https://omiyashika-kyouseishika.com/js/intersection-observer.js

1/**
2 * Copyright 2016 Google Inc. All Rights Reserved.
3 *
4 * Licensed under the W3C SOFTWARE AND DOCUMENT NOTICE AND LICENSE.
5 *
6 *  https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document
7 *
8 */
9(function() {
10'use strict';
11
12// Exit early if we're not running in a browser.
13if (typeof window !== 'object') {
14  return;
15}
16
17// Exit early if all IntersectionObserver and IntersectionObserverEntry
18// features are natively supported.
19if ('IntersectionObserver' in window &&
20    'IntersectionObserverEntry' in window &&
21    'intersectionRatio' in window.IntersectionObserverEntry.prototype) {
22
23  // Minimal polyfill for Edge 15's lack of `isIntersecting`
24  // See: https://github.com/w3c/IntersectionObserver/issues/211
25  if (!('isIntersecting' in window.IntersectionObserverEntry.prototype)) {
26    Object.defineProperty(window.IntersectionObserverEntry.prototype,
27      'isIntersecting', {
28      get: function () {
29        return this.intersectionRatio > 0;
30      }
31    });
32  }
33  return;
34}
35
36/**
37 * Returns the embedding frame element, if any.
38 * @param {!Document} doc
39 * @return {!Element}
40 */
41function getFrameElement(doc) {
42  try {
43    return doc.defaultView && doc.defaultView.frameElement || null;
44  } catch (e) {
45    // Ignore the error.
46    return null;
47  }
48}
49
50/**
51 * A local reference to the root document.
52 */
53var document = (function(startDoc) {
54  var doc = startDoc;
55  var frame = getFrameElement(doc);
56  while (frame) {
57    doc = frame.ownerDocument;
58    frame = getFrameElement(doc);
59  }
60  return doc;
61})(window.document);
62
63/**
64 * An IntersectionObserver registry. This registry exists to hold a strong
65 * reference to IntersectionObserver instances currently observing a target
66 * element. Without this registry, instances without another reference may be
67 * garbage collected.
68 */
69var registry = [];
70
71/**
72 * The signal updater for cross-origin intersection. When not null, it means
73 * that the polyfill is configured to work in a cross-origin mode.
74 * @type {function(DOMRect|ClientRect, DOMRect|ClientRect)}
75 */
76var crossOriginUpdater = null;
77
78/**
79 * The current cross-origin intersection. Only used in the cross-origin mode.
80 * @type {DOMRect|ClientRect}
81 */
82var crossOriginRect = null;
83
84
85/**
86 * Creates the global IntersectionObserverEntry constructor.
87 * https://w3c.github.io/IntersectionObserver/#intersection-observer-entry
88 * @param {Object} entry A dictionary of instance properties.
89 * @constructor
90 */
91function IntersectionObserverEntry(entry) {
92  this.time = entry.time;
93  this.target = entry.target;
94  this.rootBounds = ensureDOMRect(entry.rootBounds);
95  this.boundingClientRect = ensureDOMRect(entry.boundingClientRect);
96  this.intersectionRect = ensureDOMRect(entry.intersectionRect || getEmptyRect());
97  this.isIntersecting = !!entry.intersectionRect;
98
99  // Calculates the intersection ratio.
100  var targetRect = this.boundingClientRect;
101  var targetArea = targetRect.width * targetRect.height;
102  var intersectionRect = this.intersectionRect;
103  var intersectionArea = intersectionRect.width * intersectionRect.height;
104
105  // Sets intersection ratio.
106  if (targetArea) {
107    // Round the intersection ratio to avoid floating point math issues:
108    // https://github.com/w3c/IntersectionObserver/issues/324
109    this.intersectionRatio = Number((intersectionArea / targetArea).toFixed(4));
110  } else {
111    // If area is zero and is intersecting, sets to 1, otherwise to 0
112    this.intersectionRatio = this.isIntersecting ? 1 : 0;
113  }
114}
115
116
117/**
118 * Creates the global IntersectionObserver constructor.
