title: NodeJS Express 4.9 and Socket.IO - 404 error on socket.io.js
body: <p>I am trying to create an Express app with Socket.IO. It seems like Express has changed quite a lot and most of the code online about getting the 2 to work together is out of date. This is what I have:</p>
  
  <pre><code>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');
  var users = require('./routes/users');
  
  var app = express();
  
  var http = require('http').Server(app);
  var io = require('socket.io').listen(http);
  io.on('connection', function(socket){
      console.log('a user connected');
  });
  
  // view engine setup
  app.set('views', path.join(__dirname, 'views'));
  app.set('view engine', 'jade');
  
  // uncomment after placing your favicon in /public
  //app.use(favicon(__dirname + '/public/favicon.ico'));
  app.use(logger('dev'));
  app.use(bodyParser.json());
  app.use(bodyParser.urlencoded({ extended: false }));
  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
          });
      });
  }
  
  // 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: {}
      });
  });
  
  module.exports = app;
  </code></pre>
  
  <p>The server starts ok and says</p>
  
  <pre><code>info - socket.io started
  </code></pre>
  
  <p>However the front-end has a 404 error on <a href="http://example.com:3000/socket.io/socket.io.js" rel="nofollow">http://example.com:3000/socket.io/socket.io.js</a></p>
  
  <p><em>edit</em></p>
  
  <p>If I add</p>
  
  <pre><code>http.listen(8080);
  </code></pre>
  
  <p>The server runs twice on port 3000 and 8080, the 3000 version does not load socket.io.js and the 8080 version does. How can I have it so the server is only running on 3000? changing it to 3000 errors and it tries to listen twice</p>