Javascript Date() constructor

Introduction

Date() creates a Javascript Date that represents a time.

Date objects contain a Number that represents milliseconds since 1 January 1970 UTC.

The signature of Date() method. 

new Date()
new Date(value)
new Date(dateString)
new Date(year, monthIndex [, day [, hours [, minutes [, seconds [, milliseconds]]]]])

To create Date object, use the new operator.

Parameters

Parameter Optional Description
NoParameter No the newly-created Date object represents the current date and time as of the time of instantiation.
valueNoAn integer value representing the number of milliseconds since January 1, 1970, 00:00:00 UTC (UNIX epoch).
dateString No A string value representing a date, specified in a format recognized by the Date.parse() method.
yearNo Integer value representing the year. Values from 0 to 99 map to the years 1900 to 1999. All other values are the actual year.
monthIndex NoInteger value representing the month, beginning with 0 for January to 11 for December.
day Optional Integer value representing the day of the month. The default is 1.
hours Optional Integer value representing the hour of the day. The default is 0 (midnight).
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.
millisecondsOptional Integer value representing the millisecond segment of a time. The default is 0 milliseconds past the second.

To create a new Date object call new Date() with one of the following arguments:

Code
 Description
new Date()
 without arguments will create a Date object for the current date and time:
new Date(milliseconds)
 Create a Date object with the time equal to number of milliseconds (1/1000 of a second) passed after the Jan 1st of 1970 UTC+0. // 0 means 01.01.1970 UTC+0
new Date(datestring)
 String is parsed automatically as Date.parse
new Date(year,
month,
date,
hours,
minutes,
seconds,
ms)


Create the date with the given components in the local time zone.
Only the first two arguments are obligatory.
The year must have 4 digits: 2013 is okay, 13 is not.
The month count starts with 0 (Jan), up to 11 (Dec).
The date parameter is actually the day of month, if absent then 1 is assumed.
If hours/minutes/seconds/ms is absent, they are assumed to be equal 0.
For instance:
new Date(2011, 0, 1, 0, 0, 0, 0); // 1 Jan 2011, 00:00:00
new Date(2011, 0, 1); // the same, hours etc are 0 by default The minimal precision is 1 ms (1/1000 sec):
let now = new Date();
console.log( now ); // shows current date/time

let jan01_1970 = new Date(0);
console.log( jan01_1970 );/*from   w w  w. j  a v a2 s .c  om*/

// now add 24 hours, get 02.01.1970 UTC+0
let jan02_1970 = new Date(24 * 3600 * 1000);
console.log( jan02_1970 ); 

let dec31_1969 = new Date(-24 * 3600 * 1000);
console.log( dec31_1969 );

let date = new Date("2017-01-26");
console.log(date);

let date2 = new Date(2011, 0, 1, 2, 3, 4, 567);
console.log( date2 );

let today = new Date()
console.log(today);
let birthday = new Date('December 17, 1995 03:24:00')
console.log(birthday);
birthday = new Date('1995-12-17T03:24:00')
console.log(birthday);
birthday = new Date(1995, 11, 17)
console.log(birthday);
birthday = new Date(1995, 11, 17, 3, 24, 0)
console.log(birthday);

We can set out-of-range values, and it will auto-adjust itself. 

let date = new Date(2020, 0, 32); // 32 Jan 2013 
console.log(date); //



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