Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

6.4 else if

We've seen that the
if/else statement is useful for testing a
condition and executing one of two pieces of code, depending on the
outcome. But what about when we need to execute one of many pieces of
code? One way to do this is with an else
if statement. else
if is not really a JavaScript statement, but
simply a frequently used programming idiom that results when repeated
if/else statements are used:

if (n == 1) {
// Execute code block #1
}
else if (n == 2) {
// Execute code block #2
}
else if (n == 3) {
// Execute code block #3
}
else {
// If all else fails, execute block #4
} 

There is nothing special about this code. It is just a series of
if statements, where each if is
part of the else clause of the previous statement.
Using the else if idiom is
preferable to, and more legible than, writing these statements out in
their syntactically equivalent fully nested form:

if (n == 1) {
// Execute code block #1
}
else {
if (n == 2) {
// Execute code block #2
}
else {
if (n == 3) {
// Execute code block #3
}
else {
// If all else fails, execute block #4
}
}
}