The Temporal.PlainYearMonth.from() static method creates a new Temporal.PlainYearMonth object from another Temporal.PlainYearMonth object, an object with year and month properties, or an RFC 9557 string.

Syntax

Temporal.PlainYearMonth.from(info)
Temporal.PlainYearMonth.from(info, options)

Parameters

info

One of the following:

• A Temporal.PlainYearMonth instance, which creates a copy of the instance.
• An RFC 9557 string containing a date and optionally a calendar. If the calendar is not iso8601, a day is required.
• An object containing the following properties (in the order they are retrieved and validated):

  calendar Optional

  A string that corresponds to the calendarId property. See Intl.supportedValuesOf() for a list of commonly supported calendar types. Defaults to "iso8601". All other properties are interpreted in this calendar system (unlike the Temporal.PlainYearMonth() constructor, which interprets the values in the ISO calendar system).

  era and eraYear

  A string and an integer that correspond to the era and eraYear properties. Are only used if the calendar system has eras. era and eraYear must be provided simultaneously. If they are not provided, then year must be provided. If all of era, eraYear, and year are provided, they must be consistent.

  month

  Corresponds to the month property. Must be positive regardless of the overflow option.

  monthCode

  Corresponds to the monthCode property. If it is not provided, then month must be provided. If both month and monthCode are provided, they must be consistent.

  year

  Corresponds to the year property.

options Optional

An object containing the following property:

overflow Optional

A string specifying the behavior when a date component is out of range (when using the object info). Possible values are:

"constrain" (default)

The date component is clamped to the valid range.

"reject"

A RangeError is thrown if the date component is out of range.

Return value

A new Temporal.PlainYearMonth object, representing the year and month specified by info in the specified calendar.

Each PlainYearMonth stores a whole ISO 8601 date internally, which has the same year-month in the target calendar as what's exposed. The reference day is visible when stringifying with toString(), which outputs an ISO date. The reference day is chosen arbitrarily but consistently; that is, every (year, month) pair always maps to the same ISO reference day. It does not use the day provided in the input. Instead, the reference day is always chosen to be the first valid day of the month.

This reference day canonicalization ensures that equals() can directly compare the underlying ISO dates without extra computation.

Exceptions

TypeError

Thrown in one of the following cases:

• info is not an object or a string.
• options is not an object or undefined.
• The provided properties are insufficient to unambiguously determine a date. You usually need to provide a year (or era and eraYear) and a month (or a monthCode).

RangeError

Thrown in one of the following cases:

• The provided properties that specify the same component are inconsistent.
• The provided non-numerical properties are not valid; for example, if monthCode is never a valid month code in this calendar.
• The provided numerical properties are out of range, and options.overflow is set to "reject".
• The info is not in the representable range, which is ±(10⁸ + 1) days, or about ±273,972.6 years, from the Unix epoch.

Examples

Creating a PlainYearMonth from an object

// Year + month code
const ym = Temporal.PlainYearMonth.from({ year: 2021, monthCode: "M05" });
console.log(ym.toString()); // 2021-05

// Year + month
const ym2 = Temporal.PlainYearMonth.from({ year: 2021, month: 7 });
console.log(ym2.toString()); // 2021-07

// Year + month in a different calendar
const ym3 = Temporal.PlainYearMonth.from({
  year: 5730,
  month: 6,
  calendar: "hebrew",
});
console.log(ym3.toString()); // 1970-02-07[u-ca=hebrew]

// Year + month code in a different calendar
const ym4 = Temporal.PlainYearMonth.from({
  year: 5730,
  monthCode: "M05L",
  calendar: "hebrew",
});
console.log(ym4.toString()); // 1970-02-07[u-ca=hebrew]

Controlling overflow behavior

By default, out-of-range values are clamped to the valid range.

const ym1 = Temporal.PlainYearMonth.from({ year: 2021, month: 13 });
console.log(ym1.toString()); // 2021-12

// 5732 is not a Hebrew leap year, so a different monthCode is chosen
const ym2 = Temporal.PlainYearMonth.from({
  year: 5732,
  monthCode: "M05L",
  calendar: "hebrew",
});
console.log(ym2.toLocaleString("en-US", { calendar: "hebrew" })); // Adar 5732
const underlyingDate = Temporal.PlainDate.from(ym2.toString());
console.log(underlyingDate.year, underlyingDate.monthCode); // 5732 M06

You can change this behavior to throw an error instead:

Temporal.PlainYearMonth.from({ year: 2021, month: 13 }, { overflow: "reject" });
// RangeError: date value "month" not in 1..12: 13

Specifications

Browser compatibility

See also

• Temporal.PlainYearMonth
• Temporal.PlainYearMonth()
• Temporal.PlainYearMonth.prototype.with()