HTML Code
<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>onstorage — cross-tab sync</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}label{display:block;font-size:.875rem;font-weight:600;margin-bottom:.35rem}input{padding:.5rem .75rem;border:1px solid #cbd5e1;border-radius:8px;font-size:.875rem;width:100%;max-width:280px;box-sizing:border-box}button{margin-top:.5rem;padding:.5rem 1rem;border:none;border-radius:8px;background:#2563eb;color:#fff;font-size:.875rem;font-weight:600;cursor:pointer}#display{margin-top:1rem;padding:.75rem 1rem;border-radius:8px;font-size:.875rem;font-weight:600;max-width:420px;background:#eff6ff;border:1px solid #bfdbfe;color:#1e40af}.hint{font-size:.875rem;color:#64748b;max-width:420px}</style>

</head>

<body>

  <h1>Cross-tab username sync</h1>

  <p class=hint>Save a name here, then open this page in another tab — both tabs stay in sync via the storage event.</p>



  <label for=nameInput>Username</label>

  <input id=nameInput placeholder="Enter your name">

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



  <p id=display aria-live=polite>Signed in as: Guest</p>



  <script>var STORAGE_KEY="syncUsername",display=document.getElementById("display"),input=document.getElementById("nameInput");function renderName(){var e=localStorage.getItem(STORAGE_KEY)||"Guest";display.textContent="Signed in as: "+e,input.value="Guest"===e?"":e}document.getElementById("saveBtn").addEventListener("click",(function(){var e=input.value.trim()||"Guest";localStorage.setItem(STORAGE_KEY,e),renderName()})),window.addEventListener("storage",(function(e){e.key===STORAGE_KEY&&(renderName(),display.style.background="#f0fdf4",display.style.borderColor="#bbf7d0",display.style.color="#166534")})),renderName()</script>

</body>

</html>
Lines: 0 | Characters: 0
Live Preview Auto-refresh on Run
HTML onstorage Attribute — cross-tab sync
