const rtf = new Intl.RelativeTimeFormat('en', { numeric: 'auto' });
const DIVISIONS = [
  [60, 'second'], [60, 'minute'], [24, 'hour'],
  [7, 'day'], [4.34524, 'week'], [12, 'month'],
];

function ago(date) {
  let duration = (date - Date.now()) / 1000;
  for (const [amount, unit] of DIVISIONS) {
    if (Math.abs(duration) < amount) return rtf.format(Math.round(duration), unit);
    duration /= amount;
  }
  return rtf.format(Math.round(duration), 'year');
}