Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The day accessor property of Temporal.PlainDateTime instances returns a positive integer representing the 1-based day index in the month of this date, which is the same day number you would see on a calendar. It is calendar-dependent.
The set accessor of day is undefined. You cannot change this property directly. Use the with() method to create a new Temporal.PlainDateTime object with the desired new value.
For general information and more examples, see Temporal.PlainDate.prototype.day.