QWebEngineView not working from js

I need to invoke a dialog from the JS side, which contains a qwebengineview to display the video, but it does not work properly.

MainWindow contains a QWebEngineView A for the main UI, it is a local web page.

And Dialog also contains a QWebEngineView B, it is used as a H5 video player.

My requirement is invoke B from within A.

please see the attachments for details.