Bun Development

Bun runtime → native APIs → zero-dependency patterns.

<when_to_use>

• Bun runtime development
• SQLite database with bun:sqlite
• HTTP server with Bun.serve
• Testing with bun:test
• File operations with Bun.file/Bun.write
• Shell operations with $ template
• Password hashing with Bun.password
• Environment variable handling
• Building and bundling

NOT for: Node.js-only patterns, cross-runtime libraries, non-Bun projects </when_to_use>

<runtime_basics> Package management:

bun install          # Install dependencies (faster than npm/yarn)
bun add zod          # Add package
bun remove zod       # Remove package
bun update           # Update all dependencies

Script execution:

bun run dev          # Run script from package.json
bun run src/index.ts # Execute TypeScript directly
bun --watch index.ts # Watch mode with auto-reload

Testing:

bun test             # Run all tests
bun test src/        # Run tests in directory
bun test --watch     # Watch mode
bun test --coverage  # With coverage

Building:

bun build ./index.ts --outfile dist/bundle.js
bun build ./index.ts --compile --outfile myapp  # Standalone executable

</runtime_basics>

File Operations

<file_operations>

// Read file (lazy, efficient)
const file = Bun.file('./data.json');

// Check existence
if (!(await file.exists())) {
  throw new Error('File not found');
}

// Read as different formats
const text = await file.text();
const json = await file.json();
const buffer = await file.arrayBuffer();
const stream = file.stream(); // For large files

// File metadata
console.log(file.size);  // bytes
console.log(file.type);  // MIME type

// Write file
await Bun.write('./output.txt', 'content');
await Bun.write('./data.json', JSON.stringify(data));

// Write blob
const blob = new Blob(['data'], { type: 'text/plain' });
await Bun.write('./blob.txt', blob);

// Write stream (for large data)
const readable = new ReadableStream({ ... });
await Bun.write('./stream.txt', readable);

</file_operations>

SQLite (bun:sqlite)

<sqlite> ```typescript import { Database } from 'bun:sqlite';

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

// Create tables db.run( CREATE TABLE IF NOT EXISTS users ( id TEXT PRIMARY KEY, email TEXT UNIQUE NOT NULL, name TEXT NOT NULL, created_at TEXT DEFAULT CURRENT_TIMESTAMP ));

// Prepared statements (recommended) const getUser = db.prepare('SELECT * FROM users WHERE id = ?'); const createUser = db.prepare('INSERT INTO users (id, email, name) VALUES (?, ?, ?) RETURNING *'); const updateUser = db.prepare('UPDATE users SET email = ?, name = ? WHERE id = ? RETURNING *'); const deleteUser = db.prepare('DELETE FROM users WHERE id = ? RETURNING *');

// Query execution const user = getUser.get('user-123'); // Single row const allUsers = db.prepare('SELECT * FROM users').all(); // All rows db.prepare('DELETE FROM users WHERE id = ?').run('user-123'); // No return

// Parameter binding const stmt = db.prepare('SELECT * FROM users WHERE email = ? AND role = ?'); const user = stmt.get('alice@example.com', 'admin');

// Named parameters const stmt2 = db.prepare('SELECT * FROM users WHERE email = $email'); const user2 = stmt2.get({ $email: 'alice@example.com' });

// Transactions const transfer = db.transaction((fromId: string, toId: string, amount: number) => { db.run('UPDATE accounts SET balance = balance - ? WHERE id = ?', [amount, fromId]); db.run('UPDATE accounts SET balance = balance + ? WHERE id = ?', [amount, toId]); });

transfer('alice', 'bob', 100); // Atomic // Automatically rolled back on error

// Close when done db.close();

See [sqlite-patterns.md](references/sqlite-patterns.md) for migrations and advanced patterns.
</sqlite>

