How to perform intersection of two sets in JavaScript ?

An intersection of two sets means the element which occurs in both sets. In mathematical terms, the intersection of two sets is shown by A ∩ B. It means all the elements which is common in set A and set B should occur in a single array. In javascript, the intersection of two sets means getting the common from both sets.

We can find the intersection of two sets in many ways:

• JavaScript Sets: Set can store any type of value whether primitive or objects.
• JavaScript filter() Method: Create a new array from a given array consisting of only those elements from the given array which satisfy a condition set by the argument method. 
• JavaScript set.has() Method: Check whether an element with a specified value exists in a Set or not.

Using Sets & has() Method: A set is a collection of items that are unique i.e no element can be repeated. Set in ES6 are ordered: elements of the set can be iterated in the insertion order. A set can store any type of value whether primitive or objects.

Example 1: In this example, we will see the intersection of sets by using the set.has() method.

function getIntersection(set1, set2) {
    const ans = new Set();
    for (let i of set2) {
        if (set1.has(i)) {
            ans.add(i);
        }
    }
    return ans;
}
const set1 = new Set([1, 2, 3, 8, 11]);
const set2 = new Set([1, 2, 5, 8]);

const result = getIntersection(set1, set2);
console.log(result);

Output:

Set(3) { 1, 2, 8 }

Using the has() & filter() Method: We check if the element is present in set1 also then we are going to add that element to the new set. 

Example 2: In this example, we will see the intersection of sets by using the filter() method. We have also used the spread operator for separating the element.

let set1 = new Set([1, 2, 3]);
let set2 = new Set([4, 3, 2]);
let set = new Set([...set1].filter(x => set2.has(x)));
console.log(set);

Output:

Set(2) { 2, 3 }