# How can I check if an array is a superset of another array in JavaScript?

A **superset** is a set that contains all the elements of another set, and possibly more. Knowing how to check if an array is a superset of another array might come in handy from time to time.

As the mathematical definition refers to a set, **duplicates are not considered**. This is why using a `Set`

object is a good idea. Combining it with `Array.prototype.every()`

and `Set.prototype.has()`

is all that's needed to perform the check.

Checking for a **subset** is as simple as reversing the order of the arguments. Note that you can use this function for **any type of iterable**, not just arrays.

const superset = (a, b) => { const sA = new Set(a), sB = new Set(b); return [...sB].every(v => sA.has(v)); }; const subset = (a, b) => superset(b, a); superset([1, 2, 3, 4], [1, 2, 2]); // true superset([1, 2, 3, 4], [1, 3, 5]); // false subset(new Set([1, 2]), new Set([1, 2, 3, 4])); // true subset(new Set([1, 5]), new Set([1, 2, 3, 4])); // false