Calendar.jsx

....
import { format, startOfWeek, addDays } from "date-fns";

const Calendar = () => {
....
  const getWeekDaysNames = () => {
    const weekStartDate = startOfWeek(activeDate);
    const weekDays = [];
    for (let day = 0; day < 7; day++) {
      weekDays.push(
        <div className="day weekNames">
          {format(addDays(weekStartDate, day), "E")}
        </div>
      );
    }
    return <div className="weekContainer">{weekDays}</div>;
  };
....
}