Temporal.PlainYearMonth.compare()
Limited availability
This feature is not Baseline because it does not work in some of the most widely-used browsers.
The Temporal.PlainYearMonth.compare() static method returns a number (-1, 0, or 1) indicating whether the first year-month comes before, is the same as, or comes after the second year-month. It is equivalent to comparing their underlying ISO 8601 dates. Two year-months from different calendars may be considered equal if they start on the same ISO date.
Note:
PlainYearMonth objects keep track of a reference ISO day, which is also used in the comparison. This day is automatically set when using the Temporal.PlainYearMonth.from() method, but can be set manually using the Temporal.PlainYearMonth() constructor, causing two equivalent year-months to be considered different if they have different reference days. For this reason, you should avoid using the constructor directly and prefer the from() method.
Syntax
Temporal.PlainYearMonth.compare(yearMonth1, yearMonth2)
Parameters
yearMonth1-
A string, an object, or a
Temporal.PlainYearMonthinstance representing the first year-month to compare. It is converted to aTemporal.PlainYearMonthobject using the same algorithm asTemporal.PlainYearMonth.from(). yearMonth2-
The second year-month to compare, converted to a
Temporal.PlainYearMonthobject using the same algorithm asyearMonth1.
Return value
Returns -1 if yearMonth1 comes before yearMonth2, 0 if they are the same, and 1 if yearMonth1 comes after yearMonth2. They are compared by their underlying date values (usually the first day of the month), ignoring their calendars.
Examples
Using Temporal.PlainYearMonth.compare()
const ym1 = Temporal.PlainYearMonth.from("2021-08");
const ym2 = Temporal.PlainYearMonth.from("2021-09");
console.log(Temporal.PlainYearMonth.compare(ym1, ym2)); // -1
const ym3 = Temporal.PlainYearMonth.from("2021-07");
console.log(Temporal.PlainYearMonth.compare(ym1, ym3)); // 1
Comparing year-months in different calendars
const ym1 = Temporal.PlainYearMonth.from({ year: 2021, month: 8 });
const ym2 = Temporal.PlainYearMonth.from({
year: 2021,
month: 8,
calendar: "islamic-umalqura",
});
const ym3 = Temporal.PlainYearMonth.from({
year: 2021,
month: 8,
calendar: "hebrew",
});
console.log(ym1.toString()); // "2021-08"
console.log(ym2.toString()); // "2582-12-17[u-ca=islamic-umalqura]"
console.log(ym3.toString()); // "-001739-04-06[u-ca=hebrew]"
console.log(Temporal.PlainYearMonth.compare(ym1, ym2)); // -1
console.log(Temporal.PlainYearMonth.compare(ym1, ym3)); // 1
Sorting an array of year-months
The purpose of this compare() function is to act as a comparator to be passed to Array.prototype.sort() and related functions.
const months = [
Temporal.PlainYearMonth.from({ year: 2021, month: 8 }),
Temporal.PlainYearMonth.from({
year: 2021,
month: 8,
calendar: "islamic-umalqura",
}),
Temporal.PlainYearMonth.from({ year: 2021, month: 8, calendar: "hebrew" }),
];
months.sort(Temporal.PlainYearMonth.compare);
console.log(months.map((d) => d.toString()));
// [ "-001739-04-06[u-ca=hebrew]", "2021-08", "2582-12-17[u-ca=islamic-umalqura]" ]
Specifications
| Specification |
|---|
| Temporal # sec-temporal.plainyearmonth.compare |
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- See implementation notes.