Set. What's special about it? What properties and methods does it have? How to iterate?

const set = new Set([1, 2, 2, 3, 3, 4]);
console.log(set); // Set { 1, 2, 3, 4 } (duplicates removed)
console.log(set.size); // 4
console.log(set.has(2)); // true

// Creating Set
const numberSet = new Set();
 
// Adding elements
numberSet.add(1);
numberSet.add(2);
numberSet.add(2); // won't be added — duplicate!
 
console.log(numberSet); // Set { 1, 2 }
console.log(numberSet.size); // 2
 
// Checking existence
console.log(numberSet.has(1)); // true
console.log(numberSet.has(3)); // false
 
// Deletion
numberSet.delete(1);
console.log(numberSet.has(1)); // false

// Removing duplicates from array
const arrayWithDuplicates = [1, 2, 2, 3, 3, 4];
const uniqueArray = [...new Set(arrayWithDuplicates)];
console.log(uniqueArray); // [1, 2, 3, 4]

const set = new Set(['a', 'b', 'c']);
console.log(set.size); // 3 (number of elements)

const set = new Set();
 
// add(value) — adds value
set.add('value');
 
// has(value) — checks value existence
const exists = set.has('value');
 
// delete(value) — removes value
set.delete('value');
 
// clear() — clears entire Set
set.clear();
 
// size — property, returns element count
console.log(set.size);

const set = new Set(['apple', 'banana', 'orange']);
 
// Iterating values
for (const value of set) {
  console.log(value);
}

const set = new Set([1, 2, 3]);
 
set.forEach(value => {
  console.log(value);
});

// List of unique tags
const tags = new Set();
tags.add('JavaScript');
tags.add('React');
tags.add('JavaScript'); // won't be added
console.log(tags); // Set { 'JavaScript', 'React' }

// Fast checking if value exists
const allowedRoles = new Set(['admin', 'moderator', 'user']);
 
function checkRole(role) {
  return allowedRoles.has(role);
}
 
console.log(checkRole('admin')); // true
console.log(checkRole('guest')); // false

// ❌ Error — thinking Set is like array
const set = new Set([1, 2, 3]);
// set[0]; // undefined! Set has no indices
// set.length; // undefined! Set has no length
 
// ✅ Correctly — use Set methods
console.log(set.size); // 3
console.log(set.has(1)); // true

// ❌ Error — forgot new
// const set = Set(); // TypeError!
 
// ✅ Correctly
const set = new Set();