nodejs-backend-patterns

Node.js Backend Patterns

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Node.js Backend Patterns

Comprehensive guidance for building scalable, maintainable, and production-ready Node.js backend applications with modern frameworks, architectural patterns, and best practices.

When to Use This Skill

  • Building REST APIs or GraphQL servers

  • Creating microservices with Node.js

  • Implementing authentication and authorization

  • Designing scalable backend architectures

  • Setting up middleware and error handling

  • Integrating databases (SQL and NoSQL)

  • Building real-time applications with WebSockets

  • Implementing background job processing

Core Frameworks

Express.js - Minimalist Framework

Basic Setup:

import express, { Request, Response, NextFunction } from "express"; import helmet from "helmet"; import cors from "cors"; import compression from "compression";

const app = express();

// Security middleware app.use(helmet()); app.use(cors({ origin: process.env.ALLOWED_ORIGINS?.split(",") })); app.use(compression());

// Body parsing app.use(express.json({ limit: "10mb" })); app.use(express.urlencoded({ extended: true, limit: "10mb" }));

// Request logging app.use((req: Request, res: Response, next: NextFunction) => { console.log(${req.method} ${req.path}); next(); });

const PORT = process.env.PORT || 3000; app.listen(PORT, () => { console.log(Server running on port ${PORT}); });

Fastify - High Performance Framework

Basic Setup:

import Fastify from "fastify"; import helmet from "@fastify/helmet"; import cors from "@fastify/cors"; import compress from "@fastify/compress";

const fastify = Fastify({ logger: { level: process.env.LOG_LEVEL || "info", transport: { target: "pino-pretty", options: { colorize: true }, }, }, });

// Plugins await fastify.register(helmet); await fastify.register(cors, { origin: true }); await fastify.register(compress);

// Type-safe routes with schema validation fastify.post<{ Body: { name: string; email: string }; Reply: { id: string; name: string }; }>( "/users", { schema: { body: { type: "object", required: ["name", "email"], properties: { name: { type: "string", minLength: 1 }, email: { type: "string", format: "email" }, }, }, }, }, async (request, reply) => { const { name, email } = request.body; return { id: "123", name }; }, );

await fastify.listen({ port: 3000, host: "0.0.0.0" });

Architectural Patterns

Pattern 1: Layered Architecture

Structure:

src/ ├── controllers/ # Handle HTTP requests/responses ├── services/ # Business logic ├── repositories/ # Data access layer ├── models/ # Data models ├── middleware/ # Express/Fastify middleware ├── routes/ # Route definitions ├── utils/ # Helper functions ├── config/ # Configuration └── types/ # TypeScript types

Controller Layer:

// controllers/user.controller.ts import { Request, Response, NextFunction } from "express"; import { UserService } from "../services/user.service"; import { CreateUserDTO, UpdateUserDTO } from "../types/user.types";

export class UserController { constructor(private userService: UserService) {}

async createUser(req: Request, res: Response, next: NextFunction) { try { const userData: CreateUserDTO = req.body; const user = await this.userService.createUser(userData); res.status(201).json(user); } catch (error) { next(error); } }

async getUser(req: Request, res: Response, next: NextFunction) { try { const { id } = req.params; const user = await this.userService.getUserById(id); res.json(user); } catch (error) { next(error); } }

async updateUser(req: Request, res: Response, next: NextFunction) { try { const { id } = req.params; const updates: UpdateUserDTO = req.body; const user = await this.userService.updateUser(id, updates); res.json(user); } catch (error) { next(error); } }

async deleteUser(req: Request, res: Response, next: NextFunction) { try { const { id } = req.params; await this.userService.deleteUser(id); res.status(204).send(); } catch (error) { next(error); } } }

Service Layer:

// services/user.service.ts import { UserRepository } from "../repositories/user.repository"; import { CreateUserDTO, UpdateUserDTO, User } from "../types/user.types"; import { NotFoundError, ValidationError } from "../utils/errors"; import bcrypt from "bcrypt";

export class UserService { constructor(private userRepository: UserRepository) {}

async createUser(userData: CreateUserDTO): Promise<User> { // Validation const existingUser = await this.userRepository.findByEmail(userData.email); if (existingUser) { throw new ValidationError("Email already exists"); }

