setDate() method sets the day of the Date object relative to the beginning of the currently set month.
The value returned by
setDate() is the number of milliseconds since 1 January 1970 00:00:00 UTC of the resulting date (the Date object is also changed in place).
dayValue is outside of the range of date values for the month,
setDate() will update the Date object accordingly. For example, if 0 is provided for
dayValue, the date will be set to the last day of the previous month.
var theBigDay = new Date(1962, 6, 7); // 1962-07-07 theBigDay.setDate(24); // 1962-07-24 theBigDay.setDate(32); // 1962-08-01 theBigDay.setDate(22); // 1962-08-22