JavaScript Dates
The Date object lets you work with dates (years, months, days, hours, minutes, seconds, and milliseconds)
JavaScript Date Formats
A JavaScript date can be written as a string:Sun Nov 26 2017 07:46:59 GMT-0800 (Pacific Standard Time)
or as a number:
Dates written as numbers, specifiy 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> 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) Example
<script>
var d = new Date();
document.getElementById("demo").innerHTML = d;</script> Example
<script>
var d = new Date("October 13, 2014 11:13:00");
document.getElementById("demo").innerHTML = d;</script> 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> JavaScript dates are calculated in milliseconds from 01 January, 1970 00:00:00 Universal Time (UTC). One day (24 hours) contains 86,400,000 milliseconds.
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> Example
<script>
var d = new Date(99, 5, 24);
document.getElementById("demo").innerHTML = d;</script> 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:<p id="demo"></p>
<script>
d = new Date();
document.getElementById("demo").innerHTML = d.toString();</script> Example
<script>
var d = new Date();
document.getElementById("demo").innerHTML = d.toUTCString();</script> Example
<script>
var d = new Date();
document.getElementById("demo").innerHTML = d.toDateString();</script> 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.
