async.js return value form last function

Question

I would like create find method in my User object. This function should returns user. But for this example it returns only the text.

But I don't know how return value for waterfall.

When I run

console.log(User.find("575578a9f95d6de1354327ef"));

I got 'undefined' in my output, but I except 'function find shoud return this value', What I should to do if I want get 'function find shoud return this value' text on my output

User = {
    collectionName: 'users',

    find: function(id){
        async.waterfall(
            [
            function(callback) {
                MongoClient.connect('mongodb://127.0.0.1:27017/lingogo', function(err,db) {
                    if(err) { throw err}
                    callback(null, db, id);

                });
            },
            function(db,id, callback) {
                var collection = db.collection(User.collectionName);
                collection.find({'_id': ObjectID(id)}).toArray(function (err, result) {

                    if (err) { throw err };

                    if (result[0] && result[0]._id != '') {
                        return callback(null,result[0]);
                    }

                    return callback(null,null);
                })
            },
            ],
            function (err, user) {

                return 'function find shoud return this value';
            }
        );
    }
}
console.log(User.find("575578a9f95d6de1354327ef"));

connect before each .find is bad idea.

vp_arth
– vp_arth

2016-06-10 10:08:06 +00:00
Commented Jun 10, 2016 at 10:08 — vp_arth
– vp_arth, Commented Jun 10, 2016 at 10:08

polkovnikov.ph · Accepted Answer · 2016-06-10 10:29:24Z

2

Function find must have a callback too, that you call in a callback of waterfall. You cannot return a value synchronously from an asynchronous function.

find: function (id, callback) {
    async.waterfall(..., function (...) {
        callback(null, return_value);
    });
}

That should be called like

User.find("575578a9f95d6de1354327ef", function (err, return_value) {
    console.log(return_value);
});

edited Jun 10, 2016 at 10:29

answered Jun 10, 2016 at 10:15

polkovnikov.ph

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3 Comments

Thomas Shelby Over a year ago

I try this but I got error: TypeError: undefined is not a function I you want, you can see my update. pastebin.com/qVXTpNWS

polkovnikov.ph Over a year ago

@PawełBrzoski You still call that method synchronously. Once you're into asynchronous code, there's no way out, your calls have to be asynchronous too. Take a look on updated answer.

polkovnikov.ph Over a year ago

@PawełBrzoski Though I recommend looking into more Promise-like API, because code with callbacks becomes unwieldy quite soon.

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