Do not delay, MongoJS function is ready to go!

Question

Do not delay, MongoJS function is ready to go!

I have a function set up in my Express JS endpoint that uses 'await' to retrieve data from a Mongo DB using Mongo JS.

Function:-

async function getIntroducer(company){

  const intro = await dbIntro.collection('introducers').findOne({company: company},  function(err, doc) {
 
 console.log("🚀 ~ file: app.js ~ line 289 ~ intro ~ doc.introducer", doc.introducer)
   return doc.introducer
  });
  
  return intro;

};

Express JS Endpoint:-

app.post(
  "/case",
  passport.authenticate("accessToken", { session: false }),
  async function (req, res) {
    const body = req?.body;
    
    const intro = await getIntroducer(req.user.company);
    console.log("🚀 ~ file: app.js ~ line 1152 ~ intro", intro)

Current behavior:-


🚀 ~ file: app.js ~ line 1152 ~ intro undefined

After the result is sent, I see this in the console (indicating it's not awaiting properly):-


🚀 ~ file: app.js ~ line 289 ~ intro ~ doc.introducer 347501

I've also attempted removing 'const intro' and just directly returning it. I have also tried removing the callback function but MongoJS gives an error 'CB is not a function.'

Any assistance would be appreciated?

javascript express mongojs

Answer 1

Answer №1

You are blending different approaches to asynchronous programming (callbacks and promises) when interacting with the collection.

Since the mongojs library only supports callback style, you must convert the findOne operation into a promise in order to use await.

The promisify function from the standard library module util can be of help here, as it transforms a function that takes a callback into one that returns a promise. This is achieved by ensuring the callback signature includes an error and/or a result parameter.

To promisify the findOne operation for await usage, you could implement it like this:

const util = require('util');

async function getIntroducer(company){
  const findIntroAsync = util.promisify(dbIntro.collection('introducers').findOne);
  let intro;
  try {
    intro = await findIntroAsync({company: company});
  }
  catch (err) 
  {
    // handle errors using your preferred logging method.
  }
//...
}

This approach yields a similar outcome as manual implementation. For further understanding, the Promise object is extensively discussed on MDN:

async function getIntroducer(company){
  let intro;
  try {
    intro = await new Promise(
      (resolve, reject) => {
        dbIntro.collection('introducers').findOne({company: company},
          function (err, doc) {
          if(err) {
            reject(err);
          }
          resolve(doc);
       });
    });
  } catch (err) 
  {
    // log error with your logging library.
  }
    //...
}

Answer 2

You are blending different approaches to asynchronous programming (callbacks and promises) when interacting with the collection.

Since the mongojs library only supports callback style, you must convert the findOne operation into a promise in order to use await.

The promisify function from the standard library module util can be of help here, as it transforms a function that takes a callback into one that returns a promise. This is achieved by ensuring the callback signature includes an error and/or a result parameter.

To promisify the findOne operation for await usage, you could implement it like this:

const util = require('util');

async function getIntroducer(company){
  const findIntroAsync = util.promisify(dbIntro.collection('introducers').findOne);
  let intro;
  try {
    intro = await findIntroAsync({company: company});
  }
  catch (err) 
  {
    // handle errors using your preferred logging method.
  }
//...
}

This approach yields a similar outcome as manual implementation. For further understanding, the Promise object is extensively discussed on MDN:

async function getIntroducer(company){
  let intro;
  try {
    intro = await new Promise(
      (resolve, reject) => {
        dbIntro.collection('introducers').findOne({company: company},
          function (err, doc) {
          if(err) {
            reject(err);
          }
          resolve(doc);
       });
    });
  } catch (err) 
  {
    // log error with your logging library.
  }
    //...
}

Do not delay, MongoJS function is ready to go!

Answer №1

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