Countdown minutes and write them to a file, useful for OBS or other programs that want to read files.

countdown.js

let fs = require("fs");

let [, , time] = process.argv;

if (!time) throw new Error("Define a countdown in minutes");

let minutes = Number(time);

if (!minutes || minutes <= 0)
  throw new Error(`${time} parsed as ${minutes} which is not a valid time");`);

let timeRemaining = minutes * 60 * 1000;
let lastUpdate = Date.now();

let interval = setInterval(() => {
  let now = Date.now();
  let dt = now - lastUpdate;
  lastUpdate = now;

  timeRemaining = timeRemaining - dt;
  let minutes = Math.floor(timeRemaining / 1000 / 60);
  let seconds = Math.floor(timeRemaining / 1000) % 60;

  let timeStr =
    String(minutes).padStart(2, "0") + ":" + String(seconds).padStart(2, "0");

  fs.writeFileSync("./countdown.txt", timeStr);

  if (minutes === 0 && seconds === 0) {
    clearInterval(interval);
  }
}, 1000);