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JavaScript判斷元素是否在可視區(qū)域的三種方法

 更新時間：2023年12月07日 09:58:27   作者：WebGirl  
這這篇文章給大家總結了JavaScript判斷元素是否在可視區(qū)域的三種方法,getBoundingClientRect,IntersectionObserver和offsetTop、scrollTop這三種方法,文中通過代碼示例給大家介紹的非常詳細,需要的朋友可以參考下

方法1：getBoundingClientRect

用法

let domRect = dom.getBoundingClientRect()；


DOMRect：{
　　x/left：視圖原點（左上角）距離dom左邊框距離，
　　y/top：視圖原點（左上角）距離dom上邊框距離，
    right：視圖原點（左上角）距離dom右邊框距離，
    bottom：視圖原點（左上角）距離dom底邊框距離，
    width：dom的寬度，標準盒模型，width = 寬度+padding+border；怪異盒模型，width = 設置的寬度，
    height：dom的高度，
}

所以我們可以根據DOMRect的中的各個屬性來判斷dom是否在可視區(qū)域內。

eg:

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>getBoundingClientRect可視區(qū)域</title>
  <style>
    * {
      margin: 0
    }
    .circle-wrap {
      position: fixed;
      top: 50px;
      right: 50px;
      padding: 10px;
      box-shadow: 0 2px 12px 0 rgba(0, 0, 0, 0.1);
      width: 140px;
      background: #fff;
    }

    .circle-wrap .circle {
      display: inline-block;
      width: 20px;
      height: 20px;
      border-radius: 50%;
      background: red;
    }

    .card-wrap {
      height: 2000px;
      width: 3000px;
      margin-top: 100px;
    }

    .card-wrap .card {
      width: 200px;
      height: 200px;
      padding: 20px;
      box-sizing: border-box;
      box-shadow: 0 2px 12px 0 rgba(0, 0, 0, 0.1);
      margin-top: 500px;
      margin-left: 500px;
    }
  </style>
</head>

<body>
  <div class="circle-wrap">
    <span>當下方的卡片在可視區(qū)域內，我的圈圈是綠色，否則是紅色</span>
    <span class="circle"></span>
  </div>
  <div class="card-wrap">
    <div class="card">我是一個卡片</div>
  </div>
  <script src="https://cdn.bootcdn.net/ajax/libs/lodash.js/4.17.20/lodash.js"></script>
  <script>
    const card = document.querySelector(".card");
    const circle = document.querySelector(".circle");
    const getBoundingClientRectJudge = () => {
      let domRect = card.getBoundingClientRect();
      console.log(domRect)
      let ch = document.documentElement.clientHeight;
      let cw = document.documentElement.clientWidth;
      let isInsert = true;
      if (domRect.bottom < 0 || domRect.top > ch || domRect.right < 0 || domRect.left > cw) {
        isInsert = false;
      }
      let background = null
      if (isInsert) {
        background = "green"
      } else {
        background = "red"
      }
      circle.style.background = background
    }
    window.addEventListener("scroll", _.throttle(getBoundingClientRectJudge, 500))
    getBoundingClientRectJudge()
  </script>
</body>

</html>

效果圖：

問題

getBoundingClientRect并不能滿足所有情況，甚至說，它只能滿足一種情況的判斷，那就是需要判斷的那個dom節(jié)點，它只身處在一個滾動條的情況下。什么意思呢，就是它所有的祖先節(jié)點，加起來的滾動條只有1個，如果它父節(jié)點有滾動條，父父節(jié)點也有滾動條，那這種方法就不好用了，請看示例：

下面展示的結果是錯誤的，圈圈應該是紅色才對。

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>getBoundingClientRect可視區(qū)域</title>
  <style>
    * {
      margin: 0
    }

    body {
      height: 2000px;
      width: 3000px;
    }

    .circle-wrap {
      position: fixed;
      top: 50px;
      right: 50px;
      padding: 10px;
      box-shadow: 0 2px 12px 0 rgba(0, 0, 0, 0.1);
      width: 140px;
      background: #fff;
    }

    .circle-wrap .circle {
      display: inline-block;
      width: 20px;
      height: 20px;
      border-radius: 50%;
      background: red;
    }

    .card-wrap {
      height: 400px;
      width: 600px;
      margin-top: 100px;
      margin-left: 100px;
      border: 1px solid green;
      overflow: auto;
    }

    .card-wrap .card {
      width: 200px;
      height: 200px;
      padding: 20px;
      box-sizing: border-box;
      box-shadow: 0 2px 12px 0 rgba(0, 0, 0, 0.1);
      margin-top: 500px;
      margin-left: 500px;
    }

    .head {
      width: 100%;
      height: 100px;
      background: pink;
      /* position: fixed; */
      top: 0;
      left: 0;
    }
  </style>
</head>

