'use strict';

function Singleton() {

const { instance } = Singleton;

if (instance) return instance;

Singleton.instance = this;

}

// Usage

console.assert(new Singleton() === new Singleton());

console.log('instances are equal');

// But instance is accessible

const a1 = new Singleton();

Singleton.instance = null;

console.log('Remove instance');

const a2 = new Singleton();

if (a1 !== a2) console.log('a1 !== a2');