AS3 Error reporting from event callback - actionscript-3

Question

I have been experimenting with supplying better debugging information when an error happens in asynchronous code in AS3.
As an example of the poor error reporting be default, take the case where I force a null pointer in a Timer callback (github gist), I get the following stacktrace back on the console:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Function/<anonymous>()[/[path-to-source-file]/TestClass.as:14]
at flash.utils::Timer/_timerDispatch()
at flash.utils::Timer/tick()
This tells me very little about how the timer callback actually links to my code.
The question is: How can I get information about what code created the callback?
I have added one of my solutions below. I'm interested to see if this can be improved.

Answer 1

One possible solution is to pre-create an Error object in the consumer "thread"/"scope"
var errorInConsumerScope:Error = new Error()
var timer:Timer = new Timer(1000, 1)
timer.addEventListener(TimerEvent.TIMER, internalCallback)
timer.start()
function internalCallback(e:TimerEvent):void
{
try
{
// do something that could cause an error
}
catch (e:Error)
{
errorInConsumerScope.message = e.message
throw errorInConsumerScope
}
}
This now gives me the stacktrace back into my calling code:
Error: Error #1009: Cannot access a property or method of a null object reference.
at TestClass()[/[path-to-source-file]/TestClass.as:10]
at Main()[/[path-to-source-file]/Main.as:9]
The complete gist is here

Answer 2

Interesting thing.
The doc to Error.getStackTrace() says:
Returns the call stack for an error as a string at the time of the
error's construction
According to this, the stacktrace works as expected. The error is constructed in your event handler which is called by the timer tick event.
In your second example you create the error to be dispatched in the constructor of the TestClass. So your stacktrace will show the chain up to the TestClass constructor.

Answer 3

You probably ask for a general solution. I would go with unit tests and proper debugging using breakpoints and object inspection. But here another idea:
TestClass:
package {
import flash.events.TimerEvent;
import flash.utils.Timer;
public class TestClass {
public function TestClass(userCallback : Function, fail : Function) {
var timer : Timer = new Timer(1000, 1);
timer.addEventListener(TimerEvent.TIMER, internalCallback);
timer.start();
function internalCallback(e : TimerEvent):void {
try {
var nullProperty : String;
nullProperty.length;
} catch (e:Error) {
fail();
return;
}
userCallback();
}
}
}
}
Main:
package {
import flash.display.Sprite;
public class Main extends Sprite {
public function Main() {
new TestClass(
function() : void { trace('Call me back when your done.'); },
function() : void { throw new Error('Something went wrong.'); }
);
}
}
}
Output:
Exception fault: Error: Something went wrong.
at Function/<anonymous>()[Main.as:8]
at Function/TestClass/$construct/internalCallback()[TestClass.as:16]
at flash.utils::Timer/_timerDispatch()
at flash.utils::Timer/tick()