What design patterns have you used in your practice?

In practice with Node.js, the following design patterns are often used:

• Module Pattern — for organizing code into separate files and exporting functionality.
• Factory Pattern — for creating objects with different configurations.
• Singleton — for creating a single instance of an object, such as a database connection.
• Observer (Listener) — for implementing events and subscriptions, often through EventEmitter.
• Middleware — in Express.js for processing requests in a chain.

Example of Singleton for database connection:

class Database {
  constructor() {
    if (Database.instance) {
      return Database.instance;
    }
    this.connection = this.connect();
    Database.instance = this;
  }
  connect() {
    // connection logic
    return {};
  }
}

const db1 = new Database();
const db2 = new Database();
console.log(db1 === db2); // true

These patterns help write more structured, maintainable, and scalable code.