function fill(array, value, start, end) {
      var length = array ? array.length : 0;
      if (!length) {
        return [];
      }
      if (start && typeof start != 'number' && isIterateeCall(array, value, start)) {
        start = 0;
        end = length;
      }
      return baseFill(array, value, start, end);
    }
This method is like `_.find` except that it returns the index of the first
element `predicate` returns truthy for instead of the element itself.

If a property name is provided for `predicate` the created `_.property`
style callback returns the property value of the given element.

If a value is also provided for `thisArg` the created `_.matchesProperty`
style callback returns `true` for elements that have a matching property
value, else `false`.

If an object is provided for `predicate` the created `_.matches` style
callback returns `true` for elements that have the properties of the given
object, else `false`.

@static
@memberOf _
@category Array
@param {Array} array The array to search.
@param {Function|Object|string} [predicate=_.identity] The function invoked
 per iteration.
@param {*} [thisArg] The `this` binding of `predicate`.
@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(chr) {
  return chr.user == 'barney';
});
// => 0

// using the `_.matches` callback shorthand
_.findIndex(users, { 'user': 'fred', 'active': false });
// => 1

// using the `_.matchesProperty` callback shorthand
_.findIndex(users, 'active', false);
// => 0

// using the `_.property` callback shorthand
_.findIndex(users, 'active');
// => 2