(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory(require('react')) :
  typeof define === 'function' && define.amd ? define(['react'], factory) :
  (global = global || self, global.useIntersectionObserver = factory(global.React));
}(this, (function (React) { 'use strict';

  function _objectWithoutPropertiesLoose(source, excluded) {
    if (source == null) return {};
    var target = {};
    var sourceKeys = Object.keys(source);
    var key, i;

    for (i = 0; i < sourceKeys.length; i++) {
      key = sourceKeys[i];
      if (excluded.indexOf(key) >= 0) continue;
      target[key] = source[key];
    }

    return target;
  }

  function _unsupportedIterableToArray(o, minLen) {
    if (!o) return;
    if (typeof o === "string") return _arrayLikeToArray(o, minLen);
    var n = Object.prototype.toString.call(o).slice(8, -1);
    if (n === "Object" && o.constructor) n = o.constructor.name;
    if (n === "Map" || n === "Set") return Array.from(o);
    if (n === "Arguments" || /^(?:Ui|I)nt(?:8|16|32)(?:Clamped)?Array$/.test(n)) return _arrayLikeToArray(o, minLen);
  }

  function _arrayLikeToArray(arr, len) {
    if (len == null || len > arr.length) len = arr.length;

    for (var i = 0, arr2 = new Array(len); i < len; i++) arr2[i] = arr[i];

    return arr2;
  }

  function _createForOfIteratorHelperLoose(o, allowArrayLike) {
    var it;

    if (typeof Symbol === "undefined" || o[Symbol.iterator] == null) {
      if (Array.isArray(o) || (it = _unsupportedIterableToArray(o)) || allowArrayLike && o && typeof o.length === "number") {
        if (it) o = it;
        var i = 0;
        return function () {
          if (i >= o.length) return {
            done: true
          };
          return {
            done: false,
            value: o[i++]
          };
        };
      }

      throw new TypeError("Invalid attempt to iterate non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method.");
    }

    it = o[Symbol.iterator]();
    return it.next.bind(it);
  }

  function _get() {
    return this.intersectionRatio > 0;
  }

  function _ref(margin) {
    return margin.value + margin.unit;
  }

  function _ref2(observer) {
    observer._checkForIntersections();
  }

  function _ref3(target) {
    var isTargetAlreadyObserved = this._observationTargets.some(function (item) {
      return item.element == target;
    });

    if (isTargetAlreadyObserved) {
      return;
    }

    if (!(target && target.nodeType == 1)) {
      throw new Error('target must be an Element');
    }

    this._registerInstance();

    this._observationTargets.push({
      element: target,
      entry: null
    });

    this._monitorIntersections(target.ownerDocument);

    this._checkForIntersections();
  }

  function _ref4(target) {
    this._observationTargets = this._observationTargets.filter(function (item) {
      return item.element != target;
    });

    this._unmonitorIntersections(target.ownerDocument);

    if (this._observationTargets.length == 0) {
      this._unregisterInstance();
    }
  }

  function _ref5() {
    this._observationTargets = [];

    this._unmonitorAllIntersections();

    this._unregisterInstance();
  }

  function _ref6() {
    var records = this._queuedEntries.slice();

    this._queuedEntries = [];
    return records;
  }

  function _ref7(t, i, a) {
    if (typeof t != 'number' || isNaN(t) || t < 0 || t > 1) {
      throw new Error('threshold must be a number between 0 and 1 inclusively');
    }

    return t !== a[i - 1];
  }

  function _ref8(opt_threshold) {
    var threshold = opt_threshold || [0];
    if (!Array.isArray(threshold)) threshold = [threshold];
    return threshold.sort().filter(_ref7);
  }

  function _ref9(margin) {
    var parts = /^(-?\d*\.?\d+)(px|%)$/.exec(margin);

    if (!parts) {
      throw new Error('rootMargin must be specified in pixels or percent');
    }

    return {
      value: parseFloat(parts[1]),
      unit: parts[2]
    };
  }

  function _ref10(opt_rootMargin) {
    var marginString = opt_rootMargin || '0px';
    var margins = marginString.split(/\s+/).map(_ref9); // Handles shorthand.

