Javascript Node.js Express Login route with ajax responses

route.js

app.post('/login', function(req, res) {
    console.log(res);
    passport.authenticate('local', function(err, user, params) {
      if (req.xhr) {
        //thanks @jkevinburton
        if (err)   { return res.json({ error: err.message }); }

        // e.g. in auth.js:
        // if (!user.emailVerified) { return done(null, false, { message: 'Email is not verified. Please check your email for the link.' }); }
        if (!user && params) { return res.json({error : params.error}); }
        if (!user) { return res.json({error : "Invalid Login"}); }
        req.login(user, {}, function(err) {
          if (err) { return res.json({error:err}); }
          return res.json(
            { user: {
                      id: req.user.id,
                      email: req.user.email,
                      joined: req.user.joined
              },
              success: true
            });
        });
      } else {
        if (err)   { return res.redirect('/login'); }
        if (!user) { return res.redirect('/login'); }
        req.login(user, {}, function(err) {
          if (err) { return res.redirect('/login'); }
          return res.redirect('/');
        });
      }
    })(req, res);
  });