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