Emit cheatsheet

Server-side

  1. io.on("connection", (socket) => {
  3.   // basic emit
  4.   socket.emit(/* ... */);
  6.   // to all clients in the current namespace except the sender
  7.   socket.broadcast.emit(/* ... */);
  9.   // to all clients in room1 except the sender
  10.   socket.to("room1").emit(/* ... */);
  12.   // to all clients in room1 and/or room2 except the sender
  13.   socket.to("room1").to("room2").emit(/* ... */);
  15.   // to all clients in room1
  16.   io.in("room1").emit(/* ... */);
  18.   // to all clients in namespace "myNamespace"
  19.   io.of("myNamespace").emit(/* ... */);
  21.   // to all clients in room1 in namespace "myNamespace"
  22.   io.of("myNamespace").to("room1").emit(/* ... */);
  24.   // to individual socketid (private message)
  25.   io.to(socketId).emit(/* ... */);
  27.   // to all clients on this node (when using multiple nodes)
  28.   io.local.emit(/* ... */);
  30.   // to all connected clients
  31.   io.emit(/* ... */);
  33.   // WARNING: `socket.to(socket.id).emit()` will NOT work, as it will send to everyone in the room
  34.   // named `socket.id` but the sender. Please use the classic `socket.emit()` instead.
  36.   // with acknowledgement
  37.   socket.emit("question", (answer) => {
  38.     // ...
  39.   });
  41.   // without compression
  42.   socket.compress(false).emit(/* ... */);
  44.   // a message that might be dropped if the low-level transport is not writable
  45.   socket.volatile.emit(/* ... */);
  47. });

Client-side

  1. // basic emit
  2. socket.emit(/* ... */);
  4. // with acknowledgement
  5. socket.emit("question", (answer) => {
  6.   // ...
  7. });
  9. // without compression
  10. socket.compress(false).emit(/* ... */);
  12. // a message that might be dropped if the low-level transport is not writable
  13. socket.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
  1. // BAD, will throw an error
  2. socket.emit("disconnecting");