    margins[1] = margins[1] || margins[0];
    margins[2] = margins[2] || margins[0];
    margins[3] = margins[3] || margins[1];
    return margins;
  }

  function _ref11() {
    var unsubscribes = this._monitoringUnsubscribes.slice(0);

    this._monitoringDocuments.length = 0;
    this._monitoringUnsubscribes.length = 0;

    for (var i = 0; i < unsubscribes.length; i++) {
      unsubscribes[i]();
    }
  }

  function _ref12(rect) {
    var margins = this._rootMarginValues.map(function (margin, i) {
      return margin.unit == 'px' ? margin.value : margin.value * (i % 2 ? rect.width : rect.height) / 100;
    });

    var newRect = {
      top: rect.top - margins[0],
      right: rect.right + margins[1],
      bottom: rect.bottom + margins[2],
      left: rect.left - margins[3]
    };
    newRect.width = newRect.right - newRect.left;
    newRect.height = newRect.bottom - newRect.top;
    return newRect;
  }

  function _ref13(oldEntry, newEntry) {
    // To make comparing easier, an entry that has a ratio of 0
    // but does not actually intersect is given a value of -1
    var oldRatio = oldEntry && oldEntry.isIntersecting ? oldEntry.intersectionRatio || 0 : -1;
    var newRatio = newEntry.isIntersecting ? newEntry.intersectionRatio || 0 : -1; // Ignore unchanged ratios

    if (oldRatio === newRatio) return;

    for (var i = 0; i < this.thresholds.length; i++) {
      var threshold = this.thresholds[i]; // Return true if an entry matches a threshold or if the new ratio
      // and the old ratio are on the opposite sides of a threshold.

      if (threshold == oldRatio || threshold == newRatio || threshold < oldRatio !== threshold < newRatio) {
        return true;
      }
    }
  }

  /**
   * Returns the result of the performance.now() method or null in browsers
   * that don't support the API.
   * @return {number} The elapsed time since the page was requested.
   */
  function now() {
    return window.performance && performance.now && performance.now();
  }
  /**
   * Throttles a function and delays its execution, so it's only called at most
   * once within a given time period.
   * @param {Function} fn The function to throttle.
   * @param {number} timeout The amount of time that must pass before the
   *     function can be called again.
   * @return {Function} The throttled function.
   */


  function throttle(fn, timeout) {
    var timer = null;

    function _ref14() {
      fn();
      timer = null;
    }

    return function () {
      if (!timer) {
        timer = setTimeout(_ref14, timeout);
      }
    };
  }
  /**
   * Adds an event handler to a DOM node ensuring cross-browser compatibility.
   * @param {Node} node The DOM node to add the event handler to.
   * @param {string} event The event name.
   * @param {Function} fn The event handler to add.
   * @param {boolean} opt_useCapture Optionally adds the even to the capture
   *     phase. Note: this only works in modern browsers.
   */


  function addEvent(node, event, fn, opt_useCapture) {
    if (typeof node.addEventListener == 'function') {
      node.addEventListener(event, fn, opt_useCapture || false);
    } else if (typeof node.attachEvent == 'function') {
      node.attachEvent('on' + event, fn);
    }
  }
  /**
   * Removes a previously added event handler from a DOM node.
   * @param {Node} node The DOM node to remove the event handler from.
   * @param {string} event The event name.
   * @param {Function} fn The event handler to remove.
   * @param {boolean} opt_useCapture If the event handler was added with this
   *     flag set to true, it should be set to true here in order to remove it.
   */


  function removeEvent(node, event, fn, opt_useCapture) {
    if (typeof node.removeEventListener == 'function') {
      node.removeEventListener(event, fn, opt_useCapture || false);
    } else if (typeof node.detatchEvent == 'function') {
      node.detatchEvent('on' + event, fn);
    }
  }
  /**
   * Returns the intersection between two rect objects.
   * @param {Object} rect1 The first rect.
   * @param {Object} rect2 The second rect.
   * @return {?Object|?ClientRect} The intersection rect or undefined if no
   *     intersection is found.
   */


  function computeRectIntersection(rect1, rect2) {
    var top = Math.max(rect1.top, rect2.top);
    var bottom = Math.min(rect1.bottom, rect2.bottom);
    var left = Math.max(rect1.left, rect2.left);
    var right = Math.min(rect1.right, rect2.right);
    var width = right - left;
    var height = bottom - top;
    return width >= 0 && height >= 0 && {
      top: top,
      bottom: bottom,
      left: left,
      right: right,
      width: width,
      height: height
    } || null;
  }
  /**
   * Shims the native getBoundingClientRect for compatibility with older IE.
   * @param {Element} el The element whose bounding rect to get.
   * @return {DOMRect|ClientRect} The (possibly shimmed) rect of the element.
   */


