HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>menu delegation</title>
  <style>
    body { font-family: sans-serif; padding: 16px; }
    #menu { list-style: none; padding: 0; margin: 0 0 12px; max-width: 200px; border: 1px solid #cbd5e1; border-radius: 6px; overflow: hidden; }
    #menu li { padding: 10px 14px; border-bottom: 1px solid #e2e8f0; cursor: default; }
    #menu li:last-child { border-bottom: none; }
    #menu li.active { background: #dbeafe; color: #1d4ed8; font-weight: bold; }
    #add { padding: 8px 14px; background: #6366f1; color: #fff; border: none; border-radius: 6px; cursor: pointer; }
    #hint { color: #64748b; font-size: 14px; margin-top: 10px; }
  </style>
</head>
<body>
  <ul id="menu">
    <li>Home</li>
    <li>Products</li>
    <li>Contact</li>
  </ul>
  <button type="button" id="add">Add menu item</button>
  <p id="hint">Hover items — delegation covers new items too.</p>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <script>
    var count = 3;
    $("#menu")
      .on("mouseenter", "li", function() {
        $(this).addClass("active");
      })
      .on("mouseleave", "li", function() {
        $(this).removeClass("active");
      });
    $("#add").on("click", function() {
      count++;
      $("#menu").append("<li>Item " + count + "</li>");
    });
  </script>
</body>
</html>

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jQuery mouseenter — delegated menu items (Try It)