txt-to-json-parser.js

///////////////////////////////////////////////////////
// $ node txt-to-json-parser.js [file_you_want_to_parse]
///////////////////////////////////////////////////////
var fs = require('fs');

var arr = []
var file_name = process.argv[2];

var stream = fs.createReadStream(file_name + '.txt', { flags: 'r+', encoding: 'utf-8' });
var buf = '';

stream.on('data', function(d) {
  buf += d.toString(); // when data is read, stash it in a string buffer
  pump(); // then process the buffer
});

function pump() {
  var pos;

  while ((pos = buf.indexOf('\n')) >= 0) { // keep going while there's a newline somewhere in the buffer
    if (pos == 0) { // if there's more than one newline in a row, the buffer will now start with a newline
      buf = buf.slice(1); // discard it
      continue; // so that the next iteration will start with data
    }
    processLine(buf.slice(0, pos)); // hand off the line
    buf = buf.slice(pos + 1); // and slice the processed data off the buffer
  }
}

function processLine(line) { // here's where we do something with a line
  var data = line.split(',');
  var obj = {};
  obj["key"] = data[0]
  arr.push(obj);
  if (arr.length == 499999) { // file upto 500k lines
    write(file_name+'.json', JSON.stringify(arr, null, 4))
  }
}

function write(path, data) {
  fs.writeFile(path, data, function(err) {
    if (err) return console.log(err);
    console.log('File Written > ' + file_name + '.json');
  });
}