json-to-csv example for https://www.reddit.com/r/node/comments/iapf5u/fastest_csvformatter_library/

eg.jsonstream

{ "one": "hello", "two": "venus", "three": "help", "four": "I'm stuck here" }
{ "one": "hello", "two": "mercury", "three": "help", "four": "I'm stuck here" }
{ "one": "hello", "two": "earth", "three": "help", "four": "I'm stuck here" }
{ "one": "hello", "two": "mars", "three": "help", "four": "I'm stuck here" }

json-to-csv.js

// usage: node json-to-csv.js < input > output.csv
// example: node json-to-csv.js < eg.jsonstream

var pump = require('pump')
var split = require('split')
var through = require('through2')

var keys = ['one', 'two', 'four']

console.log(keys.join(','))

pump(
  process.stdin,
  split(JSON.parse, null, { trailing: false }),
  through.obj(csvify),
  process.stdout,
  done
)

var n = 0

function arrayToCSV (d) { return d.map(v => `"${v}"`).join(',') + "\n" }

function csvify (data, enc, next) {
  var csvline = arrayToCSV(keys.map(k => data[k]))
  this.push(csvline)
  n += 1
  next()
}

function done (err) {
  if (err) throw err
  console.error(`converted ${n} JSON objects to CSV`)
}