How to have Meteor.Collection without MongoDB? - reactjs

Question

While developing a small project, there is absolutely no need for a MongoDB persistence layer, but I would like the benefit of publishing and subscribing for client synchronization.
From a related question, I implemented a very crude interface (untested) :
// server
const _cache = new Map();
const rooms = {
registerObserver: (roomHash, observer) => {
if (!_cache.has(roomHash)) {
_cache.add(roomHash, { messages:[], observers:[] );
}
const room = _cache.get(roomHash);
room.observers.add(observer);
observer.added("rooms", roomHash, { messages:room.messages });
observer.onStop(() => room.observers.delete(observer));
observer.ready();
}
}
Meteor.publish('chatroom', function (roomHash) {
check(roomHash, String);
rooms.registerObserver(roomHash, this);
});
Meteor.methods({
pushMessage: function (roomHash, message) {
check(roomHash, String);
check(message, String);
const room = _cache.get(roomHash);
room.messages.push(message);
room.observers.forEach(observer =>
observer.changed("rooms", roomHash, { messages:room.messags })
);
}
});
But, now, I need to fetch the messages from the given room, so I added :
// client, React hook
const useChatMessages = roomHash => {
const loading = useTracker(() => {
const handle = Meteor.subscribe("chatroom", roomHash);
return !handle.ready();
}, [orderHash]);
const pushMessage = useCallback(message => {
Meteor.call('pushMessage', roomHash, message);
}, [roomHash]);
const messages = []; // .... ???
return { loading, messages, pushMessage };
};
I have no idea how to fetch the messages. Since I removed the MongoDB dependencies, I do not have access to Mongo.Colllection, and it seems like Meteor.Collection is also unavailable (i.e. Meteor.Collection === undefined)
So, I publish, and also subscribe, but how do I fetch the published messages?
(Note: the above code compiles, but it is mostly untested as explained in the question.)