JavaScript Sets Overview

A Set in JavaScript is a built-in object that stores unique values of any type, whether primitive or reference. Unlike arrays, sets do not allow duplicate entries and do not maintain an index-based order.

1. Creating a Set

// Using the Set constructor
const numbers = new Set([1, 2, 3, 4]);
console.log(numbers); // Set {1, 2, 3, 4}

// Empty set
const emptySet = new Set();

2. Key Features

• Stores unique values only (duplicates are ignored).
• Values can be of any type: numbers, strings, objects, arrays, or even other sets.
• Order is insertion-based but no numeric index access.
• Iterable: you can loop through a set with for...of or .forEach().

3. Common Set Methods

Method	Description	Example
add(value)	Adds a new element	numbers.add(5);
delete(value)	Removes a value	numbers.delete(2);
has(value)	Checks if value exists	numbers.has(3); // true
clear()	Removes all elements	numbers.clear();
size	Returns the number of elements	numbers.size; // 4

4. Iterating Over a Set

const fruits = new Set(["apple", "banana", "mango"]);

// Using for...of
for (const fruit of fruits) {
  console.log(fruit);
}

// Using forEach
fruits.forEach(fruit => console.log(fruit));

5. Converting Between Sets and Arrays

Array → Set: Removes duplicates automatically.

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

Set → Array: Use spread operator or Array.from().

const arr = [...uniqueNums]; // [1, 2, 3, 4]