关于前端:positionsticky-粘性定位的几种巧妙应用

背景：position:sticky 又称为粘性定位，粘性定位的元素是依赖于用户的滚动，在 position:relative 与 position:fixed 定位之间切换。元素依据失常文档流进行定位，而后绝对它的最近滚动先人（nearest scrolling ancestor）和 containing block (最近块级先人 nearest block-level ancestor)，包含 table-related 元素，基于 top, right, bottom, 和 left 的值进行偏移。

粘性定位能够被认为是绝对定位和固定定位的混合。元素在逾越特定阈值前为绝对定位，之后为固定定位。例如：

#one {position: sticky; top: 10px;}

设置了以上款式的元素，在 viewport 视口滚动到元素 top 间隔小于 10px 之前，元素为绝对定位。之后，元素将固定在与顶部间隔 10px 的地位，直到 viewport 视口回滚到阈值以下。

留神：

• 元素定位体现为在逾越特定阈值前为绝对定位，之后为固定定位。
• 须指定 top, right, bottom 或 left 四个阈值其中之一，才可使粘性定位失效。否则其行为与绝对定位雷同。
• 偏移值不会影响任何其余元素的地位。该值总是创立一个新的层叠上下文（stacking context）。
• 一个 sticky 元素 会 固定 在离它最近的一个领有 滚动机制 的先人上（当该先人的 overflow 是 hidden, scroll, auto, 或 overlay 时），即使这个先人不是最近的实在可滚动先人。

利用示例

1. 根底：头部固定

头部导航栏开始时绝对定位顶部，当页面元素产生滚动时，变为和 fixed 相似的固定定位。

<main class="main-container">
  <header class="main-header">HEADER</header>
  <div class="main-content">MAIN CONTENT</div>
  <footer class="main-footer">FOOTER</footer>
</main>

.main-container {
  max-width: 500px;
  height: 500px;
  margin: 0 auto;
  margin-top: 40px;
  overflow: auto;
}
.main-container *+* {margin-top: 20px;}
.main-header {height: 50px;}
.main-content {min-height: 600px;}
.main-header {
  position: -webkit-sticky;
  position: sticky;
  top: 0;
}

2. 根底：页脚固定

页脚固定成果，开始时也较为固定定位成果，当页面滚动超过页脚时，页脚定位成果变为绝对定位成果，可用于显示一些底部信息或广告。

<main class="main-container">
  <header class="main-header">HEADER</header>
  <div class="main-content">MAIN CONTENT</div>
  <footer class="main-footer">FOOTER</footer>
</main>
<div class="devide"></div>

.main-container *+* {margin-top: 20px;}
.main-header {height: 50px;}
.main-content {min-height: 600px;}
.main-footer {
  position: -webkit-sticky;
  position: sticky;
  bottom: 0;
  border-color: red;
}
.devide {height: 600px;}

3. 根底：侧边栏固定

当页面产生滚动，地位超过侧边栏的 顶部阈值 后，侧边栏变为固定定位，可用于实现侧边导航栏或侧边提示信息及广告展现。

<div class="scroll">
  <div class="wrapper cf">
    <div class="content">
      <h1>Scroll Down!</h1>
      <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Minus suscipit blanditiis delectus quos, soluta fuga voluptatem, facere inventore neque voluptate quaerat unde laboriosam molestiae repellat, sapiente accusamus cumque! Ipsam, illo!</p>
    </div>
    <div class="sidebar">
      <h3>Sidebar</h3>
      <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ab maxime fugiat perspiciatis.</p>
    </div>
  </div>
</div>

.cf:before, .cf:after {
  content: " ";
  display: table;
  clear: both;
}
.cf {*zoom: 1;}
.scroll {
  height: 500px;
  overflow: scroll;
  padding: 0 10px;
  max-width: 500px;
  margin: 40px auto;
  background: #FFFFFF;
}
.content {
  padding: 0 15px;
  width: 280px;
}
.sidebar {
  padding: 20px;
  width: 170px;
  background: #2D2D2D;
  color: #FFFFFF;
}
.content, .sidebar {float: left;}
.sidebar {
  position: -webkit-sticky;
  position: sticky;
  top: 15px;
}

