022.消息訂閱與發佈

1. 工具庫：PubSubJs
2. 下載：npm install pubsub-js --save
3. 使用：
   • 1. import PubSub from 'pubsub-js' //引入
   • 2. PubSub.subscribe('delete',function(data)); //訂閱
   • 3. PubSub.publish('delete',data) //發佈消息

舉個栗子：

**1.引入工具庫**  
import PubSub from 'pubsub-js'

**2.發佈消息**  
PubSub.publish('TOPIC','hello react');

**訂閱消息**  
this.token = PubSub.subscribe('TOPIC',callback);

var callBack = function (msg,data) {
    console.log(msg,data) //TOPIC 'hello react'
}
   
   
**取消訂閱**  
componentWillUnmount(){
    PubSub.unsubscribe(this.token)
}
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