HTML and CSS Reference
In-Depth Information
Setting Date and Time Values
In addition to retrieving date and time values, you can also use the
Date
object method
to change these values. This is most often used in programs that involve setting the value
of a future date or time, such as an expiration date for an online membership or an
online calendar used for event scheduling. Figure 11-9 summarizes the methods sup-
ported by JavaScript for setting date and time values.
Figure 11-9
setting values within a date object
Method
Sets
dateObject
.setSeconds(
value
)
the seconds value of
dateObject
to
value
dateObject
.setMinutes(
value
)
the minutes value of
dateObject
to
value
dateObject
.setHours(
value
)
the hours value of
dateObject
to
value
dateObject
.setDate(
value
)
the day of the month value of
dateObject
to
value
dateObject
.setMonth(
value
)
the month number of
dateObject
(0 = January,
1 = February, etc.) to
value
dateObject
.setFullYear(
value
)
the four-digit year value of
dateObject
to
value
dateObject
.setTime(
value
)
the time of
dateObject
in milliseconds since January 1,
1970 at 12:00 a.m. to
value
For example, the following code shows how to use the
setFullYear()
method to change
the date stored in the
thisDate
variable from February 24, 2015 to February 24, 2016:
thisDate = new Date(“February 24, 2015”);
thisDate.setFullYear(2016);
In the same fashion, you'll create a function that uses the
setFullYear()
method in
the next session.
Creating a Date and Time Function
You'll use the methods associated with
Date
objects that you just learned to create func-
tions that extract the date and time values from specified dates, and then return those
values in formatted text strings. The first function you'll create is named
showDate()
and has the following code:
JavaScript does not sup-
port daylight saving time
(also known as summer
time); instead, a com-
puter's operating system
makes adjustments for
daylight saving time when
needed.
function showDate(dateObj) {
thisDate = dateObj.getDate();
thisMonth = dateObj.getMonth()+1;
thisYear = dateObj.getFullYear();
return thisMonth + “/” + thisDate + “/” + thisYear;
}
The
showDate()
function has a single parameter named
dateObj
, which stores the
Date
object to be evaluated. The function extracts the day of the month, the month number,
and the four-digit year value, and returns a text string combining all of the values in the
format
month
/
day
/
year
where
month
is the value of the
thisMonth
variable,
day
is the value of the
thisDate
vari-
able, and
year
is the value of the
thisYear
variable. You'll place the text generated by this
function into the
dateNow
field of the Web form on the clock Web page.
