Different ways to create Date in JavaScript.

Learn about Date object in JavaScript

To get the current time and date create a Date object without any arguments.

var now = new Date(); 
log(now) // Tue Mar 12 2019 21:14:43 GMT+0530 (India Standard Time)

There are many ways of creating a Date object

Passing milliseconds as arguments

If there is single argument and it is of type number then the number is considered as millisecond value.

The milliseconds is counted from the Thu Jan 01 1970 05:30:00 GMT+0530 (India Standard Time) to check this you can create a Date object passing 0 as argument

// passing milliseconds
var sunDec17 = new Date(819138600000);
sunDec17 //Sun Dec 17 1995 00:00:00 GMT+0530 (India Standard Time)
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passing 0 
var date = new Date(0);
date // Thu Jan 01 1970 05:30:00 GMT+0530 (India Standard Time)
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passing negative value will go back from Jan-1-1970
var date = new Date(-86,400,000); // -1 day from Jan-1-1970
date // Wed Dec 31 1969 05:30:00 GMT+0530 (India Standard Time)

NOTE :To get millisecond of a Date object use DateObj.getTime() method.

Passing Date String

If you pass a string value then it is considered as DateString.

Example “2019–01–22”

To learn more about dateString format visit this link

let date = new Date("2019-01-22");
date  //Tue Jan 22 2019 05:30:00 GMT+0530 (India Standard Time)

Passing all the year, month, date, hours, minutes, seconds, ms

• year should have 4 digit
• if we pass less then 4 digits and that value is less then 100 then it is added to 1900.
• month counts from 0–11
• date counts from 1–31(max)
• If date value is not passed or invalid then it takes date value as 1
• If hours/minutes/seconds/ms is not passed , then it takes 0 as default value.

var date = new Date(1997, 0, 22);
date; // Wed Jan 22 1997 00:00:00 GMT+0530 (India Standard Time)
var date = new Date(1997, 0);
date; // Wed Jan 01 1997 00:00:00 GMT+0530 (India Standard Time)
var date = new Date(97, 0);
date; //Wed Jan 01 1997 00:00:00 GMT+0530 (India Standard Time)
var date = new Date(107, 2);
date; //Tue Mar 01 0107 00:00:00 GMT+0553 (India Standard Time)

if we pass invalid string then it returns invalid date

new Date(undefined) // Invalid Date
new Date(null)  
//Thu Jan 01 1970 05:30:00 GMT+0530 (India Standard Time)
new Date("hi") // Invalid Date
new Date("")  // Invalid Date

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