intersection-observer.js
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intersection-observer.js
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	/**
	* 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() {
	'use strict';

	// Exit early if we're not running in a browser.
	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: function () {
	return this.intersectionRatio > 0;
	}
	});
	}
	return;
	}

	/**
	* 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;
	}
	}

	/**
	* A local reference to the root document.
	*/
	var document = (function(startDoc) {
	var doc = startDoc;
	var frame = getFrameElement(doc);
	while (frame) {
	doc = frame.ownerDocument;
	frame = getFrameElement(doc);
	}
	return doc;
	})(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 &&
	options.root.nodeType != 9
	) {
	throw new Error('root must be a Document or 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(function(margin) {
	return margin.value + margin.unit;
	}).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)}
	*/
	IntersectionObserver._setupCrossOriginUpdater = function() {
	if (!crossOriginUpdater) {
	/**
	* @param {DOMRect\|ClientRect} boundingClientRect
	* @param {DOMRect\|ClientRect} intersectionRect
	*/
	crossOriginUpdater = function(boundingClientRect, intersectionRect) {
	if (!boundingClientRect \|\| !intersectionRect) {
	crossOriginRect = getEmptyRect();
	} else {
	crossOriginRect = convertFromParentRect(boundingClientRect, intersectionRect);
	}
	registry.forEach(function(observer) {
	observer._checkForIntersections();
	});
	};
	}
	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 = function(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();
	};


	/**
	* Stops observing a target element for intersection changes.
	* @param {Element} target The DOM element to observe.
	*/
	IntersectionObserver.prototype.unobserve = function(target) {
	this._observationTargets =
	this._observationTargets.filter(function(item) {
	return item.element != target;
	});
	this._unmonitorIntersections(target.ownerDocument);
	if (this._observationTargets.length == 0) {
	this._unregisterInstance();
	}
	};


	/**
	* Stops observing all target elements for intersection changes.
	*/
	IntersectionObserver.prototype.disconnect = function() {
	this._observationTargets = [];
	this._unmonitorAllIntersections();
	this._unregisterInstance();
	};


	/**
	* 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 = function() {
	var records = this._queuedEntries.slice();
	this._queuedEntries = [];
	return records;
	};


	/**
	* 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 = function(opt_threshold) {
	var threshold = opt_threshold \|\| [0];
	if (!Array.isArray(threshold)) threshold = [threshold];

	return threshold.sort().filter(function(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];
	});
	};


	/**
	* 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 = function(opt_rootMargin) {
	var marginString = opt_rootMargin \|\| '0px';
	var margins = marginString.split(/\s+/).map(function(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]};
	});

	// Handles shorthand.
	margins[1] = margins[1] \|\| margins[0];
	margins[2] = margins[2] \|\| margins[0];
	margins[3] = margins[3] \|\| margins[1];

	return margins;
	};


	/**
	* 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.
	var rootDoc =
	(this.root && (this.root.ownerDocument \|\| this.root)) \|\| document;
	if (doc != rootDoc) {
	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 \|\| this.root)) \|\| 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 = function() {
	var unsubscribes = this._monitoringUnsubscribes.slice(0);
	this._monitoringDocuments.length = 0;
	this._monitoringUnsubscribes.length = 0;
	for (var i = 0; i < unsubscribes.length; i++) {
	unsubscribes[i]();
	}
	};


	/**
	* 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 rootBounds = null;
	if (!this._rootContainsTarget(target)) {
	rootBounds = getEmptyRect();
	} else if (!crossOriginUpdater \|\| this.root) {
	rootBounds = rootRect;
	}

	var newEntry = item.entry = new IntersectionObserverEntry({
	time: now(),
	target: target,
	boundingClientRect: targetRect,
	rootBounds: rootBounds,
	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 && !isDoc(this.root)) {
	rootRect = getBoundingClientRect(this.root);
	} else {
	// Use <html>/<body> instead of window since scroll bars affect size.
	var doc = isDoc(this.root) ? this.root : document;
	var html = doc.documentElement;
	var body = doc.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 = function(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;
	};


	/**
	* 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 =
	function(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 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) {
	var rootDoc =
	(this.root && (this.root.ownerDocument \|\| this.root)) \|\| document;
	return (
	containsDeep(rootDoc, target) &&
	(!this.root \|\| rootDoc == 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);
	};


	/**
	* 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;
	return function () {
	if (!timer) {
	timer = setTimeout(function() {
	fn();
	timer = null;
	}, 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.
	*/
	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;
	}


	/**
	* 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.
	*/
	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 the parent has element that is assigned through shadow root slot
	if (parent && parent.assignedSlot) {
	parent = parent.assignedSlot.parentNode
	}

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

	return parent;
	}

	/**
	* Returns true if `node` is a Document.
	* @param {!Node} node
	* @returns {boolean}
	*/
	function isDoc(node) {
	return node && node.nodeType === 9;
	}


	// Exposes the constructors globally.
	window.IntersectionObserver = IntersectionObserver;
	window.IntersectionObserverEntry = IntersectionObserverEntry;

	}());

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