shorthand http:// as // for script and link tags? anyone see / use this before?

Question

the question is as follows:

if you take a look at any site using addthis (the share button)...

once you float over the addthis button, and all of the require

Answer 1

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"

Answer 2

To build upon Quentin's answer, these URLs are commonly called protocol-less URLs (although, as Nick points out in the comments, the proper name is scheme-less).

Also, be wary of the case where you use them in local development (i.e. linking to jQuery from an HTML page that you load from your hard disk, through the file:// protocol). In such scenarios, all outbound links will be treated as local ones - //jquery.com/ will refer to file://jquery.com/