  /**
   * Returns an empty rect object. An empty rect is returned when an element
   * is not in the DOM.
   * @return {ClientRect} The empty rect.
   */
  function getEmptyRect() {
    return {
      top: 0,
      bottom: 0,
      left: 0,
      right: 0,
      width: 0,
      height: 0
    };
  }
  /**
   * Ensure that the result has all of the necessary fields of the DOMRect.
   * Specifically this ensures that `x` and `y` fields are set.
   *
   * @param {?DOMRect|?ClientRect} rect
   * @return {?DOMRect}
   */


  function ensureDOMRect(rect) {
    // A `DOMRect` object has `x` and `y` fields.
    if (!rect || 'x' in rect) {
      return rect;
    } // A IE's `ClientRect` type does not have `x` and `y`. The same is the case
    // for internally calculated Rect objects. For the purposes of
    // `IntersectionObserver`, it's sufficient to simply mirror `left` and `top`
    // for these fields.


    return {
      top: rect.top,
      y: rect.top,
      bottom: rect.bottom,
      left: rect.left,
      x: rect.left,
      right: rect.right,
      width: rect.width,
      height: rect.height
    };
  }
  /**
   * Inverts the intersection and bounding rect from the parent (frame) BCR to
   * the local BCR space.
   * @param {DOMRect|ClientRect} parentBoundingRect The parent's bound client rect.
   * @param {DOMRect|ClientRect} parentIntersectionRect The parent's own intersection rect.
   * @return {ClientRect} The local root bounding rect for the parent's children.
   */


  function convertFromParentRect(parentBoundingRect, parentIntersectionRect) {
    var top = parentIntersectionRect.top - parentBoundingRect.top;
    var left = parentIntersectionRect.left - parentBoundingRect.left;
    return {
      top: top,
      left: left,
      height: parentIntersectionRect.height,
      width: parentIntersectionRect.width,
      bottom: top + parentIntersectionRect.height,
      right: left + parentIntersectionRect.width
    };
  }
  /**
   * Checks to see if a parent element contains a child element (including inside
   * shadow DOM).
   * @param {Node} parent The parent element.
   * @param {Node} child The child element.
   * @return {boolean} True if the parent node contains the child node.
   */


  /**
   * Returns the embedding frame element, if any.
   * @param {!Document} doc
   * @return {!Element}
   */
  function getFrameElement(doc) {
    try {
      return doc.defaultView && doc.defaultView.frameElement || null;
    } catch (e) {
      // Ignore the error.
      return null;
    }
  } // Exposes the constructors globally.


  /**
   * Copyright 2016 Google Inc. All Rights Reserved.
   *
   * Licensed under the W3C SOFTWARE AND DOCUMENT NOTICE AND LICENSE.
   *
   *  https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document
   *
   */
  (function () {

    if (typeof window !== 'object') {
      return;
    } // Exit early if all IntersectionObserver and IntersectionObserverEntry
    // features are natively supported.


    if ('IntersectionObserver' in window && 'IntersectionObserverEntry' in window && 'intersectionRatio' in window.IntersectionObserverEntry.prototype) {
      // Minimal polyfill for Edge 15's lack of `isIntersecting`
      // See: https://github.com/w3c/IntersectionObserver/issues/211
      if (!('isIntersecting' in window.IntersectionObserverEntry.prototype)) {
        Object.defineProperty(window.IntersectionObserverEntry.prototype, 'isIntersecting', {
          get: _get
        });
      }

      return;
    }
    /**
     * A local reference to the document.
     */


    var document = window.document;
    /**
     * An IntersectionObserver registry. This registry exists to hold a strong
     * reference to IntersectionObserver instances currently observing a target
     * element. Without this registry, instances without another reference may be
     * garbage collected.
     */

    var registry = [];
    /**
     * The signal updater for cross-origin intersection. When not null, it means
     * that the polyfill is configured to work in a cross-origin mode.
     * @type {function(DOMRect|ClientRect, DOMRect|ClientRect)}
     */

    var crossOriginUpdater = null;
    /**
     * The current cross-origin intersection. Only used in the cross-origin mode.
     * @type {DOMRect|ClientRect}
     */

    var crossOriginRect = null;
    /**
     * Creates the global IntersectionObserverEntry constructor.
     * https://w3c.github.io/IntersectionObserver/#intersection-observer-entry
     * @param {Object} entry A dictionary of instance properties.
     * @constructor
     */

    function IntersectionObserverEntry(entry) {
      this.time = entry.time;
      this.target = entry.target;
      this.rootBounds = ensureDOMRect(entry.rootBounds);
      this.boundingClientRect = ensureDOMRect(entry.boundingClientRect);
      this.intersectionRect = ensureDOMRect(entry.intersectionRect || getEmptyRect());
      this.isIntersecting = !!entry.intersectionRect; // Calculates the intersection ratio.

