Warning: This blog post is outdated. Instead, read section “Missing Set operations” in “JavaScript for impatient programmers”. A recent question by Dmitry Moskowski reminded me: ECMAScript 6 sets have no methods for computing the union (e.g. addAll), intersection (e.g. retainAll) or difference (e.g. removeAll). This blog post explains how to work around that limitation. Union # Union (a ∪ b): cre