NodeJS with ESM: internal/process/promises:246 | triggerUncaughtException(err, true /* fromPromise */) | finalizer.unsubscribe is not a function

Question

I am creating an observable (RxJS) in NodeJS using ESM. Inside the observable I am performing a query with mongoose. I get the result, but the console returns errors (detailed at the end of the question).

I have tried to perform the operation with Javascript promises and without promises trying to handle the errors with the operators (try catch).

//-----------------------------------------------------------------//
// WITHOUT PROMISES:
//-----------------------------------------------------------------//
// Create observable obsAuth:
const obsAuth = new Observable(async (observer) => {
  try{
    const doc = await people.Model.findOne();
    observer.next(doc);
  } catch (err) {
      observer.error(err);
  }

  // Finish observer:
  observer.complete();
});

// Observe sub-element content (Subscribe):
let subAuth = obsAuth.subscribe({
  next: doc => {
    res.status(200).send({ success: true, people_data: doc });
    console.log(doc);
  },
  error: err => {
    res.status(500).send({ success: false, error: err });
    console.error('Error: ' + err);
  },
  complete: () => console.log('Suscripción finalizada')
});

// Unsuscribe:
subAuth.unsubscribe();
//-----------------------------------------------------------------//


//-----------------------------------------------------------------//
// WITH PROMISES:
//-----------------------------------------------------------------//
// Build people query:
const peopleQueryMongoDB = people.Model.findOne();

// Create observable obsAuth:
const obsAuth = new Observable(async (observer) => {
  // Excecute people query (Promise):
  await peopleQueryMongoDB.exec()
  .then((doc) => {
    observer.next(doc);
  })
  .catch((err) => {
    observer.error(err);
  });

  // Finish observer:
  observer.complete();
});

// Observe sub-element content (Subscribe):
let subAuth = obsAuth.subscribe({
  next: doc => {
    res.status(200).send({ success: true, people_data: doc });
    console.log(doc);
  },
  error: err => {
    res.status(500).send({ success: false, error: err });
    console.error('Error: ' + err);
  },
  complete: () => console.log('Suscripción finalizada')
});

// Unsuscribe:
subAuth.unsubscribe();
//-----------------------------------------------------------------//

In both cases I have exactly the same behavior. I get the results and with the following error in the console.

CONSOLE ERRORS:

node:internal/process/promises:246
          triggerUncaughtException(err, true /* fromPromise */);
          ^
Error
...
...
at processTicksAndRejections (node:internal/process/task_queues:96:5) {
  message: '1 errors occurred during unsubscription:\n' +
    '1) TypeError: finalizer.unsubscribe is not a function',
  errors: [
    TypeError: finalizer.unsubscribe is not a function
...
...
at processTicksAndRejections (node:internal/process/task_queues:96:5)
  ]
}

Thanks a lot in advance!!

Answer 1

Experienced the same issue yesterday.
The problem with your code is that you are giving the Observable a promise as Teardown logic.

The easiest way to restructure your code so it works would be

const obsAuth = new Observable((observer) => {
    (async () => {
        // Excecute people query (Promise):
        await peopleQueryMongoDB.exec()
        .then((doc) => {
            observer.next(doc);
        })
        .catch((err) => {
            observer.error(err);
        });

    })().then(ignored => observer.complete()) // Finish observer:
});

but you can also just use

fromPromise(peopleQueryMongoDB.exec())