// Hash password
const hashedPassword = await bcrypt.hash(userData.password, 10);

// Create user
const user = await this.userRepository.create({
  ...userData,
  password: hashedPassword,
});

// Remove password from response
const { password, ...userWithoutPassword } = user;
return userWithoutPassword as User;

}

async getUserById(id: string): Promise<User> { const user = await this.userRepository.findById(id); if (!user) { throw new NotFoundError("User not found"); } const { password, ...userWithoutPassword } = user; return userWithoutPassword as User; }

async updateUser(id: string, updates: UpdateUserDTO): Promise<User> { const user = await this.userRepository.update(id, updates); if (!user) { throw new NotFoundError("User not found"); } const { password, ...userWithoutPassword } = user; return userWithoutPassword as User; }

async deleteUser(id: string): Promise<void> { const deleted = await this.userRepository.delete(id); if (!deleted) { throw new NotFoundError("User not found"); } } }

Repository Layer:

// repositories/user.repository.ts import { Pool } from "pg"; import { CreateUserDTO, UpdateUserDTO, UserEntity } from "../types/user.types";

export class UserRepository { constructor(private db: Pool) {}

async create( userData: CreateUserDTO & { password: string }, ): Promise<UserEntity> { const query = INSERT INTO users (name, email, password) VALUES ($1, $2, $3) RETURNING id, name, email, password, created_at, updated_at ; const { rows } = await this.db.query(query, [ userData.name, userData.email, userData.password, ]); return rows[0]; }

async findById(id: string): Promise<UserEntity | null> { const query = "SELECT * FROM users WHERE id = $1"; const { rows } = await this.db.query(query, [id]); return rows[0] || null; }

async findByEmail(email: string): Promise<UserEntity | null> { const query = "SELECT * FROM users WHERE email = $1"; const { rows } = await this.db.query(query, [email]); return rows[0] || null; }

async update(id: string, updates: UpdateUserDTO): Promise<UserEntity | null> { const fields = Object.keys(updates); const values = Object.values(updates);

const setClause = fields
  .map((field, idx) => `${field} = $${idx + 2}`)
  .join(", ");

const query = `
  UPDATE users
  SET ${setClause}, updated_at = CURRENT_TIMESTAMP
  WHERE id = $1
  RETURNING *
`;

const { rows } = await this.db.query(query, [id, ...values]);
return rows[0] || null;

}

async delete(id: string): Promise<boolean> { const query = "DELETE FROM users WHERE id = $1"; const { rowCount } = await this.db.query(query, [id]); return rowCount > 0; } }

Pattern 2: Dependency Injection

DI Container:

// di-container.ts import { Pool } from "pg"; import { UserRepository } from "./repositories/user.repository"; import { UserService } from "./services/user.service"; import { UserController } from "./controllers/user.controller"; import { AuthService } from "./services/auth.service";

class Container { private instances = new Map<string, any>();

register<T>(key: string, factory: () => T): void { this.instances.set(key, factory); }

resolve<T>(key: string): T { const factory = this.instances.get(key); if (!factory) { throw new Error(No factory registered for ${key}); } return factory(); }

singleton<T>(key: string, factory: () => T): void { let instance: T; this.instances.set(key, () => { if (!instance) { instance = factory(); } return instance; }); } }

export const container = new Container();

// Register dependencies container.singleton( "db", () => new Pool({ host: process.env.DB_HOST, port: parseInt(process.env.DB_PORT || "5432"), database: process.env.DB_NAME, user: process.env.DB_USER, password: process.env.DB_PASSWORD, max: 20, idleTimeoutMillis: 30000, connectionTimeoutMillis: 2000, }), );

container.singleton( "userRepository", () => new UserRepository(container.resolve("db")), );

container.singleton( "userService", () => new UserService(container.resolve("userRepository")), );

container.register( "userController", () => new UserController(container.resolve("userService")), );

container.singleton( "authService", () => new AuthService(container.resolve("userRepository")), );

