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  <title>Leap year — nested if</title>
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  <h1>Leap year — nested conditions</h1>
  <p>Edit values in <code>tests</code>, then click <strong>Run</strong>.</p>
  <pre id="out"></pre>
  <script>
    (function () {
      function isLeapYearNested(year) {
        if (year % 4 !== 0) {
          return false;
        }
        if (year % 100 !== 0) {
          return true;
        }
        return year % 400 === 0;
      }
      var tests = [2024, 2021, 1900, 2000];
      var lines = [];
      var i;
      for (i = 0; i < tests.length; i++) {
        var value = tests[i];
        var label = isLeapYearNested(value) ? "leap" : "common";
        lines.push(value + ": " + label);
      }
      document.getElementById("out").textContent = lines.join("\n");
    })();
  </script>
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JavaScript Leap Year — Nested If (Try It)