Javascript - Date

Date Objects

The Date object is used to work with dates and times.

How to use the Date() method to get today's date.

<script type="text/javascript">

var d=new Date();
document.write(d);

</script>

getFullYear(), Use getFullYear() to get the year.

<script type="text/javascript">

var d=new Date();
document.write(d);

</script>

getTime(), returns the number of milliseconds since 01.01.1970.

<script type="text/javascript">
var d=new Date();
document.write(d.getTime() + " milliseconds since 1970/01/01");
</script>

setFullYear(), How to use setFullYear() to set a specific date.

<script type="text/javascript">

var d = new Date();
d.setFullYear(1992,10,3);
document.write(d);

</script>

toUTCString(), How to use toUTCString() to convert today's date (according to UTC) to a string.

<script type="text/javascript">

var d=new Date();
document.write("Original form: ");
document.write(d + "<br />");
document.write("To string (universal time): ");
document.write(d.toUTCString());

</script>

getDay(), Use getDay() and an array to write a weekday, and not just a number.

<script type="text/javascript">

var d=new Date();
var weekday=new Array(7);
weekday[0]="Sunday";
weekday[1]="Monday";
weekday[2]="Tuesday";
weekday[3]="Wednesday";
weekday[4]="Thursday";
weekday[5]="Friday";
weekday[6]="Saturday";

document.write("Today is " + weekday[d.getDay()]);

</script>

Display a clock, How to display a clock on your web page.

<html>
<head>
<script type="text/javascript">
function startTime()
{
var today=new Date();
var h=today.getHours();
var m=today.getMinutes();
var s=today.getSeconds();
// add a zero in front of numbers<10
m=checkTime(m);
s=checkTime(s);
document.getElementById('txt').innerHTML=h+":"+m+":"+s;
t=setTimeout('startTime()',500);
}

function checkTime(i)
{
if (i<10)
  {
  i="0" + i;
  }
return i;
}
</script>
</head>

<body onload="startTime()">
<div id="txt"></div>
</body>
</html>

Create a Date Object

The Date object is used to work with dates and times. Date objects are created with the Date() constructor. There are four ways of instantiating a date:

new Date() // current date and time
new Date(milliseconds) //milliseconds since 1970/01/01
new Date(dateString)
new Date(year, month, day, hours, minutes, seconds, milliseconds)

Most parameters above are optional. Not specifying, causes 0 to be passed in.

Once a Date object is created, a number of methods allow you to operate on it. Most methods allow you to get and set the year, month, day, hour, minute, second, and milliseconds of the object, using either local time or UTC (universal, or GMT) time.

All dates are calculated in milliseconds from 01 January, 1970 00:00:00 Universal Time (UTC) with a day containing 86,400,000 milliseconds.

Some examples of instantiating a date:

var today = new Date()
var d1 = new Date("October 13, 1975 11:13:00")
var d2 = new Date(79,5,24)
var d3 = new Date(79,5,24,11,33,0)

Set Dates

We can easily manipulate the date by using the methods available for the Date object.

In the example below we set a Date object to a specific date (14th January 2010):

var myDate=new Date();
myDate.setFullYear(2010,0,14);

And in the following example we set a Date object to be 5 days into the future:

var myDate=new Date();
myDate.setDate(myDate.getDate()+5);

Note: If adding five days to a date shifts the month or year, the changes are handled automatically by the Date object itself!

Compare Two Dates

The Date object is also used to compare two dates. The following example compares today's date with the 14th January 2010:

var myDate=new Date();
myDate.setFullYear(2010,0,14);
var today = new Date();

if (myDate>today)
  {
  alert("Today is before 14th January 2010");
  }
else
  {
  alert("Today is after 14th January 2010");
  }

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Javascript - Date

Date Objects

Create a Date Object

Some examples of instantiating a date:

Set Dates

Compare Two Dates

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References

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