publish.js

var mongo = require('mongodb');

var server = new mongo.Server('localhost', 27017);
var db = new mongo.Db('pubsub', server);

db.open(function(err) {
    if (err) throw err;

    db.collection('messages', function(err, collection) {
        if (err) throw err;

        setInterval(function() {
            collection.insert({ foo: 'bar', time: Date.now() }, function(err) {
                if (err) throw err;
                console.log('published', doc._id);
            });
        }, 2000);
    });
});

subscribe.js

var mongo = require('mongodb');

var server = new mongo.Server('localhost', 27017);
var db = new mongo.Db('pubsub', server);

db.open(function(err) {
    if (err) throw err;

    db.collection('messages', function(err, collection) {
        if (err) throw err;

        var latest = collection.find({}).sort({ $natural: -1 }).limit(1);

        latest.nextObject(function(err, doc) {
            if (err) throw err;

            var query = { _id: { $gt: doc._id }};
            
            var options = { tailable: true, awaitdata: true, numberOfRetries: -1 };
            var cursor = collection.find(query, options).sort({ $natural: 1 });

            (function next() {
                cursor.nextObject(function(err, doc) {
                    if (err) throw err;
                    console.log(doc);
                    next();
                });
            })();
        });
    });
});