现场演示：我的 HTML 文档

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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>jQuery Get HTML Contents of an Element</title>
<script src="https://code.jquery.com/jquery-3.5.1.min.js"></script>
<script>
$(document).ready(function(){
    $(".btn-one").click(function(){
        var str = $("p").html();
        alert(str);
    });
    $(".btn-two").click(function(){
        var str = $("#container").html();
        alert(str);
    });
});
</script>
</head>
<body>
    <button type="button" class="btn-one">Get Paragraph's HTML Contents</button>
    <button type="button" class="btn-two">Get Container's HTML Contents</button>
    <div id="container">
        <h1>Hello World!</h1>
        <p>The quick <b>brown fox</b> jumps over the lazy dog.</p>
    </div>
</body>
</html>