HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>onselect — textarea</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}textarea{display:block;width:100%;max-width:360px;padding:.5rem .75rem;border:1px solid #cbd5e1;border-radius:8px;font-size:.875rem;margin-bottom:.75rem;font-family:inherit}#status{padding:.75rem 1rem;border-radius:8px;font-size:.875rem;font-weight:600;max-width:420px;background:#eff6ff;border:1px solid #bfdbfe;color:#1e40af}.hint{font-size:.875rem;color:#64748b}</style>

</head>

<body>

  <h1>onselect on textarea</h1>

  <p class=hint>Highlight text below with your mouse or Shift+arrow keys.</p>



  <textarea onselect=showSelection() rows=4>Select some text here</textarea>

  <p id=status>Waiting for selection…</p>



  <script>function showSelection(){var e=document.querySelector("textarea"),t=e.selectionEnd-e.selectionStart,o=document.getElementById("status");t>0?(o.textContent=t+" character(s) selected — Text selected!",o.style.background="#f0fdf4",o.style.borderColor="#bbf7d0",o.style.color="#166534"):(o.textContent="Waiting for selection…",o.style.background="#eff6ff",o.style.borderColor="#bfdbfe",o.style.color="#1e40af")}</script>

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HTML onselect Attribute — textarea handler