Middleware Patterns

Authentication Middleware

// middleware/auth.middleware.ts import { Request, Response, NextFunction } from "express"; import jwt from "jsonwebtoken"; import { UnauthorizedError } from "../utils/errors";

interface JWTPayload { userId: string; email: string; }

declare global { namespace Express { interface Request { user?: JWTPayload; } } }

export const authenticate = async ( req: Request, res: Response, next: NextFunction, ) => { try { const token = req.headers.authorization?.replace("Bearer ", "");

if (!token) {
  throw new UnauthorizedError("No token provided");
}

const payload = jwt.verify(token, process.env.JWT_SECRET!) as JWTPayload;

req.user = payload;
next();

} catch (error) { next(new UnauthorizedError("Invalid token")); } };

export const authorize = (...roles: string[]) => { return async (req: Request, res: Response, next: NextFunction) => { if (!req.user) { return next(new UnauthorizedError("Not authenticated")); }

// Check if user has required role
const hasRole = roles.some((role) => req.user?.roles?.includes(role));

if (!hasRole) {
  return next(new UnauthorizedError("Insufficient permissions"));
}

next();

}; };

Validation Middleware

// middleware/validation.middleware.ts import { Request, Response, NextFunction } from "express"; import { AnyZodObject, ZodError } from "zod"; import { ValidationError } from "../utils/errors";

export const validate = (schema: AnyZodObject) => { return async (req: Request, res: Response, next: NextFunction) => { try { await schema.parseAsync({ body: req.body, query: req.query, params: req.params, }); next(); } catch (error) { if (error instanceof ZodError) { const errors = error.errors.map((err) => ({ field: err.path.join("."), message: err.message, })); next(new ValidationError("Validation failed", errors)); } else { next(error); } } }; };

// Usage with Zod import { z } from "zod";

const createUserSchema = z.object({ body: z.object({ name: z.string().min(1), email: z.string().email(), password: z.string().min(8), }), });

router.post("/users", validate(createUserSchema), userController.createUser);

Rate Limiting Middleware

// middleware/rate-limit.middleware.ts import rateLimit from "express-rate-limit"; import RedisStore from "rate-limit-redis"; import Redis from "ioredis";

const redis = new Redis({ host: process.env.REDIS_HOST, port: parseInt(process.env.REDIS_PORT || "6379"), });

export const apiLimiter = rateLimit({ store: new RedisStore({ client: redis, prefix: "rl:", }), windowMs: 15 * 60 * 1000, // 15 minutes max: 100, // Limit each IP to 100 requests per windowMs message: "Too many requests from this IP, please try again later", standardHeaders: true, legacyHeaders: false, });

export const authLimiter = rateLimit({ store: new RedisStore({ client: redis, prefix: "rl:auth:", }), windowMs: 15 * 60 * 1000, max: 5, // Stricter limit for auth endpoints skipSuccessfulRequests: true, });

Request Logging Middleware

// middleware/logger.middleware.ts import { Request, Response, NextFunction } from "express"; import pino from "pino";

const logger = pino({ level: process.env.LOG_LEVEL || "info", transport: { target: "pino-pretty", options: { colorize: true }, }, });

export const requestLogger = ( req: Request, res: Response, next: NextFunction, ) => { const start = Date.now();

// Log response when finished res.on("finish", () => { const duration = Date.now() - start; logger.info({ method: req.method, url: req.url, status: res.statusCode, duration: ${duration}ms, userAgent: req.headers["user-agent"], ip: req.ip, }); });

next(); };

export { logger };

Error Handling

Custom Error Classes

// utils/errors.ts export class AppError extends Error { constructor( public message: string, public statusCode: number = 500, public isOperational: boolean = true, ) { super(message); Object.setPrototypeOf(this, AppError.prototype); Error.captureStackTrace(this, this.constructor); } }

export class ValidationError extends AppError { constructor( message: string, public errors?: any[], ) { super(message, 400); } }

export class NotFoundError extends AppError { constructor(message: string = "Resource not found") { super(message, 404); } }

export class UnauthorizedError extends AppError { constructor(message: string = "Unauthorized") { super(message, 401); } }

export class ForbiddenError extends AppError { constructor(message: string = "Forbidden") { super(message, 403); } }

export class ConflictError extends AppError { constructor(message: string) { super(message, 409); } }