119 * https://w3c.github.io/IntersectionObserver/#intersection-observer-interface
120 * @param {Function} callback The function to be invoked after intersection
121 *     changes have queued. The function is not invoked if the queue has
122 *     been emptied by calling the `takeRecords` method.
123 * @param {Object=} opt_options Optional configuration options.
124 * @constructor
125 */
126function IntersectionObserver(callback, opt_options) {
127
128  var options = opt_options || {};
129
130  if (typeof callback != 'function') {
131    throw new Error('callback must be a function');
132  }
133
134  if (
135    options.root &&
136    options.root.nodeType != 1 &&
137    options.root.nodeType != 9
138  ) {
139    throw new Error('root must be a Document or Element');
140  }
141
142  // Binds and throttles `this._checkForIntersections`.
143  this._checkForIntersections = throttle(
144      this._checkForIntersections.bind(this), this.THROTTLE_TIMEOUT);
145
146  // Private properties.
147  this._callback = callback;
148  this._observationTargets = [];
149  this._queuedEntries = [];
150  this._rootMarginValues = this._parseRootMargin(options.rootMargin);
151
152  // Public properties.
153  this.thresholds = this._initThresholds(options.threshold);
154  this.root = options.root || null;
155  this.rootMargin = this._rootMarginValues.map(function(margin) {
156    return margin.value + margin.unit;
157  }).join(' ');
158
159  /** @private @const {!Array<!Document>} */
160  this._monitoringDocuments = [];
161  /** @private @const {!Array<function()>} */
162  this._monitoringUnsubscribes = [];
163}
164
165
166/**
167 * The minimum interval within which the document will be checked for
168 * intersection changes.
169 */
170IntersectionObserver.prototype.THROTTLE_TIMEOUT = 100;
171
172
173/**
174 * The frequency in which the polyfill polls for intersection changes.
175 * this can be updated on a per instance basis and must be set prior to
176 * calling `observe` on the first target.
177 */
178IntersectionObserver.prototype.POLL_INTERVAL = null;
179
180/**
181 * Use a mutation observer on the root element
182 * to detect intersection changes.
183 */
184IntersectionObserver.prototype.USE_MUTATION_OBSERVER = true;
185
186
187/**
188 * Sets up the polyfill in the cross-origin mode. The result is the
189 * updater function that accepts two arguments: `boundingClientRect` and
190 * `intersectionRect` - just as these fields would be available to the
191 * parent via `IntersectionObserverEntry`. This function should be called
192 * each time the iframe receives intersection information from the parent
193 * window, e.g. via messaging.
194 * @return {function(DOMRect|ClientRect, DOMRect|ClientRect)}
195 */
196IntersectionObserver._setupCrossOriginUpdater = function() {
197  if (!crossOriginUpdater) {
198    /**
199     * @param {DOMRect|ClientRect} boundingClientRect
200     * @param {DOMRect|ClientRect} intersectionRect
201     */
202    crossOriginUpdater = function(boundingClientRect, intersectionRect) {
203      if (!boundingClientRect || !intersectionRect) {
204        crossOriginRect = getEmptyRect();
205      } else {
206        crossOriginRect = convertFromParentRect(boundingClientRect, intersectionRect);
207      }
208      registry.forEach(function(observer) {
209        observer._checkForIntersections();
210      });
211    };
212  }
213  return crossOriginUpdater;
214};
215
216
217/**
218 * Resets the cross-origin mode.
219 */
220IntersectionObserver._resetCrossOriginUpdater = function() {
221  crossOriginUpdater = null;
222  crossOriginRect = null;
223};
224
225
226/**
227 * Starts observing a target element for intersection changes based on
228 * the thresholds values.
229 * @param {Element} target The DOM element to observe.
