Using // in a <script>'s source

Question

I was wondering if anyone had any resources, proof, or personal experience in using the age-old http/https JavaScript <script> hack:

<script src="//someserver.com/js/script.js"></script>

Has anyone encountered issues in any of these browsers (IE 5.5+, FF2+, Chrome, Opera 9+, Safari 3+)? Has anybody had success stories?

Answer 1

All modern browsers will understand that format, including IE 6. (Not sure about IE 5.5).

Actually, this is not a hack, but a perfectly valid URI syntax as per RFC 3986: Section 4.2. Therefore, I say you're good to go.

Answer 2

I can point you to exactly what you are looking for. It is an RFC document so you have to sift through a lot of noise to get to what you want but this is a legit feature (not a hack) of supposed http clients.

       b) If the embedded URL starts with a scheme name, it is
          interpreted as an absolute URL and we are done.

       c) Otherwise, the embedded URL inherits the scheme of
          the base URL.

Read more: http://www.faqs.org/rfcs/rfc1808.html (search for the heading "Resolving Relative URLs" and see steps 1 and 2 below) or here: http://freesoft.org/CIE/RFC/1808/18.htm

As an FYI, I use this in pretty much all of my production projects -- not just for JS resources, but for links to other resources such as images and CSS (UPDATED: I no longer use this for linking stylesheets).

Works pretty much everywhere. I've tried this in IE, FF, Opera, Chrome, Safari/Webkit all going back multiple previous versions (where applicable).

Examples:

• < img src="//static.example.com/img/token.png" />
• < script type="text/javascript" src="//static.example.com/js/jquery.js">

I find this method to be cleaner than writing code to figure out if we are on http/https.

The only caveat is that you should not use this for stylesheets.

While the following is legal and works:

• < link rel="stylesheet" type="text/css" href="//static.example.com/css/screen.css" media="screen" />

In IE, the above will cause two HTTP requests. Currently, this affects IE7, IE8, and early versions of IE9.

In other words, scheme relative URIs should/can be used for all resources except stylesheets.