variable in javascript in php code example

Example 1: using js variable in php

<script type="text/javascript">
var abc= 'this is text';
<?php $abc = "<script>document.write(abc)</script>"?>   
</script>
<?php echo $abc;?>

Example 2: how to use javascript variable in php

<script>
var p1 = "success";
</script>

<?php
echo "<script>document.writeln(p1);</script>";
?>