// Created on savesnippets.com · https://savesnippets.com/9DgCLFRqi0he9w
function observable(initialState) {
  const listeners = new Set();
  const state = new Proxy(initialState, {
    set(target, key, value) {
      target[key] = value;
      listeners.forEach((fn) => fn(key, value, target));
      return true;
    },
  });
  return {
    state,
    subscribe(fn) {
      listeners.add(fn);
      return () => listeners.delete(fn);
    },
  };
}

// Usage
const { state, subscribe } = observable({ count: 0, name: 'Alice' });
subscribe((key, val) => console.log(`${key} changed to`, val));
state.count++;    // count changed to 1
state.name = 'Bob'; // name changed to Bob