4. 根底：列表锚点

仅应用 css 就可实现页面滚动锚点固定成果，可用于实现通讯录滚动、日志记录滚动、其余分类列表滚动成果。

 <div class="container">
  <div class="list">
    <div class="list-group">
      <div class="list-header">A</div>
      <div class="list-content">
        <div>Apple</div>
        <div>Artichoke</div>
        <div>Aardvark</div>
        <div>Ant</div>
        <div>Acorn</div>
      </div>
    </div>
    <!-- ... -->
    <div class="list-group">
      <div class="list-header">D</div>
      <div class="list-content">
        <div>Dog</div>
        <div>Date</div>
        <div>Danish</div>
        <div>Dandelion</div>
      </div>
    </div>
  </div>
</div>

@supports CSS at-rule 您能够指定依赖于浏览器中的一个或多个特定的 CSS 性能的反对申明。这被称为个性查问。该规定能够放在代码的顶层，也能够嵌套在任何其余条件组规定中。

@supports (position: sticky) {
  .list-header {
    position: sticky;
    top: 0;
  }
}
.container {
  width: 500px;
  height: 500px;
  margin: 40px auto;
  position: relative;
  overflow: auto;
}
.list {
  min-height: 1600px;
  background: #FFFFFF;
}
.list-content {padding: 10px 20px;}
.list-header {
  padding: 10px;
  background: #2D2D2D;
  color: #FFFFFF;
  position: relative;
  font-weight: bold;
}

5. 进阶：表格表头固定

对 table 元素的 th 或 tr 设置 position: sticky; 能够实现表格头部或某行固定，也可将多个表格合并到一起，当滚动到以后表格是，固定头部主动变为以后表格的表头。

<div class="container">
  <table>
    <thead>
      <tr class="red">
        <th>Name</th>
        <th>Age</th>
        <th>Job</th>
        <th>Color</th>
        <th>URL</th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <td>Lorem.</td>
        <td>Ullam.</td>
        <td>Vel.</td>
        <td>At.</td>
        <td>Quis.</td>
      </tr>
      <!-- ... -->
      <tr class="green">
        <th>Name</th>
        <th>Age</th>
        <th>Job</th>
        <th>Color</th>
        <th>URL</th>
      </tr>
     <!-- ... -->
    </tbody>
  </table>
</div>

.container {
  height: 500px;
  width: fit-content;
  margin: 40px auto;
x  overflow: auto;
}
table {
  text-align: left;
  position: relative;
  border-collapse: collapse;
}
th, td {padding: 0.25rem;}
tr:nth-child(even) {background: #EFEFEF;}
tr.red th {
  background: #dd4a63;
  color: white;
}
tr.green th {
  background: #03C03C;
  color: white;
}
tr.blue th {
  background: #1580d8;
  color: white;
}
th {
  background: white;
  position: sticky;
  top: 0;
}

6. 进阶：页面进度条（繁难）

利用 position: sticky; 定位，能够实现页面浏览进度条成果，以下是繁难进度条的演示，理论实现中可将未滚动到顶部的元素设置为通明色，滚动到顶部时变为蓝色。

<div class="container">
  <h1>Sticky Progress</h1>
  <div class="sticky"></div>
  <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Voluptatem, cumque? A, est perferendis explicabo odit possimus quisquam rem ad tempore ipsa, obcaecati ex culpa similique, aliquam corporis. Quis, nostrum expedita.</p>
  <!-- ... -->
  <div class="sticky"></div>
  <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Voluptatem, cumque? A, est perferendis explicabo odit possimus quisquam rem ad tempore ipsa, obcaecati ex culpa similique, aliquam corporis. Quis, nostrum expedita.</p>
</div>

.container {
  width: 500px;
  height: 500px;
  overflow: auto;
  margin: 40px auto 40px;
  padding-bottom: 500px;
  box-sizing: border-box;
}
.sticky {
  width: 50px;
  height: 10px;
  background: rgba(36, 167, 254, 0.979);
  position: -webkit-sticky;
  position: sticky;
  top: 0;
}
.sticky:nth-of-type(2) {transform: translateX(50px);
}
.sticky:nth-of-type(3) {transform: translateX(100px);
}
.sticky:nth-of-type(4) {
// ... 
.sticky:nth-of-type(10) {transform: translateX(450px);
}

