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**Benefits of Bun:**
- Native TypeScript support (no transpilation setup)
- Significantly faster than Node.js
- All-in-one tool (package manager, runtime, test runner)
- Smaller node_modules footprint
- Drop-in Node.js compatibility for most packages

// Import named exports
import { UserService } from './services/user-service';
import { type User } from './types';

// Import default exports
import express from 'express';

// Import with alias
import * as helpers from './utils/helpers';

// Export named
export function getUserById(id: string): Promise<User> {
  // ...
}

// Export default
export default UserService;

// Re-export
export { type User } from './types';
export { UserService } from './services/user-service';

// Require imports
const { UserService } = require('./services/user-service');
const express = require('express');

// Module exports
module.exports = UserService;
module.exports = { UserService, UserRepository };

{
  "type": "module",
  "name": "my-app",
  "version": "1.0.0"
}

{
  "compilerOptions": {
    "target": "ES2020",
    "module": "ESNext",
    "lib": ["ES2020"],
    "moduleResolution": "bundler",
    "strict": true,
    "skipLibCheck": true,
    "esModuleInterop": true,
    "resolveJsonModule": true,
    "allowJs": false,
    "outDir": "./dist",
    "rootDir": "./src",
    "baseUrl": ".",
    "paths": {
      "@/*": ["src/*"],
      "@services/*": ["src/services/*"],
      "@models/*": ["src/models/*"]
    },
    "declaration": true,
    "declarationMap": true,
    "sourceMap": true,
    "removeComments": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "strictFunctionTypes": true,
    "strictPropertyInitialization": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true
  },
  "include": ["src"],
  "exclude": ["node_modules", "dist", "**/*.test.ts"]
}

bun add --dev @biomejs/biome

{
  "$schema": "https://biomejs.dev/schemas/1.9.4/schema.json",
  "organizeImports": {
    "enabled": true
  },
  "formatter": {
    "enabled": true,
    "indentStyle": "space",
    "indentWidth": 2,
    "lineWidth": 100
  },
  "linter": {
    "enabled": true,
    "rules": {
      "recommended": true,
      "complexity": {
        "noUselessSwitchCase": "error"
      },
      "style": {
        "noNonNullAssertion": "warn"
      }
    }
  },
  "javascript": {
    "formatter": {
      "semicolons": "always",
      "quoteStyle": "single",
      "trailingCommas": "es5"
    }
  }
}

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// Classes/Types/Interfaces/Enums: PascalCase
class UserService { /* ... */ }
interface UserRepository { /* ... */ }
enum UserRole { Admin = 'ADMIN', User = 'USER' }

// Methods, properties, variables, functions: camelCase
getUserById(id: string): Promise<User>
const userData = {};

// Private members: camelCase with leading underscore
private _cache: Map<string, User> = new Map();

// Constants: UPPER_SNAKE_CASE
const MAX_RETRIES = 3;
const API_BASE_URL = 'https://api.example.com';

// React hooks: camelCase with use prefix
function useUserData(userId: string) { /* ... */ }

// Function parameters and return types
function processUser(user: User): Promise<ProcessedUser> {
  // ...
}

// Arrow functions
const formatName = (first: string, last: string): string => {
  return `${first} ${last}`;
};

// Complex types
type ApiResponse<T> = {
  status: number;
  data: T;
  error?: string;
};

interface RequestHandler {
  handle(request: Request): Promise<Response>;
}

// Generic functions
function getById<T extends { id: string }>(items: T[], id: string): T | undefined {
  return items.find((item) => item.id === id);
}

// Generic classes
class Repository<T> {
  async getById(id: string): Promise<T | null> {
    // ...
  }
}

// Generic types
type Result<T, E = Error> = { success: true; data: T } | { success: false; error: E };

import { z } from 'zod';

// Schema definition
const UserSchema = z.object({
  id: z.string().uuid(),
  name: z.string().min(1),
  email: z.string().email(),
  age: z.number().int().positive().optional(),
});

// Type inference from schema
type User = z.infer<typeof UserSchema>;

// Runtime validation
function createUser(data: unknown): User {
  return UserSchema.parse(data);
}

// Safe parsing with error handling
const result = UserSchema.safeParse(data);
if (!result.success) {
  console.error(result.error.format());
}

project/
├── src/
│   ├── main.ts              # Entry point
│   ├── types/               # Type definitions
│   ├── services/            # Business logic
│   ├── repositories/        # Data access layer
│   ├── models/              # Data models
│   ├── handlers/            # Request/event handlers
│   ├── middleware/          # Express/web middleware
│   ├── utils/               # Utility functions
│   └── config/              # Configuration
├── tests/                   # Unit and integration tests
├── dist/                    # Compiled output (gitignored)
├── package.json
├── tsconfig.json
├── biome.json
└── bun.lock

// Absolute imports with path aliases
import { UserService } from '@services/user-service';
import type { User } from '@models/user';

// Relative imports within same feature
import { UserRepository } from '../repositories/user-repository';
import { validateUser } from '../utils/validators';

// Re-exports from index files
export { UserService, UserRepository } from './index';

// Define custom error classes
class AppError extends Error {
  constructor(message: string, public code: string, public statusCode = 500) {
    super(message);
    this.name = 'AppError';
  }
}

class ValidationError extends AppError {
  constructor(message: string, public field: string) {
    super(message, 'VALIDATION_ERROR', 400);
  }
}

class NotFoundError extends AppError {
  constructor(message: string) {
    super(message, 'NOT_FOUND', 404);
  }
}

// Result pattern for explicit error handling
type Result<T, E = Error> = { ok: true; value: T } | { ok: false; error: E };

async function safeFetchUser(id: string): Promise<Result<User, AppError>> {
  try {
    const user = await getUser(id);
    return { ok: true, value: user };
  } catch (error) {
    return { ok: false, error: error instanceof AppError ? error : new AppError('Unknown', 'UNKNOWN') };
  }
}

// env.ts
import { z } from 'zod';

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

export default EnvSchema.parse(process.env);

// Async/await with error handling
async function fetchUserData(id: string): Promise<User> {
  try {
    const response = await fetch(`/api/users/${id}`);
    if (!response.ok) throw new Error('Failed to fetch');
    return response.json();
  } catch (error) {
    console.error('Error fetching user:', error);
    throw error;
  }
}

// Concurrent operations with Promise.all
async function loadDashboardData(): Promise<DashboardData> {
  const [users, products, stats] = await Promise.all([
    fetchUsers(),
    fetchProducts(),
    fetchStats(),
  ]);
  return { users, products, stats };
}

import { describe, it, expect, beforeEach } from 'bun:test';
import { UserService } from '@services/user-service';

describe('UserService', () => {
  let service: UserService;

  beforeEach(() => {
    service = new UserService();
  });

  it('should fetch user by id', async () => {
    const user = await service.getById('123');
    expect(user).toBeDefined();
    expect(user?.id).toBe('123');
  });
});