JavaScript Date Formats
A JavaScript date can be written as a string:
Thu Aug 11 2016 15:49:17 GMT+0530 (India Standard Time)
or as a number:
1470910757434
Dates written as numbers, specifies the number of milliseconds since January 1, 1970, 00:00:00.
Displaying Dates
In this tutorial we use a script to display dates inside a <p> element with id="demo":
Example
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = Date();
</script>
Try it Yourself
The script above says: assign the value of Date() to the content (innerHTML) of the element with id="demo".
You will learn how to display a date, in a more readable format, at the bottom of this page.
Creating Date Objects
The Date object lets us work with dates.
A date consists of a year, a month, a day, an hour, a minute, a second, and milliseconds.
Date objects are created with the new Date() constructor.
There are 4 ways of initiating a date:
new Date()
new Date(milliseconds)
new Date(dateString)
new Date(year, month, day, hours, minutes, seconds, milliseconds)
Using new Date(), creates a new date object with the current date and time:
Example
<script>
var d = new Date();
document.getElementById("demo").innerHTML =
d;
</script>
Try it Yourself
Using new Date(date string), creates a new date object from the specified date and time:
Example
<script>
var d = new Date("October 13, 2014 11:13:00");
document.getElementById("demo").innerHTML =
d;
</script>
Try it Yourself
Valid date strings (date formats) are described in the next chapter.
Using new Date(number), creates a new date object as zero time plus the number.
Zero time is 01 January 1970 00:00:00 UTC. The number is specified in milliseconds:
Example
<script>
var d = new Date(86400000);
document.getElementById("demo").innerHTML =
d;
</script>
Try it Yourself
JavaScript dates are calculated in milliseconds from 01 January, 1970 00:00:00 Universal Time (UTC). One day contains 86,400,000 millisecond.
Using new Date(7 numbers), creates a new date object with the specified date and time:
The 7 numbers specify the year, month, day, hour, minute, second, and millisecond, in that order:
Example
<script>
var d = new Date(99,5,24,11,33,30,0);
document.getElementById("demo").innerHTML =
d;
</script>
Try it Yourself
Variants of the example above let us omit any of the last 4 parameters:
Example
<script>
var d = new Date(99,5,24);
document.getElementById("demo").innerHTML = d;
</script>
Try it Yourself
JavaScript counts months from 0 to 11. January is 0. December is 11.
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 objects, using either local time or UTC (universal, or GMT) time.
Date methods are covered in a later chapter.
Displaying Dates
When you display a date object in HTML, it is automatically converted to a string, with the toString() method.
Example
<p id="demo"></p>
<script>
d = new Date();
document.getElementById("demo").innerHTML = d;
</script>
Is the same as:
Example
<p id="demo"></p>
<script>
d = new Date();
document.getElementById("demo").innerHTML = d.toString();
</script>
Try it Yourself
The toUTCString() method converts a date to a UTC string (a date display standard).
Example
<script>
var d = new Date();
document.getElementById("demo").innerHTML =
d.toUTCString();
</script>
Try it Yourself
The toDateString() method converts a date to a more readable format:
Example
<script>
var d = new Date();
document.getElementById("demo").innerHTML =
d.toDateString();
</script>
Try it Yourself
Date objects are static. The computer time is ticking, but date objects, once created, are not.
Time Zones
When setting a date, without specifying the time zone, JavaScript will use the browser's time zone.
When getting a date, without specifying the time zone, the result is converted to the browser's time zone.
In other words: If a date/time is created in GMT (Greenwich Mean Time), the date/time will be converted to CDT (Central US Daylight Time) if a user browses from central US.
Read more about time zones in the next chapters.