JS 时间获取 (常用)

 /**
  *  获取几天之前日期
  */
  daysAgo(dayNum = 0) {
     let myDate = new Date()
     let lw = new Date(myDate - 1000 * 60 * 60 * 24 * dayNum) // 最后一个数字多少天前的意思
     let lastY = lw.getFullYear()
     let lastM = lw.getMonth() + 1
     let lastD = lw.getDate()
     let startdate = lastY + "-" + (lastM < 10 ? "0" + lastM : lastM) + "-" + (lastD < 10 ? "0" + lastD : lastD)
     return startdate
 }

 /**
  *  获取几个月之前日期
  */
  monthAgo(monthNum = 0) {
     let newDate = new Date();
     let year = newDate.getFullYear(); //获取当前日期的年份
     let month = newDate.getMonth() + 1; //获取当前日期的月份
     let day = newDate.getDate(); //获取当前日期的日
     let days = new Date(year, month, 0)
     days = days.getDate() //获取当前日期中月的天数
     let year2 = year

     // 进行月份计算
     let month2 = parseInt(month) - monthNum
     if (month2 <= 0) {
         year2 = parseInt(year2) - parseInt(month2 / 12 == 0 ? 1 : Math.abs(parseInt(month2 / 12)) + 1)
         month2 = 12 - (Math.abs(month2) % 12)
     }

     // 进行日期计算
     let day2 = day
     let days2 = new Date(year2, month2, 0)
     days2 = days2.getDate()
     if (day2 > days2) {
         day2 = days2
     }

     let startdate = year2 + "-" + (month2 < 10 ? "0" + month2 : month2) + "-" + (day2 < 10 ? "0" + day2 : day2)
     return startdate
 }

 /**
  *  获取几年之前日期
  */
  yearAgo(yearNum = 0) {
     let newDate = new Date();
     let year = newDate.getFullYear(); //获取当前日期的年份
     let month = newDate.getMonth() + 1; //获取当前日期的月份
     let day = newDate.getDate(); //获取当前日期的日

     let year2 = year - yearNum;

     let startdate = year2 + "-" + (month < 10 ? "0" + month : month) + "-" + (day < 10 ? "0" + day : day)
     return startdate
 }

   /**
    *  根据日期获取上一个月
    */
   preMonth(data) {
     let curMonth = new Date(data)
     let month = curMonth.getMonth() - 1;
     curMonth.setMonth(month);
     let newMonth = curMonth.getMonth() + 1;
     if (newMonth < 10) {
       newMonth = "0" + newMonth;
     }
     return curMonth.getFullYear() + '-' + newMonth;
   }

   /**
    *  获取当前年月(yyyy-MM)
    */
   theCurrentMonth() {
     let date = new Date();
     let nowMonth = date.getMonth() + 1;
     if (nowMonth >= 1 && nowMonth <= 9) {
       nowMonth = "0" + nowMonth;
     }
     let nowDate = date.getFullYear() + '-' + nowMonth;
     return nowDate
   }

   /**
    *  获取上个月第一天
    */
   firstdate() {
     let date = new Date();
     let nowMonth = date.getMonth() + 1;
     if (nowMonth >= 1 && nowMonth <= 9) {
       nowMonth = "0" + nowMonth;
     }
     let nowDate = date.getFullYear() + '-' + nowMonth + '-01';
     return nowDate
   }

  /**
   *  获取上个月最后一天
   */
  enddate() {
    let date = new Date();
    let day = new Date(date.getFullYear(), date.getMonth(), 0).getDate();
    let nowMonth = date.getMonth() + 1;
    if (nowMonth >= 1 && nowMonth <= 9) {
      nowMonth = "0" + nowMonth;
    }
    let nowDate = date.getFullYear() + '-' + nowMonth + '-' + day;

    return nowDate
  }