230 */
231IntersectionObserver.prototype.observe = function(target) {
232  var isTargetAlreadyObserved = this._observationTargets.some(function(item) {
233    return item.element == target;
234  });
235
236  if (isTargetAlreadyObserved) {
237    return;
238  }
239
240  if (!(target && target.nodeType == 1)) {
241    throw new Error('target must be an Element');
242  }
243
244  this._registerInstance();
245  this._observationTargets.push({element: target, entry: null});
246  this._monitorIntersections(target.ownerDocument);
247  this._checkForIntersections();
248};
249
250
251/**
252 * Stops observing a target element for intersection changes.
253 * @param {Element} target The DOM element to observe.
254 */
255IntersectionObserver.prototype.unobserve = function(target) {
256  this._observationTargets =
257      this._observationTargets.filter(function(item) {
258        return item.element != target;
259      });
260  this._unmonitorIntersections(target.ownerDocument);
261  if (this._observationTargets.length == 0) {
262    this._unregisterInstance();
263  }
264};
265
266
267/**
268 * Stops observing all target elements for intersection changes.
269 */
270IntersectionObserver.prototype.disconnect = function() {
271  this._observationTargets = [];
272  this._unmonitorAllIntersections();
273  this._unregisterInstance();
274};
275
276
277/**
278 * Returns any queue entries that have not yet been reported to the
279 * callback and clears the queue. This can be used in conjunction with the
280 * callback to obtain the absolute most up-to-date intersection information.
281 * @return {Array} The currently queued entries.
282 */
283IntersectionObserver.prototype.takeRecords = function() {
284  var records = this._queuedEntries.slice();
285  this._queuedEntries = [];
286  return records;
287};
288
289
290/**
291 * Accepts the threshold value from the user configuration object and
292 * returns a sorted array of unique threshold values. If a value is not
293 * between 0 and 1 and error is thrown.
294 * @private
295 * @param {Array|number=} opt_threshold An optional threshold value or
296 *     a list of threshold values, defaulting to [0].
297 * @return {Array} A sorted list of unique and valid threshold values.
298 */
299IntersectionObserver.prototype._initThresholds = function(opt_threshold) {
300  var threshold = opt_threshold || [0];
301  if (!Array.isArray(threshold)) threshold = [threshold];
302
303  return threshold.sort().filter(function(t, i, a) {
304    if (typeof t != 'number' || isNaN(t) || t < 0 || t > 1) {
305      throw new Error('threshold must be a number between 0 and 1 inclusively');
306    }
307    return t !== a[i - 1];
308  });
309};
310
311
312/**
313 * Accepts the rootMargin value from the user configuration object
314 * and returns an array of the four margin values as an object containing
315 * the value and unit properties. If any of the values are not properly
316 * formatted or use a unit other than px or %, and error is thrown.
317 * @private
318 * @param {string=} opt_rootMargin An optional rootMargin value,
319 *     defaulting to '0px'.
320 * @return {Array<Object>} An array of margin objects with the keys
321 *     value and unit.
322 */
323IntersectionObserver.prototype._parseRootMargin = function(opt_rootMargin) {
324  var marginString = opt_rootMargin || '0px';
325  var margins = marginString.split(/\s+/).map(function(margin) {
326    var parts = /^(-?\d*\.?\d+)(px|%)$/.exec(margin);
327    if (!parts) {
328      throw new Error('rootMargin must be specified in pixels or percent');
329    }
330    return {value: parseFloat(parts[1]), unit: parts[2]};
331  });
332
333  // Handles shorthand.
334  margins[1] = margins[1] || margins[0];
335  margins[2] = margins[2] || margins[0];
336  margins[3] = margins[3] || margins[1];
337
338  return margins;
339};
340
341
342/**
343 * Starts polling for intersection changes if the polling is not already
344 * happening, and if the page's visibility state is visible.
345 * @param {!Document} doc
346 * @private
347 */
348IntersectionObserver.prototype._monitorIntersections = function(doc) {
349  var win = doc.defaultView;
350  if (!win) {
351    // Already destroyed.
352    return;
353  }
354  if (this._monitoringDocuments.indexOf(doc) != -1) {
355    // Already monitoring.
356    return;
357  }
358
359  // Private state for monitoring.
