txt-to-csv.js

const readline = require('readline');
const fs = require('fs');

// CHANGE THESE TO INPUT AND OUTPUT FILES
const FILE_PATH = './11k-german-sentences.txt';
const OUTPUT_PATH = './output.csv';

const rl = readline.createInterface({
  input: fs.createReadStream(FILE_PATH),
});

const output = fs.createWriteStream(OUTPUT_PATH);

let count = 0;
rl.on('line', (line) => {
  output.write(`${++count},${line}\n`);
});