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Best way to use latest jQuery in Ruby app
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DEPRECATED: Best way to load latest jQuery in Ruby

This project is depreacted. Use Node.js build tools instead of Sprockets.

Load jQuery from CDN in production and use local copy in development. jQuery-CDN supports Ruby on Rails, Sinatra and other non-Rails environments with Sprockets.

Another gem jquery-rails contains also UJS adapter for jQuery. So it need to test any jQuery updates and will release new jQuery version after few month (for example, there is still no jQuery 2 in jquery-ujs). If you don’t need UJS, this gem will be better for you.

jQuery-CDN now has 2 branches: with jQuery 2.x and 1.x.


Load from CDN

Public CDN is a best way to serve jQuery:

  • 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.

In development gem will use local copy of jQuery, so you can develop app in airplane without Internet. In production gem will use CDN, but if it will down, gem will automatically fallback to bundled jQuery.

Latest version of jQuery

Instead of jquery-rails this gem always contain latest version of jQuery, because it doesn’t need to test compatibility with UJS adapter.

For example, jquery-rails doesn’t support jQuery 2 even after 4 months.

Gem version is same that jQuery

Instead of jquery-rails, this gem versions tell exactly what jQuery is inside. Gemfile maintaining will be much easy:

gem 'jquery-cdn', '1.10.2' # Use jQuery 1.10.2

Sinatra and plain Ruby support

You can use jQuery-CDN with Ruby on Rails, Sinatra or any other Ruby environment with Sprockets.

How To

Ruby on Rails

Add jquery-cdn gem to your Gemfile:

gem 'jquery-cdn'

If you support IE 6, 7 or 8, lock jQuery in 1.x versions:

gem 'jquery-cdn', '~> 1.0'

Call include_jquery helper in layout:

!!! 5
    %title My site
    = include_jquery
    = javascript_include_tag('application')


If you use Sinatra or other non-Rails frameworks with Sprockets, just connect your Sprockets environment to jQuery-CDN:

require 'jquery-cdn'

assets = do |env|
  # Your assets settings


Set local jQuery URL (by default, /assets/jquery.js):

JqueryCdn.local_url = proc { '/jquery.js' }

Include JqueryCdn::Helpers module to your app:

class YourApp < Sinatra::Base
  helpers { include JqueryCdn::Helpers }

And use include_jquery helper with env option:

!!! 5
    = include_jquery(env: app.environment)


Helper include_jquery has 2 options:

  • env: CDN will be used only in :production environment. Rails helper can detect it automatically. By default, :production.
  • cdn: CDN to use. By default, :google.

Other options will be used as <script> attributes.


By default, gem use Google CDN, but you can change it by cdn option:

= include_jquery cdn: :yandex

You can use :google, :microsoft, :jquery, :yandex or :cloudflare CDN.


Scripts with defer attribute will be executed only after <body> loading. They increase perfomance, because scripts without defer block DOM parsing, until script is downloading.

This attribute works like you put <script> tags to end of <body>. But defer is better, because scripts downloading will start early.

So, defer attributes is highly recommended, but you need add it to all your scripts.

!!! 5
    %title My site
    = include_jquery(defer: true)
    = javascript_include_tag('application', defer: true)

Note, that unfortunately jQuery-CDN can’t use fallback with defer now, because this options can’t work with inline scripts.


According to Murphy’s Law, even Google CDN may go down. So when you write include_jquery, jQuery CDN inserts:

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

This HTML checks, is jQuery normally loaded from Google. On any problems it will load local copy of jQuery.