js 获取时间段近一周、近一月、近三月、近半年、近一年

项目新需求获取当前时间前一周、一月、三月、六月、一年的时间段：

获取近一周时间段

// 获取近一周时间
export function getLastWeek() {
  var now = new Date()
  var year = now.getFullYear()
  var month = now.getMonth()   1 //0-11表示1-12月
  var day = now.getDate()
  var dateObj = {}

  dateObj.endTime = year   "-"   month   "-"   day
  if (day - 7 <= 0) {
    //如果在当月7日之前
    var endTimeMonthDay = new Date(year, parseInt(month) - 1, 0).getDate() //1周前所在月的总天数
    if (month - 1 <= 0) {
      //如果在当年的1月份
      dateObj.startTime = year - 1   "-"   12   "-"   (31 - (7 - day))
    } else {
      dateObj.startTime = year   "-"   (month - 1)   "-"   (endTimeMonthDay - (7 - day))
    }
  } else {
    dateObj.startTime = year   "-"   month   "-"   (day - 7)
  }
  return dateObj
}

打印发现获取一周前是时间加上今天天数多了一天，重新写了一个

/**
 * 获取近多少天时间
 * @returns
 */
export function getNumDaysAgo(n) {
  let num = n - 1  // 天数需要包含今天
  var now = new Date()
  var year = now.getFullYear()
  var month = now.getMonth()   1
  var day = now.getDate()
  var dateObj = {}

  if (day - num <= 0) {
    //如果在当月num日之前
    var endTimeMonthDay = new Date(year, parseInt(month) - 1, 0).getDate() //1周前所在月的总天数
    if (month - 1 <= 0) {
      //如果在当年的1月份
      dateObj.startTime = year - 1   "-"   12   "-"   (31 - (num - day))
    } else {
      dateObj.startTime = year   "-"   (month - 1)   "-"   (endTimeMonthDay - (num - day))
    }
  } else {
    dateObj.startTime = year   "-"   month   "-"   (day - num)
  }

  dateObj.endTime = year   "-"   month   "-"   day

  return dateObj
}

获取前几个月时间段

传参为0时获取当天

// 获取近i月的时间段
export function getLastMonth(i) {
  console.log("获取近i月的时间段", i)
  var now = new Date()
  var year = now.getFullYear()
  var month = now.getMonth()   1
  var day = now.getDate()
  var dateObj = {}
  dateObj.endTime = year   "-"   month   "-"   day
  var nowMonthDay = new Date(year, month, 0).getDate() //当前月的总天数
  if (i == 12) {
    //如果是12月，年数往前推一年<br>
    dateObj.startTime = year - 1   "-"   month   "-"   day
  } else if (month - i <= 0) {
    // 如果前推i月小于0，年数往前推一年<br>
    dateObj.startTime = year - 1   "-"   12   "-"   day
  } else {
    var endTimeMonthDay = new Date(year, parseInt(month) - i, 0).getDate()
    if (endTimeMonthDay < day) {
      // i个月前所在月的总天数小于现在的天日期
      if (day < nowMonthDay) {
        // 当前天日期小于当前月总天数
        dateObj.startTime = year   "-"   (month - i)   "-"   (endTimeMonthDay - (nowMonthDay - day))
      } else {
        dateObj.startTime = year   "-"   (month - i)   "-"   endTimeMonthDay
      }
    } else {
      dateObj.startTime = year   "-"   (month - i)   "-"   day
    }
  }
  return dateObj
}

/**
 * get当月第一天
 * @param {Date} date
 * @returns {String} 当月第一天
 */
export function getFirstDay(date) {
  const time = date ? new Date(date) : new Date()
  const y = time.getFullYear()
  let m = time.getMonth()   1
  const d = "01"
  m = m < 10 ? "0"   m : m
  return [y, m, d].join("-")
}
/**
 * get当月最后一天
 * @param {Date} date
 * @returns {String} 当月最后一天
 */
export function getLastDay(date) {
  const time = date ? new Date(date) : new Date()
  const y = time.getFullYear()
  let m = time.getMonth()   1
  let d = new Date(y, m, 0).getDate()
  m = m < 10 ? "0"   m : m
  d = d < 10 ? "0"   d : d

  return [y, m, d].join("-")
}

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