ActionScript for Flash MX: The Definitive Guide, Second Edition

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Chapter 7: Conditionals

Of course, we must describe each condition in terms the interpreter understands.

This isn’t a problem—it’s just a question of syntax, which we’ll cover next. Concep-

tually, all conditionals either allow or suppress the execution of a code block, based

on the specified condition. Now let’s see how conditionals work in practice.

The if Statement

The if statement is your everyday, all-purpose conditional. We can use an if state-

ment to create a two-pronged branch in our code, like a fork in the road. The if state-

ment contains one or more substatements that are executed only when the specified

condition is met. The if statement has the following syntax:

if (condition) {

substatements

}

An if statement starts, not surprisingly, with the keyword if. The condition that

must be satisfied for

substatements to be executed is enclosed in parentheses. The

substatements are one or more ActionScript statements. Each substatement should

be on its own line and terminated with a semicolon. The entire if statement ends

with a closing curly brace (

}), without a trailing semicolon.

The

condition of our if statement can be any valid expression. When an if statement

is executed, the interpreter checks the value of that expression (called the test expres-

sion). If it is

true, the ...