Add CDN support to jquery-rails
Switch branches/tags
Pull request Compare This branch is 1 commit ahead, 28 commits behind kenn:master.
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Failed to load latest commit information.


Add CDN support to jquery-rails.

Serving jQuery from a publicly available CDN has clear benefits:

  • Speed: Users will be able to download jQuery from the closest physical location.
  • Caching: CDN is used so widely that potentially your users may not need to download jQuery at all.
  • Parallelism: Browsers have a limitation on how many connections can be made to a single host. Using CDN for jQuery offloads a big one.


This gem offers the following features:

  • Supports multiple CDN. (Google, Microsoft,, etc.)
  • jQuery version is automatically detected via jquery-rails.
  • Automatically fallback to jquery-rails' bundled jQuery when:
    • You're on a development environment, so that you can work offline.
    • The CDN is down or unreachable.

On top of that, if you're using asset pipeline, you may have noticed that the major chunks of the code in combined application.js is jQuery. Implications of externalizing jQuery from application.js are:

  • Updating your JS code won't evict the entire cache in browsers.
    • Cached jQuery in the client browsers will survive deployments.
    • Your code changes more often than jQuery upgrades, right?
  • rake assets:precompile will run faster and use less memory.


  • v0.2.0: (Incompatible Change) Google CDN is now always scheme-less. Add Yandex CDN for Russian users. (Thanks to @ai)
  • v0.1.0: Added :google_schemeless for sites that support both ssl / non-ssl
  • v0.0.1: Initial release


Add this line to your application's Gemfile:

gem 'jquery-rails-cdn'


This gem adds two methods jquery_include_tag to generate a script tag to the jQuery on a CDN of your preference.

If you're using asset pipeline with Rails 3.1+, first remove //= require jquery from application.js.

Then in layout:

= jquery_include_tag :google
= javascript_include_tag 'application'

Note that valid CDN symbols are:


It will generate the following on production:

<script src="//" type="text/javascript"></script>
<script type="text/javascript">
window.jQuery || document.write(unescape('%3Cscript src="/assets/jquery-3aaa3fa0b0207a1abcd30555987cd4cc.js" type="text/javascript">%3C/script>'))

on development:

<script src="/assets/jquery.js?body=1" type="text/javascript"></script>

Be sure to put the following line in config/application.rb, as it will be served when CDN is not available.

config.assets.precompile += ['jquery.js']

If you want to check the production URL, you can pass :force => true as an option.

jquery_include_tag :google, :force => true