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2023-04-04 07:00:00

我如何知道一个DOM元素在当前视口中是可见的?

是否有一种有效的方法来判断DOM元素(在HTML文档中)当前是否可见(出现在视口中)?

(这个问题指的是Firefox。)

当前回答

对于类似的挑战，我非常喜欢这个要点，它为scrollIntoViewIfNeeded()暴露了一个填充。

所有必要的功夫都需要回答这个问题:

var parent = this.parentNode,
    parentComputedStyle = window.getComputedStyle(parent, null),
    parentBorderTopWidth = parseInt(parentComputedStyle.getPropertyValue('border-top-width')),
    parentBorderLeftWidth = parseInt(parentComputedStyle.getPropertyValue('border-left-width')),
    overTop = this.offsetTop - parent.offsetTop < parent.scrollTop,
    overBottom = (this.offsetTop - parent.offsetTop + this.clientHeight - parentBorderTopWidth) > (parent.scrollTop + parent.clientHeight),
    overLeft = this.offsetLeft - parent.offsetLeft < parent.scrollLeft,
    overRight = (this.offsetLeft - parent.offsetLeft + this.clientWidth - parentBorderLeftWidth) > (parent.scrollLeft + parent.clientWidth),
    alignWithTop = overTop && !overBottom;

这指的是你想知道的元素，例如，overTop或overBottom -你只需要得到漂移…

2016-03-14 13:14:21

其他回答

我发现这里公认的答案对于大多数用例来说过于复杂。这段代码很好地完成了工作(使用jQuery)，并区分了完全可见和部分可见的元素:

var element         = $("#element");
var topOfElement    = element.offset().top;
var bottomOfElement = element.offset().top + element.outerHeight(true);
var $window         = $(window);

$window.bind('scroll', function() {

    var scrollTopPosition   = $window.scrollTop()+$window.height();
    var windowScrollTop     = $window.scrollTop()

    if (windowScrollTop > topOfElement && windowScrollTop < bottomOfElement) {
        // Element is partially visible (above viewable area)
        console.log("Element is partially visible (above viewable area)");

    } else if (windowScrollTop > bottomOfElement && windowScrollTop > topOfElement) {
        // Element is hidden (above viewable area)
        console.log("Element is hidden (above viewable area)");

    } else if (scrollTopPosition < topOfElement && scrollTopPosition < bottomOfElement) {
        // Element is hidden (below viewable area)
        console.log("Element is hidden (below viewable area)");

    } else if (scrollTopPosition < bottomOfElement && scrollTopPosition > topOfElement) {
        // Element is partially visible (below viewable area)
        console.log("Element is partially visible (below viewable area)");

    } else {
        // Element is completely visible
        console.log("Element is completely visible");
    }
});
2015-01-30 14:49:11

Domysee的答案https://stackoverflow.com/a/37998526接近正确。

许多示例使用“完全包含在视口中”，他的代码使用百分比来允许部分可见。他的代码还解决了“是否是父视图剪切”的问题，大多数示例都忽略了这个问题。

一个缺失的元素是父对象滚动条的影响——getBoundingClientRect返回父对象的外部矩形(包含滚动条)，而不是内部矩形(不包含滚动条)。子滚动条可以隐藏在父滚动条后面，当它不可见时，它被认为是可见的。

推荐的观察者模式不适合我的用例:使用方向键更改表中当前选择的行，并确保新选择是可见的。使用观察器进行此操作将过于复杂。

这是一些代码

它包括一个额外的hack (fudgeY)，因为我的表有一个粘头，不是通过直接的方式检测(自动处理这个将是相当乏味的)。此外，对于所需的可见分数，它使用十进制(0到1)而不是百分比。(对于我的例子，我需要完整的y, x是不相关的)。

function intersectRect(r1, r2) {
    var r = {};
    r.left = r1.left < r2.left ? r2.left : r1.left;
    r.top = r1.top < r2.top ? r2.top : r1.top;
    r.right = r1.right < r2.right ? r1.right : r2.right;
    r.bottom = r1.bottom < r2.bottom ? r1.bottom : r2.bottom;
    if (r.left < r.right && r.top < r.bottom)
        return r;
    return null;
}

