Possible store implementation using Proxy.

proxy-store.mjs

const state = {}
const listeners = []
let aid
const handler = {
  set: function setter (obj, prop, value) {
    let old = obj[prop]
    if (old !== value) {
      obj[prop] = value
      if (aid) {
        window.cancelAnimationFrame(aid)
      }
      aid = window.requestAnimationFrame(notify)
    }
    return true
  }
}
let actual = new Proxy(state, handler)

function subscribe (l) {
  listeners.push(l)
}

function unsubscribe (l) {
  listeners.splice(listeners.indexOf(l), 1)
}

function notify () {
  let i = 0
  let l = listeners.length
  let fn
  for (i; i < l; i++) {
    fn = listeners[i]
    fn(state)
  }
}

function Store (initialState) {
  if (initialState) {
    for (let prop in initialState) {
      state[prop] = initialState[prop]
    }
  }
  return actual
}

actual.subscribe = subscribe
actual.unsubscribe = unsubscribe

module.exports = Store