What are Cookies? Tell what they're for and how you used them.

// Setting cookie
document.cookie = 'username=John; path=/; expires=Fri, 31 Dec 2024 23:59:59 GMT';
 
// Reading cookie
console.log(document.cookie); // 'username=John'

// Simple cookie
document.cookie = 'theme=dark';

// ✅ Save auth token
document.cookie = 'token=abc123; path=/; secure';
// Server will see this token in every request

// ✅ Remember user language
document.cookie = 'language=en; path=/; max-age=31536000';
// Site will know language on next visit

// ✅ Save interface settings
document.cookie = 'fontSize=large; path=/; expires=Fri, 31 Dec 2024 23:59:59 GMT';

// Basic setting
document.cookie = 'name=value';
 
// With parameters
document.cookie = 'username=John; path=/; expires=Fri, 31 Dec 2024 23:59:59 GMT; secure';

// Read all cookies
console.log(document.cookie); // 'username=John; theme=dark'
 
// Cookies come as string, need to parse

// ❌ Bad — cookies sent with every request
document.cookie = 'bigData=very_large_data'; // Slows site!
 
// ✅ Better — use localStorage
localStorage.setItem('bigData', 'very_large_data');

// ❌ Problem — cookie without expiration deleted when browser closes
document.cookie = 'temp=data';
 
// ✅ Good — set expiration
document.cookie = 'temp=data; max-age=3600'; // For one hour

// ❌ Unsafe — cookie accessible through JavaScript
document.cookie = 'token=abc123';
 
// ✅ Safer — HttpOnly cookie set by server
// Set-Cookie: token=abc123; HttpOnly; Secure

// ✅ Authentication (tokens, sessions)
// ✅ Personalization (language, theme)
// ✅ Tracking (analytics, advertising)

// ❌ Large data (4 KB limit)
// ❌ Frequent changes (loads requests)
// ❌ Confidential data (visible in requests)