Emit cheatsheet

Server-side

  1. 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

  1. // basic emit
    socket.emit(/* ... */);

    // 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(/* ... */);

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
    socket.emit("disconnecting");

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