（JS）观察者模式

（JS）观察者模式
一对多
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class Subject {
    
	constructor() {
    
		this.state = 0;
		this.observers = [];
	}
	
	getState() {
    
		return this.state;
	}
	
	setState(state) {
    
		this.state = state;
		this.notifyAllObservers();
	}
	// 触发每一个Observer的update()方法
	notifyAllObservers() {
    
		this.observers.forEach(observer => {
    
			observer.update();
		});
	}
	// 将每个新建的observer都添加进this.observers中
	attach(observer) {
    
		this.observers.push(observer);
	}
}

class Observer {
    
	constructor(name, subject) {
    
		this.name = name;
		this.subject = subject;
		this.subject.attach(this);
	}
	
	update() {
    
		console.log(`${
      this.name} update,state:${
      this.subject.getState()}`)
	}
}

let sub = new Subject();
let o1 = new Observer("11", sub);
let o2 = new Observer("22", sub);
let o3 = new Observer("33", sub);
sub.setState(5)

11 update,state:5
22 update,state:5
33 update,state:5