      var targetRect = this.boundingClientRect;
      var targetArea = targetRect.width * targetRect.height;
      var intersectionRect = this.intersectionRect;
      var intersectionArea = intersectionRect.width * intersectionRect.height; // Sets intersection ratio.

      if (targetArea) {
        // Round the intersection ratio to avoid floating point math issues:
        // https://github.com/w3c/IntersectionObserver/issues/324
        this.intersectionRatio = Number((intersectionArea / targetArea).toFixed(4));
      } else {
        // If area is zero and is intersecting, sets to 1, otherwise to 0
        this.intersectionRatio = this.isIntersecting ? 1 : 0;
      }
    }
    /**
     * Creates the global IntersectionObserver constructor.
     * https://w3c.github.io/IntersectionObserver/#intersection-observer-interface
     * @param {Function} callback The function to be invoked after intersection
     *     changes have queued. The function is not invoked if the queue has
     *     been emptied by calling the `takeRecords` method.
     * @param {Object=} opt_options Optional configuration options.
     * @constructor
     */


    function IntersectionObserver(callback, opt_options) {
      var options = opt_options || {};

      if (typeof callback != 'function') {
        throw new Error('callback must be a function');
      }

      if (options.root && options.root.nodeType != 1) {
        throw new Error('root must be an Element');
      } // Binds and throttles `this._checkForIntersections`.


      this._checkForIntersections = throttle(this._checkForIntersections.bind(this), this.THROTTLE_TIMEOUT); // Private properties.

      this._callback = callback;
      this._observationTargets = [];
      this._queuedEntries = [];
      this._rootMarginValues = this._parseRootMargin(options.rootMargin); // Public properties.

      this.thresholds = this._initThresholds(options.threshold);
      this.root = options.root || null;
      this.rootMargin = this._rootMarginValues.map(_ref).join(' ');
      /** @private @const {!Array<!Document>} */

      this._monitoringDocuments = [];
      /** @private @const {!Array<function()>} */

      this._monitoringUnsubscribes = [];
    }
    /**
     * The minimum interval within which the document will be checked for
     * intersection changes.
     */


    IntersectionObserver.prototype.THROTTLE_TIMEOUT = 100;
    /**
     * The frequency in which the polyfill polls for intersection changes.
     * this can be updated on a per instance basis and must be set prior to
     * calling `observe` on the first target.
     */

    IntersectionObserver.prototype.POLL_INTERVAL = null;
    /**
     * Use a mutation observer on the root element
     * to detect intersection changes.
     */

    IntersectionObserver.prototype.USE_MUTATION_OBSERVER = true;
    /**
     * Sets up the polyfill in the cross-origin mode. The result is the
     * updater function that accepts two arguments: `boundingClientRect` and
     * `intersectionRect` - just as these fields would be available to the
     * parent via `IntersectionObserverEntry`. This function should be called
     * each time the iframe receives intersection information from the parent
     * window, e.g. via messaging.
     * @return {function(DOMRect|ClientRect, DOMRect|ClientRect)}
     */

    function _crossOriginUpdater(boundingClientRect, intersectionRect) {
      if (!boundingClientRect || !intersectionRect) {
        crossOriginRect = getEmptyRect();
      } else {
        crossOriginRect = convertFromParentRect(boundingClientRect, intersectionRect);
      }

      registry.forEach(_ref2);
    }

    IntersectionObserver._setupCrossOriginUpdater = function () {
      if (!crossOriginUpdater) {
        /**
         * @param {DOMRect|ClientRect} boundingClientRect
         * @param {DOMRect|ClientRect} intersectionRect
         */
        crossOriginUpdater = _crossOriginUpdater;
      }

      return crossOriginUpdater;
    };
    /**
     * Resets the cross-origin mode.
     */


    IntersectionObserver._resetCrossOriginUpdater = function () {
      crossOriginUpdater = null;
      crossOriginRect = null;
    };
    /**
     * Starts observing a target element for intersection changes based on
     * the thresholds values.
     * @param {Element} target The DOM element to observe.
     */


    IntersectionObserver.prototype.observe = _ref3;
    /**
     * Stops observing a target element for intersection changes.
     * @param {Element} target The DOM element to observe.
     */

    IntersectionObserver.prototype.unobserve = _ref4;
    /**
     * Stops observing all target elements for intersection changes.
     */

    IntersectionObserver.prototype.disconnect = _ref5;
    /**
     * Returns any queue entries that have not yet been reported to the
     * callback and clears the queue. This can be used in conjunction with the
     * callback to obtain the absolute most up-to-date intersection information.
     * @return {Array} The currently queued entries.
     */

