Encode an iso8601 duration in Javascript

iso8601_duration.js

/**
 * Utility function to convert seconds to an iso8601 duration string.
 *
 * @param seconds int The number of seconds to encode.
 * @return string iso8601 formatted duration
 */
 
const iso8601Duration = (seconds = 0) => {
  let _seconds = seconds;

  const days = Math.floor(_seconds / 86400);
  _seconds %= 86400;

  const hours = Math.floor(_seconds / 3600);
  _seconds %= 3600;

  const minutes = Math.floor(_seconds / 60);
  _seconds %= 60;

  return `P${days}DT${hours}H${minutes}M${_seconds}S`;
};