HTML and CSS Reference
In-Depth Information
Figure 12-22
nested if statement for leap years
if the year is divisible by
4 and either n
ot divisible
by 100 or divisible by
400, it's a leap year
◗
3.
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Exploring the
if else
Statement
The
if
statement runs a command or a command block only if the conditional expres-
sion returns the value
true
; it does nothing if a value of
false
is returned. On some
occasions, you might want to choose between alternate command blocks. In those cases,
you will use an
if else
structure in which one command block is run if the conditional
expression is true, and a different command block is run if the expression is false. The
general structure of an
if else
statement is as follows:
if (
condition
) {
commands if condition is true
} else {
commands if otherwise
}
If only a single command is run in response to the
if
statement, you can use the follow-
ing abbreviated form:
if (
condition
)
command if condition is true
else
command if otherwise
;
The following example shows an
if else
statement that runs one of two possible
document.write()
commands depending on whether the value of the
day
variable is
Friday
or not:
if (day == “Friday”) document.write(“Thank goodness it's Friday”)
else document.write(“Today is “ + day);
In this statement, the text
Thank goodness it's Friday
is written to the document if the
value of the
day
variable is
Friday
. Otherwise, the statement writes the name of the day.
