给出年月值，获取月末和月初值

 var date = this.filters.month;
      if (!date) {
        this.$message({
          type: "info",
          message: "请选择日期"
        });
        return;
      }
      date = new Date(date);
      var startDate = "",
        endDate = "";
      startDate =
        date.getFullYear() +
        "-" +
        (date.getMonth() + 1) +
        "-" +
        "01" +
        " " +
        "00:00:00";
      if (date.getMonth() == 11) {
        return {
          startDate: startDate,
          endDate:
            date.getFullYear() +
            "-" +
            (date.getMonth() + 1) +
            "-" +
            "31" +
            " " +
            "23:59:59"
        };
      }
      var currentMonth = date.getMonth() + 1;
      var nextMonth = ++currentMonth;
      var nextMonthFirstDay = new Date(date.getFullYear(), nextMonth, 1);
      var oneDay = 1000 * 60 * 60 * 24;
      var dates = new Date(nextMonthFirstDay - oneDay);
      var day = "";

      switch (dates.getMonth()) {
        case 1:
        case 3:
        case 5:
        case 7:
        case 8:
        case 10:
        case 12:
          day = "31";
          break;
        case 2:
          if (dates.getFullYear % 4 == 0) {
            day = "29";
          } else {
            day = "28";
          }
          break;
        case 4:
        case 6:
        case 9:
        case 11:
          day = "30";
          break;
      }
      endDate =
        dates.getFullYear() + "-" + dates.getMonth() + "-" + day + " 23:59:59";

月初很简单，直接给，月末的话就需要计算一下了，然后还要判断当前月是几月，从而日期给予确定