other

A Set object, or set-like object.

A new Set object containing elements in both this set and the other set.

In mathematical notation, intersection is defined as:

$$A\cap B = {x\in A\mid x\in B}$$

And using Venn diagram:

intersection() 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 more elements in this than other.size, then it iterates over other by calling its keys() method, and constructs a new set with all elements produced that are also present in this.
• Otherwise, it iterates over the elements in this, and constructs a new set with all elements e in this that cause other.has(e) to return a truthy value.

Because of this implementation, the efficiency of intersection() mostly depends on the size of the smaller set between this and other (assuming sets can be accessed in sublinear time). The order of elements in the returned set is the same as that of the smaller of this and other.

The following example computes the intersection between the set of odd numbers (<10) and the set of perfect squares (<10). The result is the set of odd numbers that are perfect squares.

const odds = new Set([1, 3, 5, 7, 9]);
const squares = new Set([1, 4, 9]);
console.log(odds.intersection(squares)); // Set(2) { 1, 9 }

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