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, jquery.com, 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.

Changelog:

• v1.2.0: Support jQuery3. (Thanks to @CUnknown)
• v1.1.0: Support jQuery2. (Thanks to @timurkhafizov)
• v1.0.0: Options like defer: true or data-turbolinks-eval: false are allowed to be passed. (Thanks to @mkitt)
• v0.4.0: Added Cloudflare. (Thanks to @damonmorgan)
• v0.3.0: Microsoft and Yandex are now always scheme-less. (Thanks to @atipugin)
• v0.2.1: Use minified version for Yandex. (Thanks to @atipugin)
• 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 and 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 and jquery_url.

If you're using asset pipeline with Rails 3.1+,

• Remove //= require jquery from application.js.
• Put the following line in config/application.rb, so that jquery.js will be served from your server when CDN is not available.

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

Then in layout:

= jquery_include_tag :google
= javascript_include_tag 'application'

Note that valid CDN symbols are :google, :microsoft, :jquery, :cloudflare and :yandex.

Now, it will generate the following on production:

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.8.0/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
//<![CDATA[
window.jQuery || document.write(unescape('%3Cscript src="/assets/jquery-3aaa3fa0b0207a1abcd30555987cd4cc.js" type="text/javascript">%3C/script>'))
//]]>
</script>

on development:

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

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

jquery_include_tag :google, force: true

If you want to use jQuery 2, drop the following line in config/initializers/jquery_cdn.rb:

Jquery::Rails::Cdn.major_version = 2

or for jQuery 3:

Jquery::Rails::Cdn.major_version = 3

and then in config/application.rb:

config.assets.precompile += ['jquery2.js']

or for jQuery 3:

config.assets.precompile += ['jquery3.js']

To get the same CDN benefits with jQuery UI, we recommend jquery-ui-rails-cdn.