getUnboundedScrollPosition.js

/**
 * Copyright 2013-2014, 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 getUnboundedScrollPosition
 * @typechecks
 */

"use strict";

/**
 * Gets the scroll position of the supplied element or window.
 *
 * The return values are unbounded, unlike `getScrollPosition`. This means they
 * may be negative or exceed the element boundaries (which is possible using
 * inertial scrolling).
 *
 * @param {DOMWindow|DOMElement} scrollable
 * @return {object} Map with `x` and `y` keys.
 */
function getUnboundedScrollPosition(scrollable) {
  if (scrollable === window) {
    return {
      x: window.pageXOffset || document.documentElement.scrollLeft,
      y: window.pageYOffset || document.documentElement.scrollTop
    };
  }
  return {
    x: scrollable.scrollLeft,
    y: scrollable.scrollTop
  };
}

module.exports = getUnboundedScrollPosition;