position:sticky 粘性定位的幾種巧妙應用

背景：position: sticky 又稱為粘性定位，粘性定位的元素是依賴於使用者的滾動，在 position:relative 與 position:fixed 定位之間切換。元素根據正常文件流進行定位，然後相對它的最近滾動祖先（nearest scrolling ancestor）和 containing block (最近塊級祖先 nearest block-level ancestor)，包括table-related 元素，基於 top, right, bottom, 和 left的值進行偏移。

粘性定位可以被認為是相對定位和固定定位的混合。元素在跨越特定閾值前為相對定位，之後為固定定位。例如：

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

設定了以上樣式的元素，在 viewport 視口滾動到元素 top 距離小於 10px 之前，元素為相對定位。之後，元素將固定在與頂部距離 10px 的位置，直到 viewport 視口回滾到閾值以下。

注意：

• 元素定位表現為在跨越特定閾值前為相對定位，之後為固定定位。
• 須指定 top, right, bottom 或 left 四個閾值其中之一，才可使粘性定位生效。否則其行為與相對定位相同。
• 偏移值不會影響任何其他元素的位置。該值總是建立一個新的層疊上下文（stacking context）。
• 一個 sticky元素 會 固定 在離它最近的一個擁有 滾動機制 的祖先上（當該祖先的 overflow 是 hidden, scroll, auto, 或 overlay時），即便這個祖先不是最近的真實可滾動祖先。

應用示例

1. 基礎：頭部固定

頭部導航欄開始時相對定位頂部，當頁面元素髮生滾動時，變為和 fixed 類似的固定定位。

<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. 基礎：頁尾固定

頁尾固定效果，開始時也較為固定定位效果，當頁面滾動超過頁尾時，頁尾定位效果變為相對定位效果，可用於顯示一些底部資訊或廣告。

<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. 基礎：側邊欄固定

當頁面產生滾動，位置超過側邊欄的 頂部閾值 後，側邊欄變為固定定位，可用於實現側邊導航欄或側邊提示資訊及廣告展示。

<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. 基礎：列表錨點

僅使用 css 就可實現頁面滾動錨點固定效果，可用於實現通訊錄滾動、日誌記錄滾動、其他分類列表滾動效果。

 <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 您可以指定依賴於瀏覽器中的一個或多個特定的CSS功能的支援宣告。這被稱為特性查詢。該規則可以放在程式碼的頂層，也可以巢狀在任何其他條件組規則中。

@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. 進階：表格表頭固定

對 table 元素的 th 或 tr 設定 position: sticky; 可以實現表格頭部或某行固定，也可將多個表格合併到一起，當滾動到當前表格是，固定頭部自動變為當前表格的表頭。

<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. 進階：頁面進度條（簡易）

利用 position: sticky; 定位，可以實現頁面瀏覽進度條效果，以下是簡易進度條的演示，實際實現中可將未滾動到頂部的元素設定為透明色，滾動到頂部時變為藍色。

<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. 進階：頁面進度條（優化）

優化版的進度條支援瀏覽進度百分比顯示，助於提升使用者體驗。

<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);
}

計算並顯示百分比

$(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. 進階：時間軸

時間軸相當於上述列表錨點的升級版，可用於年鑑展示、記事本、tudo list 等應用中。

<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. 進階：文字堆積效果

<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(" ");
});
// 自動觸發滾動
function autoscroll() {
  document.scrollingElement.scrollBy({ top: 10, behavior: "smooth" });
}
var INTRVL = setInterval(autoscroll, 100);
function stop() {
  clearInterval(INTRVL);
}
document.documentElement.addEventListener("mousemove", stop);

10. 進階：拼圖效果

<div class="container">
  <svg xmlns="http://www.w3.org/2000/svg" version="1.0" width="450" height="450">
    <path vector-effect="non-scaling-stroke"
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其他優秀案例

• 日曆: https://codepen.io/dannievinther/details/pGdjPV
• 段落顯示 https://codepen.io/BurmesePotato/pen/qBbqpNB
• 滑動卡片 https://codepen.io/Kseso/pen/JyEWoP
• 瀑布流 https://codepen.io/collinsworth/pen/aEJGvg
• 字幕式文章標題 https://codepen.io/coderthegreat/details/abzrOpg
• 滑鼠滾輪控制元素 https://codepen.io/equinusocio/pen/GeBxJz
• 頁面佈局 https://codepen.io/havardob/details/gOPNpmm
• 頁面佈局 https://codepen.io/ncerminara/pen/VdLpzd

相容性

如下圖所示，當前並不是所有瀏覽器都支援 skicky 定位模式，不建議在大型應用中廣泛使用，但是已經有 Stickfill 類似的 js墊片 使得未實現 sticky 定位的瀏覽器也得以支援，大家可嘗試使用墊片，相容更多的專案和瀏覽器 ?。

polyfill

• Stickfill： https://github.com/wilddeer/stickyfill