How can I promisify the MongoDB native Javascript driver using bluebird?

The 2.0 branch documentation contains a better promisification guide https://github.com/petkaantonov/bluebird/blob/master/API.md#promisification

It actually has mongodb example which is much simpler:

var Promise = require("bluebird");
var MongoDB = require("mongodb");
Promise.promisifyAll(MongoDB);

When using Promise.promisifyAll(), it helps to identify a target prototype if your target object must be instantiated. In case of the MongoDB JS driver, the standard pattern is:

• Get a Db object, using either MongoClient static method or the Db constructor
• Call Db#collection() to get a Collection object.

So, borrowing from https://stackoverflow.com/a/21733446/741970, you can:

var Promise = require('bluebird');
var mongodb = require('mongodb');
var MongoClient = mongodb.MongoClient;
var Collection = mongodb.Collection;

Promise.promisifyAll(Collection.prototype);
Promise.promisifyAll(MongoClient);

Now you can:

var client = MongoClient.connectAsync('mongodb://localhost:27017/test')
    .then(function(db) {
        return db.collection("myCollection").findOneAsync({ id: 'someId' })
    })
    .then(function(item) {
      // Use `item`
    })
    .catch(function(err) {
        // An error occurred
    });

This gets you pretty far, except it'll also help to make sure the Cursor objects returned by Collection#find() are also promisified. In the MongoDB JS driver, the cursor returned by Collection#find() is not built from a prototype. So, you can wrap the method and promisify the cursor each time. This isn't necessary if you don't use cursors, or don't want to incur the overhead. Here's one approach:

Collection.prototype._find = Collection.prototype.find;
Collection.prototype.find = function() {
    var cursor = this._find.apply(this, arguments);
    cursor.toArrayAsync = Promise.promisify(cursor.toArray, cursor);
    cursor.countAsync = Promise.promisify(cursor.count, cursor);
    return cursor;
}