socket.io: send message to specific room (client side)

Alapeno's solution was for the client to send a specific room as part of the message data to the server, so that the server would know which room to broadcast the message to.

However, if you just want the client to send a message to its own room, you can have the server detect the client's room on its own via the socket.rooms object. Thus, you wouldn't need the client to send the name of its room as part of the message as you indicated.

Client.js:

socket.emit('chat message', 'hello');

Server.js:

socket.on('chat message', function(msg){
    var keys = Object.keys(socket.rooms);
    for (var i = 0; i < keys.length; i++) {
        io.to(socket.rooms[keys[i]]).emit('chat message', msg);
    }
});

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Update: The socket.rooms object includes a sort of hash such as the example below, thus you'd better send to all the rooms in the socket.rooms to be sure the room members receive it. You can't be guaranteed the ordering of the keys.

Example:

socket.rooms[keys[0]] = WMWlX-ekAxa8hP8FAAAE

socket.rooms[keys[1]] = app-chat-room

You've pretty much figured it out. Only the server can emit to specific rooms, because it is only the server that is actually connected to multiple clients. In other words, clients aren't connected to each other — the client-side library only manages communications between that one client and the server. So, if you want your client app to instruct the server to emit a message to all clients connected to a given room… that's basic API design. You could emit a socket event, or just do a regular http call to a route on your server. Either way you'll be sending metadata about which room(s) the server should broadcast to. The former (emitting) is probably preferred however, because that way on the server side you can use socket.broadcast.to to emit to all clients in the room EXCEPT the socket that initiated the call (a pretty common use case).