CssSplitter

Gem for splitting up stylesheets that go beyond the IE limit of 4096 selectors, for Rails 3.1+ apps using the Asset Pipeline. You can read this blogpost for an explanation of this gem's background story.

Install by putting gem 'css_splitter' into your Gemfile.

Older versions of Internet Explorer (version 9 and below) have a hard limit for the number of CSS selectors they can process, which is 4095. If one of your stylesheets exceeds this limit, all the rule sets beyond the 4095th selector will not be processed by IE and your app will miss some styling information.

CssSplitter integrates with the Rails 3.1+ Asset Pipeline to generate additional split stylesheets with all the CSS rules beyond the 4095th that can be served to IE browsers in order to get all the styling information.

• Sprockets 2.0+
• e.g. Rails 3.1+ with the asset pipeline

The first step is identifying the stylesheets that have more than 4095 selectors and therefore need to be split for IE.

Once you know which stylesheets need to be split, you need to create a second "container file" for those stylesheets with the _split2 suffix appended to the base filename that will contain the styles beyond the 4095 selector limit. The extension of this file should be just .css without any additional preprocessor extensions.

For example, if you want to split too_big_stylesheet.css.scss, you need to create a new file too_big_stylesheet_split2.css in the same directory. The only content of that container, will contain a require directive to the name of the original asset, e.g.:

# app/assets/stylesheets/too_big_stylesheet_split2.css

/*
 *= require 'too_big_stylesheet'
 */

If your stylesheet is big enough to need splitting into more than two more files, simply create additional _split3, _split4, etc. files, the contents of which should be identical to the _split2 file.

You also need to remember to add those new files to the asset pipeline, so they will be compiled. For example:

# config/application.rb

module MyApp
  class Application < Rails::Application
    config.assets.precompile += %w( too_big_stylesheet_split2.css )

Here is a checklist of requirements for your split stylesheet:

1. It needs to have the _splitN suffix appended to the original asset name, e.g. original_stylesheet_split2 or application_split2
2. It needs to have .css as a file extension.
3. It needs to require the orginal stylesheet.
4. It needs to be added to list of precompiled assets.

Now that you have split up your big stylesheets at the 4095 limit you need to change your HTML layout, so the split stylesheets are used for older IE versions (IE9 and older).

You can just use our split_stylesheet_link_tag helper, which would look something like this:

# app/views/layout/application.html.erb
<%= split_stylesheet_link_tag "too_big_stylesheet", :media => "all" %>

# output
<link href="/stylesheets/too_big_stylesheet.css" media="all" rel="stylesheet" type="text/css" />
<!--[if lte IE 9]>
  <link href="/stylesheets/too_big_stylesheet_split2.css" media="all" rel="stylesheet" type="text/css" />
<![endif]-->

If your stylesheet is split into more than two files, add the split_count option to specify the total number of files.

<%= split_stylesheet_link_tag "too_big_stylesheet", :split_count => 3 %>

Or you can just create similar HTML as in the above example yourself. If you want to use the split_stylesheet_link_tag helper you need to make sure the gem is loaded in production, so you can't put it in the :assets group in your Gemfile.

Basically, CssSplitter is registering a new Sprockets bundle processor that looks for CSS assets named with the _splitN suffix and will fill those files with all the selectors beyond the 4095th. Unfortunately, those _splitN files need to be created manually, because we haven't figured out a way for a Sprockets::Engine to output multiple files. They need to present before the compile step.

If you have more questions about how it works, look at the code or contact us.

Note that if you used versions below 0.4.0 of this gem, the naming and contents of the split files have changed. Split files no longer need to have the .split2 extension and now use the require directive rather than the include directive. The previous prohibition against using require_tree . and require_self directives also no longer applies. For more details see the CHANGELOG.md

This is a joint project by the two German Rails shops Zweitag and Railslove, therefore the GitHub name "Zweilove".

The original code was written by Christian Peters and Thomas Hollstegge (see this Gist) and turned into a gem by Jakob Hilden.

Major Contributors

• @Umofomia

This project rocks and uses MIT-LICENSE.