6.3.1. Loops and Conditionals

6.3.2. Expression Statements

"hi there";  // This doesn't do much
345 + 5;     // Neither does this

Some expressions, however, have side effects that change the state of a system through variable or property assignments or by physically altering the Flash environment. In this example, an expression changes the value of x:

x = 345 + 5;  // Much more useful

gotoAndStop(5);  // The value of _currentframe is changed to 5.

6.3.3. The var Statement

var x;

You can assign the new variable's initial value as part of a var statement:

var x = 10;

6.3.4. The set Statement (Set Variable)

x = 30;

That kind of expression, however, requires us to know the name of our variable in advance. If we want to generate the name of a variable dynamically during an assignment, we can use the set statement, which has the following syntax:

set (variable, expression);

where variable is a string expression to be used as the variable name in the assignment and expression is the new value to assign to it. For example:

var x;
set ("x", 10);      // x is now 10

var firstName;
set ("first" + "Name", "jane");  // firstName is now "jane"

In the following, trickier example, y is not being set in the set statement. Instead, y 's value ("x") is retrieved and that value is used as the name of the variable to set:

// Pay close attention to this one...
var y = "x";
var x;
set(y, 15);  // x is now 15, y is still "x".

6.3.5. The function Statement

function funcName (param1, param2, param3,...paramn) {
  statements
}

The keyword function begins the statement; funcName is the name of the function being declared; param1 through paramn define the parameters required by the function when it executes; statements is a list of one or more statements that will be executed when the function is called.

The function statement creates a function for later use but does not execute that function. To execute a function, we use the function's name in a function call statement.

6.3.6. Function Call Statements

funcName (arg1, arg2, ... argn);

where funcName is the name of the function we want to execute and arg1 through argn is the list of arguments (i.e., input values) that the function expects when it runs.

The function call statement is an extremely powerful and fundamental device; it's our primary means of controlling Flash movies. When we want to manipulate a movie in some way, we often call a function. Here are a few examples:

play( );                       // Plays the current movie
gotoAndStop(5);                // Sends the playhead to frame 5
startDrag("crosshair", true);  // Makes the "crosshair" instance follow
                               // the mouse pointer

Function calls are also used with objects to invoke methods:

circle.area( );
today.getDate( );

Because movie clip instances are objects, we frequently use method invocation in our scripts:

ball.play( )
intro.gotoAndStop("end");

6.3.7. The call( ) Statement

call (frame);

The call( ) statement executes the script on the frame specified by frame, which may be any frame label or frame number. If the specified frame is not loaded, the call( ) statement fails silently.

Obviously, the pseudofunctions of Flash 4 pale in comparison with real functions, so we normally have no reason to use a call( ) statement when authoring for Flash 5 or later. But when we're authoring Flash 4 movies, we need to use the old-style subroutines and the Flash 4 call( ) statement.

6.3.8. The return Statement

return;
return expression;

6.3.9. The with Statement

with (object) {
  statements
}

When a property is referenced within a with statement block, object is checked for the specified property. If the property exists in object, then object's property is used to resolve the property reference. If the property does not exist in object, the current timeline or function is consulted for the property in question.

The following example shows the difference between executing a statement inside a with statement and outside a with statement:

PI = 10;                  // Set a timeline variable, PI
with (Math) {             // Execute statements in the context of Math
  trace("pi is: " + PI);  // Displays: 3.1459... (PI is a property of Math)
}
trace("PI is: " + PI);    // Displays: 10 (Math is no longer accessed)

x = 10;
y = 11;
with (Math) {
  larger = max(x, y);
}
trace(larger);  // Displays: 11

It is not possible to define a new property on an object that is the target of a with statement. Notice in the previous example that the variable larger is not defined on the Math object, so the property reference affects the timeline or function that contains the with statement. The following code shows a misguided attempt to set a variable in myClip:

with (myClip) {
  var x = 10;  // x is set on the current timeline, not myClip
}

_root.form.userProfile.userID = "U346BX";
  _root.form.userProfile.gotoAndPlay("questionnaire");

to this:

with (_root.form.userProfile) {
  userID = "U346BX";             // Resets an existing variable
                                 // in userProfile instance
  gotoAndPlay("questionnaire");  // Function applied to userProfile instance
}

But with is not our only means of achieving this convenience. We could also simply assign our instance to a variable and use that variable in our references:

var userForm = _root.form.userProfile;
userForm.useriD = "U346BX";
userForm.gotoAndPlay("questionnaire");

6.3.10. The ifFrameLoaded Statement

ifFrameLoaded (expression) {
  statements
}

where expression must be either the number of a frame or a string indicating a frame label. If the frame indicated by expression has downloaded to the Player, statements are executed. If not, the statement block is skipped.

if (_totalframes > 0 && _framesloaded == _totalframes) {
	gotoAndPlay("beginMovie");
} else {
	gotoAndPlay(_currentframe - 1);
}

6.3.11. The Empty Statement

;

The empty statement has very little practical application except that it can be used as a placeholder anywhere a statement is normally expected. It is not needed if you simply want to add blank lines to your code. ActionScript ignores blank vertical lines, which can be used to improve code readability.

In novice authoring mode, the lone semicolon appears when the evaluate Action is added to a block of code. An arbitrary statement may then be added by typing into the Expression field of the Parameters panel.