    IntersectionObserver.prototype.takeRecords = _ref6;
    /**
     * Accepts the threshold value from the user configuration object and
     * returns a sorted array of unique threshold values. If a value is not
     * between 0 and 1 and error is thrown.
     * @private
     * @param {Array|number=} opt_threshold An optional threshold value or
     *     a list of threshold values, defaulting to [0].
     * @return {Array} A sorted list of unique and valid threshold values.
     */

    IntersectionObserver.prototype._initThresholds = _ref8;
    /**
     * Accepts the rootMargin value from the user configuration object
     * and returns an array of the four margin values as an object containing
     * the value and unit properties. If any of the values are not properly
     * formatted or use a unit other than px or %, and error is thrown.
     * @private
     * @param {string=} opt_rootMargin An optional rootMargin value,
     *     defaulting to '0px'.
     * @return {Array<Object>} An array of margin objects with the keys
     *     value and unit.
     */

    IntersectionObserver.prototype._parseRootMargin = _ref10;
    /**
     * Starts polling for intersection changes if the polling is not already
     * happening, and if the page's visibility state is visible.
     * @param {!Document} doc
     * @private
     */

    IntersectionObserver.prototype._monitorIntersections = function (doc) {
      var win = doc.defaultView;

      if (!win) {
        // Already destroyed.
        return;
      }

      if (this._monitoringDocuments.indexOf(doc) != -1) {
        // Already monitoring.
        return;
      } // Private state for monitoring.


      var callback = this._checkForIntersections;
      var monitoringInterval = null;
      var domObserver = null; // If a poll interval is set, use polling instead of listening to
      // resize and scroll events or DOM mutations.

      if (this.POLL_INTERVAL) {
        monitoringInterval = win.setInterval(callback, this.POLL_INTERVAL);
      } else {
        addEvent(win, 'resize', callback, true);
        addEvent(doc, 'scroll', callback, true);

        if (this.USE_MUTATION_OBSERVER && 'MutationObserver' in win) {
          domObserver = new win.MutationObserver(callback);
          domObserver.observe(doc, {
            attributes: true,
            childList: true,
            characterData: true,
            subtree: true
          });
        }
      }

      this._monitoringDocuments.push(doc);

      this._monitoringUnsubscribes.push(function () {
        // Get the window object again. When a friendly iframe is destroyed, it
        // will be null.
        var win = doc.defaultView;

        if (win) {
          if (monitoringInterval) {
            win.clearInterval(monitoringInterval);
          }

          removeEvent(win, 'resize', callback, true);
        }

        removeEvent(doc, 'scroll', callback, true);

        if (domObserver) {
          domObserver.disconnect();
        }
      }); // Also monitor the parent.


      if (doc != (this.root && this.root.ownerDocument || document)) {
        var frame = getFrameElement(doc);

        if (frame) {
          this._monitorIntersections(frame.ownerDocument);
        }
      }
    };
    /**
     * Stops polling for intersection changes.
     * @param {!Document} doc
     * @private
     */


    IntersectionObserver.prototype._unmonitorIntersections = function (doc) {
      var index = this._monitoringDocuments.indexOf(doc);

      if (index == -1) {
        return;
      }

      var rootDoc = this.root && this.root.ownerDocument || document; // Check if any dependent targets are still remaining.

      var hasDependentTargets = this._observationTargets.some(function (item) {
        var itemDoc = item.element.ownerDocument; // Target is in this context.

        if (itemDoc == doc) {
          return true;
        } // Target is nested in this context.


        while (itemDoc && itemDoc != rootDoc) {
          var frame = getFrameElement(itemDoc);
          itemDoc = frame && frame.ownerDocument;

          if (itemDoc == doc) {
            return true;
          }
        }

        return false;
      });

      if (hasDependentTargets) {
        return;
      } // Unsubscribe.


      var unsubscribe = this._monitoringUnsubscribes[index];

      this._monitoringDocuments.splice(index, 1);

      this._monitoringUnsubscribes.splice(index, 1);

      unsubscribe(); // Also unmonitor the parent.

      if (doc != rootDoc) {
        var frame = getFrameElement(doc);

        if (frame) {
          this._unmonitorIntersections(frame.ownerDocument);
        }
      }
    };
    /**
     * Stops polling for intersection changes.
     * @param {!Document} doc
     * @private
     */


    IntersectionObserver.prototype._unmonitorAllIntersections = _ref11;
    /**
     * Scans each observation target for intersection changes and adds them
     * to the internal entries queue. If new entries are found, it
     * schedules the callback to be invoked.
     * @private
     */

