Relative dates using date-fns

relativeDatesHelper.js

// Convert a date to "8 month ago", "1 day ago", "15 minutes ago"
// Note: We don't display this if it's older than 2 months ago (i.e. doc seems way stale)

// @flow
import {
  formatDistanceToNow,
} from 'date-fns';

export function howLongUntil(upstreamUpdatedAt: number) {
  const ageInWords = formatDistanceToNow(
    new Date(upstreamUpdatedAt * 1000),
    { addSuffix: true },
  );
  // date-fns gives "about 7 days ago", we just want "7 days ago"
  return ageInWords.replace(/about\s/g, '');
}

function howItsUsed() {
  const fullMonthsOld = differenceInMonths(new Date(), upstreamUpdatedAtDate);

  // Don't display this string for docs more than 8 weeks old
  if (fullMonthsOld >= 2) return null;

  return `Updated ${howLongUntil(upstreamUpdatedAt)}`;
}