JavaScript Sets

JavaScript Sets are a collection of unique values, which can be of any type, including primitive values and objects. They are similar to arrays, but have some key differences.

Creating a Set

There are two ways to create a Set in JavaScript:

  • Using the Set constructor:
1let mySet = new Set();
  • Using an array literal:
1let mySet = new Set([1, 2, 3, 4]);

Adding Values to a Set

You can add values to a Set using the add method.

1let mySet = new Set();
2mySet.add(1);
3mySet.add(2);
4mySet.add(3);

Retrieving Values from a Set

You can retrieve values from a Set using the has method, which returns a Boolean value indicating whether a given value exists in the Set.

1let mySet = new Set([1, 2, 3, 4]);
2console.log(mySet.has(1)); // true
3console.log(mySet.has(5)); // false

Deleting Values from a Set

You can delete values from a Set using the delete method.

1let mySet = new Set([1, 2, 3, 4]);
2mySet.delete(2);
3console.log(mySet); // Set { 1, 3, 4 }

Iterating Over a Set

You can iterate over a Set using a for...of loop, and retrieve both the values and the keys (which are the same in Sets).

1let mySet = new Set([1, 2, 3, 4]);
2for (let value of mySet) {
3  console.log(value);
4}
5
6// Output:
7// 1
8// 2
9// 3
10// 4

Other Built-in Methods

  • clear(): This method removes all elements from a Set.
1let mySet = new Set([1, 2, 3, 4]);
2mySet.clear();
3console.log(mySet); // Set {}
  • size: This property returns the number of elements in a Set.
1let mySet = new Set([1, 2, 3, 4]);
2console.log(mySet.size); // 4
  • values(): This method returns a new Iterator object that contains the values for each element in the Set, in the order they were inserted.
1let mySet = new Set([1, 2, 3, 4]);
2let values = mySet.values();
3for (let value of values) {
4  console.log(value);
5}
6
7// Output:
8// 1
9// 2
10// 3
11// 4
  • keys(): This method returns a new Iterator object that contains the values for each element in the Set, in the order they were inserted. It is the same as the values method.
1let mySet = new Set([1, 2, 3, 4]);
2let keys = mySet.keys();
3for (let key of keys) {
4  console.log(key);
5}
6
7// Output:
8// 1
9// 2
10// 3
11// 4
  • entries(): This method returns a new Iterator object that contains an array of [value, value] for each element in the Set, in the order they were inserted.
1let mySet = new Set([1, 2, 3, 4]);
2let entries = mySet.entries();
3for (let entry of entries) {
4  console.log(entry);
5}
6
7// Output:
8// [1, 1]
9// [2, 2]
10// [3, 3]
11// [4, 4]
  • forEach(): This method executes a provided function once for each value in the Set.
1let mySet = new Set([1, 2, 3, 4]);
2mySet.forEach(function(value, key) {
3  console.log(value);
4});
5
6// Output:
7// 1
8// 2
9// 3
10// 4