360  var callback = this._checkForIntersections;
361  var monitoringInterval = null;
362  var domObserver = null;
363
364  // If a poll interval is set, use polling instead of listening to
365  // resize and scroll events or DOM mutations.
366  if (this.POLL_INTERVAL) {
367    monitoringInterval = win.setInterval(callback, this.POLL_INTERVAL);
368  } else {
369    addEvent(win, 'resize', callback, true);
370    addEvent(doc, 'scroll', callback, true);
371    if (this.USE_MUTATION_OBSERVER && 'MutationObserver' in win) {
372      domObserver = new win.MutationObserver(callback);
373      domObserver.observe(doc, {
374        attributes: true,
375        childList: true,
376        characterData: true,
377        subtree: true
378      });
379    }
380  }
381
382  this._monitoringDocuments.push(doc);
383  this._monitoringUnsubscribes.push(function() {
384    // Get the window object again. When a friendly iframe is destroyed, it
385    // will be null.
386    var win = doc.defaultView;
387
388    if (win) {
389      if (monitoringInterval) {
390        win.clearInterval(monitoringInterval);
391      }
392      removeEvent(win, 'resize', callback, true);
393    }
394
395    removeEvent(doc, 'scroll', callback, true);
396    if (domObserver) {
397      domObserver.disconnect();
398    }
399  });
400
401  // Also monitor the parent.
402  var rootDoc =
403    (this.root && (this.root.ownerDocument || this.root)) || document;
404  if (doc != rootDoc) {
405    var frame = getFrameElement(doc);
406    if (frame) {
407      this._monitorIntersections(frame.ownerDocument);
408    }
409  }
410};
411
412
413/**
414 * Stops polling for intersection changes.
415 * @param {!Document} doc
416 * @private
417 */
418IntersectionObserver.prototype._unmonitorIntersections = function(doc) {
419  var index = this._monitoringDocuments.indexOf(doc);
420  if (index == -1) {
421    return;
422  }
423
424  var rootDoc =
425    (this.root && (this.root.ownerDocument || this.root)) || document;
426
427  // Check if any dependent targets are still remaining.
428  var hasDependentTargets =
429      this._observationTargets.some(function(item) {
430        var itemDoc = item.element.ownerDocument;
431        // Target is in this context.
432        if (itemDoc == doc) {
433          return true;
434        }
435        // Target is nested in this context.
436        while (itemDoc && itemDoc != rootDoc) {
437          var frame = getFrameElement(itemDoc);
438          itemDoc = frame && frame.ownerDocument;
439          if (itemDoc == doc) {
440            return true;
441          }
442        }
443        return false;
444      });
445  if (hasDependentTargets) {
446    return;
447  }
448
449  // Unsubscribe.
450  var unsubscribe = this._monitoringUnsubscribes[index];
451  this._monitoringDocuments.splice(index, 1);
452  this._monitoringUnsubscribes.splice(index, 1);
453  unsubscribe();
454
455  // Also unmonitor the parent.
456  if (doc != rootDoc) {
457    var frame = getFrameElement(doc);
458    if (frame) {
459      this._unmonitorIntersections(frame.ownerDocument);
460    }
461  }
462};
463
464
465/**
466 * Stops polling for intersection changes.
467 * @param {!Document} doc
468 * @private
469 */
470IntersectionObserver.prototype._unmonitorAllIntersections = function() {
471  var unsubscribes = this._monitoringUnsubscribes.slice(0);
472  this._monitoringDocuments.length = 0;
473  this._monitoringUnsubscribes.length = 0;
474  for (var i = 0; i < unsubscribes.length; i++) {
475    unsubscribes[i]();
476  }
477};
478
479
480/**
481 * Scans each observation target for intersection changes and adds them
482 * to the internal entries queue. If new entries are found, it
483 * schedules the callback to be invoked.
484 * @private
485 */
486IntersectionObserver.prototype._checkForIntersections = function() {
487  if (!this.root && crossOriginUpdater && !crossOriginRect) {
488    // Cross origin monitoring, but no initial data available yet.
