Javascript Set union operation

function unionSet(setA, setB) {
    var union = new Set(setA);
    for (var elem of setB) {
        union.add(elem);//from   w w w.  ja  v a2s . c o  m
    }
    return union;
}
var setA = new Set([1, 2, 3, 4]),
    setB = new Set([2, 3]),
    setC = new Set([5]);

let a = unionSet(setA, setB);
console.log(a);

let b = unionSet(setA, setC);
console.log(b);