This is Part 2 covering the step-by-step migration process and results. Part 1 covered why I switched and the key improvements.

The Migration Journey: Step by Step

Phase 1: Package Management

The first step was transitioning from npm to Bun's package manager:

// Before (package.json scripts)
"scripts": {
  "start": "ts-node src/index.ts",
  "build": "tsc",
  "dev": "nodemon --watch src --exec ts-node src/index.ts",
}

// After
"scripts": {
  "start": "bun src/index.ts",
  "build": "bun build ./src/index.ts --outdir ./dist --target=bun",
  "dev": "bun --watch src/index.ts",
}

This simple change immediately sped up command execution, as Bun runs TypeScript files directly without a separate compilation step.

Phase 2: Build Configuration

Next came transitioning the build process from TypeScript's compiler to Bun's native bundler. The simplicity is striking - Bun's sensible defaults eliminated dozens of lines of configuration.

Phase 3: CI Integration

For continuous integration, I updated GitHub Actions to use Bun:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: oven-sh/setup-bun@v1
        with:
          bun-version: 1.2.11
      - run: bun install
      - run: bun run build
      - run: bun run typecheck

This also eliminated package-lock.json (4,500+ lines removed!) in favor of bun.lock.

Phase 4: Refactoring File Operations

The most impactful changes came from converting Node's fs operations to Bun's native File API.

Using Claude Code to Drive the Migration

I used Claude Code extensively to help with this migration, asking it to identify file system operations that could be replaced with Bun's native APIs. The most effective approach was:

1. Having Claude identify patterns like fs.readFile and fs.pathExists across the codebase
2. Creating a migration plan for each file based on usage patterns
3. Asking for side-by-side rewrites with explanations of the Bun-specific benefits
4. Gradually applying these changes file by file

Claude was particularly helpful for understanding the Bun-specific implementation details and suggesting optimizations I wouldn't have considered, like using arrayBuffer() for binary file operations.

Challenges and Limitations

While the migration has been largely positive, there are a few downsides worth mentioning:

Ecosystem maturity: Not all Node packages are fully compatible with Bun yet

Documentation gaps: While improving rapidly, Bun's docs aren't as comprehensive as Node's

Error messages: Sometimes Bun's error reporting is less informative than Node's

Native extensions: Some C/C++ native extensions might not work with Bun out of the box

Despite these challenges, the benefits have far outweighed the drawbacks for my use case.

The Results: Faster Builds, Cleaner Code

The most tangible outcome has been build performance. My site now builds in approximately 20 seconds with Bun, compared to 37 seconds with Node - a 46% improvement. This makes the development cycle much more pleasant, especially when previewing content changes.

Beyond raw performance, the codebase is now cleaner, with fewer dependencies and more consistent patterns throughout:

Should You Switch to Bun?

If you're working on a project that could benefit from improved build times, simpler tooling, or more modern APIs, Bun is definitely worth considering. It's particularly well-suited for:

• Static site generators and content-heavy applications
• TypeScript projects that want to eliminate compilation overhead
• Environments where build performance is a bottleneck
• New projects that can fully embrace Bun's ecosystem
• Applications with significant file I/O operations

For existing projects, consider a gradual migration approach, starting with build tooling and then moving to runtime code as you validate compatibility. My own migration followed this path:

1. Start with package management and simple commands
2. Progress to build configuration
3. Update CI/CD pipelines
4. Refactor file operations to use native APIs
5. Clean up dependencies and refine configs

The JavaScript ecosystem continues to evolve rapidly, and Bun represents an exciting step forward in both performance and developer experience. My migration has been a clear success, and I'm looking forward to leveraging more of Bun's capabilities as the platform continues to mature.