, existingUser) => {
            if (err) { return done(err); }
            if (existingUser) {
                req.flash('errors', { msg: 'There is already a Google account that belongs to you. Sign in with that account or delete it' });
                done(err);
            } else {
                User.findById(req.user.id, (err, user) => {
                    if (err) { return done(err); }
                    user.google = profile.id;
                    user.tokens.push({ kind: 'google', accessToken });
                    user.profile.name = user.profile.name || profile.displayName;
                    user.profile.gender = user.profile.gender || profile._json.gender;
                    user.profile.picture = user.profile.picture || profile._json.image.url;
                    user.save((err) => {
                        req.flash('info', { msg: 'Google account has been linked.' });
                        done(err, user);
                    });
                });
            }
        });
    } else {
        User.findOne({ google: profile.id }, (err, existingUser) => {
            if (err) { return done(err); }
            if (existingUser) {
                return done(null, existingUser);
            }
            User.findOne({ email: profile.emails[0].value }, (err, existingEmailUser) => {
                if (err) { return done(err); }
                if (existingEmailUser) {
                    req.flash('errors', { msg: 'There is already an account using this email address. Sign in to that account and link it with Google manually from Account Settings.' });
                    done(err);
                } else {
                    const user = new User();
                    user.email = profile.emails[0].value;
                    user.google = profile.id;
                    user.tokens.push({ kind: 'google', accessToken });
                    user.profile.name = profile.displayName;
                    user.profile.gender = profile._json.gender;
                    user.profile.picture = profile._json.image.url;
                    user.save((err) => {
                        done(err, user);
                    });
                }
            });
        });
    }
}));

exports.isAuthenticated = (req, res, next) => {
    if (req.isAuthenticated()) {
        return next();
    }
    res.redirect('/login');
};

/**
 * Authorization Required middleware.
 */
exports.isAuthorized = (req, res, next) => {
    const provider = req.path.split('/').slice(-1)[0];
    const token = req.user.tokens.find(token => token.kind === provider);
    if (token) {
        next();
    } else {
        res.redirect(`/auth/${provider}`);
    }
};

it was working before i copy paste to another directory and nothing.

via yejielw