JS 时间获取 (常用)

　　最近在写的项目对日期获取的方法种类用的比较多，于是在此进行录入下来。如果一下代码有错误或者有bug还请路过的大神指点指点，这些方法对你们有帮助请给个支持，有其他的好方法也请留言哦。

/**
 *  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
  }