JavaScript Date Objects

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JavaScript Date Objects


JavaScript

Date Object

lets us work with dates:



Example

var 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:



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

var 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

var d = new Date(2018, 11, 24, 10, 33, 30, 0);


Note:

JavaScript counts months from 0 to 11.

January is 0. December is 11.

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

Example

var d = new Date(2018, 11, 24, 10, 33, 30);

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

Example

var d = new Date(2018, 11, 24, 10, 33);

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

Example

var d = new Date(2018, 11, 24, 10);

3 numbers specify year, month, and day:

Example

var d = new Date(2018, 11, 24);

2 numbers specify year and month:

Example

var d = new Date(2018, 11);

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

Example

var d = new Date(2018);


Previous Century

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

Example

var d = new Date(99, 11, 24);

Example

var d = new Date(9, 11, 24);


new Date(

dateString

)


new Date(dateString)

creates a new date object from a

date string

:

Example

var 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:



milliseconds past January 01, 1970


new Date(

milliseconds

)


new Date(

milliseconds

)

creates a new date object as

zero time plus milliseconds

:

Example

var d = new Date(0);

01 January 1970

plus

100 000 000 000 milliseconds is approximately 03 March 1973:

Example

var d = new Date(100000000000);

January 01 1970

minus

100 000 000 000 milliseconds is approximately October 31 1966:

Example

var d = new Date(-100000000000);

Example

var 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:

When you display a date object in HTML, it is automatically converted to a
string, with the

toString()

method.

Example

d = new Date();
document.getElementById(“demo”).innerHTML = d;

Same as:

d = new Date();
document.getElementById(“demo”).innerHTML = d.toString();

The

toUTCString()

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

Example

var d = new Date();
document.getElementById(“demo”).innerHTML = d.toUTCString();

The

toDateString()

method converts a date to a more readable
format:

Example

var d = new Date();
document.getElementById(“demo”).innerHTML = d.toDateString();

The

toISOString()

method converts a date to a string, using the ISO standard format:

Example

var d = new Date();
document.getElementById(“demo”).innerHTML = d.toISOString();


Test Yourself With Exercises

Exercise:

Create a Date object and alert the current date and time.

var d = ;
alert(d);

Start the Exercise