observer

main.ts

var egghead = new Producer(); 

function listener1(message) {
	console.log(message + 'from listener1');
}

function listener2(message) {
	console.log(message + 'from listener2');
}

egghead.addListener(listener1); // 註冊監聽
egghead.addListener(listener2);

egghead.notify('A new course!!') // 當某件事情方法時，執行

Producer.ts

class Producer {
    listeners = [];

	constructor() {
    }
    
	addListener(listener) {
		if(typeof listener === 'function') {
			this.listeners.push(listener)
		} else {
			throw new Error('listener 必須是 function')
		}
	}
	removeListener(listener) {
		this.listeners.splice(this.listeners.indexOf(listener), 1)
	}
	notify(message) {
		this.listeners.forEach(listener => {
			listener(message);
		})
	}
}