HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Magic number — shortcut</title>
</head>
<body>
  <h1>Digital-root shortcut</h1>
  <p>Edit values in <code>tests</code>, then click <strong>Run</strong>.</p>
  <pre id="out"></pre>
  <script>
    (function () {
      function digitalRoot(n) {
        if (n <= 0) {
          throw new Error("n must be positive");
        }
        return 1 + ((n - 1) % 9);
      }
      function isMagicShortcut(n) {
        if (n <= 0) {
          return false;
        }
        return digitalRoot(n) === 1;
      }
      var tests = [19, 18, 1, 28];
      var lines = [];
      var i;
      for (i = 0; i < tests.length; i++) {
        var value = tests[i];
        var label = isMagicShortcut(value) ? "magic" : "not magic";
        lines.push(value + ": " + label + " (root=" + digitalRoot(value) + ")");
      }
      document.getElementById("out").textContent = lines.join("\n");
    })();
  </script>
</body>
</html>

Lines: 0 | Characters: 0

Live Preview Auto-refresh on Run

JavaScript Magic Number — Digital Root Shortcut (Try It)