Global state across screens. LocalStorage for persistence. Authentication basics for "Staff Only" sections.
// LocalStorage - persist user progress
localStorage.setItem('progress', JSON.stringify({ module: 3, xp: 124 }));
const saved = JSON.parse(localStorage.getItem('progress'));
// Auth check (conceptual)
if (!isLoggedIn()) redirectToLogin();LocalStorage is synchronous. For large data, consider IndexedDB or a backend.
JWT, sessions, OAuth — always validate on the server, never trust the client.