Tips for generating and invoking a promise within NodeJS

Question

Tips for generating and invoking a promise within NodeJS

I have been attempting to access Firestore using a function I created that includes a collection variable.

var fetchDataFromFirestore = function(collection, doc){
    return promise = new Promise(function(resolve,reject){
      //If doc param is null Query collection
      if(doc == null || doc == "" || doc == undefined){
        var response = [];
        db.collection(collection).get()
        .catch((err) => {
          console.log('Error getting documents: ', err);
          reject(err);
      })
        .then((snapshot) => {
          snapshot.forEach((doc) => {
            response.push(doc.id);
          });
          console.log(response);
          resolve(response);

        });

      }

    });
}

I invoke it with appp.get

app.get('/post', (req, res) => {
    fetchDataFromFirestore('fake',null).then(response => {
       res.json(response);
    }),(err) => {
      console.log(err);
      res.send(err);
  }

});

While it functions correctly, when attempting to test the error handling by providing an incorrect collection variable, it does not display the error message as expected.

Is there anyone who can assist me in resolving this issue?

Thank you.

javascript node.js firebase promise google-cloud-firestore

Answer 1

Answer №1

You forgot to pass the catch handler properly.

Make this modification:

app.get('/post', (req, res) => {
    readFirestore('fake',null).then(response => {
       res.json(response);
    }),(err) => {
      console.log(err);
      res.send(err);
  }

});

to the following:

app.get('/post', (req, res) => {
    readFirestore('fake',null).then(response => {
       res.json(response);
    }, (err) => {
      console.log(err);
      res.send(err);
    });
});

Additionally, readFirestore() doesn't need to create its own promise as it is an anti-pattern. It can simply return the existing promise.

Here's a revised readFirestore() function:

function readFirestore(collection, doc) {
    //If doc param is null Query collection
    if (!doc) {
        return db.collection(collection).get().then((snapshot) => {
            const response = [];
            snapshot.forEach((doc) => {
                response.push(doc.id);
            });
            return response;
        }).catch((err) => {
            // log the error, then rethrow
            // or, if you don't need to log the error here, then just get rid of the .catch()
            // here entirely as it doesn't change your logic flow, it's only here for logging
            console.log('Error getting documents: ', err);
            throw err;
        });
    } else {
        // it's unclear what you want returned here, but you need to return a promise
        // that resolves to something - you need to fill in this logic
        return Promise.resolve(null);
    }
}

Answer 2

You forgot to pass the catch handler properly.

Make this modification:

app.get('/post', (req, res) => {
    readFirestore('fake',null).then(response => {
       res.json(response);
    }),(err) => {
      console.log(err);
      res.send(err);
  }

});

to the following:

app.get('/post', (req, res) => {
    readFirestore('fake',null).then(response => {
       res.json(response);
    }, (err) => {
      console.log(err);
      res.send(err);
    });
});

Additionally, readFirestore() doesn't need to create its own promise as it is an anti-pattern. It can simply return the existing promise.

Here's a revised readFirestore() function:

function readFirestore(collection, doc) {
    //If doc param is null Query collection
    if (!doc) {
        return db.collection(collection).get().then((snapshot) => {
            const response = [];
            snapshot.forEach((doc) => {
                response.push(doc.id);
            });
            return response;
        }).catch((err) => {
            // log the error, then rethrow
            // or, if you don't need to log the error here, then just get rid of the .catch()
            // here entirely as it doesn't change your logic flow, it's only here for logging
            console.log('Error getting documents: ', err);
            throw err;
        });
    } else {
        // it's unclear what you want returned here, but you need to return a promise
        // that resolves to something - you need to fill in this logic
        return Promise.resolve(null);
    }
}

Answer 3

Answer №2

If you invoke your function with a Collection that does not actually exist, it will not generate an error but instead return an empty array of QueryDocumentSnapshots. This is the behavior of the JavaScript SDK.

An error will be thrown if you attempt to retrieve a Collection that is protected by a Security Rule.

As noted by jfriend00, there is no need to create your own promise since the get() method already returns a Promise. You can modify your function like this:

var readFirestore = function(collection) {
    var result = [];
    return db
      .collection(collection)
      .get()
      .then((snapshot) => {
        snapshot.forEach((doc) => {
          result.push(doc.id);
        });
        return result;
      })
  }

Answer 4

If you invoke your function with a Collection that does not actually exist, it will not generate an error but instead return an empty array of QueryDocumentSnapshots. This is the behavior of the JavaScript SDK.

An error will be thrown if you attempt to retrieve a Collection that is protected by a Security Rule.

As noted by jfriend00, there is no need to create your own promise since the get() method already returns a Promise. You can modify your function like this:

var readFirestore = function(collection) {
    var result = [];
    return db
      .collection(collection)
      .get()
      .then((snapshot) => {
        snapshot.forEach((doc) => {
          result.push(doc.id);
        });
        return result;
      })
  }

Tips for generating and invoking a promise within NodeJS

Answer №1

Answer №2

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