Broadcasting events

Socket.IO makes it easy to send events to all the connected clients.

Please note that broadcasting is a server-only feature.

To all connected clients

io.on("connection", (socket) => {
  io.emit("hello", "world");
});

To all connected clients except the sender

// server-side
io.on("connection", (socket) => {
  socket.broadcast.emit("hello", "world");
});

With multiple Socket.IO servers

Broadcasting also works with multiple Socket.IO servers.

You just need to replace the default Adapter by the Redis Adapter. More information about it here.

In certain cases, you may want to only broadcast to clients that are connected to the current server. You can achieve this with the local flag:

io.on("connection", (socket) => {
  io.local.emit("hello", "world");
});

In order to target specific clients when broadcasting, please see the documentation about Rooms.