return results from a function (javascript, nodejs)

Question

Could anyone help me with this code? I need to return a value form a routeToRoom function:

var sys = require('sys');

function routeToRoom(userId, passw) {
    var roomId = 0;
    var nStore = require('nstore/lib/nstore').extend(require('nstore/lib/nstore/query')());
    var users = nStore.new('data/users.db', function() {

        users.find({
            user: userId,
            pass: passw
        }, (function(err, results) {
            if (err) {
                roomId = -1;
            } else {
                roomId = results.creationix.room;
            }
        }
        ));
    });
    return roomId;
}
sys.puts(routeToRoom("alex", "123"));

But I get always: 0

I guess return roomId; is executed before roomId=results.creationix.room. Could someone help me with this code?

Raynos · Accepted Answer · 2011-08-31 11:19:01Z

44

function routeToRoom(userId, passw, cb) {
    var roomId = 0;
    var nStore = require('nstore/lib/nstore').extend(require('nstore/lib/nstore/query')());
    var users = nStore.new('data/users.db', function() {
        users.find({
            user: userId,
            pass: passw
        }, function(err, results) {
            if (err) {
                roomId = -1;
            } else {
                roomId = results.creationix.room;
            }
            cb(roomId);
        });
    });
}
routeToRoom("alex", "123", function(id) {
    console.log(id);    
});

You need to use callbacks. That's how asynchronous IO works. Btw sys.puts is deprecated

answered Aug 31, 2011 at 11:19

Raynos

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2 Comments

profesoralex Over a year ago

Does exist a format like that?var roomId = takeRoom("alex","123");My problem is I need to save a result into "global" variable to use it in other functions. Thank you!

Raynos Over a year ago

@profesoralex your doing it wrong. Rewrite your code. Node is asynchronous. Learn to write asynchronously.

m2j · Accepted Answer · 2016-05-02 14:03:37Z

11

You are trying to execute an asynchronous function in a synchronous way, which is unfortunately not possible in Javascript.

As you guessed correctly, the roomId=results.... is executed when the loading from the DB completes, which is done asynchronously, so AFTER the resto of your code is completed.

Look at this article, it talks about .insert and not .find, but the idea is the same : http://metaduck.com/01-asynchronous-iteration-patterns.html

edited May 2, 2016 at 14:03

m2j

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answered Aug 31, 2011 at 11:01

Simone Gianni

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3 Comments

profesoralex Over a year ago

thank you for your response, Andrzej! The link metaduck.com/post/2675027550/… is not working,have you another source? Thanks!

Andrzej Doyle Over a year ago

I just reformatted your question; Simone supplied this answer (you can tell from the name on the right, just above these comments).

Simone Gianni Over a year ago

strange, it's working from here .. however, search on google for "nodejs asynchronous patterns", you'll find some articles.

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