不管是設定相對當前時間有多久時間差的時間，統一思路為：先獲取當前時間的時間戳，再根據需求加減時間獲得新的時間戳，然後取年月日與時分秒。例項如下：

  // 設定預設時間——先轉化為毫秒數，加上 20 分鐘的毫秒數，再轉化回來
  setDefaultTime() {
    let t = new Date().getTime() + 1200000;
    let d = new Date(t);
    let theMonth = d.getMonth() + 1;
    let theDate = d.getDate();
    let theHours = d.getHours();
    let theMinutes = d.getMinutes();
    if (theMonth < 10) {
      theMonth = '0' + theMonth
    }
    if (theDate < 10) {
      theDate = '0' + theDate
    }
    if (theHours < 10) {
      theHours = '0' + theHours
    }
    if (theMinutes < 10) {
      theMinutes = '0' + theMinutes
    }
    let date = d.getFullYear() + '-' + theMonth + '-' + theDate
    let time = theHours + ':' + theMinutes
    let Spare = date + ' ' + time
    console.log(date)
    console.log(time)
    console.log(Spare)
  },