Rename worksheet using cell value - google-apps-script

Question

I have a very basic script that takes a cell value, which is a date. Then renames the tab "day, dd/mm/yyyy".
The script has worked fine renaming sheets with the corresponding dates for weeks, but suddenly has an issues from what appears to be 19/03/2018 onwards. The script suddenly seems to be working with a duplicate, have lost or gained a day somewhere. I suspect I have not explained this very well, but it is driving me insane.
The script is;
function renameSheetsByTheContentsOfCellA1onEachSheet() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sourceSheets = SpreadsheetApp.getActiveSpreadsheet().getSheets();
var sheetNumber, sourceSheet, newSheetName;
// iterate through all sheets in the spreadsheet
for (sheetNumber = 1; sheetNumber < sourceSheets.length; sheetNumber++) {
sourceSheet = sourceSheets[sheetNumber];
// get contents of cell A2
newSheetName = sourceSheet.getRange("A2").getValue();
// rename sheet
sourceSheet.setName(Utilities.formatDate(newSheetName, "GMT", "EEEEE, dd/MM/yyyy"));
}
}
Why is the processing going wrong?

Answer 1

You are most likely passing an invalid date type to the .formatDate function (requires a Date, String, String) depending on how the A2 values in your sheets are formatted. To prevent this, you should convert newSheetName back to a date via new Date() in your script before passing it to the function. Of note, this shouldn't be a problem if all of your A2 values are properly formatted as dates--you might want to check that (most likely they are formatted as "Plain Text" which makes them a string).
Also, if you want your script to apply to the first sheet as well, you need to start your for loop at 0 (due to 0 index numbering). I modified your code to account for these changes below:
function renameSheetsByTheContentsOfCellA1onEachSheet() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sourceSheets = SpreadsheetApp.getActiveSpreadsheet().getSheets();
var sheetNumber, sourceSheet, newSheetName;
// iterate through all sheets in the spreadsheet
for (sheetNumber = 0; sheetNumber < sourceSheets.length; sheetNumber++) {
sourceSheet = sourceSheets[sheetNumber];
// get contents of cell A2
newSheetName = new Date(sourceSheet.getRange("A2").getValue());
// rename sheet
sourceSheet.setName(Utilities.formatDate(newSheetName, "GMT", "EEEEE, dd/MM/yyyy"));
}
}
Hope this helps!