parse mongodb oplog

oplog.js

const fs = require('fs')

fs.readFile('./oplog.dump', 'utf-8', (err, jsonString) => {
  const oplog = JSON.parse(jsonString)
  const operationsMap = new Map()
  oplog.forEach((oplogItem) => {
    const { ns, op } = oplogItem
    let operation = operationsMap.get(ns)
    if (operation) {
      if (op === 'd') {
        operation.delete += 1
      }
      if (op === 'i') {
        operation.insert += 1
      }
      if (op === 'u') {
        operation.update += 1
      }
      operation.total += 1
    } else {
      operation = {
        collection: ns,
        delete: (op === 'd') ? 1 : 0,
        insert: (op === 'i') ? 1 : 0,
        update: (op === 'u') ? 1 : 0,
        total: 1
      }
    }
    operationsMap.set(ns, operation)
  })
  const operations = [...operationsMap.values()]
  operations.sort((a, b) => b.total - a.total)
  const operationsJsonString = JSON.stringify(operations)
  fs.writeFile('./operations.json', operationsJsonString, (err) => {
    if (err) {
      console.log('Fail')
    } else {
      console.log('Done')
    }
  })
})

mongoexport -h dbhost -d local -c oplog.rs -u adminuser -p password -o oplog.dump --authenticationDatabase=admin