Starting a URL with //
means “Use a different server but keep the same scheme”
So if you load //example.net/script
from https://example.com/
it will get https://example.net/script
, while if you load it from http://example.com/
it will get http://example.net/script
.
If, on the other hand, you load it from file://c:/Users/You/Documents/test.html
then it will probably not resolve to anything useful. Make sure you do development with a local web server (and access http://localhost/
) if you use this syntax.
This is a standard part of URIs, it well supported, and is usually known as “scheme relative URIs”