Guide: Integrating React.js ⚛️ into a Rails 8 Application – Part 2: Install React | Add esbuild, Jsx | Integrate React View

Throw back:

rails new design_studio_react --database=postgresql -j esbuild --skip-hotwire

Here’s what our Rails app looks like after skipping Hotwire with the --skip-hotwire flag:

✅ Current JavaScript/Node.js Setup (Clean & Minimal)

📦 Package Management:

  • package.json – Clean setup with only esbuild script
  • .node-version – Node.js version 24.1.0
  • No dependencies – Ready for React installation

📁 JavaScript File Structure (Ultra-Clean):

app/javascript/
└── application.js          # Empty entry point (2 lines total!)

app/javascript/application.js content:

// Entry point for the build script in your package.json

🚫 What Got Successfully Removed:

  • ❌ No Turbo/Stimulus imports in application.js
  • ❌ No controllers/ directory at all
  • ❌ No Hotwire gems in Gemfile (only jsbundling-rails remains)
  • ❌ No @hotwired/turbo-rails or @hotwired/stimulus dependencies

⚙️ Configuration Files (Minimal – Only 4):

  1. package.json – esbuild build script only
  2. .node-version – Node.js version pinning
  3. Procfile.dev – Development processes (js: yarn build --watch)
  4. app/javascript/application.js – Empty entry point

🔧 esbuild Configuration:

{
  "scripts": {
    "build": "esbuild app/javascript/*.* --bundle --sourcemap --format=esm --outdir=app/assets/builds --public-path=/assets"
  }
}

📂 Build Output:

  • app/assets/builds/ – Contains only .keep file (empty, ready for bundles)

🎯 HTML Integration:

<!-- Still includes the JavaScript module correctly -->
<%= javascript_include_tag "application", "data-turbo-track": "reload", type: "module" %>

(Note: data-turbo-track is just an HTML attribute for cache busting, not the Turbo library)

# create db
✗ rails db:migrate

# run react-rails-app in port 3001
✗ rails s -p 3001

🚀 Next Steps: Install & Setup React

Step 1: Install react, react-dom

Your app is now perfectly clean for React! Just run:

brew install yarn
yarn add react react-dom # check node_modules/ folder for what is installed
yarn add --dev @types/react @types/react-dom  # Optional: for TypeScript support, check node_modules/@types folder

Status: ✅ Minimal JavaScript foundation – No Hotwire bloat, perfect React starting point!

Now that we have a clean Rails app with esbuild setup, here’s our step-by-step roadmap to get React working:

Step 2: Create Your First React Component

Create a simple React component to test the setup:

mkdir app/javascript/components

Then create app/javascript/components/App.jsx:

import React from 'react';

function App() {
  return (
    <div>
      <h1>React is Working!</h1>
      <p>Welcome to your Rails + React app</p>
    </div>
  );
}

export default App;

Step 3: Update JavaScript Entry Point

Modify app/javascript/application.js to render React:

// Entry point for the build script in your package.json
import React from 'react';
import { createRoot } from 'react-dom/client';
import App from './components/App';

document.addEventListener('DOMContentLoaded', () => {
  const container = document.getElementById('react-root');
  if (container) {
    const root = createRoot(container);
    root.render(<App />);
  }
});

Step 4: Create a Controller & Route

Generate a home controller:

rails generate controller Home index

Step 5: Add React Root to View

Update app/views/home/index.html.erb:

<div id="react-root"></div>

Step 6: Set Root Route

Update config/routes.rb:

Rails.application.routes.draw do
  root "home#index"
  # ... other routes
end

Step 7: Start Development

# update Procfile.dev assign port 3001
web: env RUBY_DEBUG_OPEN=true bin/rails server -p 3001

# run our rails-react app by

✗ bin/dev
21:15:27 web.1  | started with pid 12619
21:15:27 js.1   | started with pid 12620
21:15:27 js.1   | yarn run v1.22.22
21:15:27 js.1   | $ esbuild app/javascript/*.* --bundle --sourcemap --format=esm --outdir=app/assets/builds --public-path=/assets --watch
21:15:27 js.1   | /bin/sh: esbuild: command not found
21:15:27 js.1   | error Command failed with exit code 127.
21:15:27 js.1   | info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
21:15:27 web.1  | => Booting Puma
..........

