code: function allUnique(arr) {
      var hash = {},
          index,
          len;
  
      for (index = 0, len = arr.length; index < len; index++) {
          if (hash[arr[index]]) {
              return false;
          }
          hash[arr[index]] = true;
      }
      return true;
  }
docs: allUnique
  return true if every number in an array is unique