TypeError: Cannot read property 'then' of undefined using promises

Question

I am making this website as a project which is a "Walmart" version of AirBnB.

Here's what the button is supposed to do for context:

A user will click on a "Make Reservation" button on a listing. They will select a start and end date then submit. This will send an HTTP request to the server.

However, I am running into an error where it returns :

TypeError: Cannot read property 'then' of undefined at /vagrant/LightBnB/LightBnB_WEB_APP/server/apiRoutes.js:44:7 <--

The line 44:7 is the API route below:

This is causing the error:

.then((reservation) => {
            res.send(reservation);

This is the API ROUTE Logic which is causing an issue:

  router.post('/reservations', (req, res) => {
    const userId = req.session.userId;
    database
      .addReservation({ ...req.body, guest_id: userId })
      .then((reservation) => {
        res.send(reservation);
      })
      .catch((e) => {
        console.error(e);
        res.send(e);
      });
  });

That route is calling the function addReservation() which is the following:

    /**
 * Add a reservation to the database
 * @param {{}} reservation An object containing all of the reservation details.
 * @return {Promise<{}>} A promise to the reservation.
 */
const addReservation = function (reservation) {
  const queryString = `
  INSERT INTO reservations(
    start_date,
    end_date,
    property_id,
    guest_id 
  ) 
  VALUES ($1, $2, $3, $4)
  RETURNING *
  `;
  const values = [
    reservation.start_date,
    reservation.end_date,
    reservation.property_id,
    reservation.guest_id,
  ];
  pool
    .query(queryString, values)
    .then((res) => {
      res.rows;
    })
    .catch((e) => console.log(e.message));
};
exports.addReservation = addReservation;

Please let me know if you need more information.

Answer 1

TypeError: Cannot read property 'then' of undefined

addReservation() has no return value, thus it returns undefined . So, when you try to do addReservation(...).then(...) , you end up trying to access .then() on undefined which results in the error you get.

Inside of addReservation() , you need to change:

pool.query(...).then(...).catch(...)

to

return pool.query(...).then(...).catch(...)

That returns your promise so then the caller can use .then() on the returned promise.

---

Note, your .catch() handler in addReservation() is logging and then "eating" the error. You should probably rethrow the error so that the caller can see the error:

Change this:

.catch((e) => console.log(e.message));

to this:

.catch((e) => {
     console.log(e.message)
     // re-throw the error so it propagates to the caller
     throw e;
});

---

Also, note that res.send(e) probably won't provide much useful info because most properties of the Error object are not enumerable and thus won't show up when res.send() turns the Error object into JSON.