7. 进阶：页面进度条（优化）

优化版的进度条反对浏览进度百分比显示，助于晋升用户体验。

<article>
  <div class="article-title">
    <h1>Page Progress Bar Example</h1>
    <div class="progress-wrapper">
      <div class="progress-label"></div>
      <progress></progress>
    </div>
  </div>
  <img src=""/>
  <p><em>All images provided at random from Codepen assets. All ipsum text provided by officeipsum.com.</em></p>
  <p>Face time level the playing field highlights. Bake it in quick win bench mark, or paddle on both sides. Re-inventing the wheel. What do you feel you would bring to the table if you were hired for this position drink from the firehose, but quarterly sales are at an all-time low or can you ballpark the cost per unit for me we are running out of runway.</p>
  <!-- ... -->
  <img src=""/>
  <p>Meeting assassin enough to wash your face so after I ran into Helen at a restaurant, I realized she was just office pretty good optics put a record on and see who dances, yet we're ahead of the curve on that one, or personal development. Bench mark beef up helicopter view highlights take five, punch the tree, and come back in here with a clear head, so translating our vision of having a market leading platfrom nor what's the status on the deliverables for eow?.</p>
</article>

:root {
  --progress-bar-height: 4px;
  --progress-bar-color: gainsboro;
  --progress-bar-value-color: dodgerblue;
  --progress-bar-value: 20%;
}
article {
  position: relative;
  padding: 24px;
  width: 100%;
  max-width: 700px;
  margin: 60px auto;
}
.article-title {
  position: sticky;
  top: 0;
  padding-bottom: 24px;
}
img {
  width: 100%;
  margin-bottom: 18px;
}
.progress-wrapper {position: relative;}
.progress-label {
  position: absolute;
  right: 0;
  bottom: 0;
  font-size: 14px;
}
progress {
  -webkit-appearance: none;
  -moz-appearance: none;
  appearance: none;
  position: absolute;
  width: 100%;
  height: var(--progress-bar-height);
  background-color: var(--progress-bar-color);
  border: none;
}
progress::-moz-progress-bar {background-color: var(--progress-bar-value-color);
}
progress::-webkit-progress-bar {background-color: var(--progress-bar-color);
}
progress::-webkit-progress-value {background-color: var(--progress-bar-value-color);
}
progress::-ms-fill {background-color: var(--progress-bar-value-color);
}

计算并显示百分比

$(document).ready(function() {const win = $(window);
  const doc = $(document);
  const progressBar = $('progress');
  const progressLabel = $('.progress-label');
  const setValue = () => win.scrollTop();
  const setMax = () => doc.height() - win.height();
  const setPercent = () => Math.round(win.scrollTop() / (doc.height() - win.height()) * 100);
  progressLabel.text(setPercent() + '%');
  progressBar.attr({value: setValue(), max: setMax()});
  doc.on('scroll', () => {progressLabel.text(setPercent() + '%');
    progressBar.attr({value: setValue() });
  });
  win.on('resize', () => {progressLabel.text(setPercent() + '%');
    progressBar.attr({value: setValue(), max: setMax()});
  })
});

8. 进阶：时间轴

时间轴相当于上述列表锚点的升级版，可用于年鉴展现、记事本、tudo list 等利用中。

<div id="wrapper">
  <div id="container">
    <h1>Timeline</h1>
    <ol class="timeline">
      <li>
        <h2>1997</h2>
        <ol>
          <li>
            <h3>Lorem ipsum dolor sit amet, consectetur adipiscing elit</h3>
            <p>Nam non purus vel orci molestie consequat.</p>
          </li>
          <li>
            <h3>Etiam et velit in arcu consectetur aliquet et eu metus</h3>
            <p>Sed vitae diam rhoncus, imperdiet nunc quis, lacinia nulla.</p>
          </li>
        </ol>
      </li>
      <!-- ... -->
      <li>
        <h2>Today</h2>
      </li>
    </ol>
  </div>
</div>

