Displays the time difference in words for a past or future Date object, e.g. 20 seconds left or 5 days ago

timeDisplay.ts

export function renderSeconds(seconds: number, suffix: string): string {
  if (seconds < 0) return `0 seconds ${suffix}`;

  if (seconds < 60) {
    return `${seconds} second${seconds === 1 ? '' : 's'} ${suffix}`;
  }

  const minutes = Math.floor(seconds / 60);
  if (minutes < 60) {
    return `${minutes} minute${minutes === 1 ? '' : 's'} ${suffix}`;
  }

  const hours = Math.floor(minutes / 60);
  if (hours < 24) {
    return `${hours} hour${hours === 1 ? '' : 's'} ${suffix}`;
  }

  const days = Math.floor(hours / 24);
  if (days < 30) {
    return `${days} day${days === 1 ? '' : 's'} ${suffix}`;
  }

  const months = Math.floor(days / 30);
  if (months < 12) {
    return `${months} month${months === 1 ? '' : 's'} ${suffix}`;
  }

  const years = Math.floor(months / 12);
  return `${years} year${years === 1 ? '' : 's'} ${suffix}`;
};

export function timeAgo(date: Date, suffix: string = 'ago'): string {
  const seconds = Math.floor((new Date().getTime() - date.getTime()) / 1000);
  return renderSeconds(seconds, suffix);
};

export function timeTo(date: Date, suffix: string = 'left'): string {
  const seconds = Math.floor((date.getTime() - new Date().getTime()) / 1000);
  return renderSeconds(seconds, suffix);
};

export function timeDiff(date: Date | null): string {
  if (date == null || date.getTime() === 0) {
    return '-';
  }

  if (new Date() > date) {
    return timeAgo(date);
  } else {
    return timeTo(date);
  }
};