Learn JS #18

JavaScript Date Objects

Example

const d = new Date();

JavaScript Date Output

By default, JavaScript will use the browser’s time zone and display a date as a full text string:

Tue Jun 14 2022 14:51:25 GMT+0300 (Eastern European Summer Time)

You will learn much more about how to display dates, later in this tutorial.


Creating Date Objects

Date objects are created with the new Date() constructor.

There are 4 ways to create a new date object:

new Date()
new Date(year, month, day, hours, minutes, seconds, milliseconds)
new Date(milliseconds)
new Date(date string)

new Date()

new Date() creates a new date object with the current date and time:

Example

const d = new Date();

Date objects are static. The computer time is ticking, but date objects are not.


new Date(year, month, …)

new Date(year, month, ...) creates a new date object with a specified date and time.

7 numbers specify year, month, day, hour, minute, second, and millisecond (in that order):

Example

const d = new Date(201811241033300);

Note: JavaScript counts months from 0 to 11:

January = 0.

December = 11.

Specifying a month higher than 11, will not result in an error but add the overflow to the next year:

Specifying:

const d = new Date(20181524103330);

Is the same as:

const d = new Date(2019324103330);

Specifying a day higher than max, will not result in an error but add the overflow to the next month:

Specifying:

const d = new Date(2018535103330);

Is the same as:

const d = new Date(201865103330);

Using 6, 4, 3, or 2 Numbers

6 numbers specify year, month, day, hour, minute, second:

Example

const d = new Date(20181124103330);

5 numbers specify year, month, day, hour, and minute:

Example

const d = new Date(201811241033);

4 numbers specify year, month, day, and hour:

Example

const d = new Date(2018112410);

3 numbers specify year, month, and day:

Example

const d = new Date(20181124);

2 numbers specify year and month:

Example

const d = new Date(201811);

You cannot omit month. If you supply only one parameter it will be treated as milliseconds.

Example

const d = new Date(2018);

Previous Century

One and two digit years will be interpreted as 19xx:

Example

const d = new Date(991124);

Example

const d = new Date(91124);

new Date(dateString)

new Date(dateString) creates a new date object from a date string:

Example

const d = new Date("October 13, 2014 11:13:00");

Date strings are described in the next chapter.


JavaScript Stores Dates as Milliseconds

JavaScript stores dates as number of milliseconds since January 01, 1970, 00:00:00 UTC (Universal Time Coordinated).

Zero time is January 01, 1970 00:00:00 UTC.

Now the time is: 1655207485788 milliseconds past January 01, 1970


new Date(milliseconds)

new Date(milliseconds) creates a new date object as zero time plus milliseconds:

Example

const d = new Date(0);

01 January 1970 plus 100 000 000 000 milliseconds is approximately 03 March 1973:

Example

const d = new Date(100000000000);

January 01 1970 minus 100 000 000 000 milliseconds is approximately October 31 1966:

Example

const d = new Date(-100000000000);

Example

const d = new Date(86400000);

One day (24 hours) is 86 400 000 milliseconds.


Date Methods

When a Date object is created, a number of methods allow you to operate on it.

Date methods allow you to get and set the year, month, day, hour, minute, second, and millisecond of date objects, using either local time or UTC (universal, or GMT) time.

Date methods and time zones are covered in the next chapters.


Displaying Dates

JavaScript will (by default) output dates in full text string format:

Example

Tue Jun 14 2022 14:51:25 GMT+0300 (Eastern European Summer Time)

When you display a date object in HTML, it is automatically converted to a string, with the toString() method.

Example

const d = new Date();
d.toString();

The toUTCString() method converts a date to a UTC string (a date display standard).

Example

const d = new Date();
d.toUTCString();

The toDateString() method converts a date to a more readable format:

Example

const d = new Date();
d.toDateString();

The toISOString() method converts a Date object to a string, using the ISO standard format:

Example

const d = new Date();
d.toISOString();

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