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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Evil — single n</title>
</head>
<body>
  <h1>Single evil check</h1>
  <p>Edit <code>number</code>, then <strong>Run</strong>.</p>
  <pre id="out"></pre>
  <script>
    (function () {
      function popCount(n) {
        var count = 0;
        var x = n >>> 0;
        while (x !== 0) {
          count += x & 1;
          x >>>= 1;
        }
        return count;
      }
      function isEvil(n) {
        if (n < 0) {
          return false;
        }
        return popCount(n) % 2 === 0;
      }
      var number = 15;
      var msg;
      if (number < 0) {
        msg = "Evil/odious here are defined for nonnegative n only.";
      } else if (!Number.isSafeInteger(number)) {
        msg = "Use a JavaScript safe integer.";
      } else if (isEvil(number)) {
        msg = number + " is an Evil Number.";
      } else {
        msg = number + " is not an Evil Number.";
      }
      document.getElementById("out").textContent = msg;
    })();
  </script>
</body>
</html>

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JavaScript Evil Number — Bitwise popcount (Try It)