studiobeve.no/assets/js/calendar.js

const isLeapYear = (year) => {
  return (
    (year % 4 === 0 && year % 100 !== 0 && year % 400 !== 0) ||
    (year % 100 === 0 && year % 400 === 0)
  );
};
const getFebDays = (year) => {
  return isLeapYear(year) ? 29 : 28;
};
let calendar = document.querySelector('.calendar');
const month_names = [
    'Január',
    'Február',
    'Március',
    'Április',
    'Május',
    'Június',
    'Július',
    'Augusztus',
    'Szeptember',
    'Október',
    'November',
    'December',
  ];
let month_picker = document.querySelector('#month-picker');
const dayTextFormate = document.querySelector('.day-text-formate');
const timeFormate = document.querySelector('.time-formate');
const dateFormate = document.querySelector('.date-formate');

month_picker.onclick = () => {
  month_list.classList.remove('hideonce');
  month_list.classList.remove('hide');
  month_list.classList.add('show');
  dayTextFormate.classList.remove('showtime');
  dayTextFormate.classList.add('hidetime');
  timeFormate.classList.remove('showtime');
  timeFormate.classList.add('hideTime');
  dateFormate.classList.remove('showtime');
  dateFormate.classList.add('hideTime');
};

const generateCalendar = (month, year) => {
  let calendar_days = document.querySelector('.calendar-days');
  calendar_days.innerHTML = '';
  let calendar_header_year = document.querySelector('#year');
  let days_of_month = [
      31,
      getFebDays(year),
      31,
      30,
      31,
      30,
      31,
      31,
      30,
      31,
      30,
      31,
    ];

  let currentDate = new Date();

  month_picker.innerHTML = month_names[month];

  calendar_header_year.innerHTML = year;

  let first_day = new Date(year, month);


  for (let i = 1; i <= days_of_month[month] + first_day.getDay() - 1; i++) {

    let day = document.createElement('div');
    var l = hasEventDay(year, month, i);
console.log(l);
    if(hasEventDay(year, month, i)){
      day.classList.add('dayHasEvent');
      console.log('leffut');
      day.onclick = function(){
        //this.parentElement.removeChild(this);
      };
    }

    if (i >= first_day.getDay()) {
      day.innerHTML = i - first_day.getDay() + 1;

      if (i - first_day.getDay() + 1 === currentDate.getDate() &&
        year === currentDate.getFullYear() &&
        month === currentDate.getMonth()
      ) {
        day.classList.add('current-date');
      }
    }
    calendar_days.appendChild(day);
  }
};

let month_list = calendar.querySelector('.month-list');
month_names.forEach((e, index) => {
  let month = document.createElement('div');
  month.innerHTML = `<div>${e}</div>`;

  month_list.append(month);
  month.onclick = () => {
    currentMonth.value = index;
    generateCalendar(currentMonth.value, currentYear.value);
    month_list.classList.replace('show', 'hide');
    dayTextFormate.classList.remove('hideTime');
    dayTextFormate.classList.add('showtime');
    timeFormate.classList.remove('hideTime');
    timeFormate.classList.add('showtime');
    dateFormate.classList.remove('hideTime');
    dateFormate.classList.add('showtime');
  };
});

(function() {
  month_list.classList.add('hideonce');
})();
document.querySelector('#pre-year').onclick = () => {
  --currentYear.value;
  generateCalendar(currentMonth.value, currentYear.value);
};
document.querySelector('#next-year').onclick = () => {
  ++currentYear.value;
  generateCalendar(currentMonth.value, currentYear.value);
};

let currentDate = new Date();
let currentMonth = { value: currentDate.getMonth() };
let currentYear = { value: currentDate.getFullYear() };
generateCalendar(currentMonth.value, currentYear.value);

const todayShowTime = document.querySelector('.time-formate');
const todayShowDate = document.querySelector('.date-formate');

const currshowDate = new Date();
const showCurrentDateOption = {
  year: 'numeric',
  month: 'long',
  day: 'numeric',
  weekday: 'long',
};
const currentDateFormate = new Intl.DateTimeFormat(
  'hu-HU',
  showCurrentDateOption
).format(currshowDate);
todayShowDate.textContent = currentDateFormate;
setInterval(() => {
  const timer = new Date();
  const option = {
    hour: 'numeric',
    minute: 'numeric',
    second: 'numeric',
  };
  const formateTimer = new Intl.DateTimeFormat('en-us', option).format(timer);
  let time = `${`${timer.getHours()}`.padStart(
      2,
      '0'
    )}:${`${timer.getMinutes()}`.padStart(
      2,
      '0'
    )}: ${`${timer.getSeconds()}`.padStart(2, '0')}`;
  todayShowTime.textContent = formateTimer;
}, 1000);