models-user.js

User.resetToken = function(user, callback) {
  console.log('in generateResetToken')
  User.findOne({email: user.email}, function(err, user) {
    if(err) {
      console.log('error')
      res.send(500)
    } else {
      var sha = crypto.createHash('sha1');
      console.log('sha ', sha)
      sha.update((new Date()).toString() + user.email);
      console.log('sha after update ', sha)
      user.token = sha.digest('hex');
      console.log('user.token ', user.token)

      User.save(user, function(err, user) {
        console.log('token after the save in the model ',user.token)
        callback(err, user);
      });
    }
  });
}

routers-users.js

router.post('/recoverPassword', function (req, res) {
  User
    .findOne({ email: req.body.email }, function(err, user) {
      if(err) {
        res.send(500)
      }
      User.resetToken(user, function(err, user) {
        console.log('new user token', user.token);
      });
    });
});