TouchEventUtils.js.flow

/**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @providesModule TouchEventUtils
 */
const TouchEventUtils = {
  /**
   * Utility function for common case of extracting out the primary touch from a
   * touch event.
   * - `touchEnd` events usually do not have the `touches` property.
   *   http://stackoverflow.com/questions/3666929/
   *   mobile-sarai-touchend-event-not-firing-when-last-touch-is-removed
   *
   * @param {Event} nativeEvent Native event that may or may not be a touch.
   * @return {TouchesObject?} an object with pageX and pageY or null.
   */
  extractSingleTouch: function (nativeEvent) {
    const touches = nativeEvent.touches;
    const changedTouches = nativeEvent.changedTouches;
    const hasTouches = touches && touches.length > 0;
    const hasChangedTouches = changedTouches && changedTouches.length > 0;
    return !hasTouches && hasChangedTouches ? changedTouches[0] : hasTouches ? touches[0] : nativeEvent;
  }
};
module.exports = TouchEventUtils;