HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>ondurationchange — NaN to seconds</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}audio{display:block;max-width:100%;margin-bottom:.75rem}ul{margin:0;padding-left:1.25rem;font-size:.8125rem;max-width:420px}li{margin-bottom:.35rem}.duration{color:#1d4ed8;font-weight:600}code{background:#e2e8f0;padding:.1rem .35rem;border-radius:4px}</style>

</head>

<body>

  <h1>durationchange vs loadedmetadata</h1>

  <p><code>duration</code> starts as <code>NaN</code>. Both events may fire when metadata is ready — log each to compare.</p>

  <audio id=audio controls>

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

  </audio>

  <ul id=log></ul>



  <script>var audio=document.getElementById("audio"),log=document.getElementById("log");function add(a,d){var t=document.createElement("li");d&&(t.className=d),t.textContent=a,log.appendChild(t)}add("Initial duration: "+audio.duration+" (NaN until metadata)"),audio.addEventListener("loadedmetadata",(function(){add("loadedmetadata — duration now "+Math.floor(audio.duration)+" seconds")})),audio.addEventListener("durationchange",(function(){add("durationchange — duration is "+Math.floor(audio.duration)+" seconds","duration")}))</script>

</body>

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HTML ondurationchange Attribute — durationchange vs loadedmetadata