## Password Hashing

<password>
```typescript
// Hash password (argon2id recommended)
const hashedPassword = await Bun.password.hash('password123', {
  algorithm: 'argon2id',
  memoryCost: 65536,  // 64 MB
  timeCost: 3         // Iterations
});

// Or bcrypt
const bcryptHash = await Bun.password.hash('password123', {
  algorithm: 'bcrypt',
  cost: 12  // Work factor
});

// Verify password
const isValid = await Bun.password.verify('password123', hashedPassword);

if (!isValid) {
  throw new Error('Invalid password');
}

In auth flow:

app.post('/auth/register', zValidator('json', RegisterSchema), async (c) => {
  const { email, password } = c.req.valid('json');
  const db = c.get('db');

  const existing = db.prepare('SELECT id FROM users WHERE email = ?').get(email);
  if (existing) {
    throw new HTTPException(409, { message: 'Email already registered' });
  }

  const hashedPassword = await Bun.password.hash(password, { algorithm: 'argon2id' });
  const user = db.prepare(`
    INSERT INTO users (id, email, password)
    VALUES (?, ?, ?)
    RETURNING id, email
  `).get(crypto.randomUUID(), email, hashedPassword);

  return c.json({ user }, 201);
});

</password>

HTTP Server

<http_server>

Bun.serve({
  port: 3000,
  fetch(req) {
    const url = new URL(req.url);

    if (url.pathname === '/') {
      return new Response('Hello, world!');
    }

    if (url.pathname === '/json') {
      return Response.json({ message: 'Hello' });
    }

    return new Response('Not found', { status: 404 });
  },
  error(err) {
    return new Response(`Error: ${err.message}`, { status: 500 });
  }
});

console.log('Server running on http://localhost:3000');

With Hono (recommended for complex APIs):

import { Hono } from 'hono';

const app = new Hono()
  .get('/', (c) => c.text('Hello'))
  .get('/json', (c) => c.json({ ok: true }));

Bun.serve({
  port: 3000,
  fetch: app.fetch
});

</http_server>

WebSocket

<websocket> ```typescript import type { ServerWebSocket } from 'bun';

type WebSocketData = { userId: string };

Bun.serve<WebSocketData>({ port: 3000, fetch(req, server) { const url = new URL(req.url);

if (url.pathname === '/ws') {
  const userId = url.searchParams.get('userId') || 'anonymous';
  const success = server.upgrade(req, { data: { userId } });

  if (!success) {
    return new Response('WebSocket upgrade failed', { status: 400 });
  }
  return undefined;
}

return new Response('Hello');

}, websocket: { open(ws: ServerWebSocket<WebSocketData>) { console.log(Client connected: ${ws.data.userId}); ws.subscribe('chat'); ws.send(JSON.stringify({ type: 'connected' })); }, message(ws: ServerWebSocket<WebSocketData>, message: string | Buffer) { console.log(Received from ${ws.data.userId}:, message); ws.publish('chat', message); }, close(ws: ServerWebSocket<WebSocketData>) { console.log(Client disconnected: ${ws.data.userId}); ws.unsubscribe('chat'); } } });

</websocket>

## Shell Operations

<shell>
```typescript
import { $ } from 'bun';

// Run commands
const result = await $`ls -la`;
console.log(result.text());

// With variables (auto-escaped)
const dir = './src';
await $`find ${dir} -name "*.ts"`;

// Check exit code
const { exitCode } = await $`npm test`.nothrow();
if (exitCode !== 0) {
  console.error('Tests failed');
}

// Spawn process
const proc = Bun.spawn(['ls', '-la']);
await proc.exited;
console.log('Exit code:', proc.exitCode);

// Capture output
const proc2 = Bun.spawn(['echo', 'Hello'], { stdout: 'pipe' });
const output = await new Response(proc2.stdout).text();

</shell>

Testing (bun:test)

<testing> ```typescript import { describe, test, expect, beforeAll, afterAll, beforeEach, afterEach } from 'bun:test';

describe('feature', () => { let db: Database;

beforeAll(() => { console.log('Setup test suite'); });

afterAll(() => { console.log('Cleanup test suite'); });

beforeEach(() => { db = new Database(':memory:'); });

afterEach(() => { db.close(); });

test('behavior', () => { expect(result).toBe(expected); expect(arr).toContain(item); expect(fn).toThrow(); expect(obj).toEqual({ foo: 'bar' }); expect(value).toBeDefined(); expect(value).toBeTruthy(); });

test('async behavior', async () => { const result = await asyncFn(); expect(result).toBeDefined(); });

test.todo('pending feature'); test.skip('temporarily disabled'); });

