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  <meta charset=UTF-8>

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

  <title>sizes — dynamic update</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}img{max-width:100%;height:auto;border:1px solid #cbd5e1;border-radius:6px;display:block}#status{margin-top:1rem;font-size:.875rem;color:#475569}code{background:#e2e8f0;padding:.1rem .35rem;border-radius:4px}</style>

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  <h1>Dynamic sizes</h1>

  <p>Resize the window. JavaScript updates <code>img.sizes</code> so the browser can pick a different srcset file.</p>

  <img id=dynamicImage src="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='80' height='80'%3E%3Crect fill='%23bfdbfe' width='80' height='80'/%3E%3Ctext x='40' y='46' text-anchor='middle' fill='%231e40af' font-family='system-ui' font-size='12'%3E80w%3C/text%3E%3C/svg%3E" alt="Demo image updated by JavaScript" srcset="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='40' height='40'%3E%3Crect fill='%23dbeafe' width='40' height='40'/%3E%3Ctext x='20' y='24' text-anchor='middle' fill='%231e40af' font-family='system-ui' font-size='9'%3E40w%3C/text%3E%3C/svg%3E 40w, data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='80' height='80'%3E%3Crect fill='%23bfdbfe' width='80' height='80'/%3E%3Ctext x='40' y='46' text-anchor='middle' fill='%231e40af' font-family='system-ui' font-size='12'%3E80w%3C/text%3E%3C/svg%3E 80w, data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='120' height='120'%3E%3Crect fill='%2393c5fd' width='120' height='120'/%3E%3Ctext x='60' y='68' text-anchor='middle' fill='%231e40af' font-family='system-ui' font-size='14'%3E120w%3C/text%3E%3C/svg%3E 120w" sizes=80px>

  <p id=status>Current sizes: <code>80px</code></p>

  <script>function updateImageSize(){var e,n=document.getElementById("dynamicImage"),d=document.getElementById("status");e=window.innerWidth<600?"40px":window.innerWidth<1200?"80px":"120px",n.sizes=e,d.innerHTML="Current sizes: <code>"+e+"</code>"}updateImageSize(),window.addEventListener("resize",updateImageSize)</script>

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HTML sizes Attribute — Dynamic JavaScript Update
