Function makeSet

src/Set.js:223–229

(map, ownerID)

}

function makeSet(map, ownerID) {
  const set = Object.create(SetPrototype);
  set.size = map ? map.size : 0;
  set._map = map;
  set.__ownerID = ownerID;
  return set;
}

let EMPTY_SET;
function emptySet() {