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test.html
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<!doctype html>
<html lang=en-US>
<meta charset=UTF-8>
<title>Scrollspy example for mobile</title>
<meta name=viewport content="width=device-width,initial-scale=1">
<link href=node_modules/sanitize.css/sanitize.css rel=stylesheet>
<style>
:root {
--scrollspy-height: 60px;
}
body {
max-width: 600px;
padding-bottom: 30vh;
margin: 0 auto;
scroll-behavior: smooth;
line-height: 2em;
}
h1 {
text-align: center;
}
h2 {
margin: 0;
}
ul#langs {
padding: 0;
list-style: none;
text-align: right;
}
#langs li {
display: inline-block;
}
nav {
position: -webkit-sticky;
position: sticky;
top: 0;
height: var(--scrollspy-height, 2em);
z-index: 12;
overflow-y: hidden;
text-align: center;
}
nav[aria-expanded="true"] {
height: auto;
}
nav ul {
margin: 0;
padding: 0;
transition: transform 100ms;
}
nav[data-scrollspy-target="whatsthis"] ul {
transform: translateY(calc(-0 * var(--scrollspy-height)));
}
nav[data-scrollspy-target="motivation"] ul {
transform: translateY(calc(-1 * var(--scrollspy-height)));
}
nav[data-scrollspy-target="smoothscroll"] ul {
transform: translateY(calc(-2 * var(--scrollspy-height)));
}
nav[data-scrollspy-target="sticky"] ul {
transform: translateY(calc(-3 * var(--scrollspy-height)));
}
nav[data-scrollspy-target="custom-property"] ul {
transform: translateY(calc(-4 * var(--scrollspy-height)));
}
nav[data-scrollspy-target="source-code"] ul {
transform: translateY(calc(-5 * var(--scrollspy-height)));
}
nav[aria-expanded="true"] ul {
transform: translateY(0);
}
nav li {
height: var(--scrollspy-height, 2em);
}
nav li:nth-of-type(1) {
background-color: #ff0000;
}
nav li:nth-of-type(2) {
background-color: #ff7f00;
}
nav li:nth-of-type(3) {
background-color: #ffff00;
}
nav li:nth-of-type(4) {
background-color: #00ff00;
}
nav li:nth-of-type(5) {
background-color: #0000ff;
}
nav li:nth-of-type(6) {
background-color: #6600ff;
}
nav li a {
display: block;
width: 100%;
height: 100%;
text-decoration: none;
color: white;
font-weight: bold;
line-height: var(--scrollspy-height, 2em);
}
nav li:nth-of-type(3) a {
color: gray;
}
nav button {
position: absolute;
top: 0;
right: 0;
display: inline-block;
width: 100%;
height: var(--scrollspy-height, 2em);
padding: 0;
padding-right: 0.5em;
line-height: var(--scrollspy-height, 2em);
text-align: right;
text-decoration: none;
cursor: pointer;
transition: transform 300ms;
}
nav button[aria-expanded="true"] {
width: auto;
padding-right: 0.5em;
transform: rotateX(180deg);
}
section {
min-height: 80vh;
padding: var(--scrollspy-height, 2em) 1em;
border-bottom: 1px solid transparent;
}
section:nth-of-type(1) {
background-color: #ffcccc;
}
section:nth-of-type(2) {
background-color: #ffeacc;
}
section:nth-of-type(3) {
background-color: #fffecc;
}
section:nth-of-type(4) {
background-color: #c7f5c4;
}
section:nth-of-type(5) {
background-color: #c4daf4;
}
section:nth-of-type(6) {
background-color: #e1c4f4;
}
pre {
margin: 1em;
padding: 1em 0.5em;
background-color: #eeeeee;
}
code {
margin-left: 0.1em;
margin-right: 0.1em;
letter-spacing: 0.1em;
}
p code {
text-decoration: underline;
text-decoration-style: dashed;
}
</style>
<h1 id=top>Scrollspy example for mobile</h1>
<ul id="langs">
<li><a href="./">ja</a></li>
<li>en</li>
</ul>
<nav id=nav role=listbox aria-expanded=false>
<ul>
<li><a href=#whatsthis role=option>What's this?</a></li>
<li><a href=#motivation role=option>Motivation</a></li>
<li><a href=#smoothscroll role=option>Smooth scroll by CSS</a></li>
<li><a href=#sticky role=option>Sticky positioning by CSS</a></li>
<li><a href=#custom-property role=option>CSS variables</a></li>
