code: function observeDOM(obj, callback) {
      const MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
  
      /* istanbul ignore else */
      if (MutationObserver) {
          const obs = new MutationObserver(callback);
  
          obs.observe(obj, {
              childList: true,
              subtree: true
          });
      } else {
          obj.addEventListener('DOMNodeInserted', callback, false);
          obj.addEventListener('DOMNodeRemoved', callback, false);
      }
  }
docs: Observes DOM mutations and runs a callback function when
  detecting one.
  
  @param {node} obj The DOM node you want to observe
  @param {function} callback The callback function you want to call
  @return {void}