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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Harshad — single</title>
</head>
<body>
  <h1>Harshad number check</h1>
  <p>Edit <code>num</code>, then <strong>Run</strong>.</p>
  <pre id="out"></pre>
  <script>
    (function () {
      function digitSumPositive(n) {
        var sum = 0;
        while (n > 0) {
          sum += n % 10;
          n = Math.floor(n / 10);
        }
        return sum;
      }
      function isHarshad(number) {
        var original = number;
        if (number <= 0) return false;
        var sum = digitSumPositive(number);
        if (sum === 0) return false;
        return original % sum === 0;
      }
      var num = 18;
      var msg = isHarshad(num)
        ? num + " is a Harshad number."
        : num + " is not a Harshad number.";
      document.getElementById("out").textContent = msg;
    })();
  </script>
</body>
</html>

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JavaScript Harshad — Single check (Try It)