class SomeClass{
  private events: Map<string, Set<any>> = new Map()

  on(event: string, callback: (p?: any) => any) {
    if (typeof event !== 'string' || typeof callback !== 'function') {
      return
    }
    if (!this.events.has(event)) {
      this.events.set(event, new Set())
    }
    const e = this.events.get(event)
    !!e && e.add(callback)
  }

  off(event: string, callback?: (p?: any) => any) {
    if (!this.events.has(event) || !this.events.get(event)) {
      return
    }

    if (typeof callback === 'function') {
      const e = this.events.get(event)
      !!e && e.delete(callback)
    } else {
      this.events.delete(event)
    }
  }

  emit(event: string, ...args: any) {
    if (!this.events.has(event)) {
      return
    }
    const e = this.events.get(event)
    !!e &&
      e.forEach((e: (...p: any) => void) => {
        e.apply(null, args)
      })
  }
}