How to easily get the intersection of two sets in JavaScript

Tari Ibaba
Last updated on October 06, 2023
How to easily get the intersection of two sets in JavaScript

To get the intersection of two Sets in JavaScript, combine the filter() and has() array methods:

const set1 = new Set([1, 2, 3, 4, 5]);
const set2 = new Set([4, 5, 6, 7, 8]);

const intersection = new Set([...set1].filter(x => set2.has(x)));

console.log(intersection); // Set {4, 5}

The Array filter() method tests each element in an array against a condition specified by a callback function and creates a new array filled with elements that pass the test. It doesn’t modify the original array.

const arr = [1, 2, 3, 4];

const filtered = arr.filter((num) => num > 2);
console.log(filtered); // [ 3, 4 ]

The spread syntax (...) converts the Set to an array:

const set1 = new Set([1, 2, 3, 4, 5]);

const arrayFromSet = [...set1];

console.log(arrayFromSet); // [1, 2, 3, 4, 5]

We can also do this with the Array from() method, which converts Sets and other iterables into arrays:

const set1 = new Set([1, 2, 3, 4, 5]);

const arrayFromSet = Array.from(set1);

console.log(arrayFromSet); // [1, 2, 3, 4, 5]

And the Set has() method tells us whether or not the Set contains a particular element.

const set = new Set(['coding', 'beauty', 'dev']);

const hasElegance = set.has('elegance');
const hasBeauty = set.has('beauty');

console.log(hasElegance); // false
console.log(hasBeauty); // true

Get intersection of two sets with Array forEach() method

Alternatively, we can use the Array forEach() method to get the intersection of two Sets in JavaScript.

const set1 = new Set([1, 2, 3, 4, 5]);
const set2 = new Set([4, 5, 6, 7, 8]);
const intersection = new Set();

set1.forEach(value => {
  if (set2.has(value)) {
    intersection.add(value);
  }
});

console.log(intersection); // Set {4, 5}

The Set forEach loops through an array and calls a specified function on each element.

const fruits = new Set(['apple', 'orange', 'banana']);

fruits.forEach((fruit) => {
  console.log(fruit.toUpperCase());
});

// Output 👇
// APPLE
// ORANGE
// BANANA

The Set add() method adds a new element to a Set:

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

console.log(set);  // Set(3) { 1, 2, 3 }

set.add(10);

console.log(set);  // Set(4) { 1, 2, 3, 10 }

Get intersection of two Sets with for..of loop

Anywhere you see the forEach(), you can use the for..of loop in its place:

const set1 = new Set([1, 2, 3, 4, 5]);
const set2 = new Set([4, 5, 6, 7, 8]);
const intersection = new Set();

for (const value of set1) {
  if (set2.has(value)) {
    intersection.add(value);
  }
}

console.log(intersection); // Set {4, 5}

Get intersection of two Sets with reduce() method

You can also use the reduce() method to get the intersection of two Set objects in JavaScript:

const set1 = new Set([1, 2, 3, 4, 5]);
const set2 = new Set([4, 5, 6, 7, 8]);

const intersection = [...set1].reduce((acc, value) => {
  if (set2.has(value)) {
    acc.add(value);
  }
  return acc;
}, new Set());

console.log(intersection); // Set {4, 5}

The reduce() method calls a function on each element of an array to accumulate a resulting value:

const nums = [1, 2, 3, 4, 5];

const sum = nums.reduce((acc, num) => acc + num, 0);

const product = nums.reduce((acc, num) => acc * num, 1);

console.log(sum);  // 15

console.log(product);  // 120
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