    IntersectionObserver.prototype._checkForIntersections = function () {
      if (!this.root && crossOriginUpdater && !crossOriginRect) {
        // Cross origin monitoring, but no initial data available yet.
        return;
      }

      var rootIsInDom = this._rootIsInDom();

      var rootRect = rootIsInDom ? this._getRootRect() : getEmptyRect();

      this._observationTargets.forEach(function (item) {
        var target = item.element;
        var targetRect = getBoundingClientRect(target);

        var rootContainsTarget = this._rootContainsTarget(target);

        var oldEntry = item.entry;

        var intersectionRect = rootIsInDom && rootContainsTarget && this._computeTargetAndRootIntersection(target, targetRect, rootRect);

        var newEntry = item.entry = new IntersectionObserverEntry({
          time: now(),
          target: target,
          boundingClientRect: targetRect,
          rootBounds: crossOriginUpdater && !this.root ? null : rootRect,
          intersectionRect: intersectionRect
        });

        if (!oldEntry) {
          this._queuedEntries.push(newEntry);
        } else if (rootIsInDom && rootContainsTarget) {
          // If the new entry intersection ratio has crossed any of the
          // thresholds, add a new entry.
          if (this._hasCrossedThreshold(oldEntry, newEntry)) {
            this._queuedEntries.push(newEntry);
          }
        } else {
          // If the root is not in the DOM or target is not contained within
          // root but the previous entry for this target had an intersection,
          // add a new record indicating removal.
          if (oldEntry && oldEntry.isIntersecting) {
            this._queuedEntries.push(newEntry);
          }
        }
      }, this);

      if (this._queuedEntries.length) {
        this._callback(this.takeRecords(), this);
      }
    };
    /**
     * Accepts a target and root rect computes the intersection between then
     * following the algorithm in the spec.
     * TODO(philipwalton): at this time clip-path is not considered.
     * https://w3c.github.io/IntersectionObserver/#calculate-intersection-rect-algo
     * @param {Element} target The target DOM element
     * @param {Object} targetRect The bounding rect of the target.
     * @param {Object} rootRect The bounding rect of the root after being
     *     expanded by the rootMargin value.
     * @return {?Object} The final intersection rect object or undefined if no
     *     intersection is found.
     * @private
     */


    IntersectionObserver.prototype._computeTargetAndRootIntersection = function (target, targetRect, rootRect) {
      // If the element isn't displayed, an intersection can't happen.
      if (window.getComputedStyle(target).display == 'none') return;
      var intersectionRect = targetRect;
      var parent = getParentNode(target);
      var atRoot = false;

      while (!atRoot && parent) {
        var parentRect = null;
        var parentComputedStyle = parent.nodeType == 1 ? window.getComputedStyle(parent) : {}; // If the parent isn't displayed, an intersection can't happen.

        if (parentComputedStyle.display == 'none') return null;

        if (parent == this.root || parent.nodeType ==
        /* DOCUMENT */
        9) {
          atRoot = true;

          if (parent == this.root || parent == document) {
            if (crossOriginUpdater && !this.root) {
              if (!crossOriginRect || crossOriginRect.width == 0 && crossOriginRect.height == 0) {
                // A 0-size cross-origin intersection means no-intersection.
                parent = null;
                parentRect = null;
                intersectionRect = null;
              } else {
                parentRect = crossOriginRect;
              }
            } else {
              parentRect = rootRect;
            }
          } else {
            // Check if there's a frame that can be navigated to.
            var frame = getParentNode(parent);
            var frameRect = frame && getBoundingClientRect(frame);

            var frameIntersect = frame && this._computeTargetAndRootIntersection(frame, frameRect, rootRect);

            if (frameRect && frameIntersect) {
              parent = frame;
              parentRect = convertFromParentRect(frameRect, frameIntersect);
            } else {
              parent = null;
              intersectionRect = null;
            }
          }
        } else {
          // If the element has a non-visible overflow, and it's not the <body>
          // or <html> element, update the intersection rect.
          // Note: <body> and <html> cannot be clipped to a rect that's not also
          // the document rect, so no need to compute a new intersection.
          var doc = parent.ownerDocument;

          if (parent != doc.body && parent != doc.documentElement && parentComputedStyle.overflow != 'visible') {
            parentRect = getBoundingClientRect(parent);
          }
        } // If either of the above conditionals set a new parentRect,
        // calculate new intersection data.


        if (parentRect) {
          intersectionRect = computeRectIntersection(parentRect, intersectionRect);
        }

        if (!intersectionRect) break;
        parent = parent && getParentNode(parent);
      }

      return intersectionRect;
    };
    /**
     * Returns the root rect after being expanded by the rootMargin value.
     * @return {ClientRect} The expanded root rect.
     * @private
     */