<li><a href=#source-code role=option>Source code</a></li>
</ul>
<button aria-controls=nav aria-expanded=false>▼</button>
</nav>
<section id=whatsthis>
<h2>What's this?</h2>
<p>This is an example of scrollspy for mobile.</p>
<p>Scrollspy is often shown as table of contents in sidebars. But, for mobile, we rarely see scrollspy because sidebars are usually not generated.</p>
<p>This is a proposal of scrollspy for mobile which is fixed on the top, shows only single line and changes it on scrolling.</p>
</section>
<section id=motivation>
<h2>Motivation for this page</h2>
<p>I was impressed by <a href="https://blog.jxck.io/entries/2016-06-25/intersection-observer.html">Intersection Observer を用いた要素出現検出の最適化</a>("Optimization of detect of element appearance by Intersection Observer". You can see similar article in English here: <a href="https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API">Intersection Observer API</a>) and wanted to use it, then, chose scrollspy as a material.</p>
</section>
<section id=smoothscroll>
<h2>Smooth scroll by CSS</h2>
<p>CSS has <code>scroll-behavior</code> propery and by setting the value to <code>smooth</code> such as:</p>
<pre><code>body {
scroll-behavior: smooth;
}</code></pre>
<p>browsers run smooth scroll automatically. This page also uses the feature.</p>
<p>Firefox(except for on iOS) supports it as of <time datetime="2016-09">September 2016</time>. Try this page on Firefox.</p>
<p>See also: <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-behavior">scroll-behavior - CSS | MDN</a></p>
</section>
<section id=sticky>
<h2>Sticky poisitioning only by CSS（<code>position: sticky</code>）</h2>
<p>The navigation by scrollspy in this page is under the page title at first, and after scrolling, becomes fixed at the top of the page.</p>
<p>This kind of feature is often implemented by combination of JavaScript and CSS. But it was done by only CSS in this page. By setting <code>position</code> property to <code>sticky</code> such as:</p>
<pre><code>nav {
position: sticky;
/*
:
:
*/
}</code></pre>
<p>the behavior as said above is achieved.</p>
<p>As of <time datetime="2016-09">September 2016</time>, Firefox and Safari support the property.</p>
<p>See also: <a href="https://www.sitepoint.com/css-position-sticky-introduction-polyfills/">CSS "position: sticky" - Introduction and Polyfills</a></p>
</section>
<section id=custom-property>
<h2>CSS custom properties(CSS variables)</h2>
<p>The height of scrollspy is defined by a CSS custom property although you cannot see it directly in the page.</p>
<p>Each section has top padding whose height is the same to scrollspy's. Leaks of setting is prevented by managing the hight by a shared variable.</p>
<p>Now Chrome and Safari support CSS custom properties as well as Firefox.</p>
<p>See also: <a href="https://developers.google.com/web/updates/2016/02/css-variables-why-should-you-care">CSS Variables: Why Should You Care? | Web | Google Developers</a></p>
</section>
<section id=source-code>
<h2>Source code</h2>
<p>Source code of this page is hosted by <a href="https://gitlab.com">GitLab</a>.</p>
<p>Source code:<a href="https://gitlab.com/KitaitiMakoto/scrollspy-example">KitaitiMakoto/scrollspy-example</a></p>
</section>
<p>©<a href="https://gitlab.com/KitaitiMakoto">Kitaiti Makoto</a></p>
<script src=node_modules/intersection-observer/intersection-observer.js></script>
<script>
'use strict';
class Scrollspy {
constructor(element, ids, observerOptions) {
this.element = element;
this.targets = [];
this.targetIndices = {};
this.indicesInViewPort = [];
ids.forEach(function(id, index) {
this.targets.push(document.getElementById(id));
this.targetIndices[id] = index;
}.bind(this));
