sets.js is a library for set datastructure that supports operations like union, intersection, difference, symmetric difference, etc.
Usage:
var A = new Set([1,2,3,4]); var B = new Set([3,4,5,6]); C = A.union(B); // C = Set([1,2,3,4,5,6]) D = A.intersection(B); // D = Set([3,4]) E = A.difference(B); // E = Set([1,2]) F = B.difference(A); // F = Set([5,6]) G = A.symmetricDifference(B); // G = Set([1,2,5,6])