🎯 What This Gives Us:

  • ✅ React components in app/javascript/components/
  • ✅ esbuild automatically bundles JSX
  • ✅ Hot reloading with yarn build --watch
  • ✅ Rails serves your React app

🚨 Error Analysis:

  1. Rails server started fine ✅ (port 3001)

🔧 Solution: Install JavaScript Dependencies

You need to install esbuild and other JavaScript dependencies first:

yarn install

📋 Files yarn install Checks:

1. Primary: package.json

{
  "name": "app",
  "private": true,
  "scripts": {
    "build": "esbuild app/javascript/*.* --bundle --sourcemap --format=esm --outdir=app/assets/builds --public-path=/assets"
  },
  "dependencies": {
    "react": "^19.1.0",           # ✅ Already added
    "react-dom": "^19.1.0"       # ✅ Already added  
  },
  "devDependencies": {
    "@types/react": "^19.1.8",      # ✅ Already added
    "@types/react-dom": "^19.1.6"   # ✅ Already added
  }
}

2. Lockfile: yarn.lock

  • Ensures exact versions for reproducible installs
  • Contains resolved URLs and integrity hashes

🚨 The Problem: Missing esbuild!

Our package.json calls esbuild in the build script, but esbuild is not listed as a dependency anywhere!

Rails should have added it, but didn’t. We need to add esbuild:

yarn add --dev esbuild

🔧 What yarn install does:

  1. Reads package.json for dependency list
  2. Reads yarn.lock for exact versions (if exists)
  3. Downloads packages to node_modules/
  4. Updates yarn.lock with new resolutions

Current issue: Our build script expects esbuild command, but it’s not installed in node_modules/.bin/esbuild

Solution: Add esbuild as a dev dependency!

Solved~ and start servers: Error Again!

x bin/dev

* Listening on http://[::1]:3001
22:54:43 web.1  | Use Ctrl-C to stop
22:54:44 js.1   | ✘ [ERROR] The JSX syntax extension is not currently enabled
22:54:44 js.1   |
22:54:44 js.1   |     app/javascript/application.js:11:16:
22:54:44 js.1   |       11 │     root.render(<App />);
22:54:44 js.1   |          ╵                 ^
22:54:44 js.1   |
22:54:44 js.1   |   The esbuild loader for this file is currently set to "js" but it must be set to "jsx" to be able to parse JSX syntax. You can use "--loader:.js=jsx" to do that.
22:54:44 js.1   |
22:54:44 js.1   | 1 error
22:54:44 js.1   | [watch] build finished, watching for changes..

This error occurs because esbuild doesn’t know how to handle JSX syntax! The <App /> is JSX, but esbuild needs to be configured to transform it.

🚨 Problem: esbuild can’t process JSX syntax

Your application.js contains JSX (<App />), but esbuild isn’t configured to transform JSX!

JSX (JavaScript XML) is a syntax extension for JavaScript, commonly used with React, that allows you to write HTML-like code within JavaScript files.

🔧 Solution: Configure esbuild for JSX

Update your package.json build script to handle JSX:

# add this to build
--jsx=automatic --loader:.js=jsx

✅ Fixed! Added JSX support:

What I added:

  • --jsx=automatic – Enables React’s automatic JSX runtime
  • --loader:.js=jsx – Treats .js files as JSX files

📝 What this means:

  • ✅ esbuild can now process <App /> syntax
  • ✅ You don’t need to import React in every JSX file
  • ✅ Your .js files can contain JSX
bin/dev

Whola!!

Let’s see in Part 3. Happy React configuration! 🚀

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Author: Abhilash

Hi, I’m Abhilash! A seasoned web developer with 15 years of experience specializing in Ruby and Ruby on Rails. Since 2010, I’ve built scalable, robust web applications and worked with frameworks like Angular, Sinatra, Laravel, Node.js, Vue and React. Passionate about clean, maintainable code and continuous learning, I share insights, tutorials, and experiences here. Let’s explore the ever-evolving world of web development together!

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