mongo_read_pref.js

const { MongoClient } = require("mongodb");
var ReadPreference = require('mongodb').ReadPreference

// Replace the following with your MongoDB deployment's connection
// string.
const uri =
  "mongodb://cosmomongo13:==@cosmomongo13.mongo.cosmos.azure.com:10255/?ssl=true&replicaSet=globaldb&retrywrites=false&maxIdleTimeMS=120000&appName=@cosmomongo13@";
const client = new MongoClient(uri, { monitorCommands:true });
// Replace <event name> with the name of the event you are subscribing to.
const eventName = "commandStarted";
client.on(eventName, event => {
  console.log(`received ${eventName}: ${JSON.stringify(event, null, 2)}`);
});
async function run() {
  try {
    await client.connect();
    // Establish and verify connection
    const findResult = await client.db("scheduler").collection("dataplane",{readPreference: ReadPreference.SECONDARY}).find({}).toArray();
    console.log('Found documents =>', findResult);

    console.log("Connected successfully");
  } finally {
    // Ensures that the client will close when you finish/error
    await client.close();
  }
}
run().catch(console.dir);