singleton.md

Singleton Pattern

Singleton creational design pattern restricts the instantiation of a class to a single object.

Implementation

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

    Singleton.instance = this;
  }
}

Usage

const i = new Singleton();
const j = new Singleton();

console.log(i); // Singleton {}
console.log(j); // Singleton {}

console.log(i === j); // true

Caveats

• Singletons represent a global state and may reduces testability.