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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(window, document) { 'use strict'; // Exits 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; } /** * 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 = []; /** * 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 = entry.rootBounds; this.boundingClientRect = entry.boundingClientRect; this.intersectionRect = 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(function(margin) { return margin.value + margin.unit; }).join(' '); } /** * 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; /** * 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(); 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; }); if (!this._observationTargets.length) { this._unmonitorIntersections(); this._unregisterInstance(); } }; /** * Stops observing all target elements for intersection changes. */ IntersectionObserver.prototype.disconnect = function() { this._observationTargets = []; this._unmonitorIntersections(); 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. * @private */ IntersectionObserver.prototype._monitorIntersections = function() { if (!this._monitoringIntersections) { this._monitoringIntersections = true; // If a poll interval is set, use polling instead of listening to // resize and scroll events or DOM mutations. if (this.POLL_INTERVAL) { this._monitoringInterval = setInterval( this._checkForIntersections, this.POLL_INTERVAL); } else { addEvent(window, 'resize', this._checkForIntersections, true); addEvent(document, 'scroll', this._checkForIntersections, true); if (this.USE_MUTATION_OBSERVER && 'MutationObserver' in window) { this._domObserver = new MutationObserver(this._checkForIntersections); this._domObserver.observe(document, { attributes: true, childList: true, characterData: true, subtree: true }); } } } }; /** * Stops polling for intersection changes. * @private */ IntersectionObserver.prototype._unmonitorIntersections = function() { if (this._monitoringIntersections) { this._monitoringIntersections = false; clearInterval(this._monitoringInterval); this._monitoringInterval = null; removeEvent(window, 'resize', this._checkForIntersections, true); removeEvent(document, 'scroll', this._checkForIntersections, true); if (this._domObserver) { this._domObserver.disconnect(); this._domObserver = null; } } }; /** * 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() { 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, rootRect); var newEntry = item.entry = new IntersectionObserverEntry({ time: now(), target: target, boundingClientRect: targetRect, rootBounds: 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} 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, rootRect) { // If the element isn't displayed, an intersection can't happen. if (window.getComputedStyle(target).display == 'none') return; var targetRect = getBoundingClientRect(target); var intersectionRect = targetRect; var parent = getParentNode(target); var atRoot = false; while (!atRoot) { 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; if (parent == this.root || parent == document) { atRoot = true; parentRect = rootRect; } 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. if (parent != document.body && parent != document.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 = getParentNode(parent); } return intersectionRect; }; /** * Returns the root rect after being expanded by the rootMargin value. * @return {Object} 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 {Object} rect The rect object to expand. * @return {Object} 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) { return containsDeep(this.root || document, target); }; /** * 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} 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 }; } /** * Shims the native getBoundingClientRect for compatibility with older IE. * @param {Element} el The element whose bounding rect to get. * @return {Object} 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 {Object} The empty rect. */ function getEmptyRect() { return { top: 0, bottom: 0, left: 0, right: 0, width: 0, height: 0 }; } /** * 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 (parent && parent.nodeType == 11 && parent.host) { // If the parent is a shadow root, return the host element. return parent.host; } return parent; } // Exposes the constructors globally. window.IntersectionObserver = IntersectionObserver; window.IntersectionObserverEntry = IntersectionObserverEntry; }(window, document));