You can create a new date by feeding it arguments for year, month, and day.
> new Date(2017, 11, 31)
Sun Dec 31 2017 00:00:00 GMT-0600 (CST)What happens if we push the day value out of bounds?
> new Date(2017, 11, 32)
Mon Jan 01 2018 00:00:00 GMT-0600 (CST)It rolls over to the next month.
Does the same happen when we push the month value out of bounds?
> new Date(2017, 12, 31)
Wed Jan 31 2018 00:00:00 GMT-0600 (CST)Yep.
What about negative values?
> new Date(2018, -1, 31)
Sun Dec 31 2017 00:00:00 GMT-0600 (CST)It rolls the month, and consequently the year, back.