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<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

  <meta name=viewport content="width=device-width,initial-scale=1">

  <title>onunload — dynamic handler</title>

  <style>body{font-family:system-ui,sans-serif;margin:0;padding:1.5rem;background:#f8fafc;color:#334155;line-height:1.7}h1{margin:0 0 .75rem;font-size:1.25rem;color:#0f172a}#log{padding:.75rem 1rem;border-radius:8px;font-size:.875rem;max-width:480px;background:#f1f5f9;border:1px solid #e2e8f0;color:#475569}.hint{font-size:.875rem;color:#64748b;max-width:480px}</style>

</head>

<body>

  <h1>window.onunload</h1>

  <p class=hint>Handler attached in script. Reload the page — the log shows when unload last ran.</p>



  <div id=log aria-live=polite>Waiting…</div>



  <script>var KEY="dynamicUnloadDemo";window.onunload=function(){try{sessionStorage.setItem(KEY,"Dynamic unload ran at "+(new Date).toLocaleTimeString())}catch(e){}};var saved=sessionStorage.getItem(KEY),log=document.getElementById("log");log.textContent=saved||"Reload this page to see dynamic onunload fire",saved&&(log.style.background="#f0fdf4",log.style.borderColor="#bbf7d0",log.style.color="#166534")</script>

</body>

</html>

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HTML onunload Attribute — dynamic handler