// the code is below:
const db = require('mongodb').MongoClient.connect('mongodb://localhost:27017/test?connectTimeoutMS=999999999&socketTimeoutMS=99999999').then(col => col.collection('testCollection'))
const startTime = Date.now()
insert(5000)

function insert(n, i = 0) {
  if (i === n) {
    console.log('All done', Date.now() - startTime)
    return undefined
  }

  const values = []
  for (let j = -1; ++j < 2000;) {
    values.push({
      _id: i * 2000 + j,
      t: (Math.random() * 1e17).toString(36), // random text
      r: ~~(Math.random() * 1e17) // random number
    })
  }

  return db.then(col => col.insertMany(values))
    .then(() => {
      if (i % 500 === 0) console.log(i)
      return add(n, i + 1) // recursive
    })
}