Can't import module with require() in nodejs - node.js

Question

I'm developing a nodejs webapp and I have a problem.
I have a twitter.js module that expose some functions to use in other files.
My main application, app.js, import it correctly and can use the functions.
The problem is, if I import it in another .js file (via the var twitter = require(./twitter) method), it doesn't load, I can see that via console.log(twitter) and also because it doesn't recognize the functions.
This happens if app.js requires it. I copied the twitter.js file and name it differently, and if I import that it works.
How can I solve this problem?
Thanks
EDIT: Adding some code
This is the main app, app.js
var express = require("express");
var bodyParser = require("body-parser");
var path = require("path");
var twitter = require("./twitter");
var mongo = require("./mongo");
var app = express();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended:false}))
app.use(express.static(path.join(__dirname,'public')));
app.set('view engine','ejs');
app.set('views',path.join(__dirname,'views'));
app.get("/",function(req,res){
res.render("index.ejs")
});
app.get("/twitter",function(req,res){
twitter.getTrends(res);
});
app.post("/sendMessage",function(req,res){
twitter.postTwit(req.body.valore);
});
app.get("/pullData",function(req,res){
mongo.pullData(res);
});
app.listen(8080, function(){
console.log("server started on 8080");
});
Next is the twitter.js file:
var Twitter = require('twitter'); //import package
var mongo = require("./mongo");
var T = new Twitter({ ---developer keys here --})
exports.getTrends = function(res){
var params = { id: 23424853, count: 10}
T.get('trends/place',params,gotData);
function gotData(err,data,response){
res.render('tweets',{ data: data[0], length: 10});}
}
exports.postTwit = function(value){
T.post('statuses/update', {status:value}, function(error, tweet, response) {
mongo.pushdata(tweet.id_str);
});
}
exports.loadTwit = function(res,value){
var params = {id: value}
T.get('statuses/show/', params, function (err, data, response) {
console.log(data);
res.render('db',{ data: data});
});
}
and finally the mongo.js file, for the mongo database
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/mydb";
var twitter = require('./twitter');
exports.pushdata = function(value){
MongoClient.connect(url, function(err, db) {
if (err) throw err;
var myobj = {id: value};
db.collection("tweets").insertOne(myobj, function(err, res) {
if (err) throw err;
db.close();
});
});
}
exports.pullData = function(res){
MongoClient.connect(url, function(err, db) {
if (err) throw err;
db.collection("tweets").find({}).toArray(function(err, result) {
result.forEach(function(entry) {
twitter.loadTwit(res,entry);
});
db.close();
});
});
}
all these files are in the same folder.

Answer 1

You have created circular dependency between mongo.js & twitter.js.
mongo.js tries loading twitter.js which in turn requires mongo.js. Thats the problem. Remove this circular dependency.
Maybe you can pass the twitter object as a parameter when you call the functions of mongo.js. Or something else.
For e.g.
mongo.js
var twitter = require('./twitter');
// pass the twitter object as a parameter
exports.pullData = function(twitter, res){
MongoClient.connect(url, function(err, db) {
if (err) throw err;
db.collection("tweets").find({}).toArray(function(err, result) {
result.forEach(function(entry) {
twitter.loadTwit(res,entry);
});
db.close();
});
});
}