Convert CSV line by line into JSON using streams in ES6.

csv2json.js

import fs from 'fs'
import readline from 'readline'

let headers = []
let lines = 0

const rl = readline.createInterface({
  input: fs.createReadStream('input.csv'),
  output: fs.createWriteStream('output.json')
})

rl.on('line', (l) => {
  let line = l.split(',')
  let template = `{"${headers[0]}":"${line[0]}","${headers[1]}":"${line[1]}","${headers[2]}":"${line[2]}"}`
  let json = ''

  if (lines === 0) {
    headers = line
  } else if (lines === 1) {
    json += '[\n  '
    json += template
  } else {
    json += ',\n  '
    json += template
  }

  rl.output.write(json)

  lines++
})

rl.on('close', (l) => {
  rl.output.write('\n]')
})

input.csv