ActionScript 2.0 variables and scope

ActionScript 2.0 has two kinds of code with different scopes. Code in class files works with local variables and class members, resolved by the compiler. Code in the FLA, frame scripts and handlers, works with timeline variables as in ActionScript 1.0. Both share the global object.

Kinds of variable

Kind	Declared	Lives
Local	`var n:Number = 0;` inside a function or method	Until the function returns, or longer if a nested function uses it
Instance member	`var name:String;` in a class body, outside methods	As long as the object; see Classes
Static member	`static var count:Number = 0;` in a class body	As long as the movie, on the class itself
Timeline	`var score:Number = 0;` or `score = 0;` in a frame script	As long as the movie clip
Global	`_global.settings = {…};`	As long as the movie

A variable declared but never set is undefined, whatever its type.

Names in class methods

Inside a method, the compiler resolves an unqualified name in this order:

the method’s parameters and local variables;
the instance members of the class and of its superclasses, which it compiles as this.name, and the static members, compiled as ClassName.name;
imported and fully named classes;
anything else is left to be looked up when the code runs, on the global object.

So members need no this. in front, though writing it is allowed. Timeline variables are not in scope in a class; a class reaches them by a path, such as _root.score or, in a movie clip subclass, _parent.score. Assigning to an unknown unqualified name in a method does not make it a member of the object, so a misspelt member name can slip through.

Names in FLA scripts

Frame scripts and handlers follow the rules of ActionScript 1.0: locals, any with objects, the timeline the code belongs to, then the global object. Code on a frame sees its own timeline’s variables, not its parent’s. A function defined on a timeline keeps that timeline in its scope wherever it is called from. Variables there may be typed, but only uses the compiler can follow are checked.

Built-in references

Name	Means	Player
`this`	In a method, the object it was called on; in a constructor, the new object; in a frame script, the timeline	5
`super`	The superclass, for calling its constructor and methods	6
`_root`	The main timeline of the current level, or of a clip with `_lockroot` set	5
`_parent`	The containing clip	5
`_level0`, `_level1` …	The main timeline of each loaded level	4
`_global`	The global object, which also holds every class by its package path	6
`clip._lockroot`	When true, `_root` inside a loaded movie means that movie, not the one that loaded it	7

Dynamic names

Square brackets read and set a property by a name built at run time: this["item" + i]. The compiler does not check bracket access, so it also works on objects of classes that are not dynamic. eval(name) and set(name, value) still work in FLA scripts, and paths in slash syntax are still accepted in strings given to eval and the loading functions, but both are relics of Flash 4.

Variables from outside

The FlashVars parameter of the HTML page, and a query string on the SWF’s URL, set variables on _root before frame 1.
LoadVars loads URL-encoded variables into an object; every value arrives as a string and needs converting before use as a typed number.
SharedObject.getLocal(name).data keeps values on the user’s computer between visits.