Simple time formatting without the use of Date (expensive)

timeutils.js

/**
 * @param {Number} time in seconds
 **/
export function secondsToObject(time) {
  const hours = Math.floor(time / 3600);
  const minutes = Math.floor((time - hours * 3600) / 60);
  const seconds = Math.floor(time - minutes * 60);
  return { hours, minutes, seconds };
}

/**
 * @param {Object} timeObject
 **/
export function formatTimeObject(timeObject) {
  return timeObject.minutes.toString().padStart(2, '0') + ':' + timeObject.seconds.toString().padStart(2, '0');
}

/**
 * @param {Number} currentTime in seconds
 * @param {Number | String} duration in seconds or a predefined string (since the duration won't change often)
 * @returns {String}
 **/
export function formatToTimestamps(currentTime, duration) {
  const timeString = formatTimeObject(secondsToObject(currentTime));
  const durationString = typeof duration === 'string' ? duration : formatTimeObject(secondsToObject(duration));
  return timeString + ' / ' + durationString;
}