09 Jul 2020

Rails 6 with Webpack in app/assets (and no Sprockets)

The first version of Rails with Sprockets to manage JS and CSS assets shipped in May 2011. Generating a new Rails app today includes not only Sprockets, but an entire second JS and CSS asset pipeline that uses Webpack. It… sort of… makes sense to do this, for legacy reasons, but it’s confusing.

Putting CSS into app/javascript/css doesn’t really make sense. Wouldn’t it make more sense to put CSS into app/assets/css? It would make a lot more sense, but Webpack is stuck in app/javascript is because Sprockets already owns app/assets.

Despite that, I have good news! It is possible to use app/assets for the JS, CSS, images, fonts, and other… assets… that are managed by Webpack. All you have to do is completely rip out Sprockets (giving up all gem-based JS and CSS) and then strategically reconfigure Webpack. Shall we get started?

If you’re starting a new Rails 6 app, you can use rails new --no-sprockets to avoid most of Sprockets. If you have an existing app, you’re going to have to yank it out by hand.

Remove Sprockets

(Skip this step if you generated a new Rails app with the --no-sprockets option.)

  1. bundle remove sass-rails
  2. rm config/initalizers/assets.rb
  3. Replace require 'rails/all' in config/application.rb with these lines instead:

     require "rails"
     # Pick the frameworks you want:
     require "active_model/railtie"
     require "active_job/railtie"
     require "active_record/railtie"
     require "active_storage/engine"
     require "action_controller/railtie"
     require "action_mailer/railtie"
     require "action_mailbox/engine"
     require "action_text/engine"
     require "action_view/railtie"
     require "action_cable/engine"
     # require "sprockets/railtie"
     require "rails/test_unit/railtie"
  4. Remove these lines from config/application/development.rb

     # Debug mode disables concatenation and preprocessing of assets.
     # This option may cause significant delays in view rendering with a large
     # number of complex assets.
     config.assets.debug = true
     # Suppress logger output for asset requests.
     config.assets.quiet = true
  5. Remove these lines from config/application/production.rb

     # Compress CSS using a preprocessor.
     # config.assets.css_compressor = :sass
     # Do not fallback to assets pipeline if a precompiled asset is missed.
     config.assets.compile = false

Once you have Sprockets completely removed, make sure you have Webpacker installed. If you generated a fresh Rails 6 app, you already have it.

Move Webpack to app/assets/

Now that you’ve gotten rid of Sprockets, you can configure the Webpacker gem to tell Webpack to use the app/assets directory to store your Webpack-organized CSS and JS.

For some reason, Rails 6 still generates a Sprockets-style app/assets directory, even if you explicitly disable Sprockets, so we’ll have to remove that first.

rm -rf app/assets

Then, move the existing Webpack assets directory over there instead.

mv app/javascript app/assets

Create an application stylesheet in packs.

touch app/assets/packs/application.scss

(If you generate controllers, Rails will create stylesheets like app/assets/stylesheets/controller.css, and you can import those files with lines like @import "../stylesheets/controller.css in the pack.)

Update app/views/layouts/application.html.erb to use the pack instead of the now-gone Sprockets stylesheet.

sed -i '' s/stylesheet_link_tag/stylesheet_pack_tag/ app/views/layouts/application.html.erb

Finally, update the Webpacker gem config so that both Rails and Webpack will know where to look for your assets.

In config/webpacker.yml, change source_path: app/javascript to source_path: app/assets.

That’s it! Welcome to the confusing and somewhat terrifying world of modern frontend dependencies. You can’t use any Javascript provided via RubyGems anymore, but you can use any Javascript or CSS provided by npm packages. Just run yarn add package-name, and import the package in your application.js or application.scss. Enjoy it.