Create a MongoClient

Overview

To connect to a MongoDB deployment, you need two things:

• Connection URI, also known as a connection string, which tells the Node.js driver which MongoDB deployment to connect to.

• MongoClient object, which creates the connection to and performs operations on the MongoDB deployment.

You can also use MongoClientOptions to customize the way the Node.js driver behaves while connected to MongoDB.

This guide shows you how to create a connection string and use a MongoClient object to connect to MongoDB.

Connection URI

A standard connection string includes the following components:

For more information about creating a connection string, see Connection Strings in the MongoDB Server documentation.

Atlas Connection Example

You must create a client to connect to a MongoDB deployment on Atlas. To create a client, construct an instance of MongoClient, passing in your URI and a MongoClientOptions object.

Use the serverApi option in your MongoClientOptions object to enable the Stable API feature, which forces the server to run operations with behavior compatible with the specified API version.

The following code shows how you can specify the connection string and the Stable API client option when connecting to a MongoDB deployment on Atlas and verify that the connection is successful:

const { MongoClient, ServerApiVersion } = require("mongodb");
// Replace the placeholder with your Atlas connection string
const uri = "<connection string>";
// Create a MongoClient with a MongoClientOptions object to set the Stable API version
const client = new MongoClient(uri,  {
        serverApi: {
            version: ServerApiVersion.v1,
            strict: true,
            deprecationErrors: true,
        }
    }
);
async function run() {
  try {
    // Connect the client to the server (optional starting in v4.7)
    await client.connect();
    // Send a ping to confirm a successful connection
    await client.db("admin").command({ ping: 1 });
    console.log("Pinged your deployment. You successfully connected to MongoDB!");
  } finally {
    // Ensures that the client will close when you finish/error
    await client.close();
  }
}
run().catch(console.dir);

To learn more about the Stable API feature, see the Stable API page.

Prevent a Slow Operation From Delaying Other Operations

When you use the same MongoClient instance to run multiple MongoDB operations concurrently, a slow operation can cause delays to other operations. Slow operations keep a connection to MongoDB occupied, which can cause other operations to wait until another connection becomes available.

If you suspect that slow MongoDB operations are causing delays, you can check the performance of all in-progress operations by using the following methods:

• Enable the database profiler on your deployment. To learn more, see Database Profiler in the Server manual.

• Run the db.currentOp() MongoDB Shell command. To learn more, see the db.currentOp() documentation in the Server manual.

• Enable connection pool monitoring. To learn more, see Connection Pool Events.

After you determine which operations are causing delays, try to improve the performance of these operations. Read the Best Practices Guide for MongoDB Performance for possible solutions.

If you implement performance best practices but still experience delays, you can modify your connection settings to increase the size of the connection pool. A connection pool is the group of connections to the server that the driver maintains at any time.

To specify the maximum size of a connection pool, you can set the maxPoolSize option in the connection options for your MongoClient instance. The default value of maxPoolSize is 100. If the number of in-use connections to a server reaches maxPoolSize, the next operation sent to the server pauses until a connection to the driver becomes available. The following code sets maxPoolSize to 150 when creating a new MongoClient:

const client = new MongoClient(uri, { maxPoolSize: 150 });

API Documentation

For more information about creating a MongoClient object with the Node.js driver, see the following API documentation:

• MongoClient

• MongoClientOptions