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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS Alphabet Pattern 13 - Try It</title>
</head>
<body>
  <h1>Continuous letter triangle</h1>
  <p>Open the HTML code, change <code>start</code> / <code>end</code>, then click Run.</p>

  <pre id="output"></pre>

  <script>
    (() => {
      const start = "A".charCodeAt(0);
      const end = "E".charCodeAt(0);

      let k = start;
      let result = "";
      for (let i = start; i <= end; i++) {
        const parts = [];
        for (let j = start; j <= i; j++) {
          parts.push(String.fromCharCode(k++));
        }
        result += parts.join(" ") + "\n";
      }

      document.getElementById("output").textContent = result;
    })();
  </script>
</body>
</html>

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JavaScript Alphabet Pattern 13 (Try It)