code: function _findIndex(haystack, needle) {
              if (angular.isUndefined(haystack) || haystack.length === 0) {
                  return -1;
              }
  
              for (var i = 0, len = haystack.length; i < len; i++) {
                  if (haystack[i] === needle) {
                      return i;
                  }
              }
  
              return -1;
          }
docs: Find the index of an element in an array.
  
  @param  {Array}  haystack The array in which to search for the value.
  @param  {*}      needle   The value to search in the array.
  @return {number} The index of the value of the array, or -1 if not found.