HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>selected vs checked</title>
  <style>
    body { font-family: sans-serif; padding: 16px; }
    #output { margin-top: 12px; padding: 12px; background: #ecfdf5; border: 1px solid #059669; white-space: pre-line; }
  </style>
</head>
<body>
  <select><option>A</option><option selected>B</option></select>
  <label><input type="checkbox" checked> Agree</label>
  <div id="output"></div>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <script>
    $("#output").text(
      "Selected options: " + $("option:selected").length +
      "\nChecked inputs: " + $("input:checked").length
    );
  </script>
</body>
</html>

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option:selected vs input:checked (Try It)