Read from json input file and output to another file as csv.

jsontocsv.js

/**
 * Module dependencies.
 */

var readline = require('readline');
var stream = require('stream');
var fs = require('fs');

/**
 * Get file, read arguments from command line.
 */

function main() {
  var input = process.argv.slice(2);
  var output = process.argv.slice(3);
  if (input.length === 0 || output.length === 0)
    throw 'Try node /path/to/input/file.json /path/to/output/file.csv';
  jsonfileToCsv(input, output);
}

/**
 * Takes JSON string and writes it to CSV file.
 *
 * @param {String} input
 * @param {String} output
 */

function jsonfileToCsv(input, output) {
  var readStream = fs.createReadStream(input);
  var writeStream = new stream;
  var rl = readline.createInterface(readStream, writeStream);

  rl.on('line', function(line) {
    var object = JSON.parse(line);
    var csv = objToCsv(object).slice(0, -1) + '\n';
    fs.appendFile(output, csv, function (err) {
      if (err) console.log(err);
    });
  });

  rl.on('close', function() {
    console.log('Reached eof');
    process.exit(0);
  });
}

/**
 * Takes a Javascript Object and turns it into a csv line.
 *
 * @param {Object} obj
 *
 * @return {String}
 */

function objToCsv(obj) {
  if (obj === null) return 'null,';
  if (Object.keys(obj).length === 0) return ',';
  var csv = '';
  for (var prop in obj) {
    if (obj.hasOwnProperty(prop)) {
      if (typeof obj[prop] === 'object')
        csv += objToCsv(obj[prop]);
      else
        csv += obj[prop] + ',';
    }
  }
  return csv;
}

/**
 * Start.
 */

main();