create clendar component with constructor in pure js in javascript

index.tsx
function Calendar(container) {
  var date = new Date();
  var year = date.getFullYear();
  var month = date.getMonth();
  var months = [
    "January", "February", "March", "April", "May", "June", "July",
    "August", "September", "October", "November", "December"
  ];

  // create calendar
  var calendar = document.createElement("div");
  calendar.classList.add("calendar");

  // create header
  var header = document.createElement("div");
  header.classList.add("calendar-header");

  var prevBtn = document.createElement("button");
  prevBtn.innerHTML = "<";
  prevBtn.addEventListener("click", function() {
    month--;
    updateCalendar();
  });

  var nextBtn = document.createElement("button");
  nextBtn.innerHTML = ">";
  nextBtn.addEventListener("click", function() {
    month++;
    updateCalendar();
  });

  var title = document.createElement("span");
  title.classList.add("calendar-title");
  title.innerHTML = months[month] + " " + year;

  header.appendChild(prevBtn);
  header.appendChild(title);
  header.appendChild(nextBtn);

  calendar.appendChild(header);

  // create body
  var body = document.createElement("div");
  body.classList.add("calendar-body");

  function updateCalendar() {
    title.innerHTML = months[month] + " " + year;

    // clear previous cells
    while (body.hasChildNodes()) {
      body.removeChild(body.lastChild);
    }

    // get number of days in month
    var daysInMonth = new Date(year, month + 1, 0).getDate();

    // get starting day of the week
    var startDay = new Date(year, month, 1).getDay();

    // create cells
    for (var i = 0; i < startDay; i++) {
      var cell = document.createElement("span");
      cell.classList.add("calendar-cell");
      body.appendChild(cell);
    }

    for (var i = 1; i <= daysInMonth; i++) {
      var cell = document.createElement("span");
      cell.classList.add("calendar-cell");
      cell.innerHTML = i;
      body.appendChild(cell);
    }
  }

  updateCalendar();

  calendar.appendChild(body);

  // add calendar to container
  container.appendChild(calendar);
}

// usage
var container = document.getElementById("calendar-container");
var calendar = new Calendar(container);
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