first commit

node_modules/intersection-observer/.eslintrc

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+{
+  "env": {
+    "browser": true,
+    "node": true,
+    "mocha": true
+  },
+  "globals": {
+    "expect": false,
+    "sinon": false
+  },
+  "extends": [
+    "eslint:recommended"
+  ],
+  "rules": {
+    // possible errors
+    "no-cond-assign": 0,
+    "no-empty": 0,
+    "valid-jsdoc": [2, {
+      "prefer": {"return": "return"},
+      "requireReturn": false
+    }],
+    // best practices
+    "no-extra-bind": 2,
+    // style
+    "comma-spacing": [2, {"before": false, "after": true}],
+    "eol-last": [0],
+    "key-spacing": [2, {"beforeColon": false, "afterColon": true}],
+    "linebreak-style": [2, "unix"],
+    "max-len": [2, 80, {"ignoreUrls": true}],
+    "no-multiple-empty-lines": [2, {"max": 2}],
+    "no-unused-vars": ["error", {"vars": "all"}],
+    "no-trailing-spaces": 2,
+    "object-curly-spacing": [2, "never"],
+    "quotes": [2, "single"],
+    "require-jsdoc": [2, {
+      "require": {
+        "FunctionDeclaration": true,
+        "MethodDefinition": true,
+        "ClassDeclaration": true
+      }
+    }],
+    "semi": [2, "always"],
+    "semi-spacing": [2, {"before": false, "after": true}],
+  }
+}

node_modules/intersection-observer/README.md

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+# `IntersectionObserver` polyfill
+
+This library polyfills the native [`IntersectionObserver`](http://w3c.github.io/IntersectionObserver/) API in unsupporting browsers. See the [API documentation](https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API) for usage information.
+
+- [Installation](#installation)
+- [Configuring the polyfill](#configuring-the-polyfill)
+- [Limitations](#limitations)
+- [Browser support](#browser-support)
+- [Running the tests](#running-the-tests)
+
+## Installation
+
+You can install the polyfill via npm or by downloading a [zip](https://github.com/w3c/IntersectionObserver/archive/gh-pages.zip) of this repository:
+
+```sh
+npm install intersection-observer
+```
+
+### Adding the polyfill to your site
+
+The examples below show various ways to add the `IntersectionObserver` polyfill to your site. Be sure to include the polyfill prior to referencing it anywhere in your JavaScript code.
+
+**Using `<script>` tags in the HTML:**
+
+```html
+<!-- Load the polyfill first. -->
+<script src="path/to/intersection-observer.js"></script>
+
+<!-- Load all other JavaScript. -->
+<script src="app.js"></script>
+```
+
+**Using a module loader (e.g. Browserify or Webpack):**
+
+```js
+// Require the polyfill before requiring any other modules.
+require('intersection-observer');
+
+require('./foo.js');
+require('./bar.js');
+```
+
+## Configuring the polyfill
+
+It's impossible to handle all possible ways a target element could intersect with a root element without resorting to constantly polling the document for intersection changes.
+
+To avoid this extra work and performance penalty, the default configuration of the polyfill optimizes for the most common `IntersectionObserver` use cases, which primarily include target elements intersecting with a root element due to:
+
+- User scrolling.
+- Resizing the window.
+- Changes to the DOM.
+
+All of the above can be handled without polling the DOM.
+
+There are, however, additional use cases that the default configuration will not detect. These include target elements intersecting with a root element due to:
+
+- CSS changes on `:hover`, `:active`, or `:focus` states.
+- CSS changes due to transitions or animations with a long initial delay.
+- Resizable `<textarea>` elements that cause other elements to move around.
+- Scrolling of non-document elements in browsers that don't support the event capture phase.
+
+If you need to handle any of these use-cases, you can configure the polyfill to poll the document by setting the `POLL_INTERVAL` property. This can be set either globally or on a per-instance basis.
+
+**Enabling polling for all instance:**
+
+To enable polling for all instance, set a value for `POLL_INTERVAL` on the `IntersectionObserver` prototype:
+
+
+```js
+IntersectionObserver.prototype.POLL_INTERVAL = 100; // Time in milliseconds.
+```
+
+**Enabling polling for individual instance:**
+
+To enable polling on only specific instances, set a `POLL_INTERVAL` value on the instance itself:
+
+```js
+var io = new IntersectionObserver(callback);
+io.POLL_INTERVAL = 100; // Time in milliseconds.
+io.observe(someTargetElement);
+```
+
+**Note:** the `POLL_INTERVAL` property must be set prior to calling the `.observe` method, or the default configuration will be used.
+
+**Ignoring DOM changes**
+
+You can also choose to not check for intersections when the DOM changes by setting an observer's `USE_MUTATION_OBSERVER` property to `false` (either globally on the prototype or per-instance)
+
+```js
+IntersectionObserver.prototype.USE_MUTATION_OBSERVER = false; // Globally
+
+// for an instance
+var io = new IntersectionObserver(callback);
+io.USE_MUTATION_OBSERVER = false;
+```
+
+This is recommended in cases where the DOM will update frequently but you know those updates will have no affect on the position or your target elements.
+
+## Limitations
+
+This polyfill does not attempt to report intersections across same-origin `iframe` boundaries. While supporting same-origin iframes is technically possible, it would drastically reduce performance. Since most `iframe` usage on the web is cross-origin, this polyfill chooses to optimize for performantly handling the most common use cases. (Note: neither this polyfill nor native implementations support reporting intersections across cross-origin `iframe` boundaries.)
+
+This polyfill also does not support the [proposed v2 additions](https://github.com/szager-chromium/IntersectionObserver/blob/v2/explainer.md), as these features are not currently possible to do with JavaScript and existing web APIs.
+
+## Browser support
+
+The polyfill has been tested and known to work in the latest version of all browsers.
+
+Legacy support is also possible in very old browsers by including a shim for ES5 as well as the `window.getComputedStyle` method. The easiest way to load the IntersectionObserver polyfill and have it work in the widest range of browsers is via [polyfill.io](https://cdn.polyfill.io/v2/docs/), which will automatically include dependencies where necessary:
+
+```html
+<script src="https://polyfill.io/v2/polyfill.min.js?features=IntersectionObserver"></script>
+```
+
+With these polyfills, `IntersectionObserver` has been tested an known to work in the following browsers:
+
+<table>
+  <tr>
+    <td align="center">
+      <img src="https://raw.github.com/alrra/browser-logos/39.2.2/src/chrome/chrome_48x48.png" alt="Chrome"><br>
+      ✔
+    </td>
+    <td align="center">
+      <img src="https://raw.github.com/alrra/browser-logos/39.2.2/src/firefox/firefox_48x48.png" alt="Firefox"><br>
+      ✔
+    </td>
+    <td align="center">
+      <img src="https://raw.github.com/alrra/browser-logos/39.2.2/src/safari/safari_48x48.png" alt="Safari"><br>
+      6+
+    </td>
+    <td align="center">
+      <img src="https://raw.github.com/alrra/browser-logos/39.2.2/src/edge/edge_48x48.png" alt="Edge"><br>
+      ✔
+    </td>
+    <td align="center">
+      <img src="https://raw.github.com/alrra/browser-logos/39.2.2/src/archive/internet-explorer_7-8/internet-explorer_7-8_48x48.png" alt="Internet Explorer"><br>
+      7+
+    </td>
+    <td align="center">
+      <img src="https://raw.github.com/alrra/browser-logos/39.2.2/src/opera/opera_48x48.png" alt="Opera"><br>
+      ✔
+    </td>
+    <td align="center">
+      <img src="https://raw.github.com/alrra/browser-logos/39.2.2/src/android/android_48x48.png" alt="Android"><br>
+      4.4+
+    </td>
+  </tr>
+</table>
+
+## Running the tests
+
+To run the test suite for the `IntersectionObserver` polyfill, open the [`intersection-observer-test.html`](./intersection-observer-test.html) page in the browser of your choice.
+
+If you run the tests in a browser that support `IntersectionObserver` natively, the tests will be run against the native implementation. If it doesn't the tests will be run against the polyfill.