    IntersectionObserver.prototype._getRootRect = function () {
      var rootRect;

      if (this.root) {
        rootRect = getBoundingClientRect(this.root);
      } else {
        // Use <html>/<body> instead of window since scroll bars affect size.
        var html = document.documentElement;
        var body = document.body;
        rootRect = {
          top: 0,
          left: 0,
          right: html.clientWidth || body.clientWidth,
          width: html.clientWidth || body.clientWidth,
          bottom: html.clientHeight || body.clientHeight,
          height: html.clientHeight || body.clientHeight
        };
      }

      return this._expandRectByRootMargin(rootRect);
    };
    /**
     * Accepts a rect and expands it by the rootMargin value.
     * @param {DOMRect|ClientRect} rect The rect object to expand.
     * @return {ClientRect} The expanded rect.
     * @private
     */


    IntersectionObserver.prototype._expandRectByRootMargin = _ref12;
    /**
     * Accepts an old and new entry and returns true if at least one of the
     * threshold values has been crossed.
     * @param {?IntersectionObserverEntry} oldEntry The previous entry for a
     *    particular target element or null if no previous entry exists.
     * @param {IntersectionObserverEntry} newEntry The current entry for a
     *    particular target element.
     * @return {boolean} Returns true if a any threshold has been crossed.
     * @private
     */

    IntersectionObserver.prototype._hasCrossedThreshold = _ref13;
    /**
     * Returns whether or not the root element is an element and is in the DOM.
     * @return {boolean} True if the root element is an element and is in the DOM.
     * @private
     */

    IntersectionObserver.prototype._rootIsInDom = function () {
      return !this.root || containsDeep(document, this.root);
    };
    /**
     * Returns whether or not the target element is a child of root.
     * @param {Element} target The target element to check.
     * @return {boolean} True if the target element is a child of root.
     * @private
     */


    IntersectionObserver.prototype._rootContainsTarget = function (target) {
      return containsDeep(this.root || document, target) && (!this.root || this.root.ownerDocument == target.ownerDocument);
    };
    /**
     * Adds the instance to the global IntersectionObserver registry if it isn't
     * already present.
     * @private
     */


    IntersectionObserver.prototype._registerInstance = function () {
      if (registry.indexOf(this) < 0) {
        registry.push(this);
      }
    };
    /**
     * Removes the instance from the global IntersectionObserver registry.
     * @private
     */


    IntersectionObserver.prototype._unregisterInstance = function () {
      var index = registry.indexOf(this);
      if (index != -1) registry.splice(index, 1);
    };

    function getBoundingClientRect(el) {
      var rect;

      try {
        rect = el.getBoundingClientRect();
      } catch (err) {// Ignore Windows 7 IE11 "Unspecified error"
        // https://github.com/w3c/IntersectionObserver/pull/205
      }

      if (!rect) return getEmptyRect(); // Older IE

      if (!(rect.width && rect.height)) {
        rect = {
          top: rect.top,
          right: rect.right,
          bottom: rect.bottom,
          left: rect.left,
          width: rect.right - rect.left,
          height: rect.bottom - rect.top
        };
      }

      return rect;
    }

    function containsDeep(parent, child) {
      var node = child;

      while (node) {
        if (node == parent) return true;
        node = getParentNode(node);
      }

      return false;
    }
    /**
     * Gets the parent node of an element or its host element if the parent node
     * is a shadow root.
     * @param {Node} node The node whose parent to get.
     * @return {Node|null} The parent node or null if no parent exists.
     */


    function getParentNode(node) {
      var parent = node.parentNode;

      if (node.nodeType ==
      /* DOCUMENT */
      9 && node != document) {
        // If this node is a document node, look for the embedding frame.
        return getFrameElement(node);
      }

      if (parent && parent.nodeType == 11 && parent.host) {
        // If the parent is a shadow root, return the host element.
        return parent.host;
      }

      if (parent && parent.assignedSlot) {
        // If the parent is distributed in a <slot>, return the parent of a slot.
        return parent.assignedSlot.parentNode;
      }

      return parent;
    }

    window.IntersectionObserver = IntersectionObserver;
    window.IntersectionObserverEntry = IntersectionObserverEntry;
  })();

  var usePassiveLayoutEffect = React[typeof document !== 'undefined' && document.createElement !== void 0 ? 'useLayoutEffect' : 'useEffect'];

  function useIntersectionObserver(target, options) {
    if (options === void 0) {
      options = {};
    }

