Untitled

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>
  <script>
    var levels = [
      [1.1, 1.2, 1.3],
      [2.1, 2.2, 2.3, 2.4],
      [3.1, 3.2],
    ];

    var firstLevels= levels[0];
    var secondLevel = levels[1];
    secondLevel.pop();
    secondLevel.pop();
    secondLevel.push(2.4);

    var thirdLevels = levels[2];
    thirdLevels.push(3.3);

    //seconLevel.splice();
    document.writeln(firstLevels + "</br>");
    document.writeln(secondLevel + "</br>");
    document.writeln(thirdLevels + "</br>");

  </script>


</body>
</html>