警报框不能与PHP一起使用

Question

<?php if ($data == "") { ?>
    <script type="text/javascript">
        alert("review your answer1");
        window.location.href = "index1.php";
    </script>
<?php } else { ?>
    <script type="text/javascript">
        alert("review your answer2");
        window.location.href = "index2.php";
    </script>
<?php } ?>

Alert box is not showing in above code as well as page is also not redirecting. What is wrong in it?

Answer 1

Do the other way around:

<script>
  var data = <?php echo $data; ?>
  if ( data === "" ) {
    alert("review your answer1");
    window.location.href = "index1.php";
  } else {
    alert("review your answer2");
    window.location.href = "index2.php";
  }
</script>