Failed to execute 'postMessage' on 'DOMWindow': https://www.youtube.com !== http://localhost:9000

This is the error message that I get:

Failed to execute 'postMessage' on 'DOMWindow': The target origin provided
('https://www.youtube.com') does not match the recipient window's origin 
('http://localhost:9000').

I've seen other similar problems where the target origin is http://www.youtube.com and the recipient origin is https://www.youtube.com, but none like mine where the target is https://www.youtube.com and the origin is http://localhost:9000.

1. I don't get the problem. What is the problem?
2. How can I fix it?

I believe this is an issue with the target origin being https. I suspect it is because your iFrame url is using http instead of https. Try changing the url of the file you are trying to embed to be https.

For instance:

'//www.youtube.com/embed/' + id + '?showinfo=0&enablejsapi=1&origin=http://localhost:9000';

to be:

'https://www.youtube.com/embed/' + id + '?showinfo=0&enablejsapi=1&origin=http://localhost:9000';