Observer Store

store.js

export const deepCopy = (data) => {
	return typeof data === 'object' ? (
		JSON.parse(JSON.stringify(data))
	) : (
		data
	)
}

export function Store(_init) {
	let init = deepCopy(_init)
	let state = deepCopy(_init)
	let observers = []

	const broadcast = () => {
		observers.forEach(subscriber => subscriber(state))
	}

	const setState = (data) => {
		state = deepCopy(data)
		broadcast()
	}

	Object.defineProperty(this, 'state', {
		get: () => state,
		set: setState
	})

	this.subscribe = (fn) => {
		observers.push(fn)
		fn(state)
		return () => this.unsubscribe(fn)
	}

	this.unsubscribe = (fn) => {
		observers = observers.filter(subscriber => subscriber !== fn)
	}

	this.reset = () => setState(init)
	
}

test.js

const Store = require('./store')

const counter = new Store(0)

let s1 = counter.subscribe(data => console.log('subscribe 1: ', data))
// subscribe 1: 0
let s2 = counter.subscribe(data => console.log('subscribe 2: ', data))
// subscribe 2: 0

console.log(counter.state)
// 0

counter.state = 1
// subscribe 1: 1
// subscribe 2: 1
console.log(counter.state)
// 1

counter.reset()
// subscribe 1: 0
// subscribe 2: 0
console.log(counter.state)
// 0

setTimeout(() => {
    s1()
    counter.state = 2
    // subscribe 2: 2
    console.log(counter.state)
    // 2
}, 3000)

s2()