MongoDB + Promise

var MongoClient = require('mongodb').MongoClient,
	assert = require('assert');

let dropDocuments = (obj) => new Promise((resolve, reject) =>
	obj.collection.drop(function(err, result) {
		try {
			console.log("drop collection:", true===result, err);
			resolve(obj);
		} catch (e) {
			reject(e);
		}
	}))

let insertDocuments = (obj, values) => new Promise((resolve, reject) =>
	obj.collection.insertMany(values, function(err, result) {
		try {
			assert.equal(err, null);
			assert.equal(3, result.result.n);
			assert.equal(3, result.ops.length);
			console.log("Inserted %d documents into collection:", values.length, result);
			resolve(obj);
		} catch (e) {
			reject(e);
		}
	}))

let updateDocument = (obj, val1, val2) => new Promise((resolve, reject) =>
	obj.collection.updateOne(val1, val2, function(err, result) {
		try {
			assert.equal(err, null);
			assert(1, result.result.n);
			console.log("Updated the document with the field a equal to 2");
			resolve(obj);
		} catch (e) {
			reject(e);
		}
	}))

let deleteDocument = (obj, val) => new Promise((resolve, reject) =>
	obj.collection.deleteOne(val, function(err, result) {
		try {
			assert.equal(err, null);
			assert.equal(1, result.result.n);
			console.log("Removed the document with:", val);
			resolve(obj);
		} catch (e) {
			reject(e);
		}
	}))
let findDocuments = (obj, val, fmt) => new Promise((resolve, reject) =>
        obj.collection.find(val).toArray(function(err, docs) {
                try {
                        assert.equal(err, null);
                        assert.equal(2, docs.length);
                        console.log("Found the following records:");
                        docs.forEach((doc, i) => {
                                console.log("%d => %s", i,
                                        fmt.replace(/:(\w+)/g, (match, prop) =>
                                                prop + ":" + doc[prop] + "|" ));
                        });
                        resolve(obj);
                } catch (e) {
                        reject(e);
                }
        }))

let connectDB = (url) => new Promise((resolve, reject) =>
	 MongoClient.connect(url, function(err, db) {
		try {
			assert.equal(null, err);
			console.log("Connected correctly to %s", url);
			resolve({db: db});
		} catch (e) {
			 reject(e);
		}
	}))

connectDB("mongodb://localhost/test")
.then(value => ({db: value.db, collection: value.db.collection('documents')}))
.then(obj => dropDocuments(obj))
.then(obj => insertDocuments(obj, [{a: 1}, {a: 2}, {a: 3}]))
.then(obj => updateDocument(obj, {a: 2}, {$set: {b: 1}}))
.then(obj => deleteDocument(obj, {a: 3}))
.then(obj => findDocuments(obj, {}, ":a :_id"))
.then(value => {
	console.log("db.close()");
	value.db.close();
}).catch(reason => {
	console.error("!!!ERROR!!!", reason);
});

process.on('uncaughtException', function(err) {
	console.error("!!!uncaughtException!!!", err);
	process.exit();
});

Connected correctly to mongodb://localhost/test
drop collection: true null
Inserted 3 documents into collection: { result: { ok: 1, n: 3 },
  ops: 
   [ { a: 1, _id: 58ff9dde91bccba10e6557ef },
     { a: 2, _id: 58ff9dde91bccba10e6557f0 },
     { a: 3, _id: 58ff9dde91bccba10e6557f1 } ],
  insertedCount: 3,
  insertedIds: 
   [ 58ff9dde91bccba10e6557ef,
     58ff9dde91bccba10e6557f0,
     58ff9dde91bccba10e6557f1 ] }
Updated the document with the field a equal to 2
Removed the document with: { a: 3 }
Found the following records:
0 => a:1| _id:58ff9dde91bccba10e6557ef|
1 => a:2| _id:58ff9dde91bccba10e6557f0|
db.close()