var MongoClient = require('mongodb').MongoClient

const url = 'mongodb://localhost:27017,localhost:27018,localhost:27019/?replSet=replset&readPreference=secondary';

async function main() {
  const client = new MongoClient(url,{
    keepAlive: true,
    connectTimeoutMS: 30000,
    socketTimeoutMS: 30000,
    useNewUrlParser: true,
    useUnifiedTopology: true
  });
  client.on('connectionCheckOutStarted', event => console.dir(event));
  await client.connect((err, client) => {
    if (err) throw err;
  });
  const collection = client.db('foo').collection('bar');
  await collection.createIndex({ baz: 1 });
  process.exit(1);
}
main();