let state = {button:false}
const getState = ()=> localstorage.getItem('state') ? JSON.parse(localstorage.getItem('state')) : state
const save = () => localstorage.setItem('state', JSON.stringify(state))
mount(){
state = getState()
}
btn.addEventListener('click', e => {
state.button = !state.button
save()
})