Updating times according to the viewer's timezone

index.html

    <script src="moment.min.js"></script>
    <script src="moment-timezone-with-data-10-year-range.js"></script>
    <script>
      const my_zone = moment.tz.guess(true);

      // Set up timezone selector with all the zones.
      // The user's current guessed zone is selected.
      const sel = document.querySelector('select.timezone');
      moment.tz.names().forEach( zone => {
        option = document.createElement('option');
        option.text = zone;
        option.value = zone;
        if (option.text == my_zone) {
          option.selected = true;
        }
        sel.add(option);
      });

      // A function to update the times in the page.
      const set_times = (to_zone) => {
        document.querySelectorAll('th.time').forEach( el => {
          const est = el.getAttribute("est");
          const est_time = moment.tz(est, 'HH:mm', 'America/New_York');
          const disp_time = est_time.tz(to_zone);
          
          el.innerHTML = disp_time.format("HH:mm");
        });
      };

      // Call set_times when the selector changes.
      sel.addEventListener('change', (event) => {
        set_times(event.target.value);
      });

      // And, when we come up, set times to the user's guessed zone.
      set_times(my_zone);
      
    </script>