JavaScript Temporal PlainYearMonth
Temporal.PlainYearMonth Object Reference
The Temporal.PlainYearMonth object is a year and month object.
It represents the year and month of an ISO 8601 calendar (without a day).
Example: 2025-05.
Example
// Create a PlainYearMonth object
const date = Temporal.PlainYearMonth.from("2026-05");
Try it Yourself »
New to JavaScript Temporal Dates?
Temporal.PlainYearMonth Methods
Revised March 2026
| Constructing | Description |
|---|---|
| from() | Creates a PlainYearMonth object from an object or a string |
| new (constructor) | Creates a PlainYearMonth object from integer parameters |
| Arithmetic | |
| add() | Returns a new PlainYearMonth with a duration added |
| subtract() | Returns a new PlainYearMonth with a duration subtracted |
| Comparing | |
| compare() | Returns -1, 0, or 1 from comparing two dates |
| equals() | Returns true if two dates are identical |
| since() | Returns the difference since another date |
| until() | Returns the difference until another date |
| Converting | |
| toPlainDate() | Returns a new PlainDate object |
| with() | Returns a new PlainYearMonth with fields modified |
| Formatting | |
| toJSON() | Returns an RFC 9557 format string for JSON serialization |
| toLocaleString() | Returns a language-sensitive representation of the date |
| toString() | Returns an RFC 9557 format string representation |
| valueOf() | TypeError (temporals cannot be converted to primitives) |
Temporal.PlainYearMonth Properties
| Property | Description |
|---|---|
| calendarId | Calendar system identifier ("iso8601") |
| daysInMonth | The total number of days in that month |
| daysInYear | The total number of days in that year |
| era | The era name of the calendar, if applicable |
| eraYear | The year within the era, if applicable |
| inLeapYear | A boolean indicating if the date falls in a leap year |
| month | The month as an integer (1-12) |
| monthCode | A calendar-specific string code for the month ("M01") |
| monthsInYear | The total number of months in that year |
| year | The year as an integer |
Display all PlainYearMonth Properties
const date = new Temporal.PlainYearMonth(2026, 5);
Try it Yourself »
Browser Support
Temporal is a major update to the JavaScript standard (TC39).
It is currently supported in Chrome, Edge, Firefox, and Opera Safari has not shipped it yet.
| Chrome 144 |
Edge 144 |
Firefox 139 |
Safari |
Opera 128 |
| Jan 2026 | Jan 2026 | May 2025 | 🚫 | Feb 2026 |
The Safari implementation can be tested in Safari Technology Preview by enabling the --use-temporal runtime flag.
Polyfill
Until Safari supports Temporal natively, you can use the official polyfill:
<script
src="https://cdn.jsdelivr.net/npm/@js-temporal/polyfill@0.5.1/dist/index.umd.js">
</script>
