「翌月の同じ日。ただし同じ日が存在しない場合は、それより前の一番近い存在する日」とする派閥（Rails, moment js, PostgreSQL）と
「翌月の同じ日。ただし同じ日が存在しない場合は、余った日数の分、翌月にずれ込む」とする派閥（JS, Go）がある。
| 元の日付 | Rails派 | JS派 |
|---|---|---|
| 2024-01-28 | 2024-02-28 | 2024-02-28 |
| 2024-01-29 | 2024-02-29 | 2024-02-29 |
| 2024-01-30 | 2024-02-29 | 2024-03-01 |
| 2024-01-31 | 2024-02-29 | 2024-03-02 |
| 2024-02-01 | 2024-03-01 | 2024-03-01 |
Rails
irb(main):002> %w[2024-01-28 2024-01-29 2024-01-30 2024-01-31 2024-02-01].each { |d| puts "#{d} -> #{Date.parse(d) + 1.month}" }
2024-01-28 -> 2024-02-28
2024-01-29 -> 2024-02-29
2024-01-30 -> 2024-02-29
2024-01-31 -> 2024-02-29
2024-02-01 -> 2024-03-01
moment
> ["2024-01-28", "2024-01-29", "2024-01-30", "2024-01-31", "2024-02-01"].forEach(d => { console.log(d, "->", moment(d).add(1, "month").format("YYYY-MM-DD")); })
2024-01-28 -> 2024-02-28
2024-01-29 -> 2024-02-29
2024-01-30 -> 2024-02-29
2024-01-31 -> 2024-02-29
2024-02-01 -> 2024-03-01
JS: setMonth(getMonth() + 1)
["2024-01-28", "2024-01-29", "2024-01-30", "2024-01-31", "2024-02-01"].forEach(
d => {
date = new Date(d); date.setMonth(date.getMonth() + 1);
console.log(d, "->", (moment(date).format("YYYY-MM-DD")));
}
);
2024-01-28 -> 2024-02-28
2024-01-29 -> 2024-02-29
2024-01-30 -> 2024-03-01
2024-01-31 -> 2024-03-02
2024-02-01 -> 2024-03-01
Go
package main
import (
"fmt"
"time"
)
func main() {
dates := []string{"2024-01-28", "2024-01-29", "2024-01-30", "2024-01-31", "2024-02-01"}
for _, date := range dates {
added, err := time.Parse("2006-01-02", date)
if err != nil {
panic("time.Parse failed")
}
// 1ヶ月後の日付を計算
oneMonthLater := added.AddDate(0, 1, 0)
fmt.Printf("%s -> %s\n", date, oneMonthLater.Format("2006-01-02"))
}
}
2024-01-28 -> 2024-02-28
2024-01-29 -> 2024-02-29
2024-01-30 -> 2024-03-01
2024-01-31 -> 2024-03-02
2024-02-01 -> 2024-03-01
PostgreSQL
# SELECT '2024-01-28'::date + '1 month'::interval;
---------------------
2024-02-28 00:00:00
# SELECT '2024-01-29'::date + '1 month'::interval;
---------------------
2024-02-29 00:00:00
# SELECT '2024-01-30'::date + '1 month'::interval;
---------------------
2024-02-29 00:00:00
# SELECT '2024-01-31'::date + '1 month'::interval;
---------------------
2024-02-29 00:00:00
# SELECT '2024-02-01'::date + '1 month'::interval;
---------------------
2024-03-01 00:00:00