Clarification needed for Event Listener

Don't know exactly what you mean with "running once".

E.g.: The eventListener could be removed after the function was invoked once. ( But then what would be the purpose of the whole script? )

You only need to add that to the bottom of your function doJob():

app.removeEventListener( "afterOpen", doJob );

Or it could be dismissed for one special case and used again when this case is gone the next time the event fires and the listener listens:

// Pseudo code, do not execute as is:
function doJob(myEvent)
{
     if(/*pseudo code*somethingIsTrue){return};
     // Here comes the rest of my super cool function functionality:
     // ...
};

Also check for method preventDefault() of the Event object in the DOM documentation for example here:

Adobe InDesign CS6 (8.0) Object Model JS: Event

// Pseudo Code, do not execute as is:
function doJob(myEvent)
{

if (/*pseudo code*/somethingIsTrue){ myEvent.preventDefault() };

};

To make more out of doJob() you could implement the event object as well and check for property/value pairs you'd like to use in the function.
As you might have seen in the thread about "beforeOpen" and "afterOpen" events on www.hilfdirselbst.ch .

function doJob(myEvent)
{

     for(x in myEvent)
     {
          $.writeln(x +" : "+myEvent.toString() );
     };

};

Have fun while experimenting…

Uwe