The year accessor property of Temporal.PlainYearMonth instances returns an integer representing the number of years of this year-month relative to the start of a calendar-specific epoch year. It is calendar-dependent.
The set accessor of year is undefined. You cannot change this property directly. Use the with() method to create a new Temporal.PlainYearMonth object with the desired new value.
For general information and more examples, see Temporal.PlainDate.prototype.year.
const ym = Temporal.PlainYearMonth.from("2021-07"); // ISO 8601 calendar
console.log(ym.year); // 2021