How can i emit to arrays of connected socket-ids ?

[parseshyam]

Let's say I have connected socket-id stored in DB's, and i want to emit to multiple socket-id's based on some criteria or conditions
instead of looping over and sending is there any other way to send array of socket-id's or something ?
Like ....emit ( [......socket-id's array.........] ,"data" )

[darrachequesne]

There is no built-in way to do that right now. You should be able to use io.to() in a loop

ids.forEach(id => io.to(id));
io.emit("hello");

The question has already been asked on the Slack channel, so it may make sense to add io.to(<array>).emit(...) directly.

[flow-pie]

You can emit to multiple socket IDs without looping by using Socket.io's built-in room support and the to() method.

Option 1: Use Rooms (Recommended)

Instead of tracking individual socket IDs, have sockets join a room based on your criteria:

// When socket connects, join them to relevant rooms
io.on('connection', (socket) => {
  socket.join('users-online');
  socket.join('user-' + userId);
});

// Emit to an entire room
io.to('users-online').emit('notification', { msg: 'Hello everyone!' });

You can also target multiple rooms:

io.to('room-1').to('room-2').emit('event', data);

Option 2: Emit to an Array of Socket IDs

The to() method actually accepts an array of socket IDs:

const socketIds = ['abc123', 'def456', 'ghi789'];
io.to(socketIds).emit('event', { data: 'hello' });

This is equivalent to looping but cleaner and handled internally by Socket.io.

Option 3: Target Specific Users via a Map

If you need to emit based on database criteria, maintain a map of userId to socketId:

const userSockets = new Map();

io.on('connection', (socket) => {
  socket.on('register', (userId) => {
    userSockets.set(userId, socket.id);
  });
});

// Later, emit to specific users
const targetUserIds = ['user1', 'user2', 'user3'];
const socketIds = targetUserIds
  .map(uid => userSockets.get(uid))
  .filter(Boolean);

io.to(socketIds).emit('event', data);