HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>onoffline — 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}#log{padding:.75rem 1rem;background:#eff6ff;border:1px solid #bfdbfe;border-radius:8px;font-size:.875rem;max-width:420px}</style>

</head>

<body>

  <h1>window.onoffline</h1>

  <p>Disable network to trigger the offline handler.</p>

  <div id=log>Waiting for connection change…</div>



  <script>window.onoffline=function(){document.getElementById("log").textContent="Your browser is now offline.",document.getElementById("log").style.background="#fef2f2",document.getElementById("log").style.borderColor="#fecaca"},window.ononline=function(){document.getElementById("log").textContent="Back online.",document.getElementById("log").style.background="#f0fdf4",document.getElementById("log").style.borderColor="#bbf7d0"},document.getElementById("log").textContent=navigator.onLine?"Currently online.":"Currently offline."</script>

</body>

</html>

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HTML onoffline Attribute — window.onoffline