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<!DOCTYPE html>
<html lang=en>
<head>
  <meta charset=UTF-8>
  <meta name=viewport content="width=device-width,initial-scale=1">
  <title>Dynamic cols Example</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}textarea{display:block;font:inherit;max-width:100%;box-sizing:border-box;padding:.5rem .65rem;border:1px solid #cbd5e1;border-radius:6px;resize:vertical}.hint{margin-top:1rem;font-size:.8125rem;color:#64748b;max-width:480px}</style>
</head>
<body>
  <h1>Dynamic cols with JavaScript</h1>
  <textarea id=dynamicTextArea rows=4 placeholder="This textarea is 50 columns wide"></textarea>
  <script>document.getElementById("dynamicTextArea").cols=50</script>
  <p class=hint>Assign <code>textarea.cols = 50</code> or use <code>setAttribute("cols", "50")</code> to adjust width programmatically.</p>

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HTML cols Attribute — Dynamic JavaScript