第十章：useMemo & useCallback —— 省电模式

function ElectricBill({ rooms, pricePerKWh }) {
  const totalBill = useMemo(() => {
    console.log('重新计算电费...');
    return rooms.reduce((sum, room) => {
      return sum + room.runHours * room.power * pricePerKWh;
    }, 0);
  }, [rooms, pricePerKWh]);

  return <div>总电费: ¥{totalBill}</div>;
}

function LivingRoom() {
  const [temp, setTemp] = useState(26);

  const handleTempChange = useCallback((newTemp) => {
    setTemp(newTemp);
  }, []);

  return <RemoteControl onTempChange={handleTempChange} />;
}