how to check website offline status in js

https://developer.mozilla.org/en-US/docs/Web/API/NavigatorOnLine/Online_and_offline_events

navigator.onLine

const online = window.navigator.onLine;

window.addEventListener('load', function() {
  var status = document.getElementById("status");
  var log = document.getElementById("log");

  function updateOnlineStatus(event) {
    var condition = navigator.onLine ? "online" : "offline";

    status.className = condition;
    status.innerHTML = condition.toUpperCase();

    log.insertAdjacentHTML("beforeend", "Event: " + event.type + "; Status: " + condition);
  }

  window.addEventListener('online',  updateOnlineStatus);
  window.addEventListener('offline', updateOnlineStatus);
});

https://bug336359.bmoattachments.org/attachment.cgi?id=220609

http://html5-demos.appspot.com/static/navigator.onLine.html

https://caniuse.com/#feat=online-status