Flash CS3 Documentation

Learning ActionScript 2.0 in Adobe Flash > Data and Data Types > About variables > About variables and scope > Global variables

Global variables

Global variables and functions are visible to every timeline and scope in your document. To declare (or create) a variable with global scope, use the _global identifier before the variable name and do not use the var = syntax. For example, the following code creates the global variable myName:

var _global.myName = "George"; // Incorrect syntax for global variable
_global.myName = "George"; // Correct syntax for global variable

However, if you initialize a local variable with the same name as a global variable, you don't have access to the global variable while you are in the scope of the local variable, as shown in the following example:

_global.counter = 100; // Declares global variable
trace(counter); // Accesses the global variable and displays 100
function count():Void {
    for (var counter:Number = 0; counter <= 2; counter++) { // Local variable
        trace(counter); // Accesses local variable and displays 0 through 2
    }
}
count();
trace(counter); // Accesses global variable and displays 100

This example simply shows that the global variable is not accessed in the scope of the count() function. However, you could access the global-scoped variable if you prefix it with _global. For example, you could access it if you prefix the counter with _global as shown in the following code:

trace(_global.counter);

You cannot assign strict data types to variables that you create in the _global scope, because you have to use the var keyword when you assign a data type. For example, you couldn't do:

_global.foo:String = "foo";          //syntax error
var _global.foo:String = "foo"; //syntax error

The Flash Player version 7 and later security sandbox enforces restrictions when accessing global variables from SWF files loaded from separate security domains. For more information, see Understanding Security.

Flash CS3