Check if folder exists in EITHER parent folder, else create

Question

I have two parent folders that I want to check if Folder(folderName) exists in. folderName is defined by the range S2:2 in my spreadsheet

If Folder(folderName) does not exist in EITHER parent folder, then I want that folder to be created in Parent Folder 1.

So far my script is managing to check Parent Folder 1 and create in Parent Folder 1, but is not checking Parent Folder 2.

This is the script I have so far:

function myfunction() {
  
  var parent = DriveApp.getFolderById("parent Folder 1")
SpreadsheetApp.getActive().getSheetByName('Letter History').getRange('S2:S').getValues()
    .forEach(function (r) {
        if(r[0]) checkIfFolderExistElsesCreate(parent, r[0]);
    })
}

function checkIfFolderExistsElseCreate(parent, folderName) {
var folder;
try {
    folder = parent.getFoldersByName(folderName).next();
} catch (e) {
    folder = parent.createFolder(folderName);
}

Answer 1

function myFunction() {
  var parentFolder1 = DriveApp.getFolderById('<ParentFolder1 ID>').getFolders(); //Get ID for Folder 1
  var parentFolder2 = DriveApp.getFolderById('<ParentFolder2 ID>').getFolders(); //Get ID for Folder 2
  var sheet = SpreadsheetApp.getActive().getSheetByName('Letter History');

 //Iterating to read all the subfolders in ParentFolder 1 and 2
  var childNames = [];
  while (parentFolder1.hasNext()) {
    var child = parentFolder1.next();
    childNames.push([child.getName()]);
  }
  while (parentFolder2.hasNext()) {
    var child = parentFolder2.next();
    childNames.push([child.getName()]);
  }

  //Checking if the subfolder/s is existing or not, then creating in folder 1 if not yet existing
  var data = sheet.getRange(2, 19, sheet.getLastRow() - 1, 1).getValues(); //S = 19, Change 19 according to column. 
  for (var i = 0; i < data.length; i++) {
    if (childNames.flat().includes(data[i][0])) {
      console.log(data[i][0] + "- already exist")
    } else {
      DriveApp.getFolderById('<ParentFolder1 ID>').createFolder(data[i][0])
      console.log(data[i][0] + "- has been created")
    }
  };
}

The above code will create subfolder/s in Folder 1 based on range S2:S column in spreadsheet, if it is checked that the subfolder name does not yet exist either in Parent Folder 1 or 2.

Please take note to change the following:

• ParentFolder 1 ID
• ParentFolder 2 ID

Reference: How to create a folder if it doesn't exist?