Actionscript Cookbook

1.3. Performing Actions Conditionally

Problem

You want to perform an action only when a condition is true.

Solution

Use an if statement or a switch statement.

Discussion

You often need your ActionScript code to make decisions, such as whether to execute a particular action or group of actions. To execute an action under certain circumstances, use one of ActionScript’s conditional statements: if, switch, or the ternary conditional operator (? :).

The conditional statements allow you to make logical decisions, and you’ll learn from experience which is more appropriate for a given situation. The if statement is most appropriate when you want to tell your Flash movie to do something only when a certain condition is met (i.e., when the condition is true). When you have several possible conditions to test, you can use the switch statement instead. And you can use Flash’s ternary conditional operator to perform conditional checking and assignment on a single line.

First, we’ll look at the if statement. Of the conditional statements in ActionScript, the if statement is the most important to understand. In its most basic form, an if statement includes the keyword if followed by the test expression whose truthfulness you want to evaluate to determine which action or actions to execute. The test expression must be in parentheses, and the statement(s) to be executed should be within curly braces (the latter is mandatory if there is more than one statement in the statement block).

Here, we check ...