【js】元素是否在可视区范围内

公式：元素到顶部距离（最近的具有定位父级元素）- 滚动条高度  <= 可视区的高度  

  • offsetTop、scrollTop

 

 

<!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>Document</title>
    <style>
        .div {
            height: 2000px;
        }

        p {
            height: 200px;
            background: red;
        }
    </style>
</head>

<body>
    <div class="div"></div>

    <p id="p">我出现啦</p>

    <!-- 通过元素位置关系方法-->
    <script>
        function isContain(dom) {
            // 获取可视窗口的盖度。
            const screenHeight = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
            // 获取滚动条滚动的高度
            const scrollTop = document.documentElement.scrollTop;
            // 获取元素偏移的高度。就是距离可视窗口的偏移量。
            const offsetTop = dom.offsetTop;
            return offsetTop - scrollTop <= screenHeight;
        }
        const p = document.getElementById("p");
        window.onscroll = () => {
            if (isContain(p)) {
                document.body.style.backgroundColor = 'blue'
            } else {
                document.body.style.backgroundColor = 'green'
            }
        }
    </script>

    <!-- 通过 getBoundingClientRect方法-->
    <!-- <script>
        // 只有当子元素全部出现在父元素中时，才会返回true。
        function isContain(dom) {
            const totalHeight = window.innerHeight || document.documentElement.clientHeight;
            const totalWidth = window.innerWidth || document.documentElement.clientWidth;
            // 当滚动条滚动时，top, left, bottom, right时刻会发生改变。
            const { top, right, bottom, left } = dom.getBoundingClientRect();
            console.log(top, right, bottom, left)
            return (top >= 0 && left >= 0 && right <= totalWidth && bottom <= totalHeight);
        }

        const p = document.getElementById("p");
        window.onscroll = () => {
            if (isContain(p)) {
                document.body.style.backgroundColor = 'blue'
            } else {
                document.body.style.backgroundColor = 'green'
            }
        }
    </script> -->

    <!-- 通过new IntersectionObserver();  -->
    <!-- <script>
        const observer = new IntersectionObserver((entries) => {
            if (entries[0].isIntersecting) {
                document.body.style.backgroundColor = "blue"
            } else {
                document.body.style.backgroundColor = "green"
            }
        }, { threshold: .2 });
        const p = document.getElementById("p")
        observer.observe(p)
    </script> -->
</body>

</html>

 

 

posted on 2022-10-27 16:54  smile轉角  阅读(171)  评论(0)  编辑  收藏  举报

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