A Socket.IO connection can close for several reasons.

Examples include:

• The user closes the browser tab.
• The network connection disappears.
• The server shuts down.
• A reverse proxy closes an inactive connection.
• The client explicitly disconnects.
• A transport error occurs.

The server receives the disconnect event when a socket connection closes.

The event callback provides a reason describing why the disconnection happened.

Use this event to clean up connection-specific resources and update application presence information.

io.on('connection', (socket) => {
  console.log('Connected:', socket.id);

  socket.on('disconnect', (reason) => {
    console.log('Disconnected:', socket.id);
    console.log('Reason:', reason);
  });
});