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<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>src — 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 1rem;font-size:1.25rem;color:#0f172a}img{max-width:100%;border:1px solid #cbd5e1;border-radius:6px;display:block;margin-bottom:1rem}button{font:inherit;padding:.45rem .9rem;border:1px solid #cbd5e1;border-radius:6px;background:#fff;cursor:pointer}code{background:#e2e8f0;padding:.1rem .35rem;border-radius:4px}</style>

</head>

<body>

  <h1>Dynamic src</h1>

  <img id=dynamicImage src="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='200' height='100'%3E%3Crect fill='%23dbeafe' width='200' height='100'/%3E%3Ctext x='100' y='58' text-anchor='middle' fill='%231e40af' font-family='system-ui' font-size='13'%3EImage A%3C/text%3E%3C/svg%3E" alt="Swappable demo image" width=200 height=100>

  <button type=button id=swapBtn>Swap image src</button>

  <script>var img=document.getElementById("dynamicImage"),swapped=!1,a="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='200' height='100'%3E%3Crect fill='%23dbeafe' width='200' height='100'/%3E%3Ctext x='100' y='58' text-anchor='middle' fill='%231e40af' font-family='system-ui' font-size='13'%3EImage A%3C/text%3E%3C/svg%3E",b="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='200' height='100'%3E%3Crect fill='%23ffedd5' width='200' height='100'/%3E%3Ctext x='100' y='58' text-anchor='middle' fill='%239a3412' font-family='system-ui' font-size='13'%3EImage B%3C/text%3E%3C/svg%3E";document.getElementById("swapBtn").addEventListener("click",(function(){swapped=!swapped,img.src=swapped?b:a}))</script>

</body>

</html>

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HTML src Attribute — Dynamic JavaScript Update