[Node.JS Socket.io]communication between two targeted sockets - node.js

Question

I'm currently working on a small node.js game.
Game supposedly has a global chat, with a "logged in" list to challenge people.
For the chat and the logged in list, i'm using the default socket.io room/namespace.
I successfully send the challenge request with following code
// When a user sends a battle challenge
socket.on("sendChallenge", function(data) {
// Try with room
socket.join('battleRoom');
var data= {
"userID": data.targetID,
"challengerName": data.challengerName
};
console.log(data.challengerName + " challenged " + data.userID);
// broadcast the message, but only the concerned player will answer thanks to his ID
socket.broadcast.emit('receiveChallenge', data);
});
Client side, I then have this code :
socket.on('receiveChallenge', function (data) {
if (data.userID == userID) {
alert("received challenge from " + data.challengerName);
socket.emit('ack');
}
});
The right player indeed receive the alert, and sends 'ack' to the server :
socket.on('ack', function() {
socket.join('battleRoom');
socket.to('battleRoom').broadcast.emit('receiveMessage', 'SYSTEM: Battle begun');
//socket.to('battleRoom').emit('receiveMessage', 'SYSTEM: Battle begun');
})
Except that the "socket.to('battleRoom').broadcast.emit('receiveMessage', 'SYSTEM: Battle begun');" is only received by the challenger and not by the challenged, and I'm stuck.
(the 2nd line is commented because challenger received 2 messages and challenged received none)
The way i understand it, on the server, the functions socket.on() have "socket" as the client that sent the message, and then you use broadcast to send to all others.
Why is why, in the sendChallenge event, i have the socket.join('battleRoom') for the challenger to enter battleRoom.
I then broadcast the challenge, and asks the client to acknowledge the challenge.
In the ack, the client then supposedly joins battleRoom too.
But i'm obviously doing something wrong, and i can't seem to see what...
I want both the challenger and the challenged communicating through the server.
A link to an image more or less showing the situation : Here
(screen is during the second time i clicked on the quickFight button, showing the Battle begun of the 1st click on the left, and the alert that user was challenged on the right)
Thanks in advance for your help!

Answer 1

As per the socket.io documentation broadcast does the following:
Broadcasting messages
To broadcast, simply add a broadcast flag to emit and send method calls. Broadcasting means sending a message to everyone else except for the socket that starts it.
So when you do:
socket.to('battleRoom').broadcast.emit('receiveMessage', 'SYSTEM: Battle begun');
You do not emit to the socket that broadcasted to the room. Simply replace that line with the following:
io.to('battleRoom').emit('receiveMessage', 'SYSTEM: Battle begun');
This is assuming that you named your socket.io object io, if you named it differently use that.
Just as a side-note, it's not necessary here to broadcast your original message to everyone if you create an associative array with all your connected socket id's (or sockets themselves). Then you can find the challenged socket id in your array and only emit to them specifically with the challenge. This would cut down on your server calls.