理解发布/订阅

理解发布/订阅

异步编程方法

1.回调函数
2.事件发布/订阅
3.Promise
4.generator函数
5.async函数

//回调地狱
function ajax(url, callback){
 //实现省略
}

ajax('./test1.json',function(data){
 console.log(data);
 ajax('./test2.json',function(data){
   console.log(data);
   ajax('./test3.json',function(data){
     console.log(data);
   });
 });

//发布/订阅
const pbb = new PubSub();
ajax("./test1.json",function(data){
 pbb.publish("test1Success",data);
});
pbb.subscribe("test1Success",function(data){
 console.log(data);
 ajax("./test2.json",function(data){
   pbb.publish("test2Success",data);
 });
});
pbb.subscribe("test2Success",function(data){
 console.log(data);
 ajax("./test3.json",function(data){
   pbb.publish("test3Success",data);
 });
});
pbb.subscribe("test2Success",function(data){
 console.log(data);
});

实现发布/订阅

class PubSub{
  constructor(){
    this.events = {};
  }
  publish(eventName,data){
    if(this.events[eventsName]){
      this.events[eventName].forEach(cb => {
        cb.apply(this.data)
      });
    }
  }

  subscribe(eventName, callback){
    if(this.events[eventName]){
      this.events[eventName].push(callback);
    }else{
      this.events[eventName] = [callback];
    }
  }

  unSubcribe(eventName,callback){
    if(this.events[eventName]){
      this.events[eventName] = this.events[eventName].filter(
        cb => cb !== callback
      );
    }
  }
}

Node.js的发布/订阅

});