JavaScript – Convert a timestamp to a string "X days X hours X minutes X seconds X milliseconds". Useful to show elapsed time since [event]

timestamp-to-string.js

function timestampToString(timestamp, useMilliseconds) {
  const periods = {
    day: 86400000,
    hour: 3600000,
    minute: 60000,
    second: 1000,
    millisecond: 1,
  };

  if (!useMilliseconds) {
    timestamp *= 1000;
    delete periods.millisecond;
  }

  return Object.entries(periods)
    .reduce((result, [period, value]) => {
      const num = Math.floor(timestamp / value);
      const plural = num === 1 ? '' : 's';
      const str = `${num} ${period}${plural} `;

      timestamp -= num * value;

      return `${result}${num === 0 ? '' : str}`;
    }, '')
    .trim();
}

Outputs:

timestampToString(1);             // 1 second
timestampToString(1, true);       // 1 millisecond

timestampToString(1001);          // 16 minutes 41 seconds
timestampToString(1001, true);    // 1 second 1 millisecond

timestampToString(1492471);       // 17 days 6 hours 34 minutes 31 seconds
timestampToString(1492471, true); // 24 minutes 52 seconds 471 milliseconds