489    return;
490  }
491
492  var rootIsInDom = this._rootIsInDom();
493  var rootRect = rootIsInDom ? this._getRootRect() : getEmptyRect();
494
495  this._observationTargets.forEach(function(item) {
496    var target = item.element;
497    var targetRect = getBoundingClientRect(target);
498    var rootContainsTarget = this._rootContainsTarget(target);
499    var oldEntry = item.entry;
500    var intersectionRect = rootIsInDom && rootContainsTarget &&
501        this._computeTargetAndRootIntersection(target, targetRect, rootRect);
502
503    var rootBounds = null;
504    if (!this._rootContainsTarget(target)) {
505      rootBounds = getEmptyRect();
506    } else if (!crossOriginUpdater || this.root) {
507      rootBounds = rootRect;
508    }
509
510    var newEntry = item.entry = new IntersectionObserverEntry({
511      time: now(),
512      target: target,
513      boundingClientRect: targetRect,
514      rootBounds: rootBounds,
515      intersectionRect: intersectionRect
516    });
517
518    if (!oldEntry) {
519      this._queuedEntries.push(newEntry);
520    } else if (rootIsInDom && rootContainsTarget) {
521      // If the new entry intersection ratio has crossed any of the
522      // thresholds, add a new entry.
523      if (this._hasCrossedThreshold(oldEntry, newEntry)) {
524        this._queuedEntries.push(newEntry);
525      }
526    } else {
527      // If the root is not in the DOM or target is not contained within
528      // root but the previous entry for this target had an intersection,
529      // add a new record indicating removal.
530      if (oldEntry && oldEntry.isIntersecting) {
531        this._queuedEntries.push(newEntry);
532      }
533    }
534  }, this);
535
536  if (this._queuedEntries.length) {
537    this._callback(this.takeRecords(), this);
538  }
539};
540
541
542/**
543 * Accepts a target and root rect computes the intersection between then
544 * following the algorithm in the spec.
545 * TODO(philipwalton): at this time clip-path is not considered.
546 * https://w3c.github.io/IntersectionObserver/#calculate-intersection-rect-algo
547 * @param {Element} target The target DOM element
548 * @param {Object} targetRect The bounding rect of the target.
549 * @param {Object} rootRect The bounding rect of the root after being
550 *     expanded by the rootMargin value.
551 * @return {?Object} The final intersection rect object or undefined if no
552 *     intersection is found.
553 * @private
554 */
555IntersectionObserver.prototype._computeTargetAndRootIntersection =
556    function(target, targetRect, rootRect) {
557  // If the element isn't displayed, an intersection can't happen.
558  if (window.getComputedStyle(target).display == 'none') return;
559
560  var intersectionRect = targetRect;
561  var parent = getParentNode(target);
562  var atRoot = false;
563
564  while (!atRoot && parent) {
565    var parentRect = null;
566    var parentComputedStyle = parent.nodeType == 1 ?
567        window.getComputedStyle(parent) : {};
568
569    // If the parent isn't displayed, an intersection can't happen.
570    if (parentComputedStyle.display == 'none') return null;
571
572    if (parent == this.root || parent.nodeType == /* DOCUMENT */ 9) {
573      atRoot = true;
574      if (parent == this.root || parent == document) {
575        if (crossOriginUpdater && !this.root) {
576          if (!crossOriginRect ||
577              crossOriginRect.width == 0 && crossOriginRect.height == 0) {
578            // A 0-size cross-origin intersection means no-intersection.
579            parent = null;
580            parentRect = null;
581            intersectionRect = null;
582          } else {
583            parentRect = crossOriginRect;
584          }
585        } else {
586          parentRect = rootRect;
587        }
588      } else {
589        // Check if there's a frame that can be navigated to.
