JavaScript Proxy example use case

proxy_createStore.js

function createStore(target, listener) {
  const handler = {
    set(target, prop, value, receiver) {
				target[prop] = value;
				listener(receiver);
				return true;
		},
    get(target, prop) {
    	return target[prop];
  	},
  };
  return new Proxy(target, handler);
}

const initialState = {
	authenticated: false,
	userName: "Sam",
	favorites: []
};

function appListener(state) {
	if (state.authenticated) {
		 // update UI
	}
	if (state.favorites.length) {
		// update UI
	}
}

const store = createStore(initialState, appListener);

// Some other part of the application makes
// these updates
store.authenticated = true;
store.favorites = ["Pizza", "Tacos"];