Working with Arrays, Loops, and Conditional Statements - HTML, CSS, and Dynamic HTML - page 861

Like if statements, if else statements can be nested as in the following code, which
chooses between three possible text strings to write to a document:

if (day == “Friday”) document.write(“Thank goodness it's Friday”)
else {
if (day == “Monday”) document.write(“Blue Monday”)
else document.write(“Today is “ + day);
}
Some programmers advocate always using curly braces even if the command block
contains only a single command. This practice visually separates one else clause from
another. Also, when reading through nested statements, it can be helpful to remember
that an else clause usually pairs with the nearest preceding if statement.

To make it easier to
interpret nested if state-
ments, always indent your
code, lining up all of the
commands for one set of
nested statements.

Using Multiple else if Statements
For more complex scripts, you might need to choose from several alternatives. In these
cases, you can specify multiple else clauses, each with its own if statement. This is not
a new type of conditional structure, but rather a way of taking advantage of the syntax
rules inherent in the if else statement. The general structure for choosing from several
alternatives is

if ( condition 1 ) {
first command block
} else if ( condition 2 ) {
second command block
} else if ( condition 3 ) {
third command block
...
} else {
default command block
}
where condition 1 , condition 2 , condition 3 , and so on are the different condi-
tions to be tested. This construction always should include a final else clause that is run
by default if none of the preceding conditional expressions returns the value true .
When a browser runs a series of statements like this one, it stops examining the remain-
ing else clauses when it encounters the first true else clause because there no longer
is an else condition to investigate. The structure in the following example employs
multiple else if conditions:

To simplify code, keep
your nesting of multiple
if statements to three or
less, if possible. For more
conditions, use the case /
switch structure.

if (day == “Friday”) {
document.write(“Thank goodness it's Friday”);
} else if (day == “Monday”) {
document.write(“Blue Monday”);
} else if (day == “Saturday”) {
document.write(“Sleep in today”);
} else {
document.write(“Today is “ + day);
}