Client-Side State Manager

For small apps without a framework, a simple pub-sub state manager gives you predictable data flow without external libraries.

const Store = (() => {
  const KEY = 'app-state';
  const subscribers = [];

  function getState() {
    const raw = localStorage.getItem(KEY);
    return raw ? JSON.parse(raw) : { todos: [], theme: 'light' };
  }

  function setState(partial) {
    const next = { ...getState(), ...partial };
    localStorage.setItem(KEY, JSON.stringify(next));
    subscribers.forEach(fn => fn(next));
  }

  function subscribe(fn) {
    subscribers.push(fn);
    return () => subscribers.splice(subscribers.indexOf(fn), 1);
  }

  return { getState, setState, subscribe };
})();

// Usage
Store.subscribe(state => renderApp(state));
Store.setState({ theme: 'dark' });

Call the returned unsubscribe function when a component is removed from the DOM to prevent memory leaks.