util.ts

/**
 * @license
 * Copyright 2018 Google Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

import {cssClasses} from './constants';

/**
 * Stores result from computeHorizontalScrollbarHeight to avoid redundant
 * processing.
 */
let horizontalScrollbarHeight_: number|undefined;

/**
 * Computes the height of browser-rendered horizontal scrollbars using a
 * self-created test element. May return 0 (e.g. on OS X browsers under default
 * configuration).
 */
export function computeHorizontalScrollbarHeight(
    documentObj: Document, shouldCacheResult = true): number {
  if (shouldCacheResult && typeof horizontalScrollbarHeight_ !== 'undefined') {
    return horizontalScrollbarHeight_;
  }

  const el = documentObj.createElement('div');
  el.classList.add(cssClasses.SCROLL_TEST);
  documentObj.body.appendChild(el);

  const horizontalScrollbarHeight = el.offsetHeight - el.clientHeight;
  documentObj.body.removeChild(el);

  if (shouldCacheResult) {
    horizontalScrollbarHeight_ = horizontalScrollbarHeight;
  }
  return horizontalScrollbarHeight;
}