send to backend socket io code example

Example 1: socket io emit from socket instance or server

socket.emit('message', "this is a test"); //sending to sender-client only
socket.broadcast.emit('message', "this is a test"); //sending to all clients except sender
socket.broadcast.to('game').emit('message', 'nice game'); //sending to all clients in 'game' room(channel) except sender
socket.to('game').emit('message', 'enjoy the game'); //sending to sender client, only if they are in 'game' room(channel)
socket.broadcast.to(socketid).emit('message', 'for your eyes only'); //sending to individual socketid
io.emit('message', "this is a test"); //sending to all clients, include sender
io.in('game').emit('message', 'cool game'); //sending to all clients in 'game' room(channel), include sender
io.of('myNamespace').emit('message', 'gg'); //sending to all clients in namespace 'myNamespace', include sender
socket.emit(); //send to all connected clients
socket.broadcast.emit(); //send to all connected clients except the one that sent the message
socket.on(); //event listener, can be called on client to execute on server
io.sockets.socket(); //for emiting to specific clients
io.sockets.emit(); //send to all connected clients (same as socket.emit)
io.sockets.on() ; //initial connection from a client.

Example 2: socket io middleware

const express = require('express');
const socketio = require('socket.io');

// Setup server and socket
const port = 3000;
const app = express();
const server = app.listen(port, console.log(`Listening on port ${port}...`));
const io = socketio(server);

// Calls the middleware on every new connection
io.use((socket, next) => {
  if (/* should connect socket */) {
    next();
  } else {
    next(new Error('Connection failed.'));
  }
});

io.on('connection', (socket) => {
  // Calls the middleware on every event
  socket.use((packet, next) => {
    const event = packet[0];
    const data = packet.slice(1);
    
    if (/* should run event */) {
      next();
    } else {
      next(new Error('Failed to emit the event.'));
    }
  });

  // Example event
  socket.on('msg', (data) => {
    socket.broadcast.emit('msg', data.msg);
  });
});