How do you export a variable from app.js into another route in Node js

Question

i'm using socket.io in my node project and wanted to know how to possibly export the io variable

this is what i have done so far but i get this error: Object #<Object> has no method 'on'

in app.js:

        var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');

var routes = require('./routes/index')(io);
var users = require('./routes/user');

var app = require('express')();
var server = require('http').Server(app);
var io = require('socket.io')(server);
server.listen(4000);

require('./routes/index')(io);

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

// app.use(favicon(__dirname + '/public/img/favicon.ico'));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
  extended: true
}));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/', routes);
app.use('/users', users);

/// catch 404 and forward to error handler
app.use(function(req, res, next) {
    var err = new Error('Not Found');
    err.status = 404;
    next(err);
});

/// error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
    app.use(function(err, req, res, next) {
        res.status(err.status || 500);
        res.render('error', {
            message: err.message,
            error: err,
            title: 'error'
        });
    });
}

// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
        message: err.message,
        error: {},
        title: 'error'
    });
});
/*
io.on('connection', function (socket) {
  socket.emit('news', { hello: 'world' });
  socket.on('my other event', function (data) {
    console.log(data);
  });
});
*/

module.exports = app;

in index.js

var io = require('../app');

io.on('connection', function (socket) {
  socket.emit('news', { hello: 'world' });
  socket.on('my other event', function (data) {
    console.log(data);
  });
});

the reason i want export the variable is so that i dont have to define io is index.js like i did in app.js which leads to me basically defining both server and app variable !

I just want to do all my socket.io stuff in the index.js route essentially (except from having to redefine the app, server and io variables in index.js ) !

Hope i have explained my self enough

Thank you !

Am I mistaken, or do you have a circular dependency? [http://selfcontained.us/2012/05/08/node-js-circular-dependencies/](http://selfcontained.us/2012/05/08/node-js-circular-dependencies/) — mattr, Nov 04 '14 at 17:54
i mean app.js requires index.js and index.js requires app.js. Also, it looks like index is required before you had a chance to initialize app. i think this is a chicken-and-egg problem — mattr, Nov 04 '14 at 18:18
still sort of new to node js. this is how yomean generated the file and really haven't done anything in app.js. how can i solve this please ? — ipalibowhyte, Nov 04 '14 at 18:21
ok ill add an answer to refactor the code that may band-aid the problem, stay tuned! ;) — mattr, Nov 04 '14 at 18:22
just to clarify `var routes = require('./routes/index');`...that is the same `index.js` shown, correct? — mattr, Nov 04 '14 at 18:24

score 14 · Accepted Answer · answered Nov 04 '14 at 19:22

Your dependencies are not set up correctly. You are executing index.js before io is initialized

var routes = require('./routes/index');
/* index.js starts being executed at this point
 * hence, io is undefined inside index.js
 */

Instead, why don't you try

app.js

var app = require('express')();
var server = require('http').Server(app);
var io = require('socket.io')(server);
server.listen(4000);
module.exports = io;

var routes = require('./routes/index');
var users = require('./routes/user');

index.js

 var io = require('../app');

io.on('connection', function (socket) {
    socket.emit('news', { hello: 'world' });
    socket.on('my other event', function (data) {
    console.log(data);
    });
});

score 1 · Answer 2 · answered Nov 04 '14 at 17:50

1

I think you need to use the sockets.

io.sockets.on('connection', ... );

answered Nov 04 '14 at 17:50

corn3lius

4,857
2
31
36

added that in index.js and got `Cannot call method 'on' of undefined` – ipalibowhyte Nov 04 '14 at 18:10

mattr · Answer 3 · 2014-11-04T18:47:10.283

It looks like a circular dependency (app.js requires index.js and index.js requires app.js)

Try this.

change app.js to:

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');

var users = require('./routes/user');

var app = require('express')();
var server = require('http').Server(app);
var io = require('socket.io')(server);
server.listen(4000);

require('./routes/index')(io);

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

// app.use(favicon(__dirname + '/public/img/favicon.ico'));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({
  extended: true
}));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/users', users);

/// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

/// error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
  app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
      message: err.message,
      error: err,
      title: 'error'
    });
  });
}

// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
  res.status(err.status || 500);
  res.render('error', {
    message: err.message,
    error: {},
    title: 'error'
  });
});
/*
 io.on('connection', function (socket) {
 socket.emit('news', { hello: 'world' });
 socket.on('my other event', function (data) {
 console.log(data);
 });
 });
 */

module.exports = app;

change index.js to:

module.exports = function(io){
  io.on('connection', function (socket) {
    socket.emit('news', { hello: 'world' });
    socket.on('my other event', function (data) {
      console.log(data);
    });
  });
}

gives me this error `/Desktop/blah Site/node_modules/express/lib/router/index.js:114 debug('dispatching %s %s', req.method, req.url);` :( — ipalibowhyte, Nov 04 '14 at 18:40
you didnt change the code exactly as i specified. i see `require('./routes/index')(io)` twice and once before `io` is even defined. remove the first version. — mattr, Nov 04 '14 at 18:44
did exactly what you said now getting this error `/node_modules/express/lib/router/index.js:116 var method = req.method.toLowerCase();` — ipalibowhyte, Nov 04 '14 at 18:47
apparently the error is from the io part of this `require('./routes/index')(io);` — ipalibowhyte, Nov 04 '14 at 18:51
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/64264/discussion-between-mattyice-and-pizzy213codes). — mattr, Nov 04 '14 at 18:52

score 0 · Answer 4 · answered Feb 10 '22 at 17:02

0

Use "global.io" instead of "var io" in app.js

answered Feb 10 '22 at 17:02

Prithiviy

1
1

How do you export a variable from app.js into another route in Node js

4 Answers4