node_modules/intersection-observer/intersection-observer-test.html

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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
+-->
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="utf-8">
+  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
+  <title>IntersectionObserver Tests</title>
+
+  <!-- Dependencies -->
+  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/mocha/2.5.3/mocha.min.css">
+  <script src="https://cdnjs.cloudflare.com/ajax/libs/mocha/2.5.3/mocha.min.js"></script>
+  <script src="https://cdnjs.cloudflare.com/ajax/libs/expect.js/0.2.0/expect.min.js"></script>
+  <script src="https://cdnjs.cloudflare.com/ajax/libs/sinon.js/3.2.1/sinon.min.js"></script>
+
+  <!-- Polyfills for IE7-8 -->
+  <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=es5,getComputedStyle"></script>
+</head>
+<body>
+  <div id="mocha"></div>
+
+  <!-- Setup -->
+  <script>mocha.setup({ui:'bdd'});</script>
+
+  <!-- Script under test -->
+  <script src="intersection-observer.js"></script>
+
+  <!-- Tests -->
+  <script src="intersection-observer-test.js"></script>
+
+  <!-- Reporting -->
+  <script>
+  var runner = mocha.run();
+  var failedTests = [];
+
+  runner.on('end', function(){
+    window.mochaResults = runner.stats;
+    window.mochaResults.reports = failedTests;
+  });
+
+  runner.on('fail', function(test, err){
+    var flattenTitles = function(test){
+      var titles = [];
+      while (test.parent.title){
+        titles.push(test.parent.title);
+        test = test.parent;
+      }
+      return titles.reverse();
+    };
+
+    failedTests.push({
+      name: test.title,
+      result: false,
+      message: err.message,
+      stack: err.stack,
+      titles: flattenTitles(test)
+    });
+  });
+  </script>
+</body>
+</html>

node_modules/intersection-observer/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;
+}
+
+
+/**
+ * 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 = [];
+
+
+/**
+ * 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;
+  }
+
+  if (parent && parent.assignedSlot) {
+    // If the parent is distributed in a <slot>, return the parent of a slot.
+    return parent.assignedSlot.parentNode;
+  }
+
+  return parent;
+}
+
+
+// Exposes the constructors globally.
+window.IntersectionObserver = IntersectionObserver;
+window.IntersectionObserverEntry = IntersectionObserverEntry;
+
+}());

node_modules/intersection-observer/package.json

@@ -0,0 +1,23 @@
+{
+  "name": "intersection-observer",
+  "version": "0.7.0",
+  "description": "A polyfill for IntersectionObserver",
+  "main": "intersection-observer",
+  "repository": {
+    "type": "git",
+    "url": "git@github.com:w3c/IntersectionObserver.git"
+  },
+  "keywords": [
+    "Intersection",
+    "Observer"
+  ],
+  "author": {
+    "name": "Philip Walton",
+    "email": "philip@philipwalton.com",
+    "url": "http://philipwalton.com"
+  },
+  "license": "W3C-20150513",
+  "bugs": {
+    "url": "https://github.com/w3c/IntersectionObserver/issues"
+  }
+}