function innerRect(e) {
    var b,r;
    b = e.getBoundingClientRect();
    r = {};
    r.left = b.left;
    r.top = b.top;
    r.right = b.left + e.clientWidth;
    r.bottom = b.top + e.clientHeight;
    return r;
}

function isViewable(e, fracX, fracY, fudgeY) {
    // ref https://stackoverflow.com/a/37998526
    // intersect all the rects and then check the result once
    // innerRect: mind the scroll bars
    // fudgeY: handle "sticky" thead in parent table.  Ugh.
    var r, pr, er;

    er = e.getBoundingClientRect();
    r = er;
    for (;;) {
        e = e.parentElement;
        if (!e)
            break;
        pr = innerRect(e);
        if (fudgeY)
            pr.top += fudgeY;
        r = intersectRect(r, pr);
        if (!r)
            return false;
    }

    if (fracX && ((r.right-r.left) / (er.right-er.left)) < (fracX-0.001))
        return false;
    if (fracY && ((r.bottom-r.top) / (er.bottom-er.top)) < (fracY-0.001))
        return false;
    return true;
}
2021-10-04 03:25:06

作为公共服务: Dan的答案与正确的计算(元素可以>窗口，特别是在手机屏幕上)，并正确的jQuery测试，以及添加isElementPartiallyInViewport:

顺便说一下，窗户和窗户的区别。innerWidth和document.documentElement.clientWidth是clientWidth/clientHeight不包括滚动条，while窗口。innerWidth /高。

function isElementPartiallyInViewport(el)
{
    // Special bonus for those using jQuery
    if (typeof jQuery !== 'undefined' && el instanceof jQuery) 
        el = el[0];

    var rect = el.getBoundingClientRect();
    // DOMRect { x: 8, y: 8, width: 100, height: 100, top: 8, right: 108, bottom: 108, left: 8 }
    var windowHeight = (window.innerHeight || document.documentElement.clientHeight);
    var windowWidth = (window.innerWidth || document.documentElement.clientWidth);

    // http://stackoverflow.com/questions/325933/determine-whether-two-date-ranges-overlap
    var vertInView = (rect.top <= windowHeight) && ((rect.top + rect.height) >= 0);
    var horInView = (rect.left <= windowWidth) && ((rect.left + rect.width) >= 0);

    return (vertInView && horInView);
}


// http://stackoverflow.com/questions/123999/how-to-tell-if-a-dom-element-is-visible-in-the-current-viewport
function isElementInViewport (el)
{
    // Special bonus for those using jQuery
    if (typeof jQuery !== 'undefined' && el instanceof jQuery) 
        el = el[0];

    var rect = el.getBoundingClientRect();
    var windowHeight = (window.innerHeight || document.documentElement.clientHeight);
    var windowWidth = (window.innerWidth || document.documentElement.clientWidth);

    return (
           (rect.left >= 0)
        && (rect.top >= 0)
        && ((rect.left + rect.width) <= windowWidth)
        && ((rect.top + rect.height) <= windowHeight)
    );
}


function fnIsVis(ele)
{
    var inVpFull = isElementInViewport(ele);
    var inVpPartial = isElementPartiallyInViewport(ele);
    console.clear();
    console.log("Fully in viewport: " + inVpFull);
    console.log("Partially in viewport: " + inVpPartial);
}

测试用例

<!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">
    <meta name="description" content="">
    <meta name="author" content="">
    <title>Test</title>
    <!--
    <script src="http://cdnjs.cloudflare.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script src="scrollMonitor.js"></script>
    -->

    <script type="text/javascript">

        function isElementPartiallyInViewport(el)
        {
            // Special bonus for those using jQuery
            if (typeof jQuery !== 'undefined' && el instanceof jQuery) 
                el = el[0];

            var rect = el.getBoundingClientRect();
            // DOMRect { x: 8, y: 8, width: 100, height: 100, top: 8, right: 108, bottom: 108, left: 8 }
            var windowHeight = (window.innerHeight || document.documentElement.clientHeight);
            var windowWidth = (window.innerWidth || document.documentElement.clientWidth);

