Socket.IO handling disconnect event

Can't handle this disconnect event, don't know why socket is not sent to the client / client doesn't respond!

Server

io.sockets.on('connection', function (socket) {

  socket.on('NewPlayer', function(data1) {

    online = online + 1;
    console.log('Online players : ' + online);
    console.log('New player connected : ' + data1);
    Players[data1] = data1;
    console.log(Players);

  });

  socket.on('DelPlayer', function(data) {

    delete Players[data];
    console.log(Players);
    console.log('Adios' + data);

  });

  socket.on('disconnect', function () {

      socket.emit('disconnected');
      online = online - 1;

  });

});

Client

 var socket = io.connect('http://localhost');

    socket.on('connect', function () { 

        person_name = prompt("Welcome. Please enter your name");

        socket.emit('NewPlayer', person_name);

        socket.on('disconnected', function() {

            socket.emit('DelPlayer', person_name);

        });

    });

As you can see when a client disconnects the Array object[person_name] should be deleted, but it's not.

Ok, instead of identifying players by name track with sockets through which they have connected. You can have a implementation like

Server

var allClients = [];
io.sockets.on('connection', function(socket) {
   allClients.push(socket);

   socket.on('disconnect', function() {
      console.log('Got disconnect!');

      var i = allClients.indexOf(socket);
      allClients.splice(i, 1);
   });
});

Hope this will help you to think in another way

For those like @sha1 wondering why the OP's code doesn't work -

OP's logic for deleting player at server side is in the handler for DelPlayer event, and the code that emits this event (DelPlayer) is in inside disconnected event callback of client.

The server side code that emits this disconnected event is inside the disconnect event callback which is fired when the socket loses connection. Since the socket already lost connection, disconnected event doesn't reach the client.

---

Accepted solution executes the logic on disconnect event at server side, which is fired when the socket disconnects, hence works.

Create a Map or a Set, and using "on connection" event set to it each connected socket, in reverse "once disconnect" event delete that socket from the Map we created earlier

import * as Server from 'socket.io';

const io = Server();
io.listen(3000);

const connections = new Set();

io.on('connection', function (s) {
  
  connections.add(s);
  
  s.once('disconnect', function () {
    connections.delete(s);
  });
  
});

You can also, if you like use socket id to manage your player list like this.

io.on('connection', function(socket){
  socket.on('disconnect', function() {
    console.log("disconnect")
    for(var i = 0; i < onlineplayers.length; i++ ){
      if(onlineplayers[i].socket === socket.id){
        console.log(onlineplayers[i].code + " just disconnected")
        onlineplayers.splice(i, 1)
      }
    }
    io.emit('players', onlineplayers)
  })

  socket.on('lobby_join', function(player) {
    if(player.available === false) return
    var exists = false
    for(var i = 0; i < onlineplayers.length; i++ ){
      if(onlineplayers[i].code === player.code){
        exists = true
      }
    }
    if(exists === false){
      onlineplayers.push({
        code: player.code,
        socket:socket.id
      })
    }
    io.emit('players', onlineplayers)
  })

  socket.on('lobby_leave', function(player) {
    var exists = false
    for(var i = 0; i < onlineplayers.length; i++ ){
      if(onlineplayers[i].code === player.code){
        onlineplayers.splice(i, 1)
      }
    }
    io.emit('players', onlineplayers)
  })
})