When you query the collection for documents with createdAt equal to new Date() i.e. the current timestamp, you won't likely to get any result because the createdAt field will have values less than the current timestamp as time
passes.
What you need is to query a date range that encompasses today, not the current date time. In other words, create a date object that represents that start of today, with that you can then query your collection for documents
that have the createdAt field greater than that date. A mongo shell example follows:
var startOfToday = new Date();
startOfToday.setHours(0,0,0,0);
db.collection.find({ "createdAt": { "$gte": startOfToday } });
The above will query the collection for documents created today.