asynchronously iterate on mongodb records

example.js

const { MongoClient } = require('mongodb')
const MongoSeries = require('./mongo-run-series')

const { host } = process.env // mongodb://localhost:27017/database

const task = (doc, done) => {
  // do something async with the mongodb document
  done(null, {})
}

MongoClient.connect(host, (err, db) => {
  if (err) throw err
  
  const cursor = db.collection('example').find() // some query
  
  MongoSeries(cursor, task, (err, results) => {
    if (err) throw err
    
    // results is an array of results from each document
    console.log(results)
    db.close()
  })
})

mongo-run-series.js

module.exports = (cursor, task, done) => {
  const results = []

  const next = (err, doc) => {
    if (err || !doc) return done(err, results)

    process.nextTick(task, doc, (err, result) => {
      if (err) return done(err)

      results.push(result)
      cursor.nextObject(next)
    })
  }

  cursor.nextObject(next)
}

mongo-each provides a similar process, but does not collect and yield results for each iteration