Calendar dates with Temporal.PlainDate
Represent a calendar date without a time or time zone. Temporal.PlainDate is useful for values such as an all-day event date or a birthday.
if (typeof Temporal === 'undefined') {
console.info('This browser needs a Temporal polyfill.');
} else {
const date = Temporal.PlainDate.from('2026-12-31');
const nextDay = date.add({ days: 1 });
console.log(nextDay.toString()); // 2027-01-01
console.log(date.toString()); // 2026-12-31 (unchanged)
const january = Temporal.PlainDate.from('2026-01-31');
console.log(january.add({ months: 1 }).toString()); // 2026-02-28
} Arithmetic returns a new object rather than mutating the original. With the default constrain overflow policy, adding a month to January 31 gives the last valid day of February.
A plain date is not a timestamp or a moment on the global timeline. Use Temporal.Instant for an instant, or Temporal.ZonedDateTime when time-zone-aware date and time behavior is needed.
Temporal has limited stable-browser support. Detect it before use and provide a polyfill or another deliberate fallback in an application. The guard here only reports its absence; it does not implement the missing API.