var observer = new IntersectionObserver(this.onIntersectionChange.bind(this), observerOptions);
this.targets.forEach(observer.observe.bind(observer));
}
onIntersectionChange(changes) {
var oldTargetIndex = this.indicesInViewPort[0] || 0;
for (var i = changes.length - 1; i >= 0; i--) {
this.updateIndicesInViewPort(changes[i], oldTargetIndex);
}
if (this.indicesInViewPort.length === 0) {
return;
}
if (oldTargetIndex === this.indicesInViewPort[0]) {
return;
}
var event = new CustomEvent('targetchange', {
detail: {
newTarget: this.targets[this.indicesInViewPort[0]],
oldTarget: this.targets[oldTargetIndex]
}
});
this.element.dispatchEvent(event);
}
updateIndicesInViewPort(change, oldTargetIndex) {
var index = this.targetIndices[change.target.id];
if (change.intersectionRatio === 0) {
var indexInViewPort = this.indicesInViewPort.indexOf(index);
if (indexInViewPort !== -1) {
this.indicesInViewPort.splice(indexInViewPort, 1);
}
} else {
if (index < oldTargetIndex) {
this.indicesInViewPort.unshift(index);
} else if (index > this.indicesInViewPort[this.indicesInViewPort.length - 1]) {
this.indicesInViewPort.push(index);
} else {
this.indicesInViewPort.push(index);
this.indicesInViewPort.sort();
}
}
}
}
class Navigation {
constructor(element) {
this.element = element;
this.links = {};
var as = this.element.getElementsByTagName('a');
for (var i = 0, l = as.length; i < l; i++) {
var a = as[i];
this.links[a.hash.slice(1)] = a;
a.addEventListener('click', this.collapse.bind(this), {passive: true});
}
this.button = this.element.getElementsByTagName('button')[0];
this.button.addEventListener('click', this.toggle.bind(this)), {passive: true};
}
get expanded() {
return this.element.getAttribute('aria-expanded') === 'true';
}
get height() {
return getComputedStyle(this.element).getPropertyValue('--scrollspy-height').trim();
}
onTargetChange(event) {
var newTargetId = event.detail.newTarget.id;
this.links[event.detail.oldTarget.id].setAttribute('aria-selected', 'false');
this.links[newTargetId].setAttribute('aria-selected', 'true');
this.element.dataset.scrollspyTarget = newTargetId;
history.pushState(null, null, location.href);
console.log(location.href);
}
expand() {
this.element.setAttribute('aria-expanded', 'true');
this.button.setAttribute('aria-expanded', 'true');
}
collapse() {
this.element.setAttribute('aria-expanded', 'false');
this.button.setAttribute('aria-expanded', 'false');
}
toggle() {
if (this.expanded) {
this.collapse();
} else {
this.expand();
}
}
}
class HistoryManager {
onTargetChange(event) {
history.replaceState(null, null, '#' + event.detail.newTarget.id);
}
}
class HashchangeDispatcher {
onTargetChange(event) {
var hashchangeEvent = new Event('hashchange');
var oldURL = new URL(location.href);
if (event.detail.oldTarget) {
oldURL.hash = '#' + event.detail.oldTarget.id;
}
hashchangeEvent.oldURL = oldURL.toString();
if (event.detail.newTarget) {
var newURL = new URL(location.href);
newURL.hash = '#' + event.detail.newTarget.id;
hashchangeEvent.newURL = newURL.toString();
}
dispatchEvent(hashchangeEvent);
}
}
document.addEventListener('DOMContentLoaded', function() {
var nav = document.getElementsByTagName('nav')[0];
var navigation = new Navigation(nav);
var historyManager = new HistoryManager();
var hashchangeDispatcher = new HashchangeDispatcher();
[navigation, historyManager, hashchangeDispatcher].forEach(function(listener) {
nav.addEventListener('targetchange', listener.onTargetChange.bind(listener), {passive: true});
});
addEventListener('hashchange', function(event) {
console.dir(event);
}, {passive: true});
new Scrollspy(nav, Object.keys(navigation.links), {rootMargin: `-${navigation.height}`});
});
</script>
</html>