Cookies & Local Storage Cheat Sheet

// Set a cookie (document.cookie is a single string interface)document.cookie = "theme=dark; max-age=" + 60 * 60 * 24 * 30 + "; path=/; SameSite=Lax; Secure";// Read all cookies (must parse manually)function getCookie(name) {  const match = document.cookie.match(new RegExp('(^| )' + name + '=([^;]+)'));  return match ? decodeURIComponent(match[2]) : null;}getCookie('theme'); // "dark"// Delete a cookie: set max-age to 0document.cookie = "theme=; max-age=0; path=/";// Server-side (Express) — httpOnly cookies aren't readable by JS at allres.cookie('session_id', token, {  httpOnly: true, secure: true, sameSite: 'strict', maxAge: 3600000,});

// localStorage: persists until explicitly cleared, ~5-10MB per originlocalStorage.setItem('user', JSON.stringify({ id: 1, name: 'Ada' }));const user = JSON.parse(localStorage.getItem('user'));localStorage.removeItem('user');localStorage.clear(); // wipes everything for this origin// sessionStorage: same API, but scoped to a single tab and cleared on tab closesessionStorage.setItem('draft', 'unsaved text');// React to changes from OTHER tabs (storage event doesn't fire in the same tab)window.addEventListener('storage', (event) => {  console.log(event.key, event.oldValue, event.newValue);});