window.onload = function HRTTimer() {
  let interval = 1000;
  let times = getTimes(interval);
  let expected = times["expected"];
  setTimeout(step, interval);
  function step() {
    const dt = Date.now() - expected; // the drift (positive for overshooting)
    if (dt > interval) {
      // something really bad happened. Maybe the browser (tab) was inactive?
      // possibly special handling to avoid futile "catch up" run
    }
    times["days"] = Math.round(expected / 1000 / 60 / 60 / 24);
    times["hours"] = (new Date(expected).getHours() + 6) % 24;
    times["minutes"] = new Date(expected).getMinutes();
    times["seconds"] = new Date(expected).getSeconds();
    if (document.getElementById("time_0") != null) {
      document.getElementById("time_0").textContent = times["days"] + " days, ";
      document.getElementById("time_1").textContent =
        times["hours"] + " hours, ";
      document.getElementById("time_2").textContent =
        times["minutes"] + " minutes, ";
      document.getElementById("time_3").textContent =
        "and " + times["seconds"] + " seconds";
    }
    expected += interval;
    setTimeout(step, Math.max(interval - dt, 1000)); // take into account drift
  }
};

function getTimes(interval) {
  let expected = Date.now() - new Date("December 11, 2020 00:00:00") + interval;
  let days = Math.floor(expected / 1000 / 60 / 60 / 24);
  let hours = new Date(expected).getHours();
  let minutes = new Date(expected).getMinutes();
  let seconds = new Date(expected).getSeconds();
  return {
    expected: expected,
    days: days,
    hours: hours,
    minutes: minutes,
    seconds: seconds,
  };
}