Solving Array issues with Asynchronous Programming

Someone recommended I try using the async module, specifically the waterfall method, but I'm a bit confused on how to implement it for my issue.

The original code I wrote had issues with asynchronicity.

        var Image    = require('./models/image');
        var User     = require('./models/user');

        var query = Image.find({});

        query.limit(10);
        query.sort('-date')

        query.exec(function (err, collected) {
          if (err) return console.error(err);
            var i = 0;
            var authors = [];

            while (i < 8) {
                var search = User.find({'twitter.id' : collected[i].author});


                search.exec(function (err, user){
                    if (err) return console.error(err);

                    var result = (user[0].twitter.username);
                    authors.push(result);
                });

                i = i + 1;
            }
        }

        console.log(authors);

I want to populate the authors array with all the discovered usernames, but right now when I call 'console.log()', it returns '[]'.

Answer №1

If you're looking to ensure all search operations are completed before proceeding, one approach is to store all asynchronous calls in an array and then use a library to run them sequentially (waterfall) or concurrently (parallel). Typically, parallel execution is faster:

var searches = [];
while (i < 8) {
    var search = User.find({'twitter.id' : collected[i].author});
    searches.push(function(cb) {
        search.exec(function (err, user){
            if (err) cb(err, null);
            else cb(null, user[0].twitter.username);
        });
    });
    i++;
}
async.parallel(searches, function( err, authors ) {
    if ( err ) return console.error( err );
    console.log(authors);
    // Authors only defined here.
    //  TODO: More code
});
// Authors not defined here.

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