JavaScript Development Guide

JavaScript ES2024+ / Node.js 22 개발을 위한 간결한 가이드.

Quick Reference

Project Setup

# Node.js
npm init -y
npm install express

# Bun
bun init
bun add express

Express Patterns

Basic API

import express from 'express';

const app = express();
app.use(express.json());

// Routes
app.get('/api/users', async (req, res) => {
  const users = await UserService.list();
  res.json(users);
});

app.get('/api/users/:id', async (req, res) => {
  const user = await UserService.get(req.params.id);
  if (!user) {
    return res.status(404).json({ error: 'Not found' });
  }
  res.json(user);
});

app.post('/api/users', async (req, res) => {
  const user = await UserService.create(req.body);
  res.status(201).json(user);
});

app.listen(3000);

Middleware

// Error handler
app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).json({ error: 'Something went wrong' });
});

// Auth middleware
const authenticate = async (req, res, next) => {
  const token = req.headers.authorization?.split(' ')[1];
  if (!token) {
    return res.status(401).json({ error: 'No token' });
  }

  const user = await verifyToken(token);
  if (!user) {
    return res.status(401).json({ error: 'Invalid token' });
  }

  req.user = user;
  next();
};

app.get('/api/me', authenticate, (req, res) => {
  res.json(req.user);
});

Bun Patterns

HTTP Server

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

    if (url.pathname === '/api/users' && req.method === 'GET') {
      const users = await getUsers();
      return Response.json(users);
    }

    return new Response('Not Found', { status: 404 });
  },
});

SQLite (Built-in)

import { Database } from 'bun:sqlite';

const db = new Database('app.db');

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

const insert = db.prepare('INSERT INTO users (name, email) VALUES (?, ?)');
insert.run('John', '[email protected]');

const users = db.query('SELECT * FROM users').all();

Modern JavaScript

ES2024 Features

// Array grouping
const grouped = Object.groupBy(users, user => user.role);

// Promise.withResolvers
const { promise, resolve, reject } = Promise.withResolvers();

// Top-level await
const config = await loadConfig();

// Optional chaining & nullish coalescing
const name = user?.profile?.name ?? 'Anonymous';

Async Patterns

// Promise.all for parallel
const [users, posts] = await Promise.all([
  fetchUsers(),
  fetchPosts()
]);

// Promise.allSettled for error tolerance
const results = await Promise.allSettled([
  fetchUser(1),
  fetchUser(2),
  fetchUser(3)
]);

// Async iterator
async function* fetchPages() {
  let page = 1;
  while (true) {
    const data = await fetchPage(page++);
    if (!data.length) break;
    yield data;
  }
}

for await (const page of fetchPages()) {
  console.log(page);
}

Testing with Vitest

import { describe, it, expect, vi } from 'vitest';

describe('UserService', () => {
  it('creates user successfully', async () => {
    const user = await UserService.create({
      name: 'John',
      email: '[email protected]'
    });

    expect(user.id).toBeDefined();
    expect(user.name).toBe('John');
  });

  it('throws on duplicate email', async () => {
    await expect(
      UserService.create({ name: 'John', email: '[email protected]' })
    ).rejects.toThrow('Email already exists');
  });
});

// Mocking
vi.mock('./database', () => ({
  query: vi.fn(() => Promise.resolve([{ id: 1, name: 'John' }]))
}));

Project Structure

project/
├── src/
│   ├── index.js
│   ├── routes/
│   ├── services/
│   ├── models/
│   └── middleware/
├── tests/
├── package.json
└── README.md

Best Practices

• ESM: "type": "module" 사용
• Async/Await: Promise 체인 대신 async/await
• Error Handling: try/catch와 에러 미들웨어 사용
• 환경변수: dotenv 또는 Bun 내장 사용
• Validation: Zod로 입력 검증

Last Updated: 2026-01-21 Version: 2.0.0