Singleton

Singleton is a creational design pattern that lets you ensure that a class has only one instance, while providing a global access point to this instance.

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

class Singleton {
  constructor() {
    if (!Singleton.instance) {
      Singleton.instance = this;
    }

    return Singleton.instance;
  }

  someMethod() {
    console.log("Some method of the singleton instance");
  }
}

// Usage
const instance1 = new Singleton();
const instance2 = new Singleton();

console.log(instance1 === instance2); // Output: true

instance1.someMethod(); // Output: "Some method of the singleton instance"
instance2.someMethod(); // Output: "Some method of the singleton instance"

In this example:

• The Singleton class has a private static property instance to hold the single instance of the class.

• The constructor checks if an instance already exists. If it does not, it creates one and assigns it to Singleton.instance.

• If an instance already exists, it returns the existing instance.

• The someMethod is just a placeholder method to demonstrate usage.

When you create multiple instances of Singleton, they all refer to the same instance.

Thus, only one instance of the Singleton class exists throughout the application.