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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Alphabet Pattern 1 - Try It (Browser)</title>
</head>
<body>
  <h1>Alphabet Pattern (Browser Demo)</h1>
  <p>This demo uses <code>document.write</code> and <code>&lt;br&gt;</code>. Edit the loops, then click Run.</p>

  <script>
    for (let i = 65; i <= 69; i++) {
      for (let j = 65; j <= i; j++) {
        document.write(String.fromCharCode(j));
      }
      document.write("<br>");
    }
  </script>
</body>
</html>

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JavaScript Alphabet Pattern 1 (Try It — Browser)