How does javascript determine the protocol of a site?

Question

JavaScript

I have a client script that, depending on the protocol of the domain it's running on, pulls resources from my server, either via https: or http. In the script itself there is a simple check

//..something code..
const url = document.location.protocol === "https:" ? `https://myserver.com` : `http://myserver.com`;
//..something code..

And everything is fine, but on one secure site where my script is running, resources are pulled over http. I got into the debugger and saw something strange: the value of document.location.protocol is "about:".
Has anyone experienced something similar? What is the "about:" protocol anyway? Maybe someone knows how JS determines the protocol of the page on which it works?
Checked in the latest versions of Chrome, Mozilla, Yandex.Browser and Safari.

Answer 1

about are browser service pages, for example, a blank page is about:blank, a new tab is about:newtab, and so on. I do not know how it can be that the script on the site sees this protocol.
https://ru.m.wikipedia.org/wiki/About:_URI