Symmetric difference of two Sets in CoffeeScript

symmetricDiff.coffee

##
# Given two sets A and B, returns a triple with the set of elements
# in A only, in both and in B only.
#
symmetricDiff = (setA, setB) ->
  [inAOnly, inBoth, inBOnly] = [new Set(), new Set(), new Set()]
  setA.forEach (eid) ->
    (if setB.has( eid) then inBoth else inAOnly).add eid
  setB.forEach (eid) ->
    inBOnly.add( eid) unless inBoth.has( eid)
  [inAOnly, inBoth, inBOnly]

a = new Set [55, 44, 33, 22, 11]
b = new Set [55, 1, 2, 3]

[A, both, B] = symmetricDiff a, b
console.info A, both, B

# Console output:
# -> Set {44, 33, 22, 11} Set {55} Set {1, 2, 3}