HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>id length demo</title>
  <style>
    body { font-family: sans-serif; padding: 16px; max-width: 28rem; }
    #existingPanel { padding: 12px; background: #e0e7ff; border-radius: 6px; }
    #existingPanel.active { outline: 3px solid #2563eb; }
    #log { margin-top: 12px; font-family: monospace; white-space: pre-wrap; }
  </style>
</head>
<body>
  <div id="existingPanel">Existing panel</div>
  <div id="log"></div>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <script>
    var lines = [];
    var $found = $("#existingPanel");
    if ($found.length) {
      $found.addClass("active");
      lines.push("existingPanel → found, class added");
    }
    var $missing = $("#missingPanel");
    if ($missing.length) {
      lines.push("missingPanel → found");
    } else {
      lines.push("missingPanel → not found (.length 0)");
    }
    $("#log").text(lines.join("\n"));
  </script>
</body>
</html>

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