iframe-content-observer.js

    iframe.contentWindow.addEventListener('beforeunload',() => this.middlewareCleanupWrapper() );
 
    if (this.observer) {
      this.observer.disconnect();
    }

    this.observer = new MutationObserver(mutations => {
      iframe.parentElement.style.height = iframe.contentDocument.documentElement.offsetHeight + 'px';
    });

    this.observer.observe(iframe.contentDocument.body, {
      attributes: true,
      attributesFilter: ['style'],
      subtree: true
    });
    
    iframe.parentElement.style.height = iframe.contentDocument.documentElement.offsetHeight + 'px';