function formatDateCustom(date, format) {
  const year = date.getFullYear().toString();
  const month = (date.getMonth() + 1).toString().padStart(2, '0');
  const day = date.getDate().toString().padStart(2, '0');

  return format
    .replace('YYY', year)
    .replace('MM', month)
    .replace('DD', day);
}

const inputDate = new Date('2023-08-11');
const customFormat = 'YYYMMDD';
const formattedDate = formatDateCustom(inputDate, customFormat);
console.log(formattedDate); // Output: "20230811"