Stimulus is a JavaScript framework with modest ambitions. It doesn’t seek to take over your entire front-end in fact, it’s not concerned with rendering HTML at all. Instead, it’s designed to augment your HTML with just enough behavior to make it shine. Stimulus pairs beautifully with Turbo to provide a complete solution for fast, compelling applications with a minimal amount of effort. Together they form the core of Hotwire.

Stimulus for Rails makes it easy to use this modest framework with both import-mapped and JavaScript-bundled apps. It relies on either importmap-rails to make Stimulus available via ESM or a Node-capable Rails (like via jsbundling-rails) to include Stimulus in the bundle. Make sure to install one of these first!

This gem is automatically configured for applications made with Rails 7+ (unless --skip-hotwire is passed to the generator). But if you're on Rails 6, you can install it with the installer or manually:

1. Add the stimulus-rails gem to your Gemfile: gem 'stimulus-rails'
2. Run ./bin/bundle install.
3. Run ./bin/rails stimulus:install

The installer will automatically detect whether you're using an import map or JavaScript bundler to manage your application's JavaScript. If you're using an import map, the Stimulus dependencies will be pinned to the versions of the library included with this gem. If you're using Node, yarn will add the dependencies to your package.json file.

The installer amends your JavaScript entry point at app/javascript/application.js to import the app/javascript/controllers/index.js file, which is responsible for setting up your Stimulus application and registering your controllers.

Note that we recommend running the installer as described above. But the following is helpful if you encounter errors while running the installer (e.g., if there are conflicts with existing files) or if you just like doing stuff manually. Follow the instructions for import map or JavaScript bundler, depending on your setup.

1. Add the stimulus-rails gem to your Gemfile: gem 'stimulus-rails'
2. Run ./bin/bundle install.

3. Create app/javascript/controllers/index.js and load your controllers like this:

import { application } from "controllers/application"

// Eager load all controllers defined in the import map under controllers/**/*_controller
import { eagerLoadControllersFrom } from "@hotwired/stimulus-loading"
eagerLoadControllersFrom("controllers", application)

4. Create app/javascript/controllers/application.js with the following content:

import { Application } from "@hotwired/stimulus"

const application = Application.start()

// Configure Stimulus development experience
application.debug = false
window.Stimulus   = application

export { application }

5. Add the following line to app/javascript/application.js to import all your controllers:

import "controllers"

6. Finally, Pin Stimulus and controllers in config/importmap.rb by adding:

pin "@hotwired/stimulus", to: "stimulus.min.js"
pin "@hotwired/stimulus-loading", to: "stimulus-loading.js"
pin_all_from "app/javascript/controllers", under: "controllers"

3. Create app/javascript/controllers/index.js and load your controllers.

Make sure to change HelloController to an actual controller and repeat for every controller you have or use the command mentioned in the comments below:

// This file is auto-generated by ./bin/rails stimulus:manifest:update
// Run that command whenever you add a new controller or create them with
// ./bin/rails generate stimulus controllerName

import { application } from "./application"

import HelloController from "./hello_controller"
application.register("hello", HelloController)

4. Create app/javascript/controllers/application.js with the following content:

import { Application } from "@hotwired/stimulus"

const application = Application.start()

// Configure Stimulus development experience
application.debug = false
window.Stimulus   = application

export { application }

5. Add the following line to app/javascript/application.js to import all your controllers:

import "./controllers"

6. Finally, add the Stimulus package to yarn:

yarn add @hotwired/stimulus

With an import-mapped application, controllers are automatically pinned and registered based on the file structure. The installer will amend your config/importmap.rb to configure this such that all controllers in app/javascript/controllers are pinned.

By default, your application will be setup to eager load all the controllers mentioned in your import map under "controllers". This works well together with preloading in the import map when you have a modest number of controllers.

If you have a lot of controllers, you may well want to lazy load them instead. This can be done by changing from eagerLoadControllersFrom to lazyLoadControllersFrom in your app/javascript/controllers/index.js file.

When lazy loading, controllers are not loaded until their data-controller identifier is encountered in the DOM.

With an application using a JavaScript bundler, controllers need to be imported and registered directly in the index.js file. But this can be done automatically using either the Stimulus generator (./bin/rails generate stimulus [controller]) or the dedicated stimulus:manifest:update task. Either will overwrite the controllers/index.js file.

You're encouraged to use the generator to add new controllers like so:

// Run "./bin/rails g stimulus hello" to create the file and update the index, then amend:

// app/assets/javascripts/controllers/hello_controller.js
import { Controller } from "@hotwired/stimulus"

// Connects with data-controller="hello"
export default class extends Controller {
  static targets = [ "name", "output" ]

  greet() {
    this.outputTarget.textContent = `Hello, ${this.nameTarget.value}!`
  }
}

Stimulus for Rails is released under the MIT License.