The default way to handle javascript in Rails 6 is Webpack, via the webpacker gem. This is great in many scenarios, but sometimes it just feels too much for a simple app with some jquery plugins. The following steps will allow you to use Sprockets as in Rails 5/4/3.

For new apps, pass --skip-webpack-install and you’re good to go.

For existing apps follow these steps:

1. Remove the webpacker gem, bundle install and restart.
2. yarn remove @rails/webpacker.
3. rm -r config/webpacker.
4. rm config/webpack.yml.
5. Change any javascript_pack_tag to javascript_include_tag.
6. Create app/assets/javascripts/application.js and //= require X any libs you need.
7. Add //= link_directory ../javascripts .js to app/assets/config/manifest.js

You can still use yarn to handle the js dependencies. An example application.js file from a recent project:

//= require jquery
//= require bootstrap/dist/js/bootstrap
//= require tablesorter

Heroku compilation issues

Without the webpacker gem installed, if you are deploying on heroku, you will need to add the nodejs buildpack to ensure your npm packages are installed before the app is built:

heroku buildpacks:add --index 1 heroku/nodejs

Done and dusted.