See if two arrays contain the same elements
function equalArrayElements (needle, haystack) {
  let missingNeedle = needle.filter(n => haystack.indexOf(n) === -1)
  if (missingNeedle.length !== 0) {
    return false
  }

  let missingHaystack = haystack.filter(h => needle.indexOf(h) === -1)
  return missingHaystack.length === 0
}