Temporal.PlainDate.prototype.daysInMonth

The daysInMonth accessor property of {{jsxref("Temporal.PlainDate")}} instances returns a positive integer representing the number of days in the month of this date. It is calendar-dependent.

Note that the days in month is not always equal to the {{jsxref("Temporal/PlainDate/day", "day")}} of the last day of the month, in the rare case where a month may have a few days skipped.

The set accessor of daysInMonth is undefined. You cannot change this property directly.

Examples#

Using daysInMonth#

const date = Temporal.PlainDate.from("2021-07-01");
console.log(date.daysInMonth); // 31

const date2 = Temporal.PlainDate.from("2021-02-01");
console.log(date2.daysInMonth); // 28; 2021 is not a leap year

const date3 = Temporal.PlainDate.from("2020-02-01");
console.log(date3.daysInMonth); // 29; 2020 is a leap year

const date4 = Temporal.PlainDate.from("2021-04-01[u-ca=chinese]");
console.log(date4.month); // 2
console.log(date4.daysInMonth); // 30; the Chinese 2nd month has 30 days

Changing to the second last day of the month#

You can use daysInMonth to change to the second last day of the month:

const date = Temporal.PlainDate.from("2021-07-01");
const secondLastDay = date.with({ day: date.daysInMonth - 1 });
console.log(secondLastDay.toString()); // 2021-07-30

This is not totally safe, though, because daysInMonth is not guaranteed to have any connection with the day index. Here's a safer way to get the second last day:

const date = Temporal.PlainDate.from("2021-07-01");
const secondLastDay = date
  .with({ day: Number.MAX_SAFE_INTEGER })
  .subtract({ days: 1 });
console.log(secondLastDay.toString()); // 2021-07-30

Specifications#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• {{jsxref("Temporal.PlainDate")}}
• {{jsxref("Temporal/PlainDate/with", "Temporal.PlainDate.prototype.with()")}}
• {{jsxref("Temporal/PlainDate/add", "Temporal.PlainDate.prototype.add()")}}
• {{jsxref("Temporal/PlainDate/subtract", "Temporal.PlainDate.prototype.subtract()")}}
• {{jsxref("Temporal/PlainDate/year", "Temporal.PlainDate.prototype.year")}}
• {{jsxref("Temporal/PlainDate/month", "Temporal.PlainDate.prototype.month")}}
• {{jsxref("Temporal/PlainDate/day", "Temporal.PlainDate.prototype.day")}}
• {{jsxref("Temporal/PlainDate/daysInWeek", "Temporal.PlainDate.prototype.daysInWeek")}}
• {{jsxref("Temporal/PlainDate/daysInYear", "Temporal.PlainDate.prototype.daysInYear")}}