            // http://stackoverflow.com/questions/325933/determine-whether-two-date-ranges-overlap
            var vertInView = (rect.top <= windowHeight) && ((rect.top + rect.height) >= 0);
            var horInView = (rect.left <= windowWidth) && ((rect.left + rect.width) >= 0);

            return (vertInView && horInView);
        }


        // http://stackoverflow.com/questions/123999/how-to-tell-if-a-dom-element-is-visible-in-the-current-viewport
        function isElementInViewport (el)
        {
            // Special bonus for those using jQuery
            if (typeof jQuery !== 'undefined' && el instanceof jQuery) 
                el = el[0];

            var rect = el.getBoundingClientRect();
            var windowHeight = (window.innerHeight || document.documentElement.clientHeight);
            var windowWidth = (window.innerWidth || document.documentElement.clientWidth);

            return (
                   (rect.left >= 0)
                && (rect.top >= 0)
                && ((rect.left + rect.width) <= windowWidth)
                && ((rect.top + rect.height) <= windowHeight)
            );
        }


        function fnIsVis(ele)
        {
            var inVpFull = isElementInViewport(ele);
            var inVpPartial = isElementPartiallyInViewport(ele);
            console.clear();
            console.log("Fully in viewport: " + inVpFull);
            console.log("Partially in viewport: " + inVpPartial);
        }


        // var scrollLeft = (window.pageXOffset !== undefined) ? window.pageXOffset : (document.documentElement || document.body.parentNode || document.body).scrollLeft,
        // var scrollTop = (window.pageYOffset !== undefined) ? window.pageYOffset : (document.documentElement || document.body.parentNode || document.body).scrollTop;
    </script>
</head>

<body>
    <div style="display: block; width: 2000px; height: 10000px; background-color: green;">

        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />

        <input type="button" onclick="fnIsVis(document.getElementById('myele'));" value="det" />

        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />

        <div style="background-color: crimson; display: inline-block; width: 800px; height: 500px;" ></div>
        <div id="myele" onclick="fnIsVis(this);" style="display: inline-block; width: 100px; height: 100px; background-color: hotpink;">
        t
        </div>

        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />
        <br /><br /><br /><br /><br /><br />

        <input type="button" onclick="fnIsVis(document.getElementById('myele'));" value="det" />
    </div>

    <!--
    <script type="text/javascript">

        var element = document.getElementById("myele");
        var watcher = scrollMonitor.create(element);

        watcher.lock();

        watcher.stateChange(function() {
            console.log("state changed");
            // $(element).toggleClass('fixed', this.isAboveViewport)
        });
    </script>
    -->
</body>
</html>
2014-09-25 12:54:30

在Android上放大谷歌Chrome浏览器时，最被接受的答案是不工作的。结合Dan的回答，要考虑Android上的Chrome，必须使用visualViewport。下面的例子只考虑了垂直检查，并使用jQuery来计算窗口高度:

var Rect = YOUR_ELEMENT.getBoundingClientRect();
var ElTop = Rect.top, ElBottom = Rect.bottom;
var WindowHeight = $(window).height();
if(window.visualViewport) {
    ElTop -= window.visualViewport.offsetTop;
    ElBottom -= window.visualViewport.offsetTop;
    WindowHeight = window.visualViewport.height;
}
var WithinScreen = (ElTop >= 0 && ElBottom <= WindowHeight);
2019-11-17 09:37:42

新的交集观察者API非常直接地解决了这个问题。

这个解决方案将需要一个polyfill，因为Safari, Opera和Internet Explorer还不支持这个(polyfill包含在解决方案中)。

在这个解决方案中，在视图外有一个框，即目标(观察到的)。当它进入视图时，头部顶部的按钮是隐藏的。一旦框离开视图，就会显示它。

const buttonToHide = document.querySelector('button'); const hideWhenBoxInView = new IntersectionObserver((entries) => { if (entries[0].intersectionRatio <= 0) { // If not in view buttonToHide.style.display = "inherit"; } else { buttonToHide.style.display = "none"; } }); hideWhenBoxInView.observe(document.getElementById('box')); header { position: fixed; top: 0; width: 100vw; height: 30px; background-color: lightgreen; } .wrapper { position: relative; margin-top: 600px; } #box { position: relative; left: 175px; width: 150px; height: 135px; background-color: lightblue; border: 2px solid; } <script src="https://polyfill.io/v2/polyfill.min.js?features=IntersectionObserver"></script> <header> <button>NAVIGATION BUTTON TO HIDE</button> </header> <div class="wrapper"> <div id="box"> </div> </div>

2019-03-15 11:32:46

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