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copied!<p>You'll need to obtain the number of clients from a different location:</p> <pre><code> io.sockets.clients().length </code></pre> <p>However, when you read <a href="https://github.com/LearnBoost/socket.io/issues/463">this active GitHub issue</a>, you might want to avoid that operation as it can cause an additional memory leak (beyond what's already happening with sockets).</p> <p>Here's a complete working example:</p> <pre><code>var app = require('express')(); var server = require("http").createServer(app); var io = require('socket.io').listen(server); server.listen(1339); app.get('/', function(req, res) { return res.sendfile(__dirname + "/index.html"); }); /* to obtain number of connected clients io.sockets.clients().length */ console.log("INIT", io.sockets.clients().length ); io.sockets.on("connection", function(socket) { console.log("CONNECT:" + io.sockets.clients().length); socket.on("disconnect", function(data){ console.log("DISCONNECT: ", io.sockets.clients().length); }); }); </code></pre> <p>The disconnect event happens before the client has been removed, so the count will be one higher than the total number of clients (depending on how you look at it).</p> <p>Also, you had the <code>on</code> event handlers returning values for some reason, so I removed that.</p> <p>Instead of using that function, you might have better luck with just a simple counter:</p> <pre><code>var clientsConnected = 0; console.log("INIT", io.sockets.clients().length ); io.sockets.on("connection", function(socket) { console.log("CONNECT:" + ++clientsConnected); socket.on("disconnect", function(data){ console.log("DISCONNECT: ", --clientsConnected); }); }); </code></pre> <p>Some have apparently reported that the number of disconnects can exceed the number of connections, so you may want to prevent a counter from dropping below zero. </p> <p>Connected two clients (and then disconnected one):</p> <pre><code>info: socket.io started INIT 0 debug: served static content /socket.io.js debug: client authorized info: handshake authorized eJcvVsr60fmRzhVpQ6rO debug: setting request GET /socket.io/1/websocket/eJcvVsr60fmRzhVpQ6rO debug: set heartbeat interval for client eJcvVsr60fmRzhVpQ6rO debug: client authorized for debug: websocket writing 1:: CONNECT:1 debug: served static content /socket.io.js debug: client authorized info: handshake authorized 28lUudTS3KtCphd0Q6rP debug: setting request GET /socket.io/1/websocket/28lUudTS3KtCphd0Q6rP debug: set heartbeat interval for client 28lUudTS3KtCphd0Q6rP debug: client authorized for debug: websocket writing 1:: CONNECT:2 info: transport end (socket end) debug: set close timeout for client 28lUudTS3KtCphd0Q6rP debug: cleared close timeout for client 28lUudTS3KtCphd0Q6rP debug: cleared heartbeat interval for client 28lUudTS3KtCphd0Q6rP DISCONNECT: 2 debug: discarding transport info: transport end (socket end) debug: set close timeout for client eJcvVsr60fmRzhVpQ6rO debug: cleared close timeout for client eJcvVsr60fmRzhVpQ6rO debug: cleared heartbeat interval for client eJcvVsr60fmRzhVpQ6rO DISCONNECT: 1 debug: discarding transport </code></pre>

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