Sets

Sets are a data structure that allows you to store a collection of unique values. They are unordered and they do not allow duplicates. Sets are useful when you want to store a collection of values that you want to check for membership, but you don't care about the order of the values.

Creating a Set

To create a set, you use the new Set() constructor. You can pass in an iterable, such as an array, to initialize the set with values.

const set = new Set([1, 2, 3, 4]);

Sets contain only unique values. If you try to add a value that already exists in the set, it will be ignored.

const set = new Set([1, 2, 2, 3, 3, 4]);
// set = {1, 2, 3, 4, 5}

Adding to a Set

To add a value to a set, you use the add() method.

set.add(5);

Checking for Membership

To check if a value is in a set, you use the has() method.

set.has(5); // true
set.has(6); // false

Removing from a Set

To remove a value from a set, you use the delete() method.

set.delete(5);
set.has(5); // false

Converting a Set to an Array

To convert a set to an array, you use the Array.from() method.

const setArray = Array.from(set);

Converting an Array to a Set

To convert an array to a set, you use the new Set() constructor.

const arraySet = new Set([1, 2, 3, 4, 5]);

Iterating using a for...of loop

To iterate through a set, you can use a for...of loop.

for (let item of set) {
  console.log(item);
}

Create an iterator

To create an iterator, you use the values() method.

const iterator = set.values();

console.log(iterator.next()); // {value: 1, done: false}
console.log(iterator.next()); // {value: 2, done: false}
console.log(iterator.next()); // {value: 3, done: false}
console.log(iterator.next()); // {value: 4, done: false}
console.log(iterator.next()); // {value: undefined, done: true}

This should make sense after the last few lessons.

Clear the set

set.clear();

In the next lesson, we'll look at maps.