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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Alphabet Pattern 21 - Try It (Browser)</title>
</head>
<body>
  <h1>Diamond (document.write)</h1>
  <p>Edit the loops, then click Run.</p>

  <script>
    // Top half
    for (let i = 1; i <= 5; i++) {
      for (let j = 1; j < i * 2; j++) {
        if (j % 2 === 0) document.write("*");
        else document.write(String.fromCharCode(i + 64));
      }
      document.write("<br>");
    }

    // Bottom half
    for (let i = 4; i >= 1; i--) {
      for (let j = 1; j < i * 2; j++) {
        if (j % 2 === 0) document.write("*");
        else document.write(String.fromCharCode(i + 64));
      }
      document.write("<br>");
    }
  </script>
</body>
</html>

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JavaScript Alphabet Pattern 21 (Try It — Browser)