<body>
  <!-- <div class="head"></div> -->
  <div class="circle-wrap">
    <span>當下方的卡片在可視區(qū)域內，我的圈圈是綠色，否則是紅色</span>
    <span class="circle"></span>
  </div>
  <div class="card-wrap">
    <div class="card">我是一個卡片</div>
  </div>
  <script src="https://cdn.bootcdn.net/ajax/libs/lodash.js/4.17.20/lodash.js"></script>
  <script>
    const card = document.querySelector(".card");
    const circle = document.querySelector(".circle");
    const getBoundingClientRectJudge = () => {
      let domRect = card.getBoundingClientRect();
      let ch = document.documentElement.clientHeight;
      let cw = document.documentElement.clientWidth;
      let isInsert = true;
      if (domRect.bottom < 0 || domRect.top > ch || domRect.right < 0 || domRect.left > cw) {
        isInsert = false;
      }
      let background = null
      if (isInsert) {
        background = "green"
      } else {
        background = "red"
      }
      circle.style.background = background
    }
    window.addEventListener("scroll", _.throttle(getBoundingClientRectJudge, 500))
    getBoundingClientRectJudge()
  </script>
</body>

</html>

由此，我們引出第二種方法，IntersectionObserver。

方法2：IntersectionObserver

用法

eg:

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>getBoundingClientRect可視區(qū)域</title>
  <style>
    * {
      margin: 0
    }

    body {
      height: 2000px;
      width: 3000px;
    }

    .circle-wrap {
      position: fixed;
      top: 50px;
      right: 50px;
      padding: 10px;
      box-shadow: 0 2px 12px 0 rgba(0, 0, 0, 0.1);
      width: 140px;
      background: #fff;
    }

    .circle-wrap .circle {
      display: inline-block;
      width: 20px;
      height: 20px;
      border-radius: 50%;
      background: red;
    }

    .card-wrap {
      height: 400px;
      width: 600px;
      margin-top: 100px;
      margin-left: 100px;
      border: 1px solid green;
      overflow: auto;
    }

    .card-wrap .card {
      width: 200px;
      height: 200px;
      padding: 20px;
      box-sizing: border-box;
      box-shadow: 0 2px 12px 0 rgba(0, 0, 0, 0.1);
      margin-top: 500px;
      margin-left: 500px;
    }
    .head{
      width: 100%;
      height: 100px;
      background: pink;
      /* position: fixed; */
      top:0;
      left: 0;
    }
  </style>
</head>

<body>
  <!-- <div class="head"></div> -->
  <div class="circle-wrap">
    <span>當下方的卡片在可視區(qū)域內，我的圈圈是綠色，否則是紅色</span>
    <span class="circle"></span>
  </div>
  <div class="card-wrap">
    <div class="card">我是一個卡片</div>
  </div>
  <script src="https://cdn.bootcdn.net/ajax/libs/lodash.js/4.17.20/lodash.js"></script>
  <script>
    const card = document.querySelector(".card");
    const circle = document.querySelector(".circle");
    const observer = new IntersectionObserver((changes) => {
      // changes是數(shù)組
      changes.forEach(one => {
        console.log(one)
        let isIntersecting = one.isIntersecting
        let background = null
        if (isIntersecting) {
          background = "green"
        } else {
          background = "red"
        }
        circle.style.background = background
      })
    })
    observer.observe(card)
    // console.log(observer)
    /* 取消觀察特定的元素：observer.unobserve(dom) */
    /* 對象停止監(jiān)聽目標 observer.disconnect() */
  </script>
</body>

</html>

補充說明

IntersectionObserver可以傳root,進一步判斷dom是相對于哪個節(jié)點，來判斷是否在可視區(qū)域內，默認root是document。

const observer = new IntersectionObserver((changes) => {
      console.log(changes)
      changes.forEach(one => {
        console.log(one)
        let isIntersecting = one.isIntersecting
        let background = null
        if (isIntersecting) {
          background = "green"
        } else {
          background = "red"
        }
        circle.style.background = background
      })
    },{root:document.querySelector(".card-wrap")})

方法3：offsetTop、scrollTop

說明

  • offsetTop：元素的上外邊框至包含元素的上內邊框之間的像素距離，其他方向相同
  • offsetWidth:元素兩端算上外邊框的寬度，其他方向相同
  • scrollLeft 和 scrollTop:既可以確定當前元素的滾動狀態(tài)，也可以設置元素的滾動位置
  • scrollWidth 和 scrollHeight:確定元素內容的實際大小
  • clientWidth:元素內容區(qū)寬度加上左右內邊距寬度，即clientWidth = content + padding
  • clientHeight:元素內容區(qū)高度加上上下內邊距高度，即clientHeight = content + padding

使用

公式：

0 <= el.offsetTop - document.documentElement.scrollTop <= viewPortHeight

寫法：

function isInViePortOfOne(el){
    const viewPortHeight = window.innerHeight || document.documentElement.clientHeight||document.body.clientHeight
    const offsetTop = el.offsetTop;
    const scollTop = document.documentElement.scrollTop
    const top = offsetTop - scollTop;
    return top <= viewPortHeight && top >= 0
}

以上就是JavaScript判斷元素是否在可視區(qū)域的三種方法的詳細內容，更多關于JavaScript判斷元素是否在可視區(qū)域的資料請關注腳本之家其它相關文章！

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