Compares items in two lists (List 1 and List 2) removing any individual item found in both lists from List 1 and returning the remaining items.
Example:

If List 1 = [1,1,2,3] and List 2 = [1,2,3,3,3], Reconciler will return [1].

In the opposite case, List 1 = [1,2,3,3,3] and List 2 = [1,1,2,3], Reconciler will return [3, 3].

The algorithm implemented is exactly the following:

function reconcile(list1, list2) {
   var arr1 = [...list1], arr2 = [...list2]
   arr2.forEach(item => {
       var index = arr1.indexOf(item)
       index > -1 && arr1.splice(index, 1)
   })
   return arr1
}