HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>onpaste — uppercase</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}input{width:100%;max-width:320px;padding:.5rem .75rem;border:1px solid #cbd5e1;border-radius:8px;font-size:.875rem}</style>

</head>

<body>

  <h1>Uppercase on paste</h1>

  <p>Paste any text — it becomes uppercase automatically.</p>

  <input id=pasteInput onpaste=handlePaste(event) placeholder="Paste here (Ctrl+V)">



  <script>function handlePaste(e){e.preventDefault();var t=e.clipboardData.getData("text");document.getElementById("pasteInput").value=t.toUpperCase()}</script>

</body>

</html>

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HTML onpaste Attribute — Uppercase on paste