Rocket.Chat/client/startup/roomObserve.js

import { Meteor } from 'meteor/meteor';
import { Session } from 'meteor/session';

import { ChatRoom } from '../../app/models';

Meteor.startup(function() {
	ChatRoom.find().observe({
		added(data) {
			Session.set(`roomData${ data._id }`, data);
		},
		changed(data) {
			Session.set(`roomData${ data._id }`, data);
		},
		removed(data) {
			Session.set(`roomData${ data._id }`, undefined);
		},
	});
});