What is the Singleton pattern?

What is the Singleton pattern?

Singleton design pattern exposes a single instance that can be used by multiple components.

Singleton is a design pattern that tell us that we can create only one instance of a class and that instance can be accessed globally. This is one of the basic types of design pattern. It makes sure that the class acts as a single source of entry for all the consumer components that want to access this state.

✅ Ensures that it creates only one instance of the class
✅ Provides a global access point to the state.
✅ Makes sure that the instance is only created the first time.

example code for understanding

class Singleton {
  constructor() {
    if (Singleton.instance) {
      return console.log('warning, singleton class already instantiated')
    }
    Signleton.instance = this
    this.version = Date.now()
    this.config = 'test'
  }
  static getInstance() {
    if (!this.instance) {
      this.instance = new Singleton()
    }
    return this.instance
  }
}

// const s1 = new Singleton()
// console.log(s1)
// const s2 = new Signleton()
// console.log(s2)

// const s3 = Singleton.getInstance();
// const s4 = Singleton.getInstance();
// console.log(s3 === s4)   true

The singleton design pattern can be useful in creating a global state that can be accessed by any component. Only a single instance exists, and the object is accessed through static functions. Since management is done within a single instance, code duplication can be prevented. Static functions allow global access.