观察者模式

//发布者的构造函数
function Publish() {
  this.subscribers = []; //订阅者列表，每个订阅者其实是一个处理得到信息的函数
}

//发布者的发布方法
Publish.prototype.next = function (news) {
  this.subscribers.forEach(fn => fn(news)) //将信息发布给每个订阅者，fn代表订阅者
  return this //链式编程
}

//观察者的订阅方法
Publish.prototype.subscribe = function (callback) {
  let alreadyIn = this.subscribers.some(sub => sub == this)
  if (!alreadyIn) {
    this.subscribers.push(callback)
  }
  return this
}

//取消订阅
Publish.prototype.unsubscribe = function () {
  // this.subscribers.filter(subscriber=>subscriber!==this);
  this.subscribers = [];
  return this
}
//   //观察者的订阅方法
//   Function.prototype.subscribe = function(publisher){  
//     let alreadyIn = publisher.subscribers.some( subscriber => subscriber == this)
//     if(!alreadyIn){
//       publisher.subscribers.push(this)
//     }
//     return this
//   }

//   //取消订阅
//   Function.prototype.unsubscribe = function(publisher){
//     publisher.subscribers.filter(subscriber=>subscriber!==this)
//     return this
//   }

<script>
    function fn() {
        const demo = new Publish();
        setInterval(() => {
            demo.next(Math.random());
        }, 1000);
        return demo;
    }
    const result = fn().subscribe(a => {
        console.log('--------', a);
    });

    function cancel() {
        result.unsubscribe()
    }
</script>