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Alex Aslam
Alex Aslam

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Bun + Ruby: The New Full-Stack Duo

#webdev #programming #javascript #rails

"We replaced Webpack, Node, and esbuild with one tool—and our stack got 10x simpler."

For years, Rails developers grudgingly accepted JavaScript tooling fatigue as the price of modern frontends. Then Bun arrived—a runtime so fast it makes Node.js feel like dial-up.

After migrating a production app to Bun + Ruby, we discovered a shocking truth: this combo eliminates 90% of frontend pain while keeping Rails’ magic intact. Here’s why it works and when to make the jump.

1. Why Bun Changes Everything

The Speed Revolution

Task Node/yarn Bun
Install deps 42s 0.9s
Start dev server 4.2s 0.3s
Build production 28s 1.1s 
# Goodbye node_modules
bun install  # Installs all deps in a blink
bun run dev  # HMR faster than Vite
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Built for Rails

✅ Works with jsbundling-rails
✅ Seamless integration with importmap-rails
✅ Auto-detects Rails asset paths

2. The Perfect Pairing

Case 1: Modern Frontends Without Node Headaches 

# Gemfile
gem "jsbundling-rails"

# Install Bun builder
rails javascript:install:bun
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How it works:

  1. Bun handles JS bundling via jsbundling-rails
  2. Rails serves assets through the asset pipeline
  3. Zero Webpack config

Case 2: Hybrid Architecture 

// Use Bun for React components
import Chart from "./react/Chart"

// Keep Stimulus for progressive enhancement
application.register("chart", ChartController)
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Best of both worlds:

  • Complex screens: React + Bun
  • Traditional views: Turbo + Import Maps

3. Real-World Wins

1. CI Pipelines Got 6x Faster 

# Before (Node + Webpack)
- run: yarn install && yarn build # 3.1min

# After (Bun)
- run: bun install && bun build # 31s
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2. Memory Usage Dropped 40%

  • No more Node duplicate caches
  • Bun’s Zig-based runtime is leaner

3. Unified Tooling 

bun test       # Run Ruby + JS tests together
bun run rails  # Start Rails with Bun’s JS runtime
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4. Migration Guide

  1. Install Bun: 
   curl -fsSL https://bun.sh/install | bash
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  1. Add to Rails: 
   bundle add jsbundling-rails
   rails javascript:install:bun
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  1. Update package.json: 
   {
     "scripts": {
       "build": "bun build app/javascript/*.* --outdir=app/assets/builds"
     }
   }
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  1. Celebrate deleting:
    • node_modules (mostly)
    • babel.config.js
    • webpack.config.js

5. When to Think Twice

❌ Legacy apps with complex Webpacker setups
❌ Teams using npm-specific packages
❌ Projects requiring Node worker threads

Golden Rule:

Use Bun when you want modern JS without the tooling circus.

"But We're Heavily Invested in Node!"
Try this:

  1. Use Bun for one new feature branch
  2. Compare CI times and memory usage
  3. Let the numbers decide

Made the switch? Share your war stories below!

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