Install the MongoDB Driver for Node.js: You'll need to use the official MongoDB Node.js driver to interact with your MongoDB Atlas database. You can install it using npm:

npm install mongodb
Create a Node.js Application:

You can create a Node.js application or use an existing one. Here's an example of how you can connect to your Atlas database and make API calls in a simple Node.js script:

const { MongoClient } = require("mongodb");

// Replace with your MongoDB Atlas connection string
const uri = "mongodb+srv://<username>:<password>@<cluster>.mongodb.net/test?retryWrites=true&w=majority";

async function main() {
  const client = new MongoClient(uri, { useNewUrlParser: true });

  try {
    // Connect to the MongoDB Atlas cluster
    await client.connect();

    // Access your database and collection
    const database = client.db("your-database-name");
    const collection = database.collection("your-collection-name");

    // Example: Find documents in a collection
    const query = { yourField: "someValue" };
    const documents = await collection.find(query).toArray();
    console.log(documents);

    // Perform other database operations here

  } finally {
    // Close the MongoDB Atlas connection when done
    await client.close();
  }
}

main().catch(console.error);
Replace Placeholder Values:
Replace <username>, <password>, <cluster>, your-database-name, and your-collection-name with your actual MongoDB Atlas connection details.

API Logic: In your Node.js application, you can define your API logic as needed. For example, you can use Express.js to set up routes, handle HTTP requests, and interact with your MongoDB Atlas database as shown in the previous example.

Start Your Node.js Application: You can run your Node.js application with the appropriate entry point, and it will connect to your MongoDB Atlas database and handle API calls as needed.

This approach allows you to make direct API calls to your MongoDB Atlas database using Node.js without the need for an intermediate serverless layer like AWS Lambda. It's suitable when you have an existing MongoDB Atlas deployment and want to build a custom API or application using Node.js to interact with the database.