Manage multiple tabs (but same user) in socket.io

It sounds like you may be referring to the socket id in your question, not the session id. If you have an express session you can use the session id, which will be the same regardless of how many tabs are open as long as they use the same browser and it's not in "private" mode. Take a look at this question for how to enable sessions in socket.io.

socket.io and session?

Update: When you're saving the session id, you'll associate it with the user's nickname and the connected sockets. Then you can iterate through each socket and send the message. Something like the following:

[
    {sessionId: '12345', nickname: 'timmay!', socketIds: [1, 2, 3]},
    {sessionId: '23456', nickname: 'pete', socketIds: [4, 5, 6]}
]

When another connection is established you push the new socket id into the socketIds array, and when a user disconnects you remove the id.

Another option might be to only allow one tab per user per session. You can store a single socketId and when a new socket connects for the same user, you can disconnect the original socket and use the new one instead.

You can use hash like that:

var sessionHash = {};
sessionHash['userName'] = socket;

and check on io.sockets.on('connection',..) whether a socket exist under that key.

If it does, you can execute sessionHash['userName'].disconnect(); on it and save the brand new socket.

I know it has been a long time since you asked this, but Just 4 ago I published a module for node js, express and socket.io which manages that exactly thing you wanted. Check the Usage and Example, I hope you will find this module helpful!

You can install it via NPM socket.io.users This is a node js module for socket.io applications. One user per client.

Some of the usage code

var express = require('express');
var app = express();
var server = require('http').createServer(app);
var socketUsers = require('socket.io.users');
//....
socketUsers.Session(app);//IMPORTANT 
//...
var rootIo = require('socket.io')(server); //default '/' as namespace. 
var chatIo = rootIo.of('/chat');

var rootUsers = socketUsers.Users; /* default '/' as namespace.
Each namespace       has IT's OWN users object list,
but the Id of a user of any other namespace may 
has the same value if       request comes from the same client-machine-user.
This makes   easy to keep a kind of 
synchronization between all users of all   different namespaces. */

var chatUsers = socketUsers.Users.of('/chat'); //  


rootIo.use(socketUsers.Middleware());/*IMPORTANT but no errors if you want
to  skip it for a io.of(namespace) 
that you don't want the socket.io.users' support.  */

chatUsers.use(socketUsers.Middleware());

chatUsers.on('connected',function(user){
console.log(user.id + ' has connected to the CHAT');
user.store.username = 'username setted by server side'; /*at the store
property you can store any type of properties
and objects you want to share between your user's sockets.  */
user.socket.on('any event', function(data){ 
/*user.socket is the current socket, to get all connected sockets from this  
user, use: user.sockets */

});
chatIo.emit('set username',user.store.username);
});

rootUsers.on('connected',function(user){
   console.log('User has connected with ID: '+ user.id);
});



rootUsers.on('connection',function(user){
   console.log('Socket ID: '+user.socket.id+' is user with ID: '+user.id);
});

rootUsers.on('disconnected',function(user){
    console.log('User with ID: '+user.id+'is gone away :(');
});

//...server.listen blabla..