constructor() {
    this.pdfViewer = null;
    this.pdfThumbnailViewer = null;
    this.onIdle = null;
    this.highestPriorityPage = null;
    /** @type {number} */
    this.idleTimeout = null;
    this.printing = false;
    this.isThumbnailViewEnabled = false;

    if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
      Object.defineProperty(this, "hasViewer", {
        value: () => !!this.pdfViewer,
      });
    }
  }
Controls rendering of the views for pages and thumbnails.