Express returns empty array

Question

I currently have the following code

router.get('/uri', (request,response) => {
    let final = [];
    TP.find({userID: request.userID})
    .then(tests =>{
        tests.forEach(test => {
            A.findById(test.assignmentID)
            .then(assignment => {
                final.push({
                    testID: test._id,
                    name: assignment.title,
                    successRate: `${test.passedTests}/${test.totalTests}`
                })
            })
            .catch(error => {
                console.log(error)
            })
        })
        return response.send(final);
    })
    .catch(err => {
        console.log(err);
        return response.sendStatus(500);
    })
})

The code is supposed to query 2 MongoDB databases and construct an array of objects with specific information which will be sent to the client.

However, I always get an empty array when I call that endpoint. I have tried making the functions async and make them wait for results of the nested functions but without success - still an empty array.

Any suggestions are appreciated!

Ashish Modi · Accepted Answer · 2019-12-27 15:47:47Z

2

forEach doesn't care about promises inside it. Either use for..of loop or change it to promise.all. The above code can be simplified as

router.get('/uri', async (request,response) => {
  const tests = await TP.find({userID: request.userID});
  const final = await Promise.all(tests.map(async test => {
    const assignment = await A.findById(test.assignmentID);
    return {
      testID: test._id,
      name: assignment.title,
      successRate: `${test.passedTests}/${test.totalTests}`
    };
  }));
  return response.send(final);
  });

Hope this helps.

answered Dec 27, 2019 at 15:47

Ashish Modi

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1 Comment

Jon Doe Over a year ago

Was not aware that forEach does not care about promises. Thanks a lot for the help

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