destructor() {
    this._throwIfDestroyed();

    if (this._node) {
      if (this.hasSavedTabIndex)
        this._node.setAttribute('tabindex', this.savedTabIndex);
      else
        this._node.removeAttribute('tabindex');

      // Use `delete` to restore native focus method.
      if (this._overrodeFocusMethod)
        delete this._node.focus;
    }
    this._node = null;
    this._inertRoots = null;

    this._destroyed = true;
  }
Call this whenever this object is about to become obsolete.
This makes the managed node focusable again and deletes all of the previously stored state.