JavaScript Github source files integration

Hi,
I have added an iframe for my site which works fine but this only works properly on desktop, on mobile the scaling is not correct because iframes are not really mobile friendly to my experience.

I’m currently looking to make it more responsive via javascript integration and doing API calls that way. This is an example of what I’m looking for: www.sagenda. com/integrate-booking-system-website/javascript/
Is it possible to manage it like this? The main issue I see is that I can’t seem to find a way to import source files which are used for the configuration. I could use a hard link to Github as well but that could break the code if something changes there.

Thanks!