typia/src/internal/_isFormatByte.ts

Superfast runtime validators with only one line

export const _isFormatByte = (str: string): boolean => PATTERN.test(str);

const PATTERN =
  /^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$/;