Mongo EventStore with capped collection + throng

MongoCappedEventStore.js

const mongodb = require('mongodb')
const Bluebird = require('bluebird')

class EventStore {
  constructor(dbUrl, collectionName){
    this.db = mongodb.MongoClient.connect(dbUrl);
    this.cappedCollection = this.db.then(db=>
      db.createCollection(collectionName, { capped: true, size: 1024*1024 })
      .then(()=> db.collection(collectionName).createIndex({__t: 1}, {unique: true}))
      .then(()=> db.collection(collectionName))
    )
    this.spy();
  }
  latest() { return this.cappedCollection.then(collection=>collection
    .find().sort({ $natural: -1 })
  ) }
  insert(data) { return this.cappedCollection.then(collection=>collection
    .insert(Object.assign({}, data, {__t: mongodb.Long("0")}))
  ) }
  last__t() { return this.cappedCollection.then(collection=>collection
    .find({__t: {$gt: mongodb.Long("0")}}, {__t: 1})
    .sort({ __t: -1 }).limit(1).toArray()
    .then(docs=>docs.length ? docs[0].__t: 0)
  ) }
  spy() { return this.cappedCollection.then(collection=>collection
      .find({},{ tailable: true, awaitdata: true, numberOfRetries: -1 })
      .stream().on('data', console.log.bind(console))
  ) }
}


module.exports = new EventStore('mongodb://localhost/test', 'EventStore')

const throng = require('throng')

throng(n=>{
  let x = 0;
  while (x++<10) module.exports.insert({worker: n})
})