Can you explain the Singleton design pattern and its application?

Singleton is a design pattern that guarantees a class has only one instance and provides a global point of access to it.

Application:

• When a single object is needed, for example, for managing configuration, logging, or database connection.
• To avoid creating multiple instances that may consume resources or lead to inconsistency.

Example of implementing Singleton in Node.js:

class Singleton {
  constructor() {
    if (Singleton.instance) {
      return Singleton.instance;
    }
    this.value = Math.random();
    Singleton.instance = this;
  }
}

const a = new Singleton();
const b = new Singleton();
console.log(a === b); // true

Thus, when trying to create a new instance of the Singleton class, the same instance is always returned.