Question

Is it possible for client to send a socket data when it gets
disconnected (user closes the browser, or tab)?
Because, I found that default bind on disconnect doesn’t take any input data.

//on server side 
socket.on('disconnect',function(){ 
    //in other binds, it takes 'data' as an input but this does not 
}); 

I tried to resolve this problem by using the jQuery’s unload method
like below

//on client side 
$(window).unload(function(){ 
    socket.emit('depart','I am leaving'); 
}); 

However, it does not seem to emit at all on unload. (maybe socket gets out of scope on unload?)
Is there a way to send data through websocket to the server when client disconnects?

Secondly, Is there any way that I can store a string data in socket? For instance,
socket.userName = userNameVar;

–update–
Here is how I set up environment on the serverside

io.sockets.on('connection',function(socket){
    socket.on('depart',function(data){
        console.log(data);
        console.log("user left");
    });
    socket.on('disconnect',function(){
        console.log("user disconnected");
    });
});

and following code is in the client side.

var socket = io.connect(hostVar);

$(window).unload(function(){ 
    socket.emit('depart','I am leaving'); 
}); 

Answer 1

The reason you cannot send data on disconnect is because you are disconnected. What you are asking is somewhat akin to saying “Can i still talk to the person on the phone after they’ve hung up on me?”

If you want to emit the ‘depart’ event, then you still have to capture it inside your ‘connect’ handler on server side:

As in:

io.socket.on('connection', function(socket) {
      socket.on('depart', function(msg) {
            // you should get depart message here

      });
})

Your depart event will come BEFORE the connection is terminated. disconnect is only raised by server upon a successful disconnection and therefore it cannot receive any messages.

Give it a try and tell me if this works 🙂