What are Set and Map in JavaScript?

// Creating a Set
const set = new Set([1, 2, 3, 3, 4]);
console.log(set); // Set { 1, 2, 3, 4 }

// Methods
set.add(5);
set.has(3);     // true
set.delete(2);
set.size;       // 4
set.clear();

// Remove duplicates from array
const arr = [1, 2, 2, 3, 3, 3];
const unique = [...new Set(arr)]; // [1, 2, 3]

// Iteration
for (const value of set) {
  console.log(value);
}

// Creating a Map
const map = new Map();
map.set('name', 'John');
map.set(1, 'one');
map.set({ key: 1 }, 'object key');

// Object as key
const userRoles = new Map();
const user = { id: 1 };
userRoles.set(user, 'admin');
userRoles.get(user); // 'admin'

// Methods
map.get('name');    // 'John'
map.has('name');    // true
map.delete('name');
map.size;           // 2

// Iteration
for (const [key, value] of map) {
  console.log(key, value);
}