<body>
  <webview id="webview" nodeintegration="on" webpreferences="contextIsolation=no" src="frame.html"/>
  <script type="text/javascript" charset="utf-8">
    document.addEventListener('fullscreenchange', () => {
      require('electron').ipcRenderer.send('fullscreenchange')
    })

    function isIframeFullscreen() {
      return document.getElementById('webview').shadowRoot.lastElementChild.matches(':fullscreen')
    }
  </script>
</body>
