react-native/Libraries/Renderer/src/shared/utils/getIteratorFn.js

A framework for building native apps using React

/**
 * Copyright 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule getIteratorFn
 * @flow
 */

'use strict';

/* global Symbol */
var ITERATOR_SYMBOL = typeof Symbol === 'function' && Symbol.iterator;
var FAUX_ITERATOR_SYMBOL = '@@iterator'; // Before Symbol spec.

/**
 * Returns the iterator method function contained on the iterable object.
 *
 * Be sure to invoke the function with the iterable as context:
 *
 *     var iteratorFn = getIteratorFn(myIterable);
 *     if (iteratorFn) {
 *       var iterator = iteratorFn.call(myIterable);
 *       ...
 *     }
 *
 * @param {?object} maybeIterable
 * @return {?function}
 */
function getIteratorFn(maybeIterable: ?any): ?(() => ?Iterator<*>) {
  var iteratorFn = maybeIterable && (
    (ITERATOR_SYMBOL && maybeIterable[ITERATOR_SYMBOL]) ||
    maybeIterable[FAUX_ITERATOR_SYMBOL]
  );
  if (typeof iteratorFn === 'function') {
    return iteratorFn;
  }
}

module.exports = getIteratorFn;