一描述观察者模式和发布订阅模式的区别及各自的使用场景#

class Subject {
	constructor() {
		this.observerList = [];
	}
	addObserver(observer) {
		this.observerList.push(observer);
	}
	removeObserver(observer) {
		const index = this.observerList.findIndex(o => o.name === observer.name);
		this.observerList.splice(index, 1);
	}
	notifyObservers(message) {
		const observers = this.observeList;
		observers.forEach(observer => observer.notified(message));
	}
}

class Observer {
	constructor(name, subject) {
		this.name = name;
		if (subject) {
			subject.addObserver(this);
		}
	}
	notified(message) {
		console.log(this.name, 'got message', message);
	}
}

const subject = new Subject();
const observerA = new Observer('observerA', subject);
const observerB = new Observer('observerB');
subject.addObserver(observerB);
subject.notifyObservers('Hello from subject');
subject.removeObserver(observerA);
subject.notifyObservers('Hello again');

class PubSub {
	constructor() {
		this.messages = {};
		this.listeners = {};
	}
	// 添加发布者
	publish(type, content) {
		const existContent = this.messages[type];
		if (!existContent) {
			this.messages[type] = [];
		}
		this.messages[type].push(content);
	}
	// 添加订阅者
	subscribe(type, cb) {
		const existListener = this.listeners[type];
		if (!existListener) {
			this.listeners[type] = [];
		}
		this.listeners[type].push(cb);
	}
	// 通知
	notify(type) {
		const messages = this.messages[type];
		const subscribers = this.listeners[type] || [];
		subscribers.forEach((cb, index) => cb(messages[index]));
	}
}

class Publisher {
	constructor(name, context) {
		this.name = name;
		this.context = context;
	}
	publish(type, content) {
		this.context.publish(type, content);
	}
}

class Subscriber {
	constructor(name, context) {
		this.name = name;
		this.context = context;
	}
	subscribe(type, cb) {
		this.context.subscribe(type, cb);
	}
}

const TYPE_A = 'music';
const TYPE_B = 'movie';
const TYPE_C = 'novel';
const pubsub = new PubSub();
const publisherA = new Publisher('publisherA', pubsub);
publisherA.publish(TYPE_A, 'we are young');
publisherA.publish(TYPE_B, 'the silicon valley');
const publisherB = new Publisher('publisherB', pubsub);
publisherB.publish(TYPE_A, 'stronger');
const publisherC = new Publisher('publisherC', pubsub);
publisherC.publish(TYPE_C, 'a brief history of time');
const subscriberA = new Subscriber('subscriberA', pubsub);
subscriberA.subscribe(TYPE_A, res => {
	console.log('subscriberA received', res)
});
const subscriberB = new Subscriber('subscriberB', pubsub);
subscriberB.subscribe(TYPE_C, res => {
	console.log('subscriberB received', res)
});
const subscriberC = new Subscriber('subscriberC', pubsub);
subscriberC.subscribe(TYPE_B, res => {
	console.log('subscriberC received', res)
});
pubsub.notify(TYPE_A);
pubsub.notify(TYPE_B);
pubsub.notify(TYPE_C);