Depended dropdowns

/*
    RemcoE33
    https://docs.google.com/spreadsheets/d/1AWufAtSCDN9bxJDPCc0oSN66BWHqRY_5xdn7AVwVByk/edit?usp=sharing
*/

//Setting the ref sheet where all the columns for the dropdowns are
const dropDownRefSheet = 'Ref';
//Make a list of all the sheet where you want the dropdowns to appear. A = 1, B = 2 etc..
const validation = {
  'Sample': {
    columns: [1, 2, 3],
    rowIsGreaterThen: 1
  }
}

function onEdit(e) {
  const sheet = e.source.getActiveSheet();
  const range = e.range;
  const validatedSheet = validation[sheet.getName()]

  if (validatedSheet) {
    const columns = validatedSheet.columns;
    const currentColumn = range.getColumn();
    const currentRow = range.getRow();
    const max = Math.max(...columns);
    const min = Math.min(...columns);
    if (
      //Column check
      columns.includes(currentColumn) &&
      //Row check
      currentRow > validatedSheet.rowIsGreaterThen &&
      //Make sure that we not make another drowdown after the last one.
      currentColumn < max
    ) {
      //If you clear out the first dropdown, reset the rest.
      if (!e.value && currentColumn == min) {
        sheet.getRange(currentRow, min + 1, 1, (max - min) + 1)
          .clearContent()
          .clearDataValidations()
      } else {
        setDataValidation(e, columns)
      }
    }
  }
}

function setDataValidation(e, columns) {
  const dropdownSheet = e.source.getSheetByName(dropDownRefSheet);
  // Getting al the values from 1:1
  const headers = dropdownSheet.getRange(1, 1, 1, dropdownSheet.getLastColumn()).getValues().flat();
  //Get the column index from the value selected in the dropdown.
  const selectedHeaderIndex = headers.indexOf(e.value);
  //Get the right range for the validation rule.
  const validationRange = dropdownSheet.getRange(2, selectedHeaderIndex + 1, dropdownSheet.getLastRow());
  //Create validation rule based on range.
  const validationRule = SpreadsheetApp.newDataValidation().requireValueInRange(validationRange).build();

  //Setting the next dropdown
  e.range.offset(0, 1).clearContent().clearDataValidations();
  e.range.offset(0, 1).setDataValidation(validationRule);

  /*
    In this example there are 3 columns. Let say i have them all 3 filled in and i change the main category.
    Then i want that i set the sub offet 1 and clear all the validations and values in all the columns after offset 1
  */
  const max = Math.max(...columns);
  const currentColumn = e.range.getColumn()
  const offsetTwo = currentColumn + 2

  if (offsetTwo <= max) {
    e.source.getActiveSheet()
      .getRange(e.range.getRow(), offsetTwo, (max - offsetTwo) + 1)
      .clearContent()
      .clearDataValidations()
  }

}