Idea for a combine(list, list) function for javascript in functional style

combine.js

['Function','Array'].forEach(function(type) {
    var checkFn = 'is'+type;
    window[checkFn] = function(o){ return Object.prototype.toString.call(o) == '[object ' + type + ']'; };
});

// Return new list as combination of the two lists passed
// The second list can be a function which will be passed each item
// from the first list and should return an array to permute that item
// with. If either argument is not a list, it will be treated as a list.
//
// Ex.,   combine([a,b], [c,d]) => [[a,c],[a,d],[b,c],[b,d]]
function combine(list, listFn) {
  isArray(list) || (list = [list]);
  (isFunction(listFn) || isArray(listFn)) || (listFn = [listFn]);
  return flatMapWith(function(itemLeft){
    return mapWith(function(itemRight) {
      return [itemLeft, itemRight];
    })(isFunction(listFn) ? listFn.call(this, itemLeft) : listFn);
  })(list);
}

Pointed out to me on twitter (https://twitter.com/jeffgreenberg/status/634473978455703552) that this isn't really a permutation; because we don't care about order: [a,c] shows up alone and not [a,c],[c,a]. Have modified to use the correct name.