Nodejs Backend Patterns

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.

Use this skill when

• 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

Do not use this skill when

• The task is unrelated to node.js backend patterns
• You need a different domain or tool outside this scope

Instructions

• Clarify goals, constraints, and required inputs.
• Apply relevant best practices and validate outcomes.
• Provide actionable steps and verification.
• If detailed examples are required, open resources/implementation-playbook.md.

Resources

• resources/implementation-playbook.md for detailed patterns and examples.

Node.js Backend Patterns Implementation Playbook

This file contains detailed patterns, checklists, and code samples referenced by the skill.

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

1. Use TypeScript: Type safety prevents runtime errors 2. Implement proper error handling: Use custom error classes 3. Validate input: Use libraries like Zod or Joi 4. Use environment variables: Never hardcode secrets 5. Implement logging: Use structured logging (Pino, Winston) 6. Add rate limiting: Prevent abuse 7. Use HTTPS: Always in production 8. Implement CORS properly: Don't use * in production 9. Use dependency injection: Easier testing and maintenance 10. Write tests: Unit, integration, and E2E tests 11. Handle graceful shutdown: Clean up resources 12. Use connection pooling: For databases 13. Implement health checks: For monitoring 14. Use compression: Reduce response size 15. Monitor performance: Use APM tools

Testing Patterns

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

Resources

• Node.js Best Practices: https://github.com/goldbergyoni/nodebestpractices
• Express.js Guide: https://expressjs.com/en/guide/
• Fastify Documentation: https://www.fastify.io/docs/
• TypeScript Node Starter: https://github.com/microsoft/TypeScript-Node-Starter