Error on running the JScript to write data on Excel

function Main()

  var fileName = "<Path_To_The_File>";

}

function WriteExcelSheet(fname, sheetName)

  var maxcol = 5, maxrow = 5;

  var app = Sys.OleObject("Excel.Application");

  var book = app.Workbooks.Open(fname);

  app.DisplayAlerts = false;

  // Write an index of the current row and column to a cell

  for(var row = rowCount; row < rowCount + maxrow; row++)

      sheet.Cells(row, col) = row + ", " + col;

  book.Save();

}


Error book.Sheets is not a function.