Global Error Handler

// middleware/error-handler.ts import { Request, Response, NextFunction } from "express"; import { AppError } from "../utils/errors"; import { logger } from "./logger.middleware";

export const errorHandler = ( err: Error, req: Request, res: Response, next: NextFunction, ) => { if (err instanceof AppError) { return res.status(err.statusCode).json({ status: "error", message: err.message, ...(err instanceof ValidationError && { errors: err.errors }), }); }

// Log unexpected errors logger.error({ error: err.message, stack: err.stack, url: req.url, method: req.method, });

// Don't leak error details in production const message = process.env.NODE_ENV === "production" ? "Internal server error" : err.message;

res.status(500).json({ status: "error", message, }); };

// Async error wrapper export const asyncHandler = ( fn: (req: Request, res: Response, next: NextFunction) => Promise<any>, ) => { return (req: Request, res: Response, next: NextFunction) => { Promise.resolve(fn(req, res, next)).catch(next); }; };

Database Patterns

PostgreSQL with Connection Pool

// config/database.ts import { Pool, PoolConfig } from "pg";

const poolConfig: PoolConfig = { host: process.env.DB_HOST, port: parseInt(process.env.DB_PORT || "5432"), database: process.env.DB_NAME, user: process.env.DB_USER, password: process.env.DB_PASSWORD, max: 20, idleTimeoutMillis: 30000, connectionTimeoutMillis: 2000, };

export const pool = new Pool(poolConfig);

// Test connection pool.on("connect", () => { console.log("Database connected"); });

pool.on("error", (err) => { console.error("Unexpected database error", err); process.exit(-1); });

// Graceful shutdown export const closeDatabase = async () => { await pool.end(); console.log("Database connection closed"); };

MongoDB with Mongoose

// config/mongoose.ts import mongoose from "mongoose";

const connectDB = async () => { try { await mongoose.connect(process.env.MONGODB_URI!, { maxPoolSize: 10, serverSelectionTimeoutMS: 5000, socketTimeoutMS: 45000, });

console.log("MongoDB connected");

} catch (error) { console.error("MongoDB connection error:", error); process.exit(1); } };

mongoose.connection.on("disconnected", () => { console.log("MongoDB disconnected"); });

mongoose.connection.on("error", (err) => { console.error("MongoDB error:", err); });

export { connectDB };

// Model example import { Schema, model, Document } from "mongoose";

interface IUser extends Document { name: string; email: string; password: string; createdAt: Date; updatedAt: Date; }

const userSchema = new Schema<IUser>( { name: { type: String, required: true }, email: { type: String, required: true, unique: true }, password: { type: String, required: true }, }, { timestamps: true, }, );

// Indexes userSchema.index({ email: 1 });

export const User = model<IUser>("User", userSchema);

Transaction Pattern

// services/order.service.ts import { Pool } from "pg";

export class OrderService { constructor(private db: Pool) {}

async createOrder(userId: string, items: any[]) { const client = await this.db.connect();

try {
  await client.query("BEGIN");

  // Create order
  const orderResult = await client.query(
    "INSERT INTO orders (user_id, total) VALUES ($1, $2) RETURNING id",
    [userId, calculateTotal(items)],
  );
  const orderId = orderResult.rows[0].id;

  // Create order items
  for (const item of items) {
    await client.query(
      "INSERT INTO order_items (order_id, product_id, quantity, price) VALUES ($1, $2, $3, $4)",
      [orderId, item.productId, item.quantity, item.price],
    );

    // Update inventory
    await client.query(
      "UPDATE products SET stock = stock - $1 WHERE id = $2",
      [item.quantity, item.productId],
    );
  }

  await client.query("COMMIT");
  return orderId;
} catch (error) {
  await client.query("ROLLBACK");
  throw error;
} finally {
  client.release();
}

