HTML Code

<!DOCTYPE html>

<html lang=en>

<head>

  <meta charset=UTF-8>

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

  <title>onselect — selection count</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}#count{padding:.75rem 1rem;border-radius:8px;font-size:.875rem;font-weight:600;max-width:420px;background:#f1f5f9;border:1px solid #e2e8f0;color:#475569}</style>

</head>

<body>

  <h1>Selected character count</h1>

  <p>Highlight part of the text below.</p>



  <textarea id=field rows=4>The quick brown fox jumps over the lazy dog.</textarea>

  <p id=count aria-live=polite>0 characters selected</p>



  <script>var field=document.getElementById("field"),count=document.getElementById("count");field.addEventListener("select",(function(){var t=this.selectionStart,e=this.selectionEnd,o=e-t,n=this.value.substring(t,e);o>0?(count.textContent=o+' chars: "'+n+'"',count.style.background="#eff6ff",count.style.borderColor="#bfdbfe",count.style.color="#1e40af"):(count.textContent="0 characters selected",count.style.background="#f1f5f9",count.style.borderColor="#e2e8f0",count.style.color="#475569")}))</script>

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HTML onselect Attribute — selection count