I have a web application using socket.io. It runs on localhost:8000 on my local machine. In order to find an annoying resource leak in my application, I tried to log out the connection events on my HTTP server:

server.on('connection', function(conn) {
    //log out connection details
});

When I open the page inside my browser after the page loads, I can see multiple connection events in the log - something like these:

connection established: 127.0.0.1:54148
connection established: 127.0.0.1:54149
connection established: 127.0.0.1:54146
connection established: 127.0.0.1:54152
connection established: 127.0.0.1:54144
connection established: 127.0.0.1:54155

The strange thing is that I don't create a WebSocket connection after page load - only if the user clicks on a button. But I haven't clicked on any button and I still see these strange connections.

If I click on my button to connect with socket.io to my server, the log shows a new connection:

connection established: 127.0.0.1:54155

Fortunately every connections which I saw in the log were closed after some time - so I guess it couldn't be the reason of my resource leak.

But I'm still curious: what causes these connection events? And why is the port number so strange (not 8000 on which my server listens)?

Edit:

My server config is not a special one. In server.js:

var express = require('express');
var app = express();
var server = require('http').Server(app);
var io = require('socket.io')(server);
var configSettings = require('./configSettings');

var socketIOServer = require('./server/socketServer')(io); // config socketServer
require('./server/static.js')(app, express); // static middleware
require('./server/routes.js')(app, configSettings); // routes

exports = module.exports = server;

exports.use = function() {
     app.use.apply(app, arguments);
};

exports.configSettings = configSettings;

In start.js:

var server = require('./server');

var port = server.configSettings.serverPort;
var serverIpAddress = server.configSettings.serverIpAddress;
server.listen(port, serverIpAddress);