JavaScript: паттерны и архитектура

1const Counter = (() => {
2  let count = 0;
3  return {
4    increment: () => ++count,
5    getCount: () => count,
6  };
7})();

1class EventEmitter {
2  #listeners = new Map();
3  on(event, fn) {
4    if (!this.#listeners.has(event)) this.#listeners.set(event, []);
5    this.#listeners.get(event).push(fn);
6  }
7  emit(event, ...args) {
8    this.#listeners.get(event)?.forEach(fn => fn(...args));
9  }
10}

1class Database {
2  static #instance;
3  static getInstance() {
4    if (!Database.#instance) Database.#instance = new Database();
5    return Database.#instance;
6  }
7}