duration_readable.js

const DAY = 24 * 60 * 60;
const HOUR = 60 * 60;
const MINUTES = 60;

let ds, hs, ms, ss;

// day
if (duration >= DAY) {
  ds = Math.floor(duration / DAY);
}

// hour
if (duration >= HOUR) {
  hs = Math.floor((duration - ds * DAY) / HOUR);
}

// minutes
if (duration >= MINUTES) {
  ms = Math.floor((duration - ds * DAY - hs * HOUR) / MINUTES);
}

// seconds
ss = duration % 60;

const timeUnits = [ds, hs, ms, ss];

const UNITS = [['day', 'days'], ['hour', 'hours'], ['minute', 'minutes'], ['second', 'seconds']];

const results = [];

for (let i = 0; i < timeUnits.length; i++) {
  if (!timeUnits[i]) {
    continue;
  }
  results.push(`${timeUnits[i]} ${UNITS[i][timeUnits[i] > 1 ? 1 : 0]}`);
}

return results.join(' ');