使用发布订阅的设计模式

class EventBus {
  on(eventName, listener) {
    if (!this.listeners[eventName]) {
      this.listeners[eventName] = new Set()
    }
    this.listeners[eventName].add(listener)
  }

  emit(eventName, ...args) {
    this.listeners[eventName].forEach(listener => listener(...args))
  }

  off(eventName, listener) {
    if (!this.listeners[eventName]) {
      throw new Error(`Event with name ${eventName} is not found`)
    }
    this.listeners[eventName].delete(listener)
  }
}

export default new EventBus()