    var _options = options,
        _options$root = _options.root,
        root = _options$root === void 0 ? null : _options$root,
        _options$pollInterval = _options.pollInterval,
        pollInterval = _options$pollInterval === void 0 ? null : _options$pollInterval,
        _options$useMutationO = _options.useMutationObserver,
        useMutationObserver = _options$useMutationO === void 0 ? false : _options$useMutationO,
        _options$rootMargin = _options.rootMargin,
        rootMargin = _options$rootMargin === void 0 ? '0px 0px 0px 0px' : _options$rootMargin,
        _options$threshold = _options.threshold,
        threshold = _options$threshold === void 0 ? 0 : _options$threshold,
        _options$initialIsInt = _options.initialIsIntersecting,
        initialIsIntersecting = _options$initialIsInt === void 0 ? false : _options$initialIsInt;

    var _React$useState = React.useState(function () {
      return {
        boundingClientRect: null,
        intersectionRatio: 0,
        intersectionRect: null,
        isIntersecting: initialIsIntersecting,
        rootBounds: null,
        target: null,
        time: 0
      };
    }),
        entry = _React$useState[0],
        setEntry = _React$useState[1];

    var _React$useState2 = React.useState(function () {
      return getIntersectionObserver({
        root: root,
        pollInterval: pollInterval,
        useMutationObserver: useMutationObserver,
        rootMargin: rootMargin,
        threshold: threshold
      });
    }),
        observer = _React$useState2[0],
        setObserver = _React$useState2[1];

    React.useEffect(function () {
      var observer = getIntersectionObserver({
        root: root,
        pollInterval: pollInterval,
        useMutationObserver: useMutationObserver,
        rootMargin: rootMargin,
        threshold: threshold
      });
      setObserver(observer); // eslint-disable-next-line react-hooks/exhaustive-deps
    }, [root, rootMargin, pollInterval, useMutationObserver, JSON.stringify(threshold)]);
    usePassiveLayoutEffect(function () {
      var targetEl = target && 'current' in target ? target.current : target;
      if (!observer || !targetEl) return;
      var didUnsubscribe = false;
      observer.observer.observe(targetEl);

      var callback = function callback(entries) {
        if (didUnsubscribe) return;

        for (var i = 0; i < entries.length; i++) {
          var _entry = entries[i];

          if (_entry.target === targetEl) {
            setEntry(_entry);
          }
        }
      };

      observer.subscribe(callback);
      return function () {
        didUnsubscribe = true;
        observer.observer.unobserve(targetEl);
        observer.unsubscribe(callback);
      };
    }, [target, observer]);
    return entry;
  }

  function createIntersectionObserver(_ref) {
    var _ref$root = _ref.root,
        root = _ref$root === void 0 ? null : _ref$root,
        _ref$pollInterval = _ref.pollInterval,
        pollInterval = _ref$pollInterval === void 0 ? null : _ref$pollInterval,
        _ref$useMutationObser = _ref.useMutationObserver,
        useMutationObserver = _ref$useMutationObser === void 0 ? false : _ref$useMutationObser,
        _ref$rootMargin = _ref.rootMargin,
        rootMargin = _ref$rootMargin === void 0 ? '0px 0px 0px 0px' : _ref$rootMargin,
        _ref$threshold = _ref.threshold,
        threshold = _ref$threshold === void 0 ? 0 : _ref$threshold;
    var callbacks = new Set();
    if (typeof IntersectionObserver === 'undefined') return null;
    var observer = new IntersectionObserver(function (entries) {
      for (var _iterator = _createForOfIteratorHelperLoose(callbacks), _step; !(_step = _iterator()).done;) {
        var callback = _step.value;
        callback(entries, observer);
      }
    }, {
      root: root,
      rootMargin: rootMargin,
      threshold: threshold
    }); // @ts-ignore

    observer.POLL_INTERVAL = pollInterval; // @ts-ignore

    observer.USE_MUTATION_OBSERVER = useMutationObserver;
    return {
      observer: observer,
      getListeners: function getListeners() {
        return callbacks;
      },
      subscribe: function subscribe(callback) {
        return callbacks.add(callback);
      },
      unsubscribe: function unsubscribe(callback) {
        return callbacks.delete(callback);
      }
    };
  }

  var _intersectionObserver = /*#__PURE__*/new Map();

  function getIntersectionObserver(options) {
    var root = options.root,
        keys = _objectWithoutPropertiesLoose(options, ["root"]);

    var key = JSON.stringify(keys);

    var base = _intersectionObserver.get(root);

    if (!base) {
      base = {};

      _intersectionObserver.set(root, base);
    }

    return !base[key] ? base[key] = createIntersectionObserver(options) : base[key];
  }

  return useIntersectionObserver;

})));
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