HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>onprogress — progress bar</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}.bar-wrap{margin-top:.75rem;max-width:420px;height:10px;background:#e2e8f0;border-radius:999px;overflow:hidden}.bar-fill{height:100%;width:0%;background:linear-gradient(90deg,#2563eb,#38bdf8);transition:width .15s ease}#label{margin-top:.5rem;font-size:.875rem;font-weight:600;color:#475569}</style>

</head>

<body>

  <h1>Progress bar while loading</h1>

  <p>Reload the page to watch the bar fill as audio buffers.</p>

  <audio id=media controls preload=auto>

    <source src=/audio/count.mp3 type=audio/mpeg>

  </audio>

  <div class=bar-wrap aria-hidden=true>

    <div class=bar-fill id=bar></div>

  </div>

  <p id=label aria-live=polite>Loading… 0%</p>



  <script>var media=document.getElementById("media"),bar=document.getElementById("bar"),label=document.getElementById("label");function bufferPercent(e){if(!e.duration||!isFinite(e.duration)||0===e.buffered.length)return 0;var t=e.buffered.end(e.buffered.length-1);return Math.min(100,Math.round(t/e.duration*100))}function updateBar(){var e=bufferPercent(media);bar.style.width=e+"%",label.textContent="Loading… "+e+"%"}media.addEventListener("progress",updateBar),media.addEventListener("canplaythrough",(function(){bar.style.width="100%",label.textContent="Ready to play — 100% buffered"}))</script>

</body>

</html>

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HTML onprogress Attribute — visual progress bar