现场演示：我的 HTML 文档

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery Animate Opacity on Hover</title>
<style>
    ul{
        padding: 0;
        list-style: none;
    }
    ul li {
        float: left;        
        margin: 10px; 
    }
    ul li a img{
        opacity: 0.3;
    }
</style>
<script src="https://code.jquery.com/jquery-3.5.1.min.js"></script>
<script>
    $(document).ready(function(){
        $("a").mouseenter(function(){
            $(this).find("img").finish().animate({
                opacity: "1"
            });
        }).mouseleave(function(){
            $(this).find("img").finish().animate({
                opacity: "0.3"
            });
        });
    });
</script>
</head>
<body>
    <ul>
        <li><a href="#"><img src="/examples/images/club.jpg" alt="Club Card"></a></li>
        <li><a href="#"><img src="/examples/images/diamond.jpg" alt="Diamond Card"></a></li>
        <li><a href="#"><img src="/examples/images/spade.jpg" alt="Spade Card"></a></li>
        <li><a href="#"><img src="/examples/images/heart.jpg" alt="Heart Card"></a></li>
    </ul>
</body>
</html>

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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery Animate Opacity on Hover</title>
<style>
    ul{
        padding: 0;
        list-style: none;
    }
    ul li {
        float: left;        
        margin: 10px; 
    }
    ul li a img{
        opacity: 0.3;
    }
</style>
<script src="https://code.jquery.com/jquery-3.5.1.min.js"></script>
<script>
    $(document).ready(function(){
        $("a").mouseenter(function(){
            $(this).find("img").finish().animate({
                opacity: "1"
            });
        }).mouseleave(function(){
            $(this).find("img").finish().animate({
                opacity: "0.3"
            });
        });
    });
</script>
</head>
<body>
    <ul>
        <li><a href="#"><img src="/examples/images/club.jpg" alt="Club Card"></a></li>
        <li><a href="#"><img src="/examples/images/diamond.jpg" alt="Diamond Card"></a></li>
        <li><a href="#"><img src="/examples/images/spade.jpg" alt="Spade Card"></a></li>
        <li><a href="#"><img src="/examples/images/heart.jpg" alt="Heart Card"></a></li>
    </ul>
</body>
</html>