ServiceNow PERSPECTIUM: how to map either the last worknotes or the full history, depending on whether insert or update

//in the outbound table map, field mapping:

answer=getWNList();

function getWNList(){

    var sReturn=current.work_notes.getJournalEntry(1);

    gs.log(current.number + ': OP=' + ,'getWNList');

    if (current.operation()=='insert'){

        sReturn=current.work_notes.getJournalEntry(-1);

    }

    return sReturn;

}