Array push is not working in array forEach - Javascript

Question

I need to create a new array from iterating mongodb result. This is my code.

const result = await this.collection.find({
  referenceIds: {
    $in: [referenceId]
  }
});

var profiles = [];

result.forEach(row => {
  var profile = new HorseProfileModel(row);

  profiles.push(profile);

  console.log(profiles); //1st log
});

console.log(profiles); //2nd log

I can see update of profiles array in 1st log. But 2nd log print only empty array.

Why i couldn't push item to array?

Update I think this is not related to promises. HorseProfileModel class is simply format the code.

const uuid = require("uuid");

class HorseProfileModel {

    constructor(json, referenceId) {

        this.id = json.id || uuid.v4();
        this.referenceIds = json.referenceIds || [referenceId];
        this.name = json.name;
        this.nickName = json.nickName;
        this.gender = json.gender;
        this.yearOfBirth = json.yearOfBirth;
        this.relations = json.relations;
        this.location = json.location;
        this.profilePicture = json.profilePicture;
        this.horseCategory = json.horseCategory;
        this.followers = json.followers || [];
    }

}

module.exports = HorseProfileModel;

@Rajesh No he is pushing a new profile into a profile list... — Serge K.
– Serge K., Commented Sep 29, 2017 at 8:58
Is forEach Array.prototype.forEach or is it the MongoDB version ? — Jonas Wilms
– Jonas Wilms, Commented Sep 29, 2017 at 8:58
Possible duplicate of Wait till all items from mongoDB query are processed before continuing — ponury-kostek
– ponury-kostek, Commented Sep 29, 2017 at 8:59
Why don't you try the cursor's map() method as let profiles = result.map(r => new HorseProfileModel(r))? — chridam
– chridam, Commented Sep 29, 2017 at 9:05
@jonasw got it what you mean. Thanks. I'll not comment like that. — Dinuka Thilanga
– Dinuka Thilanga, Commented Sep 29, 2017 at 9:20

Jonas Wilms · Accepted Answer · 2017-09-29 09:06:25Z

3

 await this.collection.find(...)

that returns an array of the found data right? Nope, that would be to easy. find immeadiately returns a Cursor. Calling forEach onto that does not call the sync Array.forEach but rather Cursor.forEach which is async and weve got a race problem. The solution would be promisifying the cursor to its result:

const result = await this.collection.find(...).toArray();

Reference

answered Sep 29, 2017 at 9:06

Jonas Wilms

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