Does using //www.example.com in Javascript chose http/https protocol automatically

by

http://paulirish.com/2010/the-protocol-relative-url/

has a great article regarding this very issue. Included here:

The protocol-relative URL

October 27th, 2010

Author : Paul Irish

There’s this little trick you can get away with that’ll save you some headaches:

<img src="//domain.com/img/logo.png">

If the browser is viewing that current page in through HTTPS, then it’ll request that asset with the HTTPS protocol, otherwise it’ll typically* request it with HTTP. This prevents that awful “This Page Contains Both Secure and Non-Secure Items” error message in IE, keeping all your asset requests within the same protocol.

*Of course, if you’re viewing the file locally, it’ll try to request the file with the file:// protocol.

We use this trick in the HTML5 Boilerplate for a clever request of jQuery off the Google CDN:

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.js"></script>
<script>!window.jQuery && document.write(unescape('%3Cscript src="js/libs/jquery-1.4.2.js"%3E%3C/script%3E'))</script>

Technically, this is called a “network-path reference” according to RFC 3986. Oh and if you want to be truly correct, you’ll use the term “scheme” instead of “protocol” when talking about URLs.

This trick also works fine in CSS:

.omgomg { background: url(//websbestgifs.net/kittyonadolphin.gif); }

… assuming the site you’re pointing to has this asset available on both HTTP and HTTPS.

Caveat: When used on a <link> or @import for a stylesheet, IE7 and IE8 download the file twice. All other uses, however, are just fine.

Thx to miketaylr, ralphholzmann, annevk for smarts on this, and ajaxian, where I think I learned it like 4 years ago? maybe?

2011.01.23: But.. what about using this on the google analytics snippet?
Yes of course, wouldn’t that be nice.. So I worked with the Google Analytics javascript lead developer (God, I love working at google) to see if we could do this.. turns out we can’t. There is an edgecase bug in IE6 that causes a dialog to blow up… under some security settings (unsure if they are default) when requesting form the non-‘ssl’ subdomain. screenshot here. So feel free to take 40 bytes off your GA snippet if you don’t care about IE6.. otherwise you’re gonna need that ternary operator. 🙂

More Related Contents:

  1. can some one recommend a good client library to send data over https? [closed]
  2. In what situations would AJAX long/short polling be preferred over HTML5 WebSockets?
  3. How to create an HTTPS server in Node.js?
  4. How to Include CSS and JS files via HTTPS when needed?
  5. How can I use JavaScript on the client side to detect if the page was encrypted?
  6. Configuring HTTPS for Express and Nginx
  7. JS – Mobile – Open Safari from any browser [closed]
  8. nodejs – error self signed certificate in certificate chain
  9. Listen on HTTP and HTTPS for a single express app
  10. Determine if ajax call failed due to insecure response or connection refused
  11. Page loaded over HTTPS but requested an insecure XMLHttpRequest endpoint
  12. How can I use HTTPS in AngularJS?
  13. Ajax GET request over HTTPS
  14. x y plane coordinates – find is how many points in the list above are located a distance less than or equal to the radius [closed]
  15. How do I make the first letter of a string uppercase in JavaScript?
  16. How to fix getImageData() error The canvas has been tainted by cross-origin data?
  17. How can I set a cookie with expire time?
  18. Store jquery selector in variable
  19. Aborting jQuery().load()
  20. Event Capturing vs Event Bubbling [duplicate]
  21. Error “Uncaught SyntaxError: Unexpected token with JSON.parse”
  22. Reactjs – Setting State from props using setState in child component
  23. Delete first character of string if it is 0
  24. html download attribute redirects to url instead of downloading
  25. Nodejs: get filename of caller function
  26. How to create json by JavaScript for loop?
  27. Return an object key only if value is true
  28. How to calculate the width of the scroll bar?
  29. JavaScript prototype ‘this’ issue
  30. Process a continuous stream of JSON

Leave a Comment