590        var frame = getParentNode(parent);
591        var frameRect = frame && getBoundingClientRect(frame);
592        var frameIntersect =
593            frame &&
594            this._computeTargetAndRootIntersection(frame, frameRect, rootRect);
595        if (frameRect && frameIntersect) {
596          parent = frame;
597          parentRect = convertFromParentRect(frameRect, frameIntersect);
598        } else {
599          parent = null;
600          intersectionRect = null;
601        }
602      }
603    } else {
604      // If the element has a non-visible overflow, and it's not the <body>
605      // or <html> element, update the intersection rect.
606      // Note: <body> and <html> cannot be clipped to a rect that's not also
607      // the document rect, so no need to compute a new intersection.
608      var doc = parent.ownerDocument;
609      if (parent != doc.body &&
610          parent != doc.documentElement &&
611          parentComputedStyle.overflow != 'visible') {
612        parentRect = getBoundingClientRect(parent);
613      }
614    }
615
616    // If either of the above conditionals set a new parentRect,
617    // calculate new intersection data.
618    if (parentRect) {
619      intersectionRect = computeRectIntersection(parentRect, intersectionRect);
620    }
621    if (!intersectionRect) break;
622    parent = parent && getParentNode(parent);
623  }
624  return intersectionRect;
625};
626
627
628/**
629 * Returns the root rect after being expanded by the rootMargin value.
630 * @return {ClientRect} The expanded root rect.
631 * @private
632 */
633IntersectionObserver.prototype._getRootRect = function() {
634  var rootRect;
635  if (this.root && !isDoc(this.root)) {
636    rootRect = getBoundingClientRect(this.root);
637  } else {
638    // Use <html>/<body> instead of window since scroll bars affect size.
639    var doc = isDoc(this.root) ? this.root : document;
640    var html = doc.documentElement;
641    var body = doc.body;
642    rootRect = {
643      top: 0,
644      left: 0,
645      right: html.clientWidth || body.clientWidth,
646      width: html.clientWidth || body.clientWidth,
647      bottom: html.clientHeight || body.clientHeight,
648      height: html.clientHeight || body.clientHeight
649    };
650  }
651  return this._expandRectByRootMargin(rootRect);
652};
653
654
655/**
656 * Accepts a rect and expands it by the rootMargin value.
657 * @param {DOMRect|ClientRect} rect The rect object to expand.
658 * @return {ClientRect} The expanded rect.
659 * @private
660 */
661IntersectionObserver.prototype._expandRectByRootMargin = function(rect) {
662  var margins = this._rootMarginValues.map(function(margin, i) {
663    return margin.unit == 'px' ? margin.value :
664        margin.value * (i % 2 ? rect.width : rect.height) / 100;
665  });
666  var newRect = {
667    top: rect.top - margins[0],
668    right: rect.right + margins[1],
669    bottom: rect.bottom + margins[2],
670    left: rect.left - margins[3]
671  };
672  newRect.width = newRect.right - newRect.left;
673  newRect.height = newRect.bottom - newRect.top;
674
675  return newRect;
676};
677
678
679/**
680 * Accepts an old and new entry and returns true if at least one of the
681 * threshold values has been crossed.
682 * @param {?IntersectionObserverEntry} oldEntry The previous entry for a
683 *    particular target element or null if no previous entry exists.
684 * @param {IntersectionObserverEntry} newEntry The current entry for a
685 *    particular target element.
686 * @return {boolean} Returns true if a any threshold has been crossed.
687 * @private
688 */
689IntersectionObserver.prototype._hasCrossedThreshold =
690    function(oldEntry, newEntry) {
691
692  // To make comparing easier, an entry that has a ratio of 0
693  // but does not actually intersect is given a value of -1
694  var oldRatio = oldEntry && oldEntry.isIntersecting ?
695      oldEntry.intersectionRatio || 0 : -1;
696  var newRatio = newEntry.isIntersecting ?
697      newEntry.intersectionRatio || 0 : -1;
698
699  // Ignore unchanged ratios
700  if (oldRatio === newRatio) return;
701
702  for (var i = 0; i < this.thresholds.length; i++) {
703    var threshold = this.thresholds[i];
704
705    // Return true if an entry matches a threshold or if the new ratio
706    // and the old ratio are on the opposite sides of a threshold.
