destroy() {
    this.opened = undefined;
    this.loading = undefined;
    this.loaded = undefined;
    this.ready = undefined;
    this.isOpen = false;
    this.isRendered = false;
    this.spine && this.spine.destroy();
    this.locations && this.locations.destroy();
    this.pageList && this.pageList.destroy();
    this.archive && this.archive.destroy();
    this.resources && this.resources.destroy();
    this.container && this.container.destroy();
    this.packaging && this.packaging.destroy();
    this.rendition && this.rendition.destroy();
    this.displayOptions && this.displayOptions.destroy();
    this.spine = undefined;
    this.locations = undefined;
    this.pageList = undefined;
    this.archive = undefined;
    this.resources = undefined;
    this.container = undefined;
    this.packaging = undefined;
    this.rendition = undefined;
    this.navigation = undefined;
    this.url = undefined;
    this.path = undefined;
    this.archived = false;
  }
Destroy the Book and all associated objects