Set.prototype.isSubsetOf()

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

A⊆B⇔∀x∊A,x∊BAsubseteq B Leftrightarrow forall xin A,,xin B

!A Venn diagram with two circles. A is a subset of B because A is completely contained in B.

Note: The subset relationship is not proper subset, which means isSubsetOf() returns true if this and other contain the same elements.

isSubsetOf() 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:

Syntax example: isSubsetOf(other)