if statements execute a set of
commands if a specified condition
is true. If the condition is
false, another set of statements
can be executed through the use of
the else keyword.
The main idea behind if
statements is embodied by the
sentence: "If the weather's good
tomorrow, we'll go out and have a
picnic and Lisa will do cartwheels
-- else, we'll stay in and
Catherine will watch TV."
As you can see, the idea is
quite intuitive and, surprisingly
enough, so is the syntax:
if (condition) {
statements1
}
-or-
if (condition) {
statements1
}
else {
statements2
}
(An if statement does not
require an else statement
following it, but an else
statement must be preceded by an
if statement.)
condition can be any JavaScript
expression that evaluates to true
or false. Parentheses are required
around the condition. If condition
evaluates to true, the statements
in statements1 are executed.
statements1 and statements2 can
be any JavaScript statements,
including further nested if
statements. Multiple statements
must be enclosed in braces.
Here's an example:
if (weather == 'good') {
go_out(we);
have_a_picnic(we);
do_cartwheels(Lisa);
}
else {
stay_in(we);
watch_TV(Catherine);
