Creational Design Patterns

Creational patterns deal with object creation mechanisms.

Singleton Pattern

class DatabaseConnection {
  private static instance: DatabaseConnection;

  private constructor() {
    // Private constructor prevents direct instantiation
  }

  static getInstance(): DatabaseConnection {
    if (!DatabaseConnection.instance) {
      DatabaseConnection.instance = new DatabaseConnection();
    }
    return DatabaseConnection.instance;
  }
}

const db1 = DatabaseConnection.getInstance();
const db2 = DatabaseConnection.getInstance();
console.log(db1 === db2); // true

Factory Method Pattern

interface Notification { send(message: string): void; }

class EmailNotification implements Notification {
  send(message: string): void { console.log(`Email: ${message}`); }
}

class SMSNotification implements Notification {
  send(message: string): void { console.log(`SMS: ${message}`); }
}

class NotificationFactory {
  static create(type: 'email' | 'sms'): Notification {
    switch (type) {
      case 'email': return new EmailNotification();
      case 'sms': return new SMSNotification();
    }
  }
}

const notification = NotificationFactory.create('email');
notification.send('Hello!');

Builder Pattern

class HttpRequestBuilder {
  method: string = 'GET';
  url: string = '';
  headers: Map = new Map();
  body?: string;

  setMethod(method: string): this {
    this.method = method;
    return this;
  }

  setUrl(url: string): this {
    this.url = url;
    return this;
  }

  addHeader(key: string, value: string): this {
    this.headers.set(key, value);
    return this;
  }

  setBody(body: string): this {
    this.body = body;
    return this;
  }

  build(): HttpRequest {
    return new HttpRequest(this);
  }
}

// Fluent API usage
const request = new HttpRequestBuilder()
  .setMethod('POST')
  .setUrl('https://api.example.com/users')
  .addHeader('Content-Type', 'application/json')
  .setBody(JSON.stringify({ name: 'John' }))
  .build();

Creational Patterns

Creational Patterns

Creational Design Patterns

Singleton Pattern

Factory Method Pattern

Builder Pattern