**Run tests**:
```bash
bun test                    # All tests
bun test src/api.test.ts    # Specific file
bun test --watch            # Watch mode
bun test --coverage         # With coverage

</testing>

Environment Variables

<environment> ```typescript // Access (same as process.env) console.log(Bun.env.NODE_ENV); console.log(Bun.env.DATABASE_URL);

// With Zod validation import { z } from 'zod';

const EnvSchema = z.object({ NODE_ENV: z.enum(['development', 'production', 'test']).default('development'), DATABASE_URL: z.string(), PORT: z.coerce.number().int().positive().default(3000), API_KEY: z.string().min(32) });

const env = EnvSchema.parse(Bun.env); export default env;

Bun automatically loads `.env` files:
```bash
# .env
DATABASE_URL=sqlite://app.db
PORT=3000

# .env.local (gitignored overrides)
# .env.production (production values)

</environment>

Compression

<compression> ```typescript import { gzipSync, gunzipSync, deflateSync, inflateSync } from 'bun';

// Gzip const data = 'Large data string...'.repeat(1000); const compressed = gzipSync(data); const decompressed = gunzipSync(compressed);

// Deflate const deflated = deflateSync('data'); const inflated = inflateSync(deflated);

// In HTTP response app.get('/large-data', (c) => { const data = generateLargeDataset(); const json = JSON.stringify(data);

const acceptEncoding = c.req.header('accept-encoding') || '';

if (acceptEncoding.includes('gzip')) { const compressed = gzipSync(json); return c.body(compressed, { headers: { 'Content-Type': 'application/json', 'Content-Encoding': 'gzip' } }); }

return c.json(data); });

</compression>

## Performance Utilities

<performance>
```typescript
// High-resolution timing
const start = Bun.nanoseconds();
await doWork();
const elapsed = Bun.nanoseconds() - start;
console.log(`Took ${elapsed / 1_000_000}ms`);

// Hashing
const hash = Bun.hash(data);
const crc32 = Bun.hash.crc32(data);
const sha256 = Bun.CryptoHasher.hash('sha256', data);

// Sleep
await Bun.sleep(1000); // ms

// Memory usage
const usage = process.memoryUsage();
console.log('RSS:', usage.rss / 1024 / 1024, 'MB');
console.log('Heap Used:', usage.heapUsed / 1024 / 1024, 'MB');

</performance>

Building & Bundling

<building> ```bash # Bundle for production bun build ./index.ts --outfile dist/bundle.js --minify --sourcemap

Bundle with external dependencies

bun build ./index.ts --outfile dist/bundle.js --external hono --external zod

Compile to standalone executable

bun build ./index.ts --compile --outfile myapp

Cross-compile

bun build ./index.ts --compile --target=bun-linux-x64 --outfile myapp-linux bun build ./index.ts --compile --target=bun-darwin-arm64 --outfile myapp-macos bun build ./index.ts --compile --target=bun-windows-x64 --outfile myapp.exe

</building>

<rules>
ALWAYS:
- Use Bun APIs when available (faster, native)
- Prepared statements for database queries
- Transactions for multi-statement operations
- argon2id for password hashing
- Validate environment variables at startup
- Close database connections when done

NEVER:
- String interpolation in SQL queries (use parameters)
- Store plaintext passwords
- Ignore async disposal cleanup
- Use deprecated Node.js APIs when Bun native exists

PREFER:
- Bun.file over fs.readFile
- Bun.write over fs.writeFile
- bun:sqlite over external SQLite libraries
- Bun.password over bcrypt/argon2 packages
- $ shell template over child_process
</rules>

<references>
- [sqlite-patterns.md](references/sqlite-patterns.md) — migrations, connection pooling
- [server-patterns.md](references/server-patterns.md) — HTTP, WebSocket, streaming
- [testing.md](references/testing.md) — bun:test patterns, lifecycle hooks

**Examples:**
- [database-crud.md](examples/database-crud.md) — SQLite CRUD patterns
- [file-uploads.md](examples/file-uploads.md) — streaming file handling
</references>