Send additional data on socket connection

How to best send additional data upon socket connection?

Client:

socket.on('connect',function(){ 
//I'd like set some values and pass them up to the node server.
});

Node.js Server:

io.on('connection', function(client){
//I'd like to get the data here.
});

For example sending a user name or email address etc.

You should send your data either in connect or on create:

var s = io('http://216.157.91.131:8080/', { query: "foo=bar" });
s.connect();

var c = io.connect('http://216.157.91.131:8080/', { query: "foo=bar" });

With the new version of socket.io, on server is where the things have been changed:

var io = require('socket.io')(server);

io.use(function(socket, next) {
  var handshakeData = socket.request;
  console.log("middleware:", handshakeData._query['foo']);
  next();
});

I have a different approach - emit an event right after connecting, with the data:

socket.on('connect',function(){ 
    // Send ehlo event right after connect:
    socket.emit('ehlo', data);
});

io.on('connection', function(client){
    // Receive ehlo event with data:
    client.on('ehlo', function(data) {
    });
});

You can hold a variable/object, and say, when there is no ehlo event with data, the other events are ignored until ehlo is sent.

If this does not satisfy, you can send data right when connecting, I won't copy the code but it is in this answer: https://stackoverflow.com/a/13940399/1948292

The connection events get fired as soon as the TCP connection is established. There's no way to send anything in between.

What you can do is to simply take the first message send by the server and put the data in that message. I'd strongly suggest to roll some thin protocol for this, so you would have multiple types of messages and use those to determine how the code should process the data.

This would be more extendable too, since it's fairly easy to come up with a generic architecture for that. If you want to wait for the userdata to come in first you can simply add some state to your connections.