Singleton Pattern

The Singleton pattern ensures that a class has only one instance and provides a global point of access to it.

When to Use:

Use the Singleton pattern when you need exactly one instance of a class to control the actions, such as in logging, managing a connection pool, or in cases where a single instance should coordinate actions across the system.

Example

class Singleton {
  private static instance: Singleton;

  private constructor() {}

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

  public someBusinessLogic() {
    console.log('Executing some business logic.');
  }
}

// Usage
const singleton1 = Singleton.getInstance();
const singleton2 = Singleton.getInstance();

console.log(singleton1 === singleton2); // Output: true

Pros:

• Controlled access to the sole instance.
• Reduced memory footprint as the instance is created only once.

Cons:

• Can introduce global state into an application, which can lead to hard-to-debug issues.
• Makes unit testing difficult due to the tight coupling of code to the Singleton instance.