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Bundle and transpile JavaScript in Rails with esbuild, rollup.js, or Webpack.


>= 6.0.0
 Project Readme

JavaScript Bundling for Rails

Use esbuild, rollup.js, or Webpack to bundle your JavaScript, then deliver it via the asset pipeline in Rails. This gem provides installers to get you going with the bundler of your choice in a new Rails application, and a convention to use app/assets/builds to hold your bundled output as artifacts that are not checked into source control (the installer adds this directory to .gitignore by default).

You develop using this approach by running the bundler in watch mode in a terminal with yarn build --watch (and your Rails server in another, if you're not using something like puma-dev). Whenever the bundler detects changes to any of the JavaScript files in your project, it'll bundle app/javascript/application.js into app/assets/builds/application.js (and all other entry points configured). You can refer to the build output in your layout using the standard asset pipeline approach with <%= javascript_include_tag "application", defer: true %>.

When you deploy your application to production, the javascript:build task attaches to the assets:precompile task to ensure that all your package dependencies from package.json have been installed via yarn, and then runs yarn build to process all the entry points, as it would in development. The latter files are then picked up by the asset pipeline, digested, and copied into public/assets, as any other asset pipeline file.

This also happens in testing where the bundler attaches to the test:prepare task to ensure the JavaScript has been bundled before testing commences. (Note that this currently only applies to rails test:* tasks (like test:all or test:controllers), not "rails test", as that doesn't load test:prepare).

If your testing library of choice does not define a test:prepare Rake task, ensure that your test suite runs javascript:build to bundle JavaScript before testing commences.

That's it!

You can configure your bundler options in the build script in package.json or via the installer-generated rollup.config.js for rollup.js or webpack.config.json for Webpack (esbuild does not have a default configuration format).

If you're already using webpacker and you're wondering if you should migrate to jsbundling-rails, have a look at the high-level comparison.


You must already have node and yarn installed on your system. You will also need npx version 7.1.0 or later. Then:

  1. Add jsbundling-rails to your Gemfile with gem 'jsbundling-rails'
  2. Run ./bin/bundle install
  3. Run ./bin/rails javascript:install:[esbuild|rollup|webpack]

Or, in Rails 7+, you can preconfigure your new application to use a specific bundler with rails new myapp -j [esbuild|rollup|webpack].


JavaScript Bundling for Rails is released under the MIT License.