const year = String(new Date(createdAt!).getFullYear());
  const month = String(new Date(createdAt!).getMonth());
  const date = String(new Date(createdAt!).getDate());

  abstract class Constr {
    protected year: string;
    protected month: string;
    protected time: string;
    constructor({ year, month }: Partial<CreateAt>) {
      this.year = year!;
      this.month = month!;
      this.time = `${year}. ${month}.`;
    }
  }

  class Time extends Constr {
    public finalDate: string;
    protected date: string;
    constructor({ year, month, date }: Partial<CreateAt>) {
      super({ year, month });
      this.date = date!;
      this.finalDate = `${this.time} ${this.date}`;
    }
  }
  const times = new Time({ year, month, date });
  console.log(times.finalDate);


맘에 드는군