707    if (threshold == oldRatio || threshold == newRatio ||
708        threshold < oldRatio !== threshold < newRatio) {
709      return true;
710    }
711  }
712};
713
714
715/**
716 * Returns whether or not the root element is an element and is in the DOM.
717 * @return {boolean} True if the root element is an element and is in the DOM.
718 * @private
719 */
720IntersectionObserver.prototype._rootIsInDom = function() {
721  return !this.root || containsDeep(document, this.root);
722};
723
724
725/**
726 * Returns whether or not the target element is a child of root.
727 * @param {Element} target The target element to check.
728 * @return {boolean} True if the target element is a child of root.
729 * @private
730 */
731IntersectionObserver.prototype._rootContainsTarget = function(target) {
732  var rootDoc =
733    (this.root && (this.root.ownerDocument || this.root)) || document;
734  return (
735    containsDeep(rootDoc, target) &&
736    (!this.root || rootDoc == target.ownerDocument)
737  );
738};
739
740
741/**
742 * Adds the instance to the global IntersectionObserver registry if it isn't
743 * already present.
744 * @private
745 */
746IntersectionObserver.prototype._registerInstance = function() {
747  if (registry.indexOf(this) < 0) {
748    registry.push(this);
749  }
750};
751
752
753/**
754 * Removes the instance from the global IntersectionObserver registry.
755 * @private
756 */
757IntersectionObserver.prototype._unregisterInstance = function() {
758  var index = registry.indexOf(this);
759  if (index != -1) registry.splice(index, 1);
760};
761
762
763/**
764 * Returns the result of the performance.now() method or null in browsers
765 * that don't support the API.
766 * @return {number} The elapsed time since the page was requested.
767 */
768function now() {
769  return window.performance && performance.now && performance.now();
770}
771
772
773/**
774 * Throttles a function and delays its execution, so it's only called at most
775 * once within a given time period.
776 * @param {Function} fn The function to throttle.
777 * @param {number} timeout The amount of time that must pass before the
778 *     function can be called again.
779 * @return {Function} The throttled function.
780 */
781function throttle(fn, timeout) {
782  var timer = null;
783  return function () {
784    if (!timer) {
785      timer = setTimeout(function() {
786        fn();
787        timer = null;
788      }, timeout);
789    }
790  };
791}
792
793
794/**
795 * Adds an event handler to a DOM node ensuring cross-browser compatibility.
796 * @param {Node} node The DOM node to add the event handler to.
797 * @param {string} event The event name.
798 * @param {Function} fn The event handler to add.
799 * @param {boolean} opt_useCapture Optionally adds the even to the capture
800 *     phase. Note: this only works in modern browsers.
801 */
802function addEvent(node, event, fn, opt_useCapture) {
803  if (typeof node.addEventListener == 'function') {
804    node.addEventListener(event, fn, opt_useCapture || false);
805  }
806  else if (typeof node.attachEvent == 'function') {
807    node.attachEvent('on' + event, fn);
808  }
809}
810
811
812/**
813 * Removes a previously added event handler from a DOM node.
814 * @param {Node} node The DOM node to remove the event handler from.
815 * @param {string} event The event name.
816 * @param {Function} fn The event handler to remove.
817 * @param {boolean} opt_useCapture If the event handler was added with this
818 *     flag set to true, it should be set to true here in order to remove it.
819 */
820function removeEvent(node, event, fn, opt_useCapture) {
821  if (typeof node.removeEventListener == 'function') {
822    node.removeEventListener(event, fn, opt_useCapture || false);
823  }
824  else if (typeof node.deta

868    // https://github.com/w3c/IntersectionObserver/pull/205
869  }
870
871  if (!rect) return getEmptyRect();
872
873  // Older IE
874  if (!(rect.width && rect.height)) {
875    rect = {
876      top: rect.top,
877      right: rect.right,
878      bottom: rect.bottom,
879      left: rect.left,
880      width: rect.right - rect.left,
881      height: rect.bottom - rect.top
882    };
883  }
884  return rect;
885}
886
887
888/**
889 * Returns an empty rect object. An empty rect is returned when an element
890 * is not in the DOM.
