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<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>onstorage — window 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}button{padding:.5rem 1rem;border:none;border-radius:8px;background:#2563eb;color:#fff;font-size:.875rem;font-weight:600;cursor:pointer}button:hover{background:#1d4ed8}#event-log,#status{padding:.75rem 1rem;border-radius:8px;font-size:.875rem;max-width:480px;margin-top:.75rem}#status{background:#f1f5f9;border:1px solid #e2e8f0;color:#475569}#event-log{background:#f0fdf4;border:1px solid #bbf7d0;color:#166534;font-weight:600}.hint{font-size:.875rem;color:#64748b;max-width:480px}</style>

</head>

<body>

  <h1>window.onstorage</h1>

  <p class=hint>Open this page in <strong>another tab</strong>, then click the button here or there. The storage event fires in the tab that did <em>not</em> make the change.</p>



  <button type=button id=saveBtn>Save username to localStorage</button>

  <p id=status>Local value: (none)</p>

  <div id=event-log aria-live=polite>Waiting for storage event from another tab…</div>



  <script>var status=document.getElementById("status"),eventLog=document.getElementById("event-log");function refreshLocal(){status.textContent="Local value: "+(localStorage.getItem("username")||"(none)")}function handleStorageEvent(e){eventLog.textContent="Storage event! Key: "+e.key+" | Old: "+e.oldValue+" | New: "+e.newValue,eventLog.style.background="#fef3c7",eventLog.style.borderColor="#fde68a",eventLog.style.color="#92400e",refreshLocal()}window.onstorage=handleStorageEvent,document.getElementById("saveBtn").addEventListener("click",(function(){localStorage.setItem("username","MariSelvan"),refreshLocal(),eventLog.textContent="Saved in this tab — check the other tab for the storage event.",eventLog.style.background="#eff6ff",eventLog.style.borderColor="#bfdbfe",eventLog.style.color="#1e40af"})),refreshLocal()</script>

</body>

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HTML onstorage Attribute — inline window handler
