For loop iterating over array in NodeJS but console.log won't print to terminal?

Question

I'm using Node.JS to iterate through some data and push that data to an array. However, console.log does not seem to show any changes that I've made. I'd like to be able to process the data in twitter_ids after the function is done pushing data to it.

I'm wondering if it's due to a misunderstanding of Node.JS's asynchronous nature?

var twitter_ids = []

function sendResults (twitter_ids){
    return function(data){
        for (var num in data['results']) {
            T.get('users/lookup', { screen_name: data['results'][num]['twitter_id'] }, function(err, data, response) {
                twitter_ids.push(data[0]['id']);
            });
        }
    console.log(twitter_ids);
    }
}

sunlightResults.call(sendResults(twitter_ids));

The function is asynchronous. The array won't actually be populated until the operations complete. — Pointy
– Pointy, Commented Jun 24, 2014 at 0:21

Matt Way · Accepted Answer · 2014-06-24 00:33:52Z

2

Your problem is that you are printing to the console before T.get() has retrieved any data.

If you need to wait until multiple callbacks have been called (as per your example), I usually use a helper library function like async.eachSeries(). If you want to do it yourself, something like recursion can be your friend, but might be a little convoluted:

function lookup(list, index, output, finished) {
    if(index >= list.length) { return finished(output); }

    var num = list[index];
    T.get('users/lookup', { screen_name: data['results'][num]['twitter_id'] }, function(err, data, response) {
        output.push(data[0]['id']);
        lookup(list, index+1, output, callback);            
    });
}

var outputList = [];
lookup(data['results'], 0, outputList, function(output){
    console.log(output);
});

I am sure some genius here can make this better an more readable, but just a super quick example.

edited Jun 24, 2014 at 0:33

answered Jun 24, 2014 at 0:21

Matt Way

33.3k10 gold badges85 silver badges86 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

generalhenry · Accepted Answer · 2014-06-24 00:36:56Z

0

Here's an implementation using async

var async = require('async');
var twitter_ids = []

function sendResults (twitter_ids){
    return function(data){
        async.each(data.results, function (result, done) {
            T.get('users/lookup', { 
                screen_name: result.twitter_id 
            }, function(err, data, response) {
                if (err) {
                    return done(err);
                }
                twitter_ids.push(data[0].id);
                done();
            });
        }, function (err) {
          if (err) {
              throw err;
          }
          console.log(twitter_ids);
        });
    }
}

sunlightResults.call(sendResults(twitter_ids));

answered Jun 24, 2014 at 0:36

generalhenry

17.3k4 gold badges51 silver badges63 bronze badges

Collectives™ on Stack Overflow

For loop iterating over array in NodeJS but console.log won't print to terminal?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related