While working on a huge AS3 application last month, i discovered the magic of cross-scripting. What’s that s*** ? Following the livedocs :

If two SWF files written with ActionScript 3.0 are served from the same domain–for example, the URL for one SWF file is http://www.example.com/swfA.swf and the URL for the other is http://www.example.com/swfB.swf–then one SWF file can examine and modify variables, objects, properties, methods, and so on in the other, and vice versa. This is called cross-scripting.

But they don’t talk about the multiple problems you can find loading SWFs into SWFs. Here’s my first test with cross-scripting :

Let’s create two SWFs :

• main.swf (source) :
  • loads two times part.swf
  • has reference of the Singleton2 class (source)
• part.swf (source) :
  • has a reference of the Singleton1 (source) and Singleton2 classes

Now, run the example and take a look at the output :

You can see that the Singleton1 is instanced two times… And even if the “Qualified Class Name” of the two instances are the sames, the classes are not equals (==) and each object is not of the type of the other one’s class…

But, the Singleton2 (which the main SWF has a reference) is only instanced once.

Conclusion : when a SWF loads a class that it doesn’t hold any reference, it creates an “alias” of this class.

var obj1:Object = part1.content["singleton1"];
var cls1:Class = part1.content["singleton1Class"];
// output : [object Singleton1]
trace(obj1);
// output : [class Singleton1]
trace(cls1);
// output : com.site::Singleton1
trace(getQualifiedClassName(obj1));

//////////////////////////////////////////////////

var obj2:Object = part2.content["singleton1"];
var cls2:Class = part2.content["singleton1Class"];
// output : [object Singleton1]
trace(obj2);
// output : [class Singleton1]
trace(cls2);
// output : com.site::Singleton1
trace(getQualifiedClassName(obj2));

//////////////////////////////////////////////////

// output : true
trace(obj1 is cls1);
// output : true
trace(obj2 is cls2);

// output : false
trace(cls1 == cls2);

// output : false
trace(obj1 is cls2);
// output : false
trace(obj2 is cls1);

trace("////////////////////////////////////////");

var obj3:Object = part1.content["singleton2"];
var cls3:Class = part1.content["singleton2Class"];
// output : [object Singleton2]
trace(obj3);
// output : [class Singleton2]
trace(cls3);
// output : com.site::Singleton2
trace(getQualifiedClassName(obj3));

//////////////////////////////////////////////////

var obj4:Object = part2.content["singleton2"];
var cls4:Class = part2.content["singleton2Class"];
// output : [object Singleton2]
trace(obj4);
// output : [class Singleton2]
trace(cls4);
// output : com.site::Singleton2
trace(getQualifiedClassName(obj4));

//////////////////////////////////////////////////

// output : true
trace(obj3 is cls3);
// output : true
trace(obj4 is cls4);

// output : true
trace(cls3 == cls4);

// output : true
trace(obj3 is cls4);
// output : true

trace(obj4 is cls3);

Check out the sources.