Date() constructor

There are five basic forms for the Date() constructor:

1. No parameters When no parameters are provided, the newly-created Date object represents the current date and time as of the time of instantiation.
2. Time value or timestamp number

   value

   An integer value representing the number of milliseconds since January 1, 1970, 00:00:00 UTC (the ECMAScript epoch, equivalent to the UNIX epoch), with leap seconds ignored. Keep in mind that most UNIX Timestamp functions are only accurate to the nearest second.

3. Timestamp string

   dateString

   A string value representing a date, specified in a format recognized by the Date.parse() method. (These formats are IETF-compliant RFC 2822 timestamps, and also strings in a version of ISO8601.)

   Note: Parsing of date strings with the Date constructor (and Date.parse(), which works the same way) is strongly discouraged due to browser differences and inconsistencies.

   • Support for RFC 2822 format strings is by convention only.
   • Support for ISO 8601 formats differs in that date-only strings (e.g. "1970-01-01") are treated as UTC, not local.

4. Date object

   dateObject

   An existing Date object. This effectively makes a copy of the existing Date object with the same date and time. This is equivalent to using the new Date(value) constructor, where value can be obtained using the valueOf() method.

5. Individual date and time component values Given at least a year and month, this form of Date() returns a Date object whose component values (year, month, day, hour, minute, second, and millisecond) all come from the following parameters. Any missing fields are given the lowest possible value (1 for day and 0 for every other component). The parameter values are all evaluated against the local time zone, rather than UTC.

   year

   Integer value representing the year.

   Values from 0 to 99 map to the years 1900 to 1999. All other values are the actual year. See the example.

   monthIndex

   Integer value representing the month, beginning with 0 for January to 11 for December. If a value greater than 11 is passed in, then those months will be added to the date; for example, new Date(1990, 12, 1) will return January 1st, 1991

   day Optional

   Integer value representing the day of the month. The default is 1.

   hours Optional

   Integer value between 0 and 23 representing the hour of the day. Defaults to 0.

   minutes Optional

   Integer value representing the minute segment of a time. The default is 0 minutes past the hour.

   seconds Optional

   Integer value representing the second segment of a time. The default is 0 seconds past the minute.

   milliseconds Optional

   Integer value representing the millisecond segment of a time. The default is 0 milliseconds past the second.

Calling new Date() (the Date()constructor) returns a Date object. If called with an invalid date string, it returns a Date object whose toString() method returns the literal string Invalid Date.

Calling the Date() function (without the new keyword) returns a string representation of the current date and time, exactly as new Date().toString() does. Any arguments given in a Date() function call (without the new keyword) are ignored; regardless of whether it's called with an invalid date string — or even called wth any arbitrary object or other primitive as an argument — it always returns a string representation of the current date and time.

The following examples show several ways to create JavaScript dates:

let today = new Date()
let sameDay = new Date(today)
let birthday = new Date('December 17, 1995 13:24:00')
let birthday = new Date('1995-12-17T13:24:00')
let birthday = new Date(1995, 11, 17)            // the month is 0-indexed
let birthday = new Date(1995, 11, 17, 13, 24, 0)

• Date