} }

Authentication & Authorization

JWT Authentication

// services/auth.service.ts import jwt from "jsonwebtoken"; import bcrypt from "bcrypt"; import { UserRepository } from "../repositories/user.repository"; import { UnauthorizedError } from "../utils/errors";

export class AuthService { constructor(private userRepository: UserRepository) {}

async login(email: string, password: string) { const user = await this.userRepository.findByEmail(email);

if (!user) {
  throw new UnauthorizedError("Invalid credentials");
}

const isValid = await bcrypt.compare(password, user.password);

if (!isValid) {
  throw new UnauthorizedError("Invalid credentials");
}

const token = this.generateToken({
  userId: user.id,
  email: user.email,
});

const refreshToken = this.generateRefreshToken({
  userId: user.id,
});

return {
  token,
  refreshToken,
  user: {
    id: user.id,
    name: user.name,
    email: user.email,
  },
};

}

async refreshToken(refreshToken: string) { try { const payload = jwt.verify( refreshToken, process.env.REFRESH_TOKEN_SECRET!, ) as { userId: string };

  const user = await this.userRepository.findById(payload.userId);

  if (!user) {
    throw new UnauthorizedError("User not found");
  }

  const token = this.generateToken({
    userId: user.id,
    email: user.email,
  });

  return { token };
} catch (error) {
  throw new UnauthorizedError("Invalid refresh token");
}

}

private generateToken(payload: any): string { return jwt.sign(payload, process.env.JWT_SECRET!, { expiresIn: "15m", }); }

private generateRefreshToken(payload: any): string { return jwt.sign(payload, process.env.REFRESH_TOKEN_SECRET!, { expiresIn: "7d", }); } }

Caching Strategies

// utils/cache.ts import Redis from "ioredis";

const redis = new Redis({ host: process.env.REDIS_HOST, port: parseInt(process.env.REDIS_PORT || "6379"), retryStrategy: (times) => { const delay = Math.min(times * 50, 2000); return delay; }, });

export class CacheService { async get<T>(key: string): Promise<T | null> { const data = await redis.get(key); return data ? JSON.parse(data) : null; }

async set(key: string, value: any, ttl?: number): Promise<void> { const serialized = JSON.stringify(value); if (ttl) { await redis.setex(key, ttl, serialized); } else { await redis.set(key, serialized); } }

async delete(key: string): Promise<void> { await redis.del(key); }

async invalidatePattern(pattern: string): Promise<void> { const keys = await redis.keys(pattern); if (keys.length > 0) { await redis.del(...keys); } } }

// Cache decorator export function Cacheable(ttl: number = 300) { return function ( target: any, propertyKey: string, descriptor: PropertyDescriptor, ) { const originalMethod = descriptor.value;

descriptor.value = async function (...args: any[]) {
  const cache = new CacheService();
  const cacheKey = `${propertyKey}:${JSON.stringify(args)}`;

  const cached = await cache.get(cacheKey);
  if (cached) {
    return cached;
  }

  const result = await originalMethod.apply(this, args);
  await cache.set(cacheKey, result, ttl);

  return result;
};

return descriptor;

}; }

API Response Format

// utils/response.ts import { Response } from "express";

export class ApiResponse { static success<T>( res: Response, data: T, message?: string, statusCode = 200, ) { return res.status(statusCode).json({ status: "success", message, data, }); }

static error(res: Response, message: string, statusCode = 500, errors?: any) { return res.status(statusCode).json({ status: "error", message, ...(errors && { errors }), }); }

static paginated<T>( res: Response, data: T[], page: number, limit: number, total: number, ) { return res.json({ status: "success", data, pagination: { page, limit, total, pages: Math.ceil(total / limit), }, }); } }

Best Practices

  • Use TypeScript: Type safety prevents runtime errors

  • Implement proper error handling: Use custom error classes

  • Validate input: Use libraries like Zod or Joi

  • Use environment variables: Never hardcode secrets

  • Implement logging: Use structured logging (Pino, Winston)

  • Add rate limiting: Prevent abuse

  • Use HTTPS: Always in production

  • Implement CORS properly: Don't use * in production

  • Use dependency injection: Easier testing and maintenance

  • Write tests: Unit, integration, and E2E tests

  • Handle graceful shutdown: Clean up resources

  • Use connection pooling: For databases

  • Implement health checks: For monitoring

  • Use compression: Reduce response size

  • Monitor performance: Use APM tools

Testing Patterns

See javascript-testing-patterns skill for comprehensive testing guidance.

Resources

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