var box = document.createElement("div");
box.className = "ads AdSense adpopup adszone adslot AD300";
box.style.height = "1px";

var observer = new MutationObserver(function () {
  if (document.body.contains(box)) {
    console.log("It's in the DOM!");
    observer.disconnect();
    setTimeout(function () {
      var hasAdblocker = !box.offsetHeight;
      console.log({ hasAdblocker });
    }, 0);
  }
});

observer.observe(document.body, {
  attributes: false,
  childList: true,
  characterData: false,
  subtree: true,
});

document.body.appendChild(box);