编辑代码

class Subject{
    constructor() {
        this.subs = [];
    }
    addSub(sub) {
        this.subs.push(sub);
    }
    notify(){
        this.subs.forEach(sub=>{
            sub.update();
        })
    }
}

class Observer {
    update(){
        console.log('update...');
    }
}

let subject = new Subject();
let ob = new Observer();
// 目标添加观察者
subject.addSub(ob);
subject.notify();