TheisSubsetOf() method ofSet instances takes a set and returns a boolean indicating if all elements of this set are in the given set.

Syntax

isSubsetOf(other)

Parameters

other

ASet object, orset-like object.

Return value

true if all elements in this set are also in theother set, andfalse otherwise.

Description

In mathematical notation,subset is defined as:

And using Venn diagram:

isSubsetOf() acceptsset-like objects as theother parameter. It requiresthis to be an actualSet instance, because it directly retrieves the underlying data stored inthis without invoking any user code. Then, its behavior depends on the sizes ofthis andother:

• If there are more elements inthis thanother.size, then it directly returnsfalse.
• Otherwise, it iterates over the elements inthis, and returnsfalse if any elemente inthis causesother.has(e) to return afalsy value. Otherwise, it returnstrue.

Examples

Using isSubsetOf()

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

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

The set of prime numbers (<20) is not a subset of all odd 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(primes.isSubsetOf(odds)); // false

Equivalent sets are subsets of each other:

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

Specifications

Browser compatibility

See also

• Polyfill ofSet.prototype.isSubsetOf incore-js
• es-shims polyfill ofSet.prototype.isSubsetOf
• Set.prototype.difference()
• Set.prototype.intersection()
• Set.prototype.isDisjointFrom()
• Set.prototype.isSupersetOf()
• Set.prototype.symmetricDifference()
• Set.prototype.union()