router.route("/update/:id").post(function(req, res) {
  User.findById(req.params.id, function(err, user) {
    if (!user) res.status(404).send("user is not found");
    else firstName: req.body.firstName;
        lastName: req.body.lastName;
        email: req.body.email;
        password: req.body.password;

    user
      .save()
      .then(user => {
        res.json("User updated");
      })
      .catch(err => {
        res.status(400).send("User Update not possible");
      });
  });
});