Sprockets Rails integration
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Latest commit 45b6b84 Sep 26, 2016 @schneems schneems committed on GitHub Merge pull request #380 from dreyks/patch-1
fix changelog entry about unknown_asset_fallback


Sprockets Rails

Provides Sprockets implementation for Rails 4.x (and beyond) Asset Pipeline.


gem 'sprockets-rails', :require => 'sprockets/railtie'

Or alternatively require 'sprockets/railtie' in your config/application.rb if you have Bundler auto-require disabled.


Rake task

rake assets:precompile

Deployment task that compiles any assets listed in config.assets.precompile to public/assets.

rake assets:clean

Only removes old assets (keeps the most recent 3 copies) from public/assets. Useful when doing rolling deploys that may still be serving old assets while the new ones are being compiled.

rake assets:clobber

Nuke public/assets.


If the basic tasks don't do all that you need, it's straight forward to redefine them and replace them with something more specific to your app.

You can also redefine the task with the built in task generator.

require 'sprockets/rails/task'
Sprockets::Rails::Task.new(Rails.application) do |t|
  t.environment = lambda { Rails.application.assets }
  t.assets = %w( application.js application.css )
  t.keep = 5

Each asset task will invoke assets:environment first. By default this loads the Rails environment. You can override this task to add or remove dependencies for your specific compilation environment.

Also see Sprockets::Rails::Task and Rake::SprocketsTask.

Initializer options


When set to a truthy value, a result will be returned even if the requested asset is not found in the asset pipeline. When set to a falsey value it will raise an error when no asset is found in the pipeline. Defaults to true.


Add additional assets to compile on deploy. Defaults to application.js, application.css and any other non-js/css file under app/assets.


Add additional load paths to this Array. Rails includes app/assets, lib/assets and vendor/assets for you already. Plugins might want to add their custom paths to this.


Suppresses logger output for asset requests. Uses the config.assets.prefix path to match asset requests. Defaults to false.


Set a custom cache buster string. Changing it will cause all assets to recompile on the next build.

config.assets.version = 'v1'
# after installing a new plugin, change loads paths
config.assets.version = 'v2'


Defaults to /assets. Changes the directory to compile assets to.


When enabled, fingerprints will be added to asset filenames.


Enable expanded asset debugging mode. Individual files will be served to make referencing filenames in the web console easier. This feature will eventually be deprecated and replaced by Source Maps in Sprockets 3.x.


Enables Sprockets compile environment. If disabled, Rails.application.assets will be nil to prevent inadvertent compilation calls. View helpers will depend on assets being precompiled to public/assets in order to link to them. Initializers expecting Rails.application.assets during boot should be accessing the environment in a config.assets.configure block. See below.


Invokes block with environment when the environment is initialized. Allows direct access to the environment instance and lets you lazily load libraries only needed for asset compiling.

config.assets.configure do |env|
  env.js_compressor  = :uglifier # or :closure, :yui
  env.css_compressor = :sass   # or :yui

  require 'my_processor'
  env.register_preprocessor 'application/javascript', MyProcessor

  env.logger = Rails.logger


A list of :environment and :manifest symbols that defines the order that we try to find assets: manifest first, environment second? Manifest only?

By default, we check the manifest first if asset digests are enabled and debug is not enabled, then we check the environment if compiling is enabled:

# Dev where debug is true, or digests are disabled
%i[ environment ]

# Dev default, or production with compile enabled.
%i[ manifest environment ]

# Production default.
%i[ manifest ]

If the resolver list is empty (e.g. if debug is true and compile is false), the standard rails public path resolution will be used.


When enabled, an exception is raised for missing assets. This option is enabled by default.

Complementary plugins

The following plugins provide some extras for the Sprockets Asset Pipeline.

NOTE That these plugins are optional. The core coffee-script, sass, less, uglify, (any many more) features are built into Sprockets itself. Many of these plugins only provide generators and extra helpers. You can probably get by without them.

Changes from Rails 3.x

  • Only compiles digest filenames. Static non-digest assets should simply live in public/.
  • Unmanaged asset paths and urls fallback to linking to public/. This should make it easier to work with both compiled assets and simple static assets. As a side effect, there will never be any "asset not precompiled errors" when linking to missing assets. They will just link to a public file which may or may not exist.
  • JS and CSS compressors must be explicitly set. Magic detection has been removed to avoid loading compressors in environments where you want to avoid loading any of the asset libraries. Assign config.assets.js_compressor = :uglifier or config.assets.css_compressor = :sass for the standard compressors.
  • The manifest file is now in a JSON format. Since it lives in public/ by default, the initial filename is also randomized to obfuscate public access to the resource.
  • config.assets.manifest (if used) must now include the manifest filename, e.g. Rails.root.join('config/manifest.json'). It cannot be a directory.
  • Two cleanup tasks: rake assets:clean is now a safe cleanup that only removes older assets that are no longer used, while rake assets:clobber nukes the entire public/assets directory. The clean task allows for rolling deploys that may still be linking to an old asset while the new assets are being built.


SRI support

Sprockets 3.x adds experimental support for subresource integrity checks. The spec is still evolving and the API may change in backwards incompatible ways.

javascript_include_tag :application, integrity: true
# => "<script src="/assets/application.js" integrity="sha256-TvVUHzSfftWg1rcfL6TIJ0XKEGrgLyEq6lEpcmrG9qs="></script>"

Note that sprockets-rails only adds integrity hashes to assets when served in a secure context (over an HTTPS connection or localhost).

Contributing to Sprockets Rails

Sprockets Rails is work of many contributors. You're encouraged to submit pull requests, propose features and discuss issues.



sprockets-rails 3.x will primarily target sprockets 3.x. And future versions will target the corresponding sprockets release line.

The minor and patch version will be updated according to semver.

  • Any new APIs or config options that don't break compatibility will be in a minor release
  • Any time the sprockets dependency is bumped, there will be a new minor release
  • Simple bug fixes will be patch releases


Sprockets Rails is released under the MIT License.

Code Status

  • Travis CI
  • Gem Version
  • Dependencies