google apps script convert column number to letter

Code.gs

function columnToLetter(column, row) {
  var temp, letter = '';
  while (column > 0) {
    temp = (column - 1) % 26;
    letter = String.fromCharCode(temp + 65) + letter;
    column = (column - temp - 1) / 26;
  }
  return letter + row;
}

function getCategories() {

  var namedRanges = SpreadsheetApp.getActiveSpreadsheet().getNamedRanges();
  
  var categories = {};
  for(var i = 0; i < namedRanges.length; i++) {
    var category = namedRanges[i].getRange().getValues();
    
    categories[category.shift()] = category.map(function(each) {return each.toString();});
    
  }
  
  return categories;
}

function getCategoryList() {
  var categories = getCategories();
  
  var keyArr = [];
  for(var key in categories) {
    keyArr.push(key);
  }
  
  Logger.log(keyArr.join(','));
}

function onEdit(e) {
  
  var categories = getCategories();
  
  var subCategoryCell = columnToLetter(e.range.getColumn() + 1, e.range.getRow());
  
  var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Sheet2');
  
  var vals = categories[e.value];
  
  var rule = SpreadsheetApp.newDataValidation().requireValueInList(vals, true).build();
  
  sheet.getRange(subCategoryCell).clear().setDataValidation(rule);
  
}

colToLetter.gs

/**
* Column to Letter
* from StackOverflow: http://stackoverflow.com/questions/21229180/convert-column-index-into-corresponding-column-letter
*/
function columnToLetter(column) {
  var temp, letter = '';
  while (column > 0) {
    temp = (column - 1) % 26;
    letter = String.fromCharCode(temp + 65) + letter;
    column = (column - temp - 1) / 26;
  }
  return letter;
}