An example of using object steams in Node

streams.js

const fetch = require('node-fetch')
const { Transform, PassThrough } = require('stream')

// giving the starting point a meaningful name
const processRates = new PassThrough({
  writableObjectMode: true,
  readableObjectMode: true
})

const promiseResolve = new Transform({
  writableObjectMode: true,
  readableObjectMode: true,
  transform (promise, encoding, callback) {
    promise.then(x => callback(null, x)).catch(callback)
  }
})

const gbpRate = new Transform({
  writableObjectMode: true,
  readableObjectMode: true,
  transform (json, encoding, callback) {
    callback(null, json.rates.GBP)
  }
})

const format = new Transform({
  writableObjectMode: true,
  transform (rate, encoding, callback) {
    callback(null, rate.toString() + '\n')
  }
})

processRates
  .pipe(promiseResolve)
  .pipe(gbpRate)
  .pipe(format)
  .pipe(process.stdout)

for (let i = 1; i < 10; i++) {
  fetch(`http://api.fixer.io/2000-01-0${i}`)
    .then(processRates.write.bind(processRates))
}