/**
 * Copyright (c) 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 getDocumentScrollElement
 * @typechecks
 */

'use strict';

const isWebkit = typeof navigator !== 'undefined' && navigator.userAgent.indexOf('AppleWebKit') > -1;

/**
 * Gets the element with the document scroll properties such as `scrollLeft` and
 * `scrollHeight`. This may differ across different browsers.
 *
 * NOTE: The return value can be null if the DOM is not yet ready.
 *
 * @param {?DOMDocument} doc Defaults to current document.
 * @return {?DOMElement}
 */
function getDocumentScrollElement(doc) {
  doc = doc || document;
  return !isWebkit && doc.compatMode === 'CSS1Compat' ? doc.documentElement : doc.body;
}

module.exports = getDocumentScrollElement;