code: function findIndex(array, predicate, fromIndex) {
        var length = array == null ? 0 : array.length;
        if (!length) {
          return -1;
        }
        var index = fromIndex == null ? 0 : toInteger(fromIndex);
        if (index < 0) {
          index = nativeMax(length + index, 0);
        }
        return baseFindIndex(array, getIteratee(predicate, 3), index);
      }
docs: This method is like `_.find` except that it returns the index of the first
  element `predicate` returns truthy for instead of the element itself.
  
  @static
  @memberOf _
  @since 1.1.0
  @category Array
  @param {Array} array The array to inspect.
  @param {Function} [predicate=_.identity] The function invoked per iteration.
  @param {number} [fromIndex=0] The index to search from.
  @returns {number} Returns the index of the found element, else `-1`.
  @example
  
  var users = [
  { 'user': 'barney',  'active': false },
  { 'user': 'fred',    'active': false },
  { 'user': 'pebbles', 'active': true }
  ];
  
  _.findIndex(users, function(o) { return o.user == 'barney'; });
  // => 0
  
  // The `_.matches` iteratee shorthand.
  _.findIndex(users, { 'user': 'fred', 'active': false });
  // => 1
  
  // The `_.matchesProperty` iteratee shorthand.
  _.findIndex(users, ['active', false]);
  // => 0
  
  // The `_.property` iteratee shorthand.
  _.findIndex(users, 'active');
  // => 2