Cant Define Original Document File Name in the Function!

Hi Pros

Please help, I'm Seasonal Developer, not rememebring every aspect in javascript, please help me to fix the function code, its just continue to save file with the name (Object Document) instead of the Original File Name, I don't get what i'm missing, i will appreciate any help , thanks in advance.

function saveAsIndd()
{
     var doc = app.activeDocument;
     var folderSelect, saveFile;
     fileName = doc;
     folderSelect = Folder.selectDialog("Please select a Folder to Save InDesign File");
     if (!folderSelect) return;
     saveFile = File(folderSelect+"/"+fileName);
     doc.save(new File(saveFile+".indd"));
}

 Best Regards

Mohammad Ibrahim