891 * @return {ClientRect} The empty rect.
892 */
893function getEmptyRect() {
894  return {
895    top: 0,
896    bottom: 0,
897    left: 0,
898    right: 0,
899    width: 0,
900    height: 0
901  };
902}
903
904
905/**
906 * Ensure that the result has all of the necessary fields of the DOMRect.
907 * Specifically this ensures that `x` and `y` fields are set.
908 *
909 * @param {?DOMRect|?ClientRect} rect
910 * @return {?DOMRect}
911 */
912function ensureDOMRect(rect) {
913  // A `DOMRect` object has `x` and `y` fields.
914  if (!rect || 'x' in rect) {
915    return rect;
916  }
917  // A IE's `ClientRect` type does not have `x` and `y`. The same is the case
918  // for internally calculated Rect objects. For the purposes of
919  // `IntersectionObserver`, it's sufficient to simply mirror `left` and `top`
920  // for these fields.
921  return {
922    top: rect.top,
923    y: rect.top,
924    bottom: rect.bottom,
925    left: rect.left,
926    x: rect.left,
927    right: rect.right,
928    width: rect.width,
929    height: rect.height
930  };
931}
932
933
934/**
935 * Inverts the intersection and bounding rect from the parent (frame) BCR to
936 * the local BCR space.
937 * @param {DOMRect|ClientRect} parentBoundingRect The parent's bound client rect.
938 * @param {DOMRect|ClientRect} parentIntersectionRect The parent's own intersection rect.
939 * @return {ClientRect} The local root bounding rect for the parent's children.
940 */
941function convertFromParentRect(parentBoundingRect, parentIntersectionRect) {
942  var top = parentIntersectionRect.top - parentBoundingRect.top;
943  var left = parentIntersectionRect.left - parentBoundingRect.left;
944  return {
945    top: top,
946    left: left,
947    height: parentIntersectionRect.height,
948    width: parentIntersectionRect.width,
949    bottom: top + parentIntersectionRect.height,
950    right: left + parentIntersectionRect.width
951  };
952}
953
954
955/**
956 * Checks to see if a parent element contains a child element (including inside
957 * shadow DOM).
958 * @param {Node} parent The parent element.
959 * @param {Node} child The child element.
960 * @return {boolean} True if the parent node contains the child node.
961 */
962function containsDeep(parent, child) {
963  var node = child;
964  while (node) {
965    if (node == parent) return true;
966
967    node = getParentNode(node);
968  }
969  return false;
970}
971
972
973/**
974 * Gets the parent node of an element or its host element if the parent node
975 * is a shadow root.
976 * @param {Node} node The node whose parent to get.
977 * @return {Node|null} The parent node or null if no parent exists.
978 */
979function getParentNode(node) {
980  var parent = node.parentNode;
981
982  if (node.nodeType == /* DOCUMENT */ 9 && node != document) {
983    // If this node is a document node, look for the embedding frame.
984    return getFrameElement(node);
985  }
986
987  // If the parent has element that is assigned through shadow root slot
988  if (parent && parent.assignedSlot) {
989    parent = parent.assignedSlot.parentNode
990  }
991
992  if (parent && parent.nodeType == 11 && parent.host) {
993    // If the parent is a shadow root, return the host element.
994    return parent.host;
995  }
996
997  return parent;
998}
999
1000/**
1001 * Returns true if `node` is a Document.
1002 * @param {!Node} node
1003 * @returns {boolean}
1004 */
1005function isDoc(node) {
1006  return node && node.nodeType === 9;
1007}
1008
1009
1010// Exposes the constructors globally.
1011window.IntersectionObserver = IntersectionObserver;
1012window.IntersectionObserverEntry = IntersectionObserverEntry;
1013
1014}());