@sealsystems/mongo makes it easy to connect to MongoDB reliably.

Usage no npm install needed!

<script type="module">
  import sealsystemsMongo from 'https://cdn.skypack.dev/@sealsystems/mongo';


@sealsystems/mongo Master

@sealsystems/mongo makes it easy to connect to MongoDB reliably.


$ npm install @sealsystems/mongo

Quick start

First you need to add a reference to @sealsystems/mongo to your application:

const mongo = require('@sealsystems/mongo');

Then you can use its db function to connect to a MongoDB server. Provide the connection string as parameter:

const db = await mongo.db('mongodb://localhost:27017/mydb', options);

If no connection can be established, @sealsystems/mongo retries to connect ten times, with a pause of 1 second between two connection attempts.

If you need to pass options to the MongoDB connection, e.g. for setting write concerns, provide an additional options object. For details see the MongoClient.connect documentation. Additionally the following options can be set:

  • connectionRetries is the number of retries to connect to MongoDB server, a value of 0 tries to connect only once without retries, default is 10.
  • waitTimeBetweenRetries is the time in milliseconds waiting between the retries, default is 1000 ms.
  • noCursorTimeout boolean, a true value is indicating that read stream cursors created by subsequent calls to createReadStream are not closed automatically after a timeout.
const db = await mongo.db('mongodb://localhost:27017/mydb', {
  connectionRetries: 1
  // ...

Now you can use the db object to access the database. Please note that this is the very same object as the one that the node-mongodb-native driver provides.

Please note that if you call db twice with the same connection string, both calls will use the same underlying connection.

Accessing GridFS

If you need to access GridFS, simply call the db object's gridfs function.

const gridfs = db.gridfs();


createReadStream(fileName, options)

  • fileName String Name of the file to read

The optional options object overrides the default settings set in db and may contain:

  • noCursorTimeout boolean, true is indicating that the read stream cursor created by createReadStream is not closed automatically after a timeout.

Opens the file fileName for reading and returns as soon the file is opened. The functions returns the data of the file as a Readable stream as well as its metadata:

const { stream, metadata } = await gridfs.createReadStream('My file.txt');

const chunk = stream.read();


createWriteStream(fileName, metadata)

  • fileName String Name of the file to write
  • metadata Object Optional metadata, can be left out

Opens the file fileName for writing and returns as soon as the file is opened. The content of the file can be written with the Writable stream that is returned. The stream emits a close event when all data is written and the file is closed.

Please note: The file content is not fully written when the finish event occurs. So, do not rely on it.

const stream = await gridfs.createWriteStream('My file.txt', { foo: 'bar' });

stream.on('close', (err) => {
  if (err) {
    // Handle error on file close

stream.write('Hello World');



  • fileName String Name of the file to check

Checks if file fileName does exist. If the function returns false the file does not exist, otherwise it exists.

const doesExist = await gridfs.exist('My file.txt');

if (doesExist) {
  // File does exist
} else {
  // File does not exist



  • fileName String Name of the file to delete

Deletes the file fileName. The returned value indicates whether the file did exist or not.

const fileFound = await gridfs.unlink('My file.txt');

if (fileFound) {
  // File did exist and has been removed
} else {
  // File does not exist


The module uses @sealsystems/tlscert to obtain certificates for an encrypted connection to the database. The connection will only be encrypted if TLS_UNPROTECTED is set to none or loopback. Otherwise it is assumed that an unencrypted connection is save. If @sealsystems/tlscert provides a CA certificate, the host's certificate will be transmitted to the database server in order to allow client verification.

To always enforce TLS encrypted connections to MongoDB, regardless of the value of TLS_UNPROTECTED, you can set MONGODB_FORCE_TLSto true.

The MongoDB client option tlsAllowInvalidCertificates will be set according to NODE_TLS_REJECT_UNAUTHORIZED, so if invalid TLS certificates are allowed for NodeJS it's also allowd for MongoDB.

Running the build

To build this module use roboter.

$ bot

Test Hint

For testing start own mongo without ssl. Add the --replSet rs option if you want a replication set:

docker run -d --name db -p 27017:27017 mongo:3.6.17 --replSet rs

In case of a replication set you need to initialize it:

docker exec -it db mongo --eval 'rs.initiate()'

Run tests

npm run test