我尝试了Dan的答案，然而，用于确定边界的代数意味着元素必须既≤视口大小，又完全在视口内才能为真，很容易导致假否定。如果你想确定一个元素是否在视口中，ryanve的答案是接近的，但被测试的元素应该与视口重叠，所以试试这个:

function isElementInViewport(el) {
    var rect = el.getBoundingClientRect();

    return rect.bottom > 0 &&
        rect.right > 0 &&
        rect.left < (window.innerWidth || document.documentElement.clientWidth) /* or $(window).width() */ &&
        rect.top < (window.innerHeight || document.documentElement.clientHeight) /* or $(window).height() */;
}

/**
 * Returns Element placement information in Viewport
 * @link https://stackoverflow.com/a/70476497/2453148
 *
 * @typedef {object} ViewportInfo - Whether the element is…
 * @property {boolean} isInViewport - fully or partially in the viewport
 * @property {boolean} isPartiallyInViewport - partially in the viewport
 * @property {boolean} isInsideViewport - fully inside viewport
 * @property {boolean} isAroundViewport - completely covers the viewport
 * @property {boolean} isOnEdge - intersects the edge of viewport
 * @property {boolean} isOnTopEdge - intersects the top edge
 * @property {boolean} isOnRightEdge - intersects the right edge
 * @property {boolean} isOnBottomEdge - is intersects the bottom edge
 * @property {boolean} isOnLeftEdge - is intersects the left edge
 *
 * @param el Element
 * @return {Object} ViewportInfo
 */
function getElementViewportInfo(el) {

    let result = {};

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

    let insideX = rect.left >= 0 && rect.left + rect.width <= windowWidth;
    let insideY = rect.top >= 0 && rect.top + rect.height <= windowHeight;

    result.isInsideViewport = insideX && insideY;

    let aroundX = rect.left < 0 && rect.left + rect.width > windowWidth;
    let aroundY = rect.top < 0 && rect.top + rect.height > windowHeight;

    result.isAroundViewport = aroundX && aroundY;

    let onTop    = rect.top < 0 && rect.top + rect.height > 0;
    let onRight  = rect.left < windowWidth && rect.left + rect.width > windowWidth;
    let onLeft   = rect.left < 0 && rect.left + rect.width > 0;
    let onBottom = rect.top < windowHeight && rect.top + rect.height > windowHeight;

    let onY = insideY || aroundY || onTop || onBottom;
    let onX = insideX || aroundX || onLeft || onRight;

    result.isOnTopEdge    = onTop && onX;
    result.isOnRightEdge  = onRight && onY;
    result.isOnBottomEdge = onBottom && onX;
    result.isOnLeftEdge   = onLeft && onY;

    result.isOnEdge = result.isOnLeftEdge || result.isOnRightEdge ||
        result.isOnTopEdge || result.isOnBottomEdge;

    let isInX =
        insideX || aroundX || result.isOnLeftEdge || result.isOnRightEdge;
    let isInY =
        insideY || aroundY || result.isOnTopEdge || result.isOnBottomEdge;

    result.isInViewport = isInX && isInY;

    result.isPartiallyInViewport =
        result.isInViewport && result.isOnEdge;

    return result;
}

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>

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);

这检查元素是否至少部分在视图中(垂直维度):

function inView(element) {
    var box = element.getBoundingClientRect();
    return inViewBox(box);
}

function inViewBox(box) {
    return ((box.bottom < 0) || (box.top > getWindowSize().h)) ? false : true;
}


function getWindowSize() {
    return { w: document.body.offsetWidth || document.documentElement.offsetWidth || window.innerWidth, h: document.body.offsetHeight || document.documentElement.offsetHeight || window.innerHeight}
}

让我感到困扰的是，该功能没有以jquery为中心的版本可用。当我看到Dan的解决方案时，我发现有机会为那些喜欢用jQuery OO风格编程的人提供一些东西。它很漂亮，很时髦，对我来说很有魅力。

哒哒，哒哒，嘣

$.fn.inView = function(){
    if(!this.length) 
        return false;
    var rect = this.get(0).getBoundingClientRect();

    return (
        rect.top >= 0 &&
        rect.left >= 0 &&
        rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) &&
        rect.right <= (window.innerWidth || document.documentElement.clientWidth)
    );

};

// Additional examples for other use cases
// Is true false whether an array of elements are all in view
$.fn.allInView = function(){
    var all = [];
    this.forEach(function(){
        all.push( $(this).inView() );
    });
    return all.indexOf(false) === -1;
};

// Only the class elements in view
$('.some-class').filter(function(){
    return $(this).inView();
});

// Only the class elements not in view
$('.some-class').filter(function(){
    return !$(this).inView();
});

使用

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

    if( $('footer').inView() ) {
        // Do cool stuff
    }
});