dayjs:JavaScriptライブラリの日付

import dayjs from 'dayjs';

static formatTime (dateNumber?: number | Date | string): string {
    if (!dateNumber) {
      return '';
    }
    const now = Date.now();
    const timer = dateNumber ? +dayjs(dateNumber) : now;
    const date = new Date(timer);
    const interval = Math.floor((now - timer) / 1000);//  
    const current = new Date();
    if (interval < 60) {
      return '  ';
    } else if (interval < 3600) {
      return `${Math.floor(interval / 60)}   `;
    } else if (interval < 86400) {
      return `${Math.floor(interval / 3600)}   `;
    } else if (interval < 3 * 86400) {
      return `${Math.floor(interval / 86400)}  `;
    } else if (current.getFullYear() === date.getFullYear()) {
      return dayjs(date).format('MM-DD');
    } else {
      return dayjs(date).format('YYYY-MM-DD');
    }
  }