MongoDB cursor slow train

slowtrain.js

const mongodb = require('mongodb')

run().catch(error => console.log(error));

async function run() {
  const db = await mongodb.MongoClient.
    connect('mongodb://localhost:27017/test', {
      useNewUrlParser: true,
      poolSize: 1 // Only 1 operation can run at a time
    }).
    then(client => client.db());

  await db.dropDatabase();

  await db.collection('Test').insertMany([{ test: 1 }, { test: 2 }]);

  const cursor = db.collection('Test').find({ $where: 'sleep(1000) || true' });
  // If you uncomment the below line, the `findOne()` query will take about 1000ms,
  // instead of 2000ms
  // cursor.batchSize(1);
  cursor.next();

  const startTime = Date.now();
  await db.collection('Test').findOne();

  // "Executed query in 2013 ms"
  console.log('Executed query in', Date.now() - startTime, 'ms');
}