Какие используешь паттерны проектирования

class ApiService {
  constructor() {
    if (!ApiService.instance) {
      ApiService.instance = this;
    }
    return ApiService.instance;
  }
}

const eventBus = {
  listeners: {},
  subscribe(event, callback) {
    this.listeners[event] = callback;
  },
  emit(event, data) {
    this.listeners[event]?.(data);
  }
};

function createButton(type) {
  switch(type) {
    case 'primary': return new PrimaryButton();
    case 'secondary': return new SecondaryButton();
  }
}