ESTK System Variable Question

var book = app.ActiveBook;
var shortBookName = new File (book.Name).name;
var comp = book.FirstComponentInBook;
var i = '';
while (comp.ObjectValid())
{
var compName = comp.Name;
Open (comp.Name, GetOpenDefaultParams(), new PropVals());
var doc = app.ActiveDoc;
var shortName = new File (doc.Name).name;
var page = doc.LastBodyPageInDoc.PageNumString;
i += shortName +" last page " + page + "\n";
doc.Close (1);
comp = comp.NextBookComponentInDFSOrder;
}
var doc = SimpleNewDoc ("C:\\Program Files (x86)\\Adobe\\Adobe FrameMaker 2019 (32 Bit)\\SHELLNEW\\FrameMaker2015.fm", false);
var mainflow = doc.MainFlowInDoc;
var tframe = mainflow.FirstTextFrameInFlow;
var pgf = tframe.FirstPgf;
var tLoc= new TextLoc();
tLoc.obj = pgf;
tLoc.offset = 0;
doc.AddText (tLoc, shortBookName + "\n" + i);