Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The with() method of Temporal.PlainYearMonth instances returns a new Temporal.PlainYearMonth object representing this year-month with some fields replaced by new values. Because all Temporal objects are designed to be immutable, this method essentially functions as the setter for the year-month's fields.
There's no obvious way to create a new Temporal.PlainYearMonth object that represents the same year-month in a different calendar, so to replace its calendarId property, you need to convert it to a Temporal.PlainDate object first using toPlainDate(), change the calendar, and then convert it back.