Bun with Claude Code

Accelerating Bun Adoption With Claude Code

Bun is an all-in-one runtime for JavaScript/TypeScript. It bundles a package manager, bundler, and test runner, and runs several times faster than Node.js. Let’s use Claude Code to efficiently adopt Bun’s powerful features.

Starting a Project

> Create a new web app project with Bun.
> Include TypeScript, the Hono framework, and a test setup.

bun init my-app
cd my-app
bun add hono

// src/index.ts
import { Hono } from 'hono';
import { cors } from 'hono/cors';
import { logger } from 'hono/logger';

const app = new Hono();

app.use('*', logger());
app.use('/api/*', cors());

app.get('/api/health', (c) => {
  return c.json({ status: 'ok', runtime: 'bun' });
});

app.get('/api/users/:id', async (c) => {
  const id = c.req.param('id');
  const user = await getUser(id);
  return c.json(user);
});

export default {
  port: 3000,
  fetch: app.fetch,
};

Leveraging Bun’s Built-in APIs

> Implement a simple data store using Bun's file APIs and SQLite.

// src/db.ts
import { Database } from 'bun:sqlite';

const db = new Database('app.db', { create: true });

db.run(`
  CREATE TABLE IF NOT EXISTS users (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT NOT NULL,
    email TEXT UNIQUE NOT NULL,
    created_at DATETIME DEFAULT CURRENT_TIMESTAMP
  )
`);

export const createUser = db.prepare(
  'INSERT INTO users (name, email) VALUES ($name, $email)'
);

export const getUser = db.prepare(
  'SELECT * FROM users WHERE id = $id'
);

// Bun file operations
export async function saveUpload(file: File) {
  const path = `./uploads/${file.name}`;
  await Bun.write(path, file);
  return path;
}

export async function readConfig() {
  const file = Bun.file('./config.json');
  return await file.json();
}

Running Tests

Bun ships with a fast built-in test runner.

> Write tests for the API endpoints.
> Use Bun's test runner.

// src/index.test.ts
import { describe, expect, it, beforeAll, afterAll } from 'bun:test';

describe('API endpoints', () => {
  it('GET /api/health returns ok', async () => {
    const res = await fetch('http://localhost:3000/api/health');
    const data = await res.json();
    expect(res.status).toBe(200);
    expect(data.status).toBe('ok');
  });

  it('GET /api/users/:id returns user', async () => {
    const res = await fetch('http://localhost:3000/api/users/1');
    expect(res.status).toBe(200);
    const user = await res.json();
    expect(user).toHaveProperty('name');
  });
});

# Run tests
bun test

# Watch mode
bun test --watch

# Coverage
bun test --coverage

Bundling and Building

> Bundle the front-end code with Bun.
> Enable tree shaking and minification.

// build.ts
await Bun.build({
  entrypoints: ['./src/client/index.tsx'],
  outdir: './dist',
  target: 'browser',
  minify: true,
  splitting: true,
  sourcemap: 'external',
  define: {
    'process.env.NODE_ENV': '"production"',
  },
});

console.log('Build complete!');

Summary

With its blazing speed and integrated toolchain, Bun can significantly improve developer experience. Combine it with Claude Code to rapidly get up to speed on Bun-specific APIs and patterns. See also the API development guide and testing strategies.

For details about Bun, see the official Bun documentation.