example of using static classes for singleton

singletonCounter.js

class Counter {
  static instance;

  static get count() {
    if (!Counter.instance) {
      Counter.instance = { count: 0 };
    }
    return Counter.instance?.count;
  }
  static set count(newCount) {
    Counter.instance.count = newCount;
  }

  static increment() {
    return ++Counter.count;
  }

  static decrement() {
    return --Counter.count;
  }
}