using js variable in php

1<script type="text/javascript">
2   var php_var = "<?php echo $php_var; ?>";
3</script>

1<script type="text/javascript">
2var abc= 'this is text';
3<?php $abc = "<script>document.write(abc)</script>"?>   
4</script>
5<?php echo $abc;?>

1<script>
2   var res = "success";
3</script>
4<?php
5   echo "<script>document.writeln(res);</script>";
6?>

1<script>
2var p1 = "success";
3</script>
4
5<?php
6echo "<script>document.writeln(p1);</script>";
7?>