Как задать значение свойству когда обьект ещё не инициализирован?

import React, { useState } from "react";
import "./App.css";

function App() {
  const [state, setState] = useState({
    // для заполнения Option
    days: amountOf("days"),
    months: amountOf("months"),
    years: amountOf("years"),
    // получение текущей даты
    currentDay: new Date().getDate(),
    currentMonth: new Date().getMonth(),
    currentYear: new Date().getFullYear(),
    // сегодня (день недели)
    todayIs: getToday(),
  })
  const input1 = React.createRef();
  const input2 = React.createRef();
  const input3 = React.createRef();

  function amountOf(prop) {
    switch (prop) {
      case "days":
        let startDays = 1;
        const days = [];
        while (startDays <= 30) {
          days.push(startDays++);
        }
        return days;

      case "months":
        let startMonth = 1;
        const months = [];
        while (startMonth <= 12) {
          months.push(startMonth++);
        }
        return months;

      case "years":
        let startYears = 2016;
        const years = [];
        while (startYears <= 2022) {
          years.push(startYears++);
        }
        return years;
    }
  }

  function getToday() {
    let date = new Date(
      state.currentYear,
      state.currentMonth,
      state.currentDay
    );
    date = date.getDay();
    switch (date) {
      case 0:
        return "Sunday";
      case 1:
        return "Monday";
      case 2:
        return "Tuesday";
      case 3:
        return "Wednesday";
      case 4:
        return "Thursday";
      case 5:
        return "Friday";
      case 6:
        return "Saturday";
    }
  }

  function handleClick() {}

  return (
    <>
      <select
        ref={input1}
        onChange={handleClick}
        defaultValue={state.currentDay}
      >
        {state.days.map((item, i) => {
          return <option key={i}>{item}</option>;
        })}
      </select>

      <select
        ref={input2}
        onChange={handleClick}
        defaultValue={state.currentMonth}
      >
        {state.months.map((item, i) => {
          return <option key={i}>{item}</option>;
        })}
      </select>

      <select
        ref={input3}
        onChange={handleClick}
        defaultValue={state.currentYear}
      >
        {state.years.map((item, i) => {
          return <option key={i}>{item}</option>;
        })}
      </select>

      <p>{}</p>
    </>
  );
}

export default App;