Singleton Pattern in Express.js

Overview

Ensure a class has only one instance

Singleton Pattern 1 implementations available

When to Use

When you need to abstract data access logic
When you want to make your code testable
When you need to support multiple data sources
When you want to decouple business logic from infrastructure

Available Implementations

Error Handler

Global error handling middleware

npx hanma add error-middleware

Global error catchingEnvironment-aware responsesError logging

Basic Example

// Singleton Pattern implementation example
// This shows the basic structure of singleton pattern in Express.js

// Define your interface
interface IRepository {
  findAll(): Promise<T[]>;
  findById(id: string): Promise<T | null>;
  create(data: CreateDto): Promise<T>;
  update(id: string, data: UpdateDto): Promise<T>;
  delete(id: string): Promise<void>;
}

// Implement the pattern
class SingletonRepository implements IRepository {
  async findAll(): Promise<T[]> {
    // Implementation
  }

  async findById(id: string): Promise<T | null> {
    // Implementation
  }

  async create(data: CreateDto): Promise<T> {
    // Implementation
  }

  async update(id: string, data: UpdateDto): Promise<T> {
    // Implementation
  }

  async delete(id: string): Promise<void> {
    // Implementation
  }
}

// Use the pattern
const repository = new SingletonRepository();
const items = await repository.findAll();

Frequently Asked Questions

What is Singleton Pattern?

Ensure a class has only one instance. It's a well-established software design pattern that helps organize code for better maintainability and testability.

How does Singleton Pattern work with Express.js?

Express.js provides excellent support for this pattern through its dependency injection system and middleware composition.

What are the benefits?

Improved testability, separation of concerns, easier maintenance, and flexibility to change implementations without affecting business logic.

When should I avoid this pattern?

For very simple applications with minimal logic, the pattern may add unnecessary complexity. Use judgment based on project requirements.