Statement Syntax (ActionScript: The Definitive Guide)

Some statements can take multiple forms. For example, we can use var with or without an optional initial assignment (in this case 10 is a simple expression whose value is assigned to x):

We'll learn the specific syntax of each statement throughout the rest of this chapter.

6.2.1. Statement Blocks

Some statements actually include other statements, or substatements, as part of their syntax. For example, the if statement has this syntax:

if (expression) substatement;

The substatement, which is executed only if expression evaluates to true, can be a single statement such as a variable declaration statement:

if (x == 5) var numFrames = 2;

or it can be a series of statements grouped together as a statement block :

if (x == 5) {
  var numFrames;
  numFrames = 10;
  play( );
}

As you can see, a statement block is any number of statements on one or more lines surrounded by curly braces:

{ statement1; statement2; statement3... }

By using a statement block as the substatement of our if statement, we've managed to specify many statements where normally only one is expected. Very handy.

Anywhere ActionScript expects a single statement we may use a statement block. In fact, statement blocks are sometimes required. For example, the function statement must always include a statement block, even if the function being declared has only one statement in its body:

function aheadTwoFrames( ) {
  gotoAndStop(_currentframe + 2);
}

For the sake of readability, statement blocks are typically formatted as shown here:

parent_syntax {
  substatement1;
  substatement2;
  substatement3;
}

where parent_syntax represents the statement for which we are defining a statement block.

Note that the opening curly brace appears at the end of the first line after parent_syntax. The substatements of the statement block appear indented two spaces, each on its own line. The closing curly brace, also on its own line, is flush with the original main statement. Substatements within statement blocks should end with a semicolon, but there are no semicolons on the lines with curly braces.

The indenting format is simply a convention, not a requirement of legal syntax. This book adheres to the style used by the Flash ActionScript editor.

6.2. Statement Syntax

TIP

6.2.1. Statement Blocks