ol.timeline ol, ol.timeline, html, body {
  margin: 0;
  padding: 0;
}
*, *:before, *:after {box-sizing: border-box;}
#wrapper {
  margin: 0 auto;
  max-width: 64em;
}
#container {
  float: left;
  padding: 1em;
  width: 100%;
}
h1, h2 {text-align: center;}
ol.timeline，ol.timeline ol {list-style: none;}
ol.timeline>li {
  padding-left: 2px;
  position: relative;
}
ol.timeline>li:before {
  background-color: #a2ed56;
  content: "";
  height: 100%;
  left: 0;
  position: absolute;
  top: 0;
  width: 2px;
}
@media only screen and (min-width: 40em) {
  ol.timeline>li:before {
    left: 50%;
    transform: translateX(-50%);
  }
}
ol.timeline>li>h2 {
  background-color: #a2ed56;
  color: #1d1f20;
  margin: 0;
  position: -webkit-sticky;
  position: sticky;
  text-transform: uppercase;
  top: 0;
}
@media only screen and (min-width: 40em) {
  ol.timeline>li>h2 {
    border-radius: 0.25em;
    margin: 0 auto;
    margin-bottom: 1em;
    max-width: 200px;
  }
}
ol.timeline>li>ol {
  display: flex;
  flex-wrap: wrap;
}
ol.timeline>li>ol>li {
  border-top: 2px solid #a2ed56;
  flex: 0 0 100%;
  padding: 0 0 0.5em 1em;
}
@media only screen and (min-width: 40em) {
  ol.timeline>li>ol>li {flex-basis: 50%;}
  ol.timeline>li>ol>li:nth-child(odd) {
    padding-left: 0;
    padding-right: 1em;
  }
  ol.timeline>li>ol>li:nth-child(even) {
    margin-top: 2em;
    padding-right: 0;
  }
}
ol.timeline>li>ol>li>h3:first-child {
  color: #a2ed56;
  margin-bottom: -0.75em;
}
ol.timeline>li:nth-child(6n+2):before,
ol.timeline>li:nth-child(6n+2)>h2 {background-color: #83e4e2;}
ol.timeline>li:nth-child(6n+2)>ol>li {border-color: #83e4e2;}
ol.timeline>li:nth-child(6n+2)>ol>li h3 {color: #83e4e2;}
ol.timeline>li:nth-child(6n+3):before,
ol.timeline>li:nth-child(6n+3)>h2 {background-color: #fd6470;}
ol.timeline>li:nth-child(6n+3)>ol>li {border-color: #fd6470;}
ol.timeline>li:nth-child(6n+3)>ol>li h3 {color: #fd6470;}
ol.timeline>li:nth-child(6n+4):before,
ol.timeline>li:nth-child(6n+4)>h2 {background-color: #fca858;}
ol.timeline>li:nth-child(6n+4)>ol>li {border-color: #fca858;}
ol.timeline>li:nth-child(6n+4)>ol>li h3 {color: #fca858;}
ol.timeline>li:nth-child(6n+5):before,
ol.timeline>li:nth-child(6n+5)>h2 {background-color: #fddc32;}
ol.timeline>li:nth-child(6n+5)>ol>li {border-color: #fddc32;}
ol.timeline>li:nth-child(6n+5)>ol>li h3 {color: #fddc32;}
ol.timeline>li:nth-child(6n+6):before,
ol.timeline>li:nth-child(6n+6)>h2 {background-color: #fafafa;}
ol.timeline>li:nth-child(6n+6)>ol>li {border-color: #fafafa;}
ol.timeline>li:nth-child(6n+6)>ol>li h3 {color: #fafafa;}

9. 进阶：文字沉积成果

<p>A <b>scroll</b> (from the Old French <i>escroe</i> or <i>escroue</i>), also known as a <b>roll</b>, is a roll of papyrus, parchment, or paper containing writing.</p>
<h2>Structure</h2>
<p>A scroll is usually divided up into pages, which are sometimes separate sheets of papyrus or parchment glued
  together at the edges, or may be marked divisions of a continuous roll of writing material. The scroll is usually
  unrolled so that one page is exposed at a time, for writing or reading, with the remaining pages rolled up to the
  left and right of the visible page. It is unrolled from side to side, and the text is written in lines from the top
  to the bottom of the page. Depending on the language, the letters may be written left to right, right to left, or
  alternating in direction (boustrophedon).</p>
<p>Some scrolls are simply rolled up pages; others may have wooden rollers on each end: Torah scrolls have rather
  elaborate rollers befitting their ceremonial function.</p>
<h2>History of scroll use</h2>
<p>Scrolls were the first form of editable record keeping texts, used in Eastern Mediterranean ancient Egyptian
  civilizations. Parchment scrolls were used by the Israelites among others before the codex or bound book with
  parchment pages was invented by the Romans, which became popular around the 1st century AD. Scrolls were more highly
  regarded than codices until well into Roman times, where they were usually written in single latitudinal column.</p>
<p>The ink used in writing scrolls had to adhere to a surface that was rolled and unrolled, so special inks were
  developed. Even so, ink would slowly flake off of scrolls.</p>
<h2>Rolls</h2>
<p>Rolls recording UK Acts of Parliament held in the Parliamentary Archives, Palace of Westminster, London</p>

html {
  margin: 0 auto;
  overflow: auto;
  position: relative;
  text-align: justify;
  font-size: 32px;
  background: #FDFC47;
  background: -webkit-linear-gradient(to right, #24FE41, #FDFC47);
  background: linear-gradient(to right, #24FE41, #FDFC47);
}
body {
  max-width: 500px;
  height: 500px;
  overflow: auto;
  color: #2D2D2D;
  margin: 40px auto;
  background: #FFFFFF;
}
body::after, *::before, span {
  position: sticky;
  top: 0em;
  bottom: 0em;
  white-space: nowrap;
}
p, h2, div {
  display: inline;
  font-size: 1rem;
}
h2::before {content: "§";}
p::before {content: "¶";}
h2 {color: rgba(255, 100, 100, 1);
}
b, i {color: rgba(255, 100, 100, 0.7);
}

[].forEach.call(document.querySelectorAll("p,li,h2,a"), function (el) {
  el.innerHTML = el.innerHTML
    .split(" ")
    .map(word => `<span>${word}</span>`)
    .join(" ");
});
// 主动触发滚动
function autoscroll() {document.scrollingElement.scrollBy({ top: 10, behavior: "smooth"});
}
var INTRVL = setInterval(autoscroll, 100);
function stop() {clearInterval(INTRVL);
}
document.documentElement.addEventListener("mousemove", stop);

10. 进阶：拼图成果

<div class="container">
  <svg xmlns="http://www.w3.org/2000/svg" version="1.0" width="450" height="450">
    <path vector-effect="non-scaling-stroke"
      d="M0,0L150,0 M150,0L149.56893390347997,15.321019590342566C149.13786780695992,30.64203918068513,148.2757356139198,61.28407836137026,140.06938800617533,66.48104320534887C131.86304039843085,71.67800804932747,116.31247737598203,51.42989855659955,106.0863237976504,55.4571772015448C95.86017021931877,59.48445584649006,90.9584260851044,87.78712262910848,98.31560238205316,93.31985483432332C105.67277867900191,98.85258703953816,125.28887540711382,81.6153846673494,135.9460950819655,87.26708643206159C146.60331475681716,92.91878819677378,148.30165737840858,121.45939409838688,149.1508286892043,135.72969704919345L150,150 M150,150L136.2498867270519,151.19262015043395C122.49977345410377,152.3852403008679,94.99954690820755,154.7704806017358,88.63886136501219,149.5799358844125C82.27817582181684,144.38939116708917,97.05703128132234,131.62306143157463,91.89335174152377,123.41848757977095C86.72967220172522,115.21391372796728,61.62345766262259,111.57109575987448,57.41601665267879,118.35387216181743C53.20857564273499,125.13664856376043,69.89990816195004,142.34501933573918,63.81370097469671,149.3569730371089C57.727493787443386,156.36892673847862,28.863746893721693,153.1844633692393,14.431873446860846,151.59223168461963L0,150 M0,150L0,0">
    </path>
  </svg>
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.container {
  width: 470px;
  margin: 40px auto;
  background: #FFFFFF;
  height: 450px;
  overflow: auto;
}
svg {
  position: -webkit-sticky;
  position: sticky;
  top: 0;
}
path {
  fill: none;
  stroke: #2D2D2D;
  stroke-width: 1.5px;
}

其余优良案例

• 日历: https://codepen.io/dannievint…
• 段落显示 https://codepen.io/BurmesePot…
• 滑动卡片 https://codepen.io/Kseso/pen/…
• 瀑布流 https://codepen.io/collinswor…
• 字幕式文章题目 https://codepen.io/coderthegr…
• 鼠标滚轮管制元素 https://codepen.io/equinusoci…
• 页面布局 https://codepen.io/havardob/d…
• 页面布局 https://codepen.io/ncerminara…

兼容性

如下图所示，以后并不是所有浏览器都反对 skicky 定位模式，不倡议在大型利用中宽泛应用，然而曾经有 Stickfill 相似的 js 垫片 使得未实现 sticky 定位的浏览器也得以反对，大家可尝试应用垫片，兼容更多的我的项目和浏览器 😂。

polyfill

• Stickfill：https://github.com/wilddeer/s…