Quickly accessing variables between clients in Socket.IO - socket.io

Question

(I'm asking and answering this question because I think it might be useful, but if anything here is flawed let me know.)
Setting and getting custom variables in Socket.IO's socket object is super convenient for ephemeral data you want to associate with that connection.
In the chatroom example, (in this instance I'm using PHP but it should be readily translatable) the script stores user names there:
$socket->on('add user', function ($username) use ($socket) {
$socket->username = $username;
Which you can then use in your broadcast:
$socket->broadcast->emit('user joined', array(
'username' => $socket->username,
'numUsers' => $numUsers
));
The question I've had is how to 'share' the variable data between sockets (connections) without (or before) emitting it? This would be useful for managing more complex chatrooms, or something like a game where you may want to work with this data and not emit.
There are approaches I can think of that could do the job, such as managing distinct arrays, or storing and retrieving with a database -- but they seem redundant if you don't explicitly need to do so.
I wasn't able to find much documentation on this.

Answer 1

Sticking with the chatroom example, this is what I came up with:
Let's say you want to set and get the age of everyone in a particular room:
$socket->on('add user', function ($username,$age) use ($socket) {
$socket->age = $age;
I made a function to collect the unique connection id's of everyone who's in a room:
function clients_in_the_room($room)
{
GLOBAL $io;
$clients_in_the_room = $io->sockets->adapter->rooms[$room];
$clients_in_the_room = array_keys($clients_in_the_room);
return $clients_in_the_room;
}
$io->sockets->adapter->rooms[$room]; is just going to give us an array with booleans, so I've caught the array_keys, which are the id's I want, those are very useful.
$clients_in_the_room = clients_in_the_room('Lobby');
Now we have those id's, we can access those socket variables I wanted:
function socket_age($socketid) {
GLOBAL $io;
$age = $io->sockets->connected[$socketid]->age;
return $age;
}
Beautiful. For clarity, I could emit all this data...
foreach($clients_in_the_room as $clientsId) {
$age = socket_age($clientsId);
$output = "Connection ID: $clientsId Age: $age.";
$socket->broadcast->emit('new message', array(
'username' => $socket->username,
'message' => $output
));
};
But obviously we don't want to do that usually. It's just super useful to know how to quickly access those variables. Hope this is useful.