HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>keydown handler</title>
  <style>
    body { font-family: sans-serif; padding: 16px; max-width: 420px; }
    label { display: block; margin-bottom: 6px; font-weight: 600; }
    input { width: 100%; padding: 10px 12px; border: 2px solid #cbd5e1; border-radius: 6px; font-size: 16px; box-sizing: border-box; margin-bottom: 12px; }
    #hint { color: #64748b; font-size: 14px; margin-top: 10px; }
  </style>
</head>
<body>
  <label for="target">Type here</label>
  <input type="text" id="target" placeholder="Click then press any key">
  <p id="hint">Focus the field and press a key — alert runs on each keydown.</p>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <script>
    $("#target").on("keydown", function() {
      alert("Handler for keydown called.");
    });
  </script>
</body>
</html>

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jQuery keydown event — bind handler on #target (Try It)