HTML Code

<!DOCTYPE html>

<html lang="en">

<head>

  <meta charset="utf-8">

  <title>unload handler called</title>

  <style>

    body { font-family: sans-serif; padding: 16px; max-width: 480px; }

    button { padding: 10px 16px; background: #6366f1; color: #fff; border: none; border-radius: 6px; cursor: pointer; }

    #log { margin-top: 12px; padding: 12px; background: #eef2ff; border-radius: 6px; font-size: 14px; }

    #hint { color: #64748b; font-size: 14px; margin-top: 10px; }

  </style>

</head>

<body>

  <button type="button">Simulate unload</button>

  <div id="log">Waiting...</div>

  <p id="hint">Official pattern: $(window).on("unload", fn)</p>

  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>

  <script>

    $(window).on("unload", function() {

      var msg = "Handler for unload called.";

      $("#log").text(msg);

      sessionStorage.setItem("unloadMsg", msg);

    });

    $("button").on("click", function() {

      $(window).trigger("unload");

      $("#hint").text("Triggered unload — check #log and sessionStorage unloadMsg.");

    });

  </script>

</body>

</html>

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jQuery unload event — handler called (Try It)