手写题: 发布订阅和观察者模式

class Subject {
  constructor(name) {
    this.name = name
    this.state = '开心'
    this.observer = []
  }
  attach(o) {
    this.observer.push(o)
  }
  setState(newState) {
    this.state = newState
    this.observer.forEach(o => o.updata(this))
  }
}
class Observer {
  constructor(name) {
    this.name = name
  }
  updata(baby) {
    console.log(this.name,baby);
  }
}
let baby = new Subject('baby')
let father = new Observer('father')
let mom = new Observer('mom')
baby.attach(father)
baby.attach(mom)
baby.setState('不开心')

class EventEmitter {
  // 补全代码
  constructor() {
      this.events = {}
  }
  on(event,fn) {
      if(!this.events[event]) {
          this.events[event] = [fn]
      } else {
          this.events[event].push(fn)
      }
  }
  emit(event) {
      if(this.events[event]) {
          this.events[event].forEach(fn => fn())
      }
  }
}