NodeJS: Returning data from an async function

Question

I'm trying to write a function to create a new user on my database (mongodb) and then return that user as an object which I defined. However, since the call to insert the user is async, result.nInserted is always undefined because the async code doesn't finish in time. Therefore, I never get to return my user. I would try and use callbacks to fetch the user after it is done being inserted, but then how would I be able to return that data from my original addUser function?

User.addUser = function(db, email, username, password, firstname, lastname, company, twitter){
    var _id = new mongodb.ObjectID();

    var result = db.get('users').insert({
        _id: _id,
        email : email,
        verified : false,
        password : password,
        username : username,
        firstname : firstname,
        lastname : lastname,
        company : company,
        twitter : twitter,
        rank : config.RANK_USER
    });

    return result.nInserted == 1 ? new User(_id, email, false, username, firstname, lastname, company, twitter, config.RANK_USER) : false;
};

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

From documentation:

Insert

Records can be inserted to a collection with insert

collection.insert(docs[[, options], callback])

So what you want can be done via callback function.

I think you can solve your task

User.addUser = function(db, email, username, password, firstname, lastname, company, twitter, callback){
var _id = new mongodb.ObjectID();

db.get('users').insert({
    _id: _id,
    email : email,
    verified : false,
    password : password,
    username : username,
    firstname : firstname,
    lastname : lastname,
    company : company,
    twitter : twitter,
    rank : config.RANK_USER
}, callback);
};

So callback function will be called when insertion is completed.

It receive two arguments: error and result.

function callback(err, res){
  // some actions
}

Read this question, it can help!

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Feb 20, 2015 at 8:03

Farkhat Mikhalko

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2 Comments

terpak Over a year ago

So is there no way to make it as simple as User.addUser traditionally returning a new user object? I wanted to do this because it is neater and easier to manage, but if it's not doable then I'll try callbacks instead

Robert Rossmann Over a year ago

No, you cannot return a result of an asynchronous operation (you can return whatever you want, but the result will obviously not be available, so your options are limited). The closest to this is using a Promise, but it's not the same. Alternatively, once ECMA Sscript 6 is fully supported, you will be able to do this using a generator.

Michal Lison · Accepted Answer · 2015-02-20 08:00:55Z

0

You have to use a promise pattern here:

return result.then(function( myNewUser ){
   return new User(myNewUser._id, email, false, username, firstname, lastname, company, twitter, config.RANK_USER);
})

answered Feb 20, 2015 at 8:00

Michal Lison

4894 silver badges7 bronze badges

3 Comments

terpak Over a year ago

Doing this seems to return nothing still. I even put a console.log inside of the promise callback and nothing was logged.

terpak Over a year ago

Scratch that, I did the most dumb thing possible and put the log after the return. It seems to be returning the right stuff, but my user object located at var user = User.addUser(...); is still undefined. Does this need a promise too, like var user = User.addUser(...).then(function(user){return user;});?

Michal Lison Over a year ago

Yes, you're essentially dealing with promises and async pattern here so you'll have to use callbacks. Depending on what your use-case is, you can for example resolve user requests from the callback.

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