User Guide

About variables 27
The following example shows how you can use these operators and the difference between them:
//Create a new instance of LoadVars class
var myLV:LoadVars = new LoadVars();
//instanceof operator specifies instance of what class
if (myLV instanceof LoadVars) {
trace("yes, it's a loadvars instance");
}
//typeof operator does not specify class, only specifies that myLV is an object
var typeResult:String = typeof(myLV);
trace(typeResult);
About variables
A variable is a container that holds information. The container itself is always the same, but the
contents can change. By changing the value of a variable as the SWF file plays, you can record and
save information about what the user has done, record values that change as the SWF file plays, or
evaluate whether a condition is true or false.
It’s a good idea always to assign a variable a known value the first time you define the variable.
This is known as initializing a variable. If a variable is declared in the FLA (instead of in an
external file), it works only for the frame where the variable is declared. Only the frame code for
that frame is scanned, so the second frame would not recognize the variable if it was referenced.
Initializing a variable helps you track and compare the variable’s value as the SWF file plays.
Variables can hold any type of data (see “About data types” on page 18). The type of data a
variable contains affects how the variable’s value changes when it is assigned in a script.
Typical types of information that you can store in a variable include a URL, a user’s name, the
result of a mathematical operation, the number of times an event occurred, or whether a button
has been clicked. Each SWF file and movie clip instance has a set of variables, with each variable
having a value independent of variables in other SWF files or movie clips.
To view the value of a variable, use the
trace() statement to send the value to the log file. For
example,
trace(hoursWorked) sends the value of the variable hoursWorked to the log file. You
can then review the log file to see if your variables are being set or changed as expected.
For more information, see the following topics:
• “Naming a variable” on page 27
• “Scoping and declaring variables” on page 28
• “Using variables in a program” on page 29
Naming a variable
A variable’s name must follow these rules:
• It must be an identifier (see “Terminology” on page 11).
• It cannot be a keyword or an ActionScript literal such as true, false, null, or undefined.
• It must be unique within its scope (see “Scoping and declaring variables” on page 28).