streams

const fs = require('fs')
// app.js has one line: console.log('this is app.js')
const appReadstream = fs.createReadStream('files/app.js')
// index.js has one line: console.log('this is index.js')
const indexReadstream = fs.createReadStream('files/index.js')
const out1 = fs.createWriteStream('files/outindexfirst.js')
const out2 = fs.createWriteStream('files/outappfirst.js')

indexReadstream.pipe(appReadstream.pipe(out1))
appReadstream.pipe(indexReadstream.pipe(out2))

/* 
both of the out files are identical for me, and look like this:

console.log('this is index.js')
console.log('this is app.js')
*/