HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Natural number input check</title>
</head>
<body>
  <h1>Check typed integer</h1>
  <p>Edit <code>raw</code>, then <strong>Run</strong>.</p>
  <pre id="out"></pre>
  <script>
    (function () {
      function isNatural(num) {
        return num > 0;
      }
      var raw = "0";
      var number = Number(String(raw).trim());
      var lines = [];
      if (!Number.isInteger(number)) {
        lines.push("Could not read an integer.");
      } else {
        lines.push("Enter an integer: " + raw);
        lines.push(isNatural(number) ? number + " is a natural number." : number + " is not a natural number.");
      }
      document.getElementById("out").textContent = lines.join("\n");
    })();
  </script>
</body>
</html>

Lines: 0 | Characters: 0

Live Preview Auto-refresh on Run

JavaScript Natural Number — Input Check (Try It)