Set.prototype.isSupersetOf()

other

A Set object, or set-like object.

true if all elements in the other set are also in this set, and false otherwise.

In mathematical notation, superset is defined as:

$$A\supseteq B \Leftrightarrow \forall x\in B,,x\in A$$

And using Venn diagram:

isSupersetOf() accepts set-like objects as the other parameter. It requires this to be an actual Set instance, because it directly retrieves the underlying data stored in this without invoking any user code. Then, its behavior depends on the sizes of this and other:

• If there are fewer elements in this than other.size, then it directly returns false.
• Otherwise, it iterates over other by calling its keys() method, and if any element in other is not present in this, it returns false (and closes the keys() iterator by calling its return() method). Otherwise, it returns true.

The set of even numbers (<20) is a superset of multiples of 4 (<20):

const evens = new Set([2, 4, 6, 8, 10, 12, 14, 16, 18]);
const fours = new Set([4, 8, 12, 16]);
console.log(evens.isSupersetOf(fours)); // true

The set of all odd numbers (<20) is not a superset of prime numbers (<20), because 2 is prime but not odd:

const primes = new Set([2, 3, 5, 7, 11, 13, 17, 19]);
const odds = new Set([3, 5, 7, 9, 11, 13, 15, 17, 19]);
console.log(odds.isSupersetOf(primes)); // false

Equivalent sets are supersets of each other:

const set1 = new Set([1, 2, 3]);
const set2 = new Set([1, 2, 3]);
console.log(set1.isSupersetOf(set2)); // true
console.log(set2.isSupersetOf(set1)); // true

• Polyfill of Set.prototype.isSupersetOf in core-js
• Set.prototype.difference()
• Set.prototype.intersection()
• Set.prototype.isDisjointFrom()
• Set.prototype.isSubsetOf()
• Set.prototype.symmetricDifference()
• Set.prototype.union()