Why does the JsSIP example not work locally but work on JSFiddle?

Question

WebRTC

One wonderful person (kudos to him) posted an example of working with the JsSIP library for WebRTC calls on JSFiddle - https://jsfiddle.net/msqenm70/2/.
You drive in sip uri/password and everything works fine from the browser. But after I save it all (html, js, css) to files and run it on my computer, nothing works.
And to be more precise, the connection occurs with the server, the server responds, there are no errors in the console, the logs are identical to those that I see when I run the script from the browser (on JSFiddle), but the call button is disabled and the message "must set sip uri / password" does not disappear ".