Skip to main content
Version: 4.x

Emit cheatsheet

Server-side#

io.on("connection", (socket) => {
  // basic emit  socket.emit(/* ... */);
  // to all clients in the current namespace except the sender  socket.broadcast.emit(/* ... */);
  // to all clients in room1 except the sender  socket.to("room1").emit(/* ... */);
  // to all clients in room1 and/or room2 except the sender  socket.to(["room1", "room2"]).emit(/* ... */);
  // to all clients in room1  io.in("room1").emit(/* ... */);
  // to all clients in room1 and/or room2 except those in room3  io.to(["room1", "room2"]).except("room3").emit(/* ... */);
  // to all clients in namespace "myNamespace"  io.of("myNamespace").emit(/* ... */);
  // to all clients in room1 in namespace "myNamespace"  io.of("myNamespace").to("room1").emit(/* ... */);
  // to individual socketid (private message)  io.to(socketId).emit(/* ... */);
  // to all clients on this node (when using multiple nodes)  io.local.emit(/* ... */);
  // to all connected clients  io.emit(/* ... */);
  // WARNING: `socket.to(socket.id).emit()` will NOT work, as it will send to everyone in the room  // named `socket.id` but the sender. Please use the classic `socket.emit()` instead.
  // with acknowledgement  socket.emit("question", (answer) => {    // ...  });
  // without compression  socket.compress(false).emit(/* ... */);
  // a message that might be dropped if the low-level transport is not writable  socket.volatile.emit(/* ... */);
});

Client-side#

// basic emitsocket.emit(/* ... */);
// with acknowledgementsocket.emit("question", (answer) => {  // ...});
// without compressionsocket.compress(false).emit(/* ... */);
// a message that might be dropped if the low-level transport is not writablesocket.volatile.emit(/* ... */);

Reserved events#

On each side, the following events are reserved and should not be used as event names by your application:

  • connect
  • connect_error
  • disconnect
  • disconnecting
  • newListener
  • removeListener
// BAD, will throw an errorsocket.emit("disconnecting");