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JavaScript實(shí)現(xiàn)元素吸頂?shù)姆椒ㄔ斀?/h1>

更新時(shí)間：2023年10月22日 09:21:26 作者：Qing

頁面內(nèi)的tab導(dǎo)航需要在滾動(dòng)到視口頂部的時(shí)候進(jìn)行吸頂,這個(gè)功能算是比較常見,也比較容易實(shí)現(xiàn),下面就跟隨小編一起學(xué)習(xí)一下JavaScript是如何實(shí)現(xiàn)元素吸頂效果的吧

背景

頁面內(nèi)的tab導(dǎo)航需要在滾動(dòng)到視口頂部的時(shí)候進(jìn)行吸頂，這個(gè)功能算是比較常見，也比較容易實(shí)現(xiàn)。剛開始按照自己想到的最簡(jiǎn)單的方法來實(shí)現(xiàn)，寫完代碼后進(jìn)行測(cè)試，發(fā)現(xiàn)頁面有很明顯的bug，心里直呼大意了，特此記錄下。

錯(cuò)誤示例

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      .page-container {
        width: 1200px;
        margin: 0 auto;
      }
      .top-area {
        height: 300px;
        background-color: lightskyblue;
        margin-bottom: 20px;
      }

      .tab {
        padding: 0 20px;
        display: flex;
        justify-content: space-between;
        background-color: #f4f4f4;
      }

      .tab.fixed {
        position: fixed;
        width: 1200px;
        box-sizing: border-box;
        top: 0;
      }

      .tab > div {
        padding: 10px 20px;
      }

      .waterfall {
        display: flex;
        justify-content: space-between;
        flex-wrap: wrap;
        align-content: center;
      }

      .waterfall > div {
        margin-top: 20px;
        width: 220px;
        height: 300px;
        background-color: darkseagreen;
        margin-bottom: 12px;
      }
    </style>
  </head>
  <body>
    <div class="page-container">
      <div class="top-area">huge element</div>
      <div class="tab">
        <div class="tab1">tab1</div>
        <div class="tab2">tab2</div>
        <div class="tab3">tab3</div>
        <div class="tab4">tab4</div>
        <div class="tab5">tab5</div>
        <div class="tab6">tab6</div>
        <div class="tab7">tab7</div>
        <div class="tab8">tab8</div>
        <div class="tab9">tab9</div>
        <div class="tab10">tab10</div>
      </div>
      <div class="tab-holder"></div>
      <div class="waterfall">
        <div class="item1">item1</div>
        <div class="item2">item2</div>
        <div class="item3">item3</div>
        <div class="item4">item4</div>
        <div class="item5">item5</div>
        <div class="item6">item6</div>
        <div class="item7">item7</div>
        <div class="item8">item8</div>
        <div class="item9">item9</div>
        <div class="item10">item10</div>
        <div class="item11">item11</div>
        <div class="item12">item12</div>
        <div class="item13">item13</div>
        <div class="item14">item14</div>
        <div class="item15">item15</div>
        <div class="item16">item16</div>
        <div class="item17">item17</div>
        <div class="item18">item18</div>
        <div class="item19">item19</div>
        <div class="item20">item20</div>
        <div class="item21">item21</div>
        <div class="item22">item22</div>
        <div class="item23">item23</div>
        <div class="item24">item24</div>
        <div class="item25">item25</div>
        <div class="item26">item26</div>
        <div class="item27">item27</div>
        <div class="item28">item28</div>
        <div class="item29">item29</div>
        <div class="item30">item30</div>
        <div class="item31">item31</div>
        <div class="item32">item32</div>
        <div class="item33">item33</div>
        <div class="item34">item34</div>
        <div class="item35">item35</div>
        <div class="item36">item36</div>
        <div class="item37">item37</div>
        <div class="item38">item38</div>
        <div class="item39">item39</div>
        <div class="item40">item40</div>
        <div class="item41">item41</div>
        <div class="item42">item42</div>
        <div class="item43">item43</div>
        <div class="item44">item44</div>
        <div class="item45">item45</div>
        <div class="item46">item46</div>
        <div class="item47">item47</div>
        <div class="item48">item48</div>
        <div class="item49">item49</div>
        <div class="item50">item50</div>
      </div>
    </div>
  </body>
  <script>
    const tabElem = document.querySelector(".tab");
    const tabHolder = document.querySelector(".tab-holder");

    const handleScroll = () => {
      const { top, height } = tabElem.getBoundingClientRect();
      console.log("top", top);
      if (top < 0) {
        tabElem.classList.add("fixed");
        tabHolder.style.height = height + "px";
      } else {
        tabElem.classList.remove("fixed");
        tabHolder.style.height = 0;
      }
    };

    document.addEventListener("scroll", handleScroll);
  </script>
</html>

上面的代碼在打開頁面后，向上滾動(dòng)過程中會(huì)發(fā)現(xiàn)tab導(dǎo)航一直在閃爍，原因就是tab元素在轉(zhuǎn)變成固定定位的過程，瀏覽器需要重新計(jì)算頁面布局和重繪元素，在此期間滾動(dòng)事件執(zhí)行了很多遍，導(dǎo)致獲取到的top值會(huì)出現(xiàn)兩極跳轉(zhuǎn)現(xiàn)象，元素會(huì)固定定位和原來的定位之間來回切換。

解決方案

上面的代碼由于tab導(dǎo)航元素的定位會(huì)發(fā)生變化，導(dǎo)致在滾動(dòng)過程中獲取到的top值有問題，之前我們是使用需要定位的上邊界來進(jìn)行判斷，那么我們可以選取相鄰元素的上下邊界是否達(dá)到條件來作為tab導(dǎo)航是否應(yīng)該轉(zhuǎn)為固定定位的依據(jù)。

const topAreaElem = document.querySelector(".top-area");
const tabElem = document.querySelector(".tab");
const tabHolder = document.querySelector(".tab-holder");

const handleScroll = () => {
  const { bottom } = topAreaElem.getBoundingClientRect();
  const { height } = tabElem.getBoundingClientRect();
  // 這個(gè)20是tab導(dǎo)航與上面相鄰元素之間的margin
  if (bottom + 20 < 0) {
    tabElem.classList.add("fixed");
    tabHolder.style.height = height + "px";
  } else {
    tabElem.classList.remove("fixed");
    tabHolder.style.height = 0;
  }
};

document.addEventListener("scroll", handleScroll);

到此這篇關(guān)于JavaScript實(shí)現(xiàn)元素吸頂?shù)姆椒ㄔ斀獾奈恼戮徒榻B到這了,更多相關(guān)JavaScript元素吸頂內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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