SOURCE

class Publisher {
    constructor() {
        this.observers = [];

        console.log("Publisher  created")
    }

    //增加订阅者
    add(observer) {
        console.log("Publisher.add  invoked")

        this.observers.push(observer)
    }


    // 移出订阅者
    remove(observer) {
        console.log("Publisher.remove invoked")

        this.observers.forEach((item, i) => {
            if (item === observer) {
                this.observers.splice(i, 1)
            }
        })
    }

    //通知所有订阅者
    notify() {

        this.observers.forEach((observer) => {
            observer.updata(this)
        })
    }
}


//定义订阅类
class Observer {